CHAPTER 1

INTRODUCTION

1.1 Renewable Energy

There is an urgent need to replace fossil fuels to reduce their impact on climate
change and meet the growing worldwide demand for energy. This has resulted in
unprecedented changes to the world's energy output. This demands an immediate move
toward the widespread use of renewable energy sources of which solar radiation has the
greatest potential. Developing systems that can efficiently convert light energy into
electricity or solar fuels at a cheaper cost while maintaining sustainability is a problem for
scientists as they look into novel materials. Though they presently only make up roughly
10% of the energy supply (or 29% of the overall electrical supply), renewable energy
sources have the potential to significantly expand (Lund, 2009).

A limitless supply of energy can be obtained from renewable energy sources,

which are also sustainable. Renewable energy sources have been used in many nations in
recent years to meet an increasing number of basic household needs, including
transportation, air and water heating and cooling, electricity, and rural (off-grid) energy
services. Of all the renewable sources, solar energy is the most widely used (Ray, 2019).

The organic solar cell (OSC), which has a variety of materials, low energy
consumption, and can be printed in large areas at a low cost, is a key component of the
optoelectronics field and offers a valuable means of addressing the energy and
environmental crisis through the use of green energy order to mimic the photosynthesis
that occurs when plants use solar energy in the wild, DSSCS, a third generation of OSCs,
primarily use inexpensive metal oxide and photosensitive dyes as its raw materials.
DSSCS are clearly superior due to their long device life, large-area preparation, low cost
and availability of raw materials (Baxter, 2012).

Because of their greater absorption coefficient, ease of geometric variation,

reduced production cost, and other advantages, dye-sensitized solar cells, or DSSCS, are
referred to as third-generation solar energy devices. From 1 to 7 We are aware that there
is a constant need for energy, which leads to a rise in the use of fossil fuels. In order to
reduce global climate change and promote sustainable living, it is imperative that clean

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and renewable energy sources be used appropriately. Because of their low cost,
distributed solar power systems (DSSCS) are being used to reduce the amount of fossil
fuels used; yet, the necessary efficiency is still unattainable. It gives the DSSCS a great
deal of leeway to be creative (Shamsudin et al., 2023).

Fig 1.1 Flexible Organic Solar Cells

Solar Energy: Computational chemistry is crucial for understanding the

fundamental processes involved in solar energy conversion, including light absorption,
charge transfer, and catalytic reactions in solar cells and photocatalysts. Modeling
techniques such as density functional theory (DFT) and time-dependent DFT (TD-DFT)
are used to study the electronic and optical properties of photovoltaic materials, as well as
the mechanisms of photochemical reactions in solar fuel generation.: Computational
chemistry contributes to designing and optimizing materials used in wind turbine blades
and energy storage systems(Sharma et al., 2023)

Hydroelectric Energy: Computational chemistry aids in the development of more

efficient water-splitting catalysts for hydrogen production through electrolysis. By
simulating the electronic structure and reaction pathways of catalytic materials,
researchers can design catalysts with enhanced activity, selectivity, and stability, thus
improving the efficiency of water electrolyzers powered by renewable
electricity.Computational chemistry plays a role in bioenergy research by elucidating the
molecular mechanisms of biomass conversion processes such as enzymatic hydrolysis
and microbial fermentation. Quantum chemical calculations help unravel the enzymatic

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mechanisms involved in cellulose degradation, while molecular modeling techniques aid
in the design of enzyme catalysts with improved activity and specificity for biofuel
production. Computational chemistry is essential for optimizing materials used in
rechargeable batteries, supercapacitors, and other energy storage devices(Yang et al.,
2011).

Renewable energy research benefits significantly from computational chemistry,

which delves into the molecular-level intricacies of various energy conversion processes.
By employing techniques like density functional theory (DFT) and time-dependent DFT
(TD-DFT), researchers unravel the electronic and optical properties of photovoltaic
materials essential for solar energy conversion. Moreover, computational chemistry
elucidates the mechanisms of photochemical reactions involved in solar fuel generation.
This molecular-level understanding aids in the design and optimization of solar cells and
photocatalysts, advancing the efficiency and applicability of solar energy technologies.
Similarly, computational chemistry contributes to the development of catalysts for
biomass conversion and water splitting, essential processes for bioenergy and hydrogen
production, respectively.(Tabor et al., 2018) .

1.2 Solar Energy Resources

Fossil fuels, which have chemical and nonrenewable qualities and are associated
with the risks of the greenhouse effect, have been the primary energy sources in recent
years. Thus, the need for clean, renewable energy sources has arisen., One of the most
promising options for renewable energy sources is solar energy, which offers clean and
limitless energy resources. As a result, there has always been difficulty in developing and
using solar energy. Perovskite solar cells and polymer-based organic solar cells have
developed quickly over the last ten years.O'Regan and Grätzel published the first report
on DSSCS in 1991(Gong et al., 2017).

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 Figure 1.2. Knowledge discovery process using machine learning in material sciences

Scientists have been searching for a renewable energy alternative to meet the
present energy demand due to the depletion of conventional energy sources such as fossil
fuels. The third-generation photovoltaic technology that offers an alternative energy
source is dye-sensitized solar cells (DSSCS). DSSC, or daylight-sensing solar cells, are
photoelectrochemical devices that use light-harvesting molecules called molecular
absorbers to convert sunlight into electrical energy This is a novel energy technology that
resembles photosynthesis. The photoanode, cathode, and redox shuttle are the three parts
of a photovoltaic solar cell(Pallikkara and Ramakrishnan, 2021).

Fig 1.3 Solar Energy Resource

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 To meet the ever-increasing global energy demands, the utilization of solar energy
a clean, renewable, and naturally abundant energy resourcehas attracted considerable
attention in recent decades. Accordingly, photovoltaic devices (or solar cells) have been
extensively developed to meet this energy demand. Dye-sensitized solar cells (DSSCS)
have been widely investigated as a promising candidate for low-cost photovoltaic cells in
the past two decades because of their distinctive features, including shape flexibility,
transparency, better performance under prolonged low-light conditions, thermal dual
stress, different solar incident angles, easy material synthesis, low weight, and cost-
effectiveness. Moreover, new functional materials have been designed to increase the
solar-to-electrical energy conversion efficiency of DSSCS the public sector, DSSCS are
used in flat and curved building skins for building-integrated photovoltaics because of
(Ahmad, 2016).

1.3 Active Ways

Through the direct conversion of solar radiation into electrical energy with the aid
of efficient solar cells, scientists are attempting to reduce the problem of environmental
pollution by consuming less fuel. This is the least expensive and cleanest method of
creating energy. According to recent calculations, the amount of energy required by
humans annually may be met by the sun's light, which reaches Earth in less than an hour.
The photovoltaic effect allowed a solar cell to directly transform light energy into
electrical energy. As a result of photons absorbing light energy, the photovoltaic effect
occurs(Bosio et al., 2020).

Tandem solar cells stack multiple layers of different materials with varying
bandgaps to capture a broader spectrum of sunlight. Computational chemistry assists in
designing and optimizing the materials and interfaces of each layer to maximize light
absorption and minimize losses. Combining perovskite and silicon solar cells in a tandem
configuration has shown promise for achieving high efficiencies. Computational
chemistry helps in understanding and improving the interface between the perovskite and
silicon layers to enhance charge carrier extraction and reduce recombination
losses.DSSCS use organic dyes to absorb sunlight and generate charge carriers.
Computational chemistry aids in the design and optimization of dye molecules to improve
light absorption, charge transfer efficiency, and stability (Fahim et al., 2018)

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Quantum dots are semiconductor nanoparticles that can be tuned to absorb specific
wavelengths of light. Computational chemistry guides the synthesis and optimization of
quantum dot materials for efficient charge generation and transport in solar cells. Hot
carrier solar cells aim to capture and utilize high-energy ("hot") charge carriers before
they thermalize. Computational chemistry assists in studying hot carrier dynamics and
designing materials with low thermalization losses and efficient carrier extraction.
Plasmonic nanoparticles can enhance light absorption in solar cells by concentrating
electromagnetic fields near the cell surface(Amirjani and Sadrnezhaad, 2021)

1.4 Solar Cell

Global energy crisis confronting humanity is caused by the slow, unavoidable, and
continuous depletion of fossil fuels and the rising energy consumption to sustain the
existing economic growth paradigm. Renewable energy are quickly emerging as the most
promising alternative resource to meet the world's expanding power source
requirements.In this regard, a number of decades have seen a great deal of research into
wind power, solar energy, hydropower, geothermal energy, biomass, and biofuel from
both the scientific and industrial perspectives. Five Since the Sun shines on Earth every
day, it provides about 3 × 1024 J of green energy annually, which is more than the current
world population consumption by a factor of 104(Ellabban et al., 2014).

Fig: 1.4 PN Junction

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 Currently, nearly 80% of the world's energy needs are met by fossil fuels, which
are rapidly running out.1 But the usage of fossil fuels has created environmental risks and
the greenhouse effect, which are now irreversible. Given that global energy consumption
is predicted to increase by roughly 10 TW from present levels to approximately 23 TW in
2050, renewable green energy will undoubtedly need to develop continuously. With solar
radiation reaching 3 × 1024 J annually, which is almost ten times the current global energy
demand, harvesting solar energy is a highly tempting option. In 1954, Bell Laboratories
discovered the first viable PV cell, or first-generation solar cell, using diffused silicon p–n
junction technology. Since then, solar photovoltaic (PV) technology has advanced
(Dambhare et al., 2021).

1.5 Solar Cell Technology

Our society's constant need for energy, both electrical and otherwise, might be
met by harnessing the nearly limitless energy that solar photons provide. It is projected
that between 2011 and 2030, the planet's energy demand will rise by 1.6% year,
translating into a 36% increase in worldwide consumption. One In 2012, 104[thin space
(1/6-em)] kWh were consumed overall.426 TW h2, whereas 1[thin space (1/6-em)] is
produced annually by sunlight striking the Earth's surface.070[short gap (1/6-
em)]300[fine gap (1/6-em)]h TW.3 Compared to the usage of nuclear or fossil fuels, solar
energy conversion has the advantage of being less harmful to the environment. An
electron is produced in an n-type semiconductor when photons with energy equal to or
higher than the band gap are emitted (Bugajski and Lewandowski, 1985).

Fig 1.5 Solar Cell Technology

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 published examining DSSC as a productive, affordable substitute for traditional
solar cells.,. Three crucial phases are shown by a DSSC in converting sunlight into
electrical energy. It depends on the visible photo-excitation of dyes to initiate an electron
transfer into the metal oxide semiconductor's (usually TiO 2) conduction band. Then, the
oxidized dye molecules are regenerated by the electron donation from the redox couple in
the electrolyte, and the electrons migrate through the external load to complete the circuit.
Many DSSC components, including the hole-transport agent (redox couple in electrolyte),
the electron-transport agent (broad band-gap nanocrystalline semiconductor), and the
light-absorber (dye/sensitizer), enable the full operation (Agasti et al., 2022).

1.5 .1 Perovskites solar cells

Perovskite solar cells, polymer heterojunction solar cells, and DSP solar cells are
the three varieties of organic material-based solar cells. Perovskite solar cells have the
best efficiency among them; a single-junction perovskite solar cell recently achieved
23.3% efficiency. However, perovskite solar cells are less robust against humidity and
oxygen, and their production is still a challenging process, which makes them tough to
sell. Polymer solar cells have a lower efficiency (10%) and frequently need a complex
process to make them.The PCE associated with DSSCS has increased by 7% to around
14%, and their manufacture is substantially simpler.DSSCS offer an effective power
output under all lighting circumstances, including LED and fluorescent lights. When
exposed to weak or scattered sunlight (Karwan Wasman, 2016).

Fig:1.6 Cross section of a solar cell.

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1.5 .2 Components of solar cell

The conversion of solar energy has the potential to produce an almost infinite
supply of clean, renewable energy. Although solar power was not as cost-effective in
previous decades as electricity generated by nuclear, fossil fuel, or hydroelectric sources,
the price of photovoltaic modules has been falling consistently since the 1970s at a pace
of roughly 15% annually. The production, distribution, and consumption of electricity
will all undergo radical transformations as low-cost photovoltaics reach grid parity in an
increasing number of wealthy countries. Currently, approximately 39% of the main
energy used in the United States is produced through the usage of fossil fuels. The
remaining 61% of the US energy industry (Abas et al., 2015).

Because they could be used as a more affordable option to p-n junction solar cells
dye-sensitized solar cells have garnered a lot of attention. The semiconductor in dye-
sensitized solar cells is independently controlled for light absorption and charge carrier
transport, while in traditional solar cells these jobs are shared by the semiconductor. Light
is absorbed by a photosensitizing dye that is adhered to the surface of a wide band gap
semiconductor. Rapidly splitting photogenerated excitons left oxidized dye molecules
behind when their electrons were moved to the semiconductor's conduction band. To
lessen the iodide ion in the electrolyte, the electrons go from the external circuit to the
counter electrode. The reduction process is how the iodide ions return the electrons to the
dye. Thus far, porous TiO2 and ruthenium complexes have primarily (Reynal and
Palomares, 2011)

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 Fig 1.7:Silicon, the raw material for manufacturing a photovoltaic solar pane

1.6 Solar Cell process

We must provide a suitable response to the topic of how mankind will be able to
meet its energy needs in the near future, as the world's population is expected to reach
eight billion by the middle of this century, and it is predicted to reach ten billion by then.
In addition to being non-renewable, fossil fuels produce a significant amount of carbon
dioxide, a greenhouse gas that is today considered a serious threat to the earth's ecology.
Fossil fuels currently account for the majority of the world's electricity production.
Examining energy extraction, conversion, storage, transmission, and distribution
operations that deliver final energy to end-users, the Intergovernmental Panel on Climate
Change (IPCC) concluded that the energy supply sector is the primary source of
greenhouse gas emissions globally (Rahman et al., 2017).

Dye-sensitized solar cells (DSSCS) have attracted considerable attention due to

their relatively low production cost, transparency and flexibility. It is known that the
operating principle of DSSCS usually involves excitation of the dye followed by charge
transfer from the dye to the conduction band of TiO 2. Thus, the oxidized state of the dye
is obtained and then regenerated by receiving an electron from a redox mediator in the
electrolyte. Accordingly, the highest occupied molecular orbital (HOMO) level of the dye
should be sufficiently positive compared to the potential of the redox mediator in the
electrolyte for efficient dye regeneration. Therefore, dye regeneration depends strongly on
both the potential of the redox mediator and the HOMO level of dyes. Typically,
iodide/triiodide (I−/I3−) and [Co(bpy)3]2+/3+ are most (Gong et al., 2017).

1.6.1 Solar Cell working Mechanism

A lot of work is being done on renewable energy sources that are green and
alternative in order to reduce the negative environmental effects of burning fossil fuels
and prepare for future energy crises. Solar energy is acknowledged as a cutting-edge
replacement for traditional energy sources. A solar cell is any device that uses
photovoltaic (PV) technology to directly convert light energy into electrical energy. There
are basically three generations of solar cells. Based on crystalline silicon, first-generation
solar cells currently have a leading position in the photovoltaic sector thanks to their high

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efficiency of up to 25%.One But the methods involved in fabricating the devices are quite
costly, and high-purity silicon is needed in the production of silicon-based sun cells. The
silicon-based photovoltaics sector has been mostly dependent on (Dubey et al., 2013).

1.6.2 PN Junction

The PN junction is a semiconductor interface where P-type (positively doped) and

N-type (negatively doped) materials meet. This junction forms the basis of many
electronic devices, including solar cells.: In DSSCS, a light-absorbing dye is used to
capture photons from sunlight. This dye is typically a photosensitive organic compound
that can absorb a broad range of wavelengths. The dye-sensitized semiconductor is
immersed in an electrolyte solution. This solution contains ions that facilitate the
movement of charge within the: Conductive electrodes, typically made of materials like
platinum or carbon, are used to collect the generated electrons and transport them out of
the cell as electrical current.: The excited electrons are injected into the conduction band
of the semiconductor material, leaving behind positively charged "holes" in the dye
molecules. This creates a flow of electrons towards one electrode (typically the cathode)
and holes towards (Dutton et al., 1993).

1.7 First Generation of solar cell

As the world economy has grown so quickly since the turn of the twenty-first
century, so too has the demand for energy. After three decades of significant
advancement, solar energy could be considered a primary source of energy in the future.
In previous decades, dye-sensitized solar cells (DSSCS) were created because of their
high absorption, high stability, and potential for efficient solar energy conversion to
electrical power. With a hard conducting glass planar substrate, the photoelectric
conversion efficiency (PCE) of DSSCS has surpassed 11%. Quantum-dot-sensitized solar
cells (QDSSCS) are capable of displaying the distinct benefits of quantum size effect,
multi-exciton effect, and massive absorption by substituting semiconductor quantum dots
(QDs) for organic dyes in sensitizers (Shah et al., 2023).

1.7.1 Electronic Structure Calculations

Computational chemistry methods, such as density functional theory (DFT),

allow researchers to calculate the electronic structure of materials used in solar cells. This

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includes understanding the energy levels of electrons within the semiconductor material
(e.g., silicon) and how these levels affect the absorption and emission of light.:
Computational tools can predict the optical properties of solar cell materials, such as their
absorption spectra and optical bandgaps. This information is vital for optimizing the
design of solar cells to maximize light absorption and energy conversion efficiency.
Understanding the dynamics of charge carriers (electrons and holes) within the solar cell
is essential for improving efficiency. Computational chemistry models can simulate how
charge carriers move through the semiconductor material, encounter defects or traps, and
contribute to the generation of electricity. By combining computational chemistry with
machine learning algorithms, researchers can accelerate the discovery and optimization of
new materials for solar cells. This approach involves screening large databases of
candidate materials to identify those with desirable properties for photovoltaic
applications (Zhang et al., 2019b).

1.7.2 Mono Crystalline silicon solar cell

Solar energy technology is a promising solution that has been used more and more
recently to meet our energy needs as coal and natural resources are being depleted at
faster rates. Silicon-based solar cells are the most widely used, but their manufacturing
costs are quite high, the next challenge is to produce solar cells based on cheap materials
with straightforward manufacturing processes. This type of solar cell is called dye-
sensitized solar cells (DSSCS), which were invented by O'Regan and Gratzel in DSCs,
synthetic or natural resource dye is used as “the sensitizer”, producing electrons and holes
under illumination that are transferred to the conduction band (Shahsavari and Akbari,
2018).

1.7.3 Poly crystalline solar cells

Every day, there is a greater need for energy. Fossil fuel extraction is the primary
source of pollution in the environment. Energy demand is directly impacted by the
population's rapid growth. Since fossil fuels are burned, the amount of greenhouse gases
released into the atmosphere is rising. Elevated earth temperatures due to greenhouse gas
emissions have the potential to trigger catastrophic natural calamities. Human health has
also been impacted by environmental contamination. Nonetheless, industry needs energy
to function. There will be more poverty in the globe if the industry's wheels are stopped.
Owusu and Asumadu-Sarkodie (2016) state that as a result, it is imperative to find a

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substitute energy source to replace coal, gas, and oil. Solar power is the origin
(Govorushko, 2013).

1.7.4 Material Design and Optimization

Computational chemistry techniques, such as density functional theory (DFT)

calculations, can be employed to study the electronic structure and properties of materials
used in poly-crystalline solar cells. Researchers can simulate various material
compositions and structures to optimize their efficiency, stability, and other relevant
properties. Defect Engineering: Defects in poly-crystalline materials can significantly
affect their electronic and optical properties. Computational chemistry methods can help
in understanding the formation, migration, and impact of defects on the performance of
solar cells. This understanding can guide experimental efforts to mitigate the adverse
effects of defects and enhance the overall device performance.: Interfaces between
different layers in a solar cell structure (e.g., between the absorber layer and the
electron/hole transport layers) play a crucial role in charge separation and collection
processes. Computational chemistry can provide insights into the atomic-scale structure
and properties of these interfaces, aiding in the design of interfaces that facilitate efficient
charge transport and minimize recombination losses.: Computational chemistry
techniques can also be used to calculate the optical properties of poly-crystalline
materials, such as absorption spectra and exciton dynamics. This information is essential
for understanding light-matter interactions in solar cells and optima Computational
chemistry can help predict the stability of poly-crystalline materials under different
environmental conditions, such as exposure to light, heat, and moisture. By identifying
degradation mechanisms and designing more stable materials, computational methods can
contribute to the development of long-lasting solar cell technologies (Rahman et al.,
2023b).

Density Functional Theory (DFT)

It can be employed to understand the band structure, electronic properties, and

optical properties of mono crystalline silicon solar cells. By calculating the electronic
density of states (DOS) and band gaps, researchers can gain insights into the behavior of

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charge carriers and the efficiency of solar cells. Quantum mechanical simulations using
methods like Hartree-Fock or post-DFT approaches like Many-Body Perturbation Theory
(MBPT) can provide more accurate descriptions of electronic properties, especially for
phenomena like exciton binding energies and charge transfer processes within the solar
cell. : MD simulations can be used to investigate the structural stability and dynamics of
the silicon lattice within the solar cell under different conditions such as temperature,
pressure, and mechanical stress. This information is crucial for understanding the long-
term performance and reliability of the solar cells. Furthermore, the energy efficiency of
silicon-based computing ensures sustainable operation, minimizing environmental impact
while maximizing computational throughput. This eco-friendly approach aligns with the
growing emphasis on green technology and responsible innovation (Marzari et al., 2021).

In the realm of materials science, single-cell silicon computational chemistry

revolutionizes the dIn the pharmaceutical industry, this technology facilitates rapid virtual
screening of drug candidates, significantly reducing the time and cost associated with
traditional experimental approaches (Pandey et al., 2022).

1.8 Second Generation solar cells

With the first publication by O'Regan and Grätzel in 1991, dye-sensitized solar
cells (DSCs) have become a viable low-cost alternative energy option to the conventional
silicon-based p-n junction solar cells. With DSCs using complicated redox mediators
based on cobalt, power conversion efficiencies (PCEs) greater than 12% have been
achieved. Nevertheless, the volatile nature of the liquid electrolyte poses a risk of leakage
for these cells, which restricts the technology's applicability in mass production. Bach et
al. (1998) developed a p-type organic semiconductor known as ′-tetrakis-(N,N-di-p-
methoxyphenyl-amine)9,9′ spiro-bifluorene (Spiro-OMeTAD) to replace the liquid
electrolyte as a redox couple in the fabrication of "solid-state" dye-sensitized solar cells
(DSCs). This was done in an effort to address these problems.Four The third generation
of solar photovoltaic devices, dye sensitized solar cells (DSSCS), have garnered
significant attention in the last 20 years because of its lower fabrication costs,
straightforward manufacturing method, and improved energy conversion efficiency and a
lot of research has been done recently on metal oxide semiconductors, such as TiO 2,
Fe2O3, SnO2, ZnO, and Nb2O5, as the photo-anode for sandwich-tape construction
DSSCS. ZnO is regarded as one of the most promising photo-anode materials because to

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its favorable band-edge positions, abundance, environmental friendliness, and greater
electron mobility than TiO2. It is therefore necessary to have a flawless ZnO
nanostructure, which might offer a direct channel for electron transfer. Up to now, DSCs
have attained the maximum efficiency of 7.2% (Benesperi et al., 2018).

1.8.1 Material Discovery and Design

Computational chemistry allows researchers to explore the properties of various

materials at the atomic and molecular levels. This includes understanding their electronic
structure, optical properties, and stability. By simulating different materials and their
interactions, researchers can identify promising candidates for use in second-generation
solarSecond-generation solar cells often utilize materials like thin-film semiconductors,
organic polymers, or perovskites, which have different absorption spectra compared to
silicon. Computational chemistry can predict how these materials absorb and emit light,
helping to design structures that maximize light absorption and minimize losses due to
reflection or transmission. Efficient charge transport is essential for converting absorbed
sunlight into electrical energy. Computational chemistry can model the movement of
charge carriers (electrons and holes) within the solar cell materials. By understanding
factors such as carrier mobility and recombination rates, researchers can optimize device
structures to enhance charge transport and minimize energy losses. Interfaces between
different layers or materials within the solar cell can significantly affect device
performance. Computational chemistry can simulate these interfaces at the molecular
level, providing insights into their electronic structure, energy levels, and potential
barriers to charge transport. This information is crucial for designing interfaces that
facilitate efficient charge extraction and minimize recombination losses. Computational
chemistry can predict the stability and degradation mechanisms of solar cell materials
under different environmental conditions, such as exposure to light, heat, moisture, or
oxygen. By identifying degradation pathways and weak points, researchers can develop
strategies to enhance the stability and durability of second-generation solar cells
(Mazumdar et al., 2021).

1.8.2 Amorphous silicon thin Film Solar cells

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 Over time, there has been a sharp rise in the population, fast industrial growth, and
energy demand. Presently, non-renewable energy sources such as coal, fossil fuels, and
natural gas account for most energy usage; while they generate more than 80% of energy,
they have negative environmental effects. Fossil fuel reserves are predicted by
econometric models to be completely depleted by 2042The globe is therefore searching
for alternative renewable resources, such as solar, wind, geothermal, thermal, and so
forth. Of all the renewable energy sources that are currently accessible, solar energy is
regarded as a practical substitute because the amount of energy that is obtained from the
sun in a single hour is greater than the total amount of energy that people use in a year
(Jiang and Lin, 2012).

1.8.3 Electronic Structure Calculations

Computational chemistry techniques, such as density functional theory (DFT), are

used to calculate the electronic structure of a-Si and related materials. These calculations
provide insights into the bandgap, band structure, and defect states, which are crucial for
understanding the optical and electrical properties of the material. Computational
methods can simulate the absorption and emission spectra of a-Si thin films.
Understanding these optical properties is essential for optimizing the efficiency of solar
cells, as it governs how efficiently the material converts sunlight into electricity. Defects
in the amorphous structure of a-Si can significantly impact the performance of solar cells.
Computational chemistry allows researchers to study the formation and properties of
defects, as well as strategies for mitigating their impact through defect engineering.
Interfaces between different layers in a-Si thin-film solar cells (such as the interface
between the a-Si layer and the transparent conducting oxide layer) are critical for device
performance. Computational chemistry can be used to study the structure and electronic
properties of these interfaces and optimize their compatibility and charge transport
properties.: Understanding the stability of a-Si thin films under different environmental
conditions is crucial for the long-term performance of solar cells. Computational
chemistry can predict degradation pathways, identify stability-limiting factors, and
suggest strategies for improving the stability of the material (Porter, 2011).

1.8.4 Thin Film solar cells Made of Cadmium Tellurrate

The majority of energy sources used today are non-renewable and consist of
natural gas, coal oil, and fossil fuels. Although these sources produce more than 80% of

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the energy, they are harmful to the environment. Econometric models indicate that the
world's fossil fuel supplies will run out by 2042. For this reason, people all over the world
are looking for additional renewable resources, like solar, wind, geothermal, thermal, and
so on. Because solar energy can be produced from the sun in less than an hour and is
more abundant than human energy consumption in a day, it is considered a viable
alternative to other renewable energy sources (Asif and Muneer, 2007).

Computational chemistry tools like density functional theory (DFT) can be employed to
optimize the atomic structure of the CdTe thin film. This involves calculating the most
stable arrangement of atoms to minimize energy. DFT can also be used to calculate the
electronic band structure of CdTe. This helps in understanding how electrons move
within the material and how it absorbs light.: Computational methods can predict the
optical properties of CdTe thin films, such as absorption spectra, reflectance, and
transmittance. This is crucial for understanding how efficiently the material can convert
sunlight into electricity.: Defects in the crystal lattice can significantly affect the
performance of solar cells. Computational chemistry can simulate different types of
defects in CdTe and analyze their impact on electronic and optical properties.CdTe thin
film solar cells often include interfaces with other materials, such as transparent
conducting oxides or buffer layers. Computational chemistry can investigate the
properties of these interfaces and how they influence the overall device performance. By
combining all the above insights, computational chemistry can aid in optimizing the
performance of CdTe thin film solar cells. This could involve designing new materials or
device structures to enhance efficiency and stability. Keep in mind that while
computational chemistry is powerful, it should be complemented with experimental
validation to ensure accuracy and reliability. Additionally, the choice of computational
method and parameters can significantly impact results, so careful consideration and
validation are essential (Oberkampf and Trucano, 2002).

1.9 Third Generation Solar cells

An intriguing idea that has received a lot of attention lately is energy recycling
using indoor energy-harvesting systems. Standard 1 sun conditions (100 mW cm −2) are
commonly used for device testing in dye-sensitized solar cells (DSSCS), which imitate
outdoor lighting conditions with an intensity of more than 100,000 lux. The indoor energy
harvesting technique, on the other hand, uses a reduced photon flux between 300 and

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6000 lux when operating in low light or dim light conditions. The spaces that are
illuminated between these ranges are typically houses, schools, offices, factories,
hospitals, labs, production halls, first aid stations, and show rooms. As incandescent light
bulbs are gradually replaced with LEDs, the lighting in these locations has undergone a
full transformation these days (Sanderson and Simons, 2014).

1.9.1 Material Discovery and Design

Computational chemistry techniques like density functional theory (DFT) and

molecular dynamics simulations help identify and design novel materials with desirable
properties for solar cells. Researchers can simulate the behavior of materials under
different conditions to predict their efficiency and stability. Third-generation solar cells
often rely on complex nanostructures and organic/inorganic hybrid materials.
Computational chemistry allows researchers to optimize the electronic and optical
properties of these materials by fine-tuning their molecular structures and compositions.:
Efficient charge transfer is critical for converting solar energy into electricity.
Computational chemistry provides insights into the mechanisms of charge generation,
separation, and transport within solar cell materials. This understanding guides the design
of materials with improved charge carrier mobility and reduced recombination losses.:
Interfaces between different materials (e.g., between photoactive layers and electrodes)
significantly influence the performance of solar cells. Computational chemistry helps
model and analyze these interfaces at the atomic scale, enabling researchers to engineer
interfaces for enhanced charge extraction and reduced losses.: Stability is a key challenge
for third-generation solar cells. Computational chemistry allows researchers to predict
degradation mechanisms and identify strategies to enhance the stability of materials and
devices. By simulating degradation pathways, researchers can design materials with
improved long-term performance.: Computational screening techniques enable high-
throughput evaluation of a wide range of potential absorber materials for solar cells. By
simulating the electronic and optical properties of candidate materials, researchers can
identify promising candidates for experimental validation (Luo et al., 2021).

1.9.2 Organic solar cells

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 In recent decades, there has been a growing need for energy, which has prompted
researchers to investigate various energy sources. But growing awareness of climate
change and global warming has brought attention to renewable energy sources like
geothermal, hydro, wind, and solar power. Solar energy is thought to be the most reliable
and plentiful of all these energy sources. Energy from sunshine is absorbed by solar cells
and transformed into electrical power. Green plants use photosynthesis to produce
molecules necessary for growth and development by absorbing solar energy. Chlorophyll,
a pigment that absorbs light, is responsible for capturing photons from the sun that the
process requires to take place. Third-party solar cells that are dye-sensitized (DSSCS)
(Grätzel, 2003).

Organic solar cells are a promising technology for renewable energy generation
due to their low cost, flexibility, and potential for large-scale production. Computational
chemistry plays a crucial role in the design, optimization, and understanding of organic
solar cells. Here's how computational chemistry contributes to the development of
OSCs.Molecular Design and Screening: Computational chemistry techniques, such as
molecular dynamics simulations and quantum chemical calculations, allow researchers to
design and screen organic molecules for their suitability as photoactive materials in
OSCs. These simulations predict electronic structure, optical properties, and charge
transport behavior, aiding in the selection of candidate materials with desirable properties
(Lund et al., 2015).

Fig 1.8: Hybrid Organic polymer electrolytes for dye sensitized solar cell

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 enables the optimization of organic semiconductor materials by exploring the
effects of molecular structure, functionalization, and packing arrangement on their
electronic and optical properties. This optimization process aims to enhance light
absorption, charge mobility, and exciton diffusion within the active layer of the solar
cell.OSCs operate via the generation, diffusion, and dissociation of excitons (electron-
hole pairs). Computational chemistry techniques provide insights into exciton dynamics
within organic materials, including exciton diffusion lengths, dissociation probabilities,
and recombination rates. Understanding these processes helps improve the efficiency of
OSCs by minimizing exciton losses. Interfaces between different layers (e.g., between the
donor and acceptor materials) significantly impact the performance of OSCs.
Computational chemistry allows for the modeling of interfaces at the molecular level,
elucidating charge transfer mechanisms, interfacial energetics, and the role of interfacial
structures in charge transport.: Computational chemistry is used to simulate the
performance of complete OSC devices, including the active layer, electrodes, and
interlayers. These simulations aid in device optimization by predicting key parameters
such as power conversion efficiency, open-circuit voltage, short-circuit current, and fill
factor. Researchers can iterate device designs virtually to achieve optimal performance
(Jensen, 2017).

1.11. Polymer Based solar cells

An intense research effort has been directed toward the development and
application of sustainable technologies for energy conversion and storage, ranging from
fuel cells to Li-ion batteries from wind-power plants to photovoltaic panels due to global
concerns about the exploitation of fossil fuels and the associated environmental issues.
The most practical renewable energy source on earth is sunshine, in particular, but the
technological difficulties of attaining an efficient conversion with inexpensive materials
continue to impede the effective deployment of photovoltaics. The current workhorse
technologies for solar energy conversion in this context are solid-state silicon-based solar
panels, however they still have low efficiency under diffuse light circumstances (cloudy
days). Furthermore, while the advantages of mass production have helped to lower the
cost of Si-based devices in recent years (Mayer et al., 2007).

Organic photovoltaics or OPVs) have gained significant attention due to their

potential for low-cost, lightweight, and flexible solar energy harvesting. Computational
chemistry plays a vital role in understanding and optimizing the materials and processes
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involved in polymer-based solar cells. Computational chemistry techniques aid in the
design and screening of conjugated polymers and organic molecules for use as
photoactive materials in OPVs. Quantum chemical calculations and molecular dynamics
simulations predict electronic and optical properties, enabling the identification of
materials with suitable energy levels, absorption spectra, and charge transport properties
(Thakur and Devi, 2022).

Computational Simulation allows for the optimization of polymer structures, side-

chain engineering, and morphology control to enhance the performance of OPVS. By
simulating the effects of molecular structure, packing arrangement, and intermolecular
interactions, researchers can improve light absorption, charge mobility, and exciton
diffusion within the active layer of the solar cell. Understanding exciton dynamics is
crucial for efficient charge generation and collection in OPVS. Computational chemistry
techniques provide insights into exciton diffusion, dissociation, and recombination
processes within polymer-based materials. By modeling exciton transport and decay
pathways, researchers can optimize material properties to minimize exciton losses and
enhance device performance.Interfaces between different layers in OPVs, such as
between the photoactive layer and electrodes, significantly influence device performance.
Computational chemistry allows for the modeling of interfaces at the molecular level,
elucidating interfacial energetics, charge transfer mechanisms, and the role of interfacial
structures in charge transport and recombination. Computational chemistry assists in
predicting the stability of polymer-based materials and devices under various
environmental conditions and operational stresses. By simulating degradation pathways,
such as photochemical degradation, chemical reactions, and morphological changes,
researchers can design more stable OPVs with improved long-term performance (Park et
al., 2020).

1.11.1 Advantages

Applications include energy conversion, energy storage, and fuel generation

catalysis are being investigated for a wide variety of materials. One of the key materials,
TiO2, has become well-known for its applicability in a variety of research fields,
including water splitting, reducing CN− in water for environmental purification
antifogging and self-cleaning mechanisms and several more. As an anode in Li-ion
batteries a photo-catalyst for H2 synthesis and a solar cell application nanostructured
TiO2 is very useful. Anatase, rutile, and brookite are the three imary phases in which TiO 2

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crystallizes. The majority of the applications listed previously typically use the latter two
of these, rutile and anatase (Sun et al., 2016).

Third-generation photovoltaics (PV) have been the subject of study during the
past 20 years, with the goal of developing low-cost, high-efficiency cells based on thin-
film technologies employing organic and/or inorganic materials. Desensitized solar cells
(DSSCS) offer a lot of promise as inexpensive, simple-to-fabricate, and highly efficient
third-generation PV devices. Using liquid electrolytes based on volatile organic
compounds (VOCs) that are hazardous, like acetonitrile, is one of the primary problems
with the best-performing DSSCS. It is obvious that this makes it more difficult for our
society to use these devices widely. Other solvents, such as ionic liquids (IL), liquid
solutions adsorbed in polymeric matrices, and solvent-free solid-state cells, have been
suggested as electrolyte media to get around these problems. Every one of them (Li et al.,
2020).

1.12 Dye-sensitized solar cells (DSSCS)

The efficiency of dye-sensitized solar cells (DSSCS) has recently surpassed 14%,
one of its primary disadvantages the usage of a liquid electrolyte composed of
combinations of extremely volatile organic solvents remains. Significant obstacles to the
broad use of third-generation solar cells include high vapor pressure, flammability,
toxicity, and negative environmental effects. These factors also limit the use of organic
solvents. There have been a few intriguing substitutes for organic solvents put forth, such
as solid-state conductors and plastic crystals, but these are currently quite expensive and
show very little stability over the long run. Additionally, one significant issue that is
frequently overlooked in conventional aprotic DSSC systems is the contamination caused
by moisture or water. The performance and long-term stability of the cell are both
impacted by this undesirable behavior.6 (Gong et al., 2017).

1.12.1 cost-Effectiveness

Computational chemistry significantly reduces the cost of materials and

experimental procedures by allowing researchers to screen and optimize candidate
materials virtually before synthesis and testing. This saves both time and resources in the
research and development process.: Computational chemistry enables rapid design
iterations by quickly evaluating the electronic, optical, and structural properties of various
materials and device architectures. Researchers can explore a wide range of possibilities

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and make informed decisions to optimize solar cell performance. Computational
chemistry provides detailed insights into the fundamental processes underlying solar cell
operation, such as charge transfer, exciton dynamics, and interface behavior.
Understanding these processes at the molecular level guides the design of more efficient
and stable solar cell materials and devices. Computational chemistry allows for the
prediction of material properties, including electronic structure, optical absorption, charge
mobility, and stability. This predictive capability accelerates the discovery of new
materials with desired characteristics for solar cell applications. Computational chemistry
enables high-throughput virtual screening of large databases of candidate materials for
solar cells. By simulating the properties of numerous materials, researchers can identify
promising candidates for experimental validation, speeding up the materials discovery
process (Lewis, 2007).

Computational chemistry facilitates the optimization of solar cell performance by

modeling complete device architectures and simulating key parameters such as efficiency,
voltage, and current. Researchers can fine-tune device parameters to achieve optimal
performance without the need for extensive experimental trial and error. Computational
chemistry helps elucidate degradation mechanisms in solar cell materials and devices by
simulating degradation pathways and identifying vulnerable molecular sites. This
understanding guides the development of more stable and durable solar cell technologies
(Labat et al., 2012).

Material Design and Optimization: Computational chemistry allows researchers to

simulate the structure and properties of materials at the atomic level. This helps in the
design and optimization of materials used in solar cells to improve efficiency and
stability. Researchers can explore different chemical compositions, doping strategies, and
nanostructures to enhance light absorption, charge transport, and overall device
performance.: Solar cells operate based on the conversion of light energy into electrical
energy through photovoltaic processes. Computational chemistry techniques, such as
density functional theory (DFT) and ab initio methods, can accurately predict the
electronic structure of materials. This includes the bandgap, energy levels of electronic
states, and charge carrier mobility, which are crucial factors in determining the efficiency
of solar cells.: Understanding the dynamics of excited states is essential for optimizing the
efficiency of solar cells. Computational chemistry can simulate processes such as exciton
generation, dissociation, and recombination, which occur upon absorption of photons by

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the solar cell material. By modeling these processes, researchers can identify ways to
minimize energy loss and improve charge separation and extraction (Hafner et al., 2006).

Solar cells consist of multiple layers and interfaces where charge carriers are
generated, transported, and collected. Computational chemistry can investigate the
properties of these interfaces, such as energy level alignment, interface recombination,
and surface passivation. This knowledge helps in engineering interfaces to enhance
charge transfer and reduce losses, ultimately improving the overall performance of the
solar cell device. With the vast space of possible material compositions, computational
chemistry provides a valuable tool for screening and identifying promising candidates for
solar cell applications. High-throughput computational screening can efficiently explore
the properties of numerous materials, accelerating the discovery of novel materials with
desirable properties for solar energy conversion. Overall, computational chemistry plays a
crucial role in advancing the understanding and development of materials for solar cells,
offering insights that complement experimental investigations and guiding the design of
more efficient and cost-effective photovoltaic devices Top of Form (Graetzel et al.,
2012).

1.12.3 Concentrated photovoltaic cells

Dye-sensitized solar cells (DSSCS) have recently achieved efficiencies of over

14%, but one of their primary disadvantages the use of a liquid electrolyte made of
combinations of extremely volatile organic solvents remains Two Organic solvents have
significant limitations due to their flammability, toxicity, high vapor pressure, and
negative environmental effects. These factors also have a significant impact on the
widespread diffusion of third-generation solar cells. Though they are currently very
expensive and show very little long-term stability, a few intriguing substitutes for organic
solvents have been proposed, such as plastic crystals and solid-state conductors.
Furthermore, a crucial factor that is frequently overlooked in conventional aprotic DSSC
systems is the contamination caused by moisture or water. The performance of the cell as
well as its long-term stability are impacted by this undesirable event.Even though an
organic photosensitizer absorbs sunlight's photons, which results in the creation of
excitons (electron and hole). This is the initial stage in the production of DSSCS. The
highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital
(LUMO) gap energy of an organic photosensitizer and the conjugated system of this dye

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are required for this procedure. Inserting an electron from the dye's LUMO into the
semiconductor's conduction band (CB), like TiO 2, is the second stage. The mechanism
and efficiency of Dictyo-Semiconductor-Self-Cells (DSSCS) are significantly influenced
by molecular orbital energies, including HOMO, LUMO, and gap energy (H–L).
Determined by the type of anchoring groups, significant adsorption between the dye and
TiO2 is necessary for the electron transfer from dye to TiO2(Hasan et al., 2018).

Computational chemistry facilitates the optimization of solar cell performance by

modeling complete device architectures and simulating key parameters such as efficiency,
voltage, and current. Researchers can fine-tune device parameters to achieve optimal
performance without the need for extensive experimental trial and error. Computational
chemistry helps elucidate degradation mechanisms in solar cell materials and devices by
simulating degradation pathways and identifying vulnerable molecular sites. This
understanding guides the development of more stable and durable solar cell technologies
(Labat et al., 2012).

Material Design and Optimization: Computational chemistry allows researchers to

simulate the structure and properties of materials at the atomic level. This helps in the
design and optimization of materials used in solar cells to improve efficiency and
stability. Researchers can explore different chemical compositions, doping strategies, and
nanostructures to enhance light absorption, charge transport, and overall device
performance.: Solar cells operate based on the conversion of light energy into electrical
energy through photovoltaic processes. Computational chemistry techniques, such as
density functional theory (DFT) and ab initio methods, can accurately predict the
electronic structure of materials. This includes the bandgap, energy levels of electronic
states, and charge carrier mobility, which are crucial factors in determining the efficiency
of solar cells.: Understanding the dynamics of excited states is essential for optimizing the
efficiency of solar cells. Computational chemistry can simulate processes such as exciton
generation, dissociation, and recombination, which occur upon absorption of photons by
the solar cell material. By modeling these processes, researchers can identify ways to
minimize energy loss and improve charge separation and extraction (Hafner et al., 2006).

Solar cells consist of multiple layers and interfaces where charge carriers are
generated, transported, and collected. Computational chemistry can investigate the
properties of these interfaces, such as energy level alignment, interface recombination,

PAGE \* MERGEFORMAT 29
and surface passivation. This knowledge helps in engineering interfaces to enhance
charge transfer and reduce losses, ultimately improving the overall performance of the
solar cell device. With the vast space of possible material compositions, computational
chemistry provides a valuable tool for screening and identifying promising candidates for
solar cell applications. High-throughput computational screening can efficiently explore
the properties of numerous materials, accelerating the discovery of novel materials with
desirable properties for solar energy conversion. Overall, computational chemistry plays a
crucial role in advancing the understanding and development of materials for solar cells,
offering insights that complement experimental investigations and guiding the design of
more efficient and cost-effective photovoltaic devices Top of Form (Graetzel et al.,
2012).

1.12.3 Concentrated photovoltaic cells

Dye-sensitized solar cells (DSSCS) have recently achieved efficiencies of over

14%, but one of their primary disadvantages the use of a liquid electrolyte made of
combinations of extremely volatile organic solvents remains Two Organic solvents have
significant limitations due to their flammability, toxicity, high vapor pressure, and
negative environmental effects. These factors also have a significant impact on the
widespread diffusion of third-generation solar cells. Though they are currently very
expensive and show very little long-term stability, a few intriguing substitutes for organic
solvents have been proposed, such as plastic crystals and solid-state conductors.
Furthermore, a crucial factor that is frequently overlooked in conventional aprotic DSSC
systems is the contamination caused by moisture or water. The performance of the cell as
well as its long-term stability are impacted by this undesirable event.Even though an
organic photosensitizer absorbs sunlight's photons, which results in the creation of
excitons (electron and hole). This is the initial stage in the production of DSSCS. The
highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital
(LUMO) gap energy of an organic photosensitizer and the conjugated system of this dye
are required for this procedure. Inserting an electron from the dye's LUMO into the
semiconductor's conduction band (CB), like TiO 2, is the second stage. The mechanism
and efficiency of Dictyo-Semiconductor-Self-Cells (DSSCS) are significantly influenced
by molecular orbital energies, including HOMO, LUMO, and gap energy (H–L).
Determined by the type of anchoring groups, significant adsorption between the dye and
TiO2 is necessary for the electron transfer from dye to TiO2(Hasan et al., 2018).

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1.13 Material Simulation

Computational chemistry can model the materials used in CPV systems, such as
semiconductor materials for high-efficiency solar cells or optical materials for
concentrator lenses. While not specific to CPV, these simulations aid in understanding the
properties of materials and can guide their selection for use in CPV systems.
Computational techniques like ray tracing and optical simulations can model the behavior
of light within CPV systems. This helps optimize concentrator designs, such as
determining the ideal shape and size of lenses or mirrors to maximize light concentration
onto the solar cells.CPV systems can experience high temperatures due to concentrated
sunlight. Computational modeling, including computational fluid dynamics (CFD), can
predict thermal effects and guide the design of cooling systems to maintain optimal
operating temperatures for the solar cells.: Computational methods, such as numerical
optimization algorithms, can optimize CPV system parameters such as concentrator
geometry, solar cell arrangement, and tracking algorithms to maximize energy output and
efficiency. Computational modeling can predict the long-term performance and
degradation of CPV systems, considering factors such as material degradation, thermal
stress, and environmental conditions. This aids in designing CPV systems with extended
lifetimes and reliability. While computational chemistry isn’t directly involved in CPV
technology, other computational methods contribute to the design, optimization, and
understanding of CPV systems, ultimately improving their efficiency, reliability, and
cost-effectiveness (Liu et al., 2012).

1.14 Hybrid solar cells

Due to its ease of fabrication and ability to function well in scattered light, dye-
sensitized solar cells (DSSCS) have attracted increasing attention Due to its potential
influence on device stability and efficiency, dye sensitizer is one DSSC component that
cannot be excluded. Nanocrystalline TiO2, a counter electrode, and an electrolyte are the
final parts to achieve greater efficiency, every component must be optimized. The most
effective previous were ruthenium complexes, which demonstrated an 11% power
conversion efficiency Large-scale use of them is, however, hampered by a number of
factors, including expensive costs, depleted deposits, and environmental concerns.
Although the zinc porphyrin sensitizer demonstrated a 13% efficiency metal

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environmental concerns make it impossible(Mendizabal et al., 2015). Research on
sustainable energy alternatives has been spurred by the current climate catastrophe and
alarming trends in global warming brought on by the usage of conventional fossil fuels.
Biofuels, nuclear, solar, wind, geothermal, and hydropower are just a few of the
numerous renewable energy sources that have been researched and developed.Out of all
the potential energy options, solar energy has come to be recognized as a reliable, safe,
and affordable energy source that is also thought to be ecologically benign. Amorphous
silicon (a-Si), dye-sensitized solar cells (DSSCS), perovskites, and cadmium telluride
(CdTe) are among the materials that have been investigated in the development of solar
cell technology and have attractive photovoltaic (PV) performance. Tellurium (Te),
gallium (Ga), and indium (In) are scarce and poisonous, which pose significant obstacles
to the continued development of these technologies (Günes and Sariciftci, 2008).

Computational chemistry techniques, such as density functional theory (DFT) and

molecular dynamics simulations, aid in the design and screening of hybrid materials for
solar cells. Researchers can model the electronic structure, optical properties, and charge
transport behavior of hybrid materials to identify promising candidates with optimal
properties. Hybrid solar cells typically involve interfaces between organic and inorganic
components. Computational chemistry allows researchers to model these interfaces at the
atomic level, understanding the energetics and charge transfer mechanisms across the
interface. This insight helps optimize the interface morphology and chemistry to enhance
charge separation and reduce recombination losses (Tong et al., 2018).

Computational chemistry provides insights into the mechanisms of charge transfer

and transport within hybrid solar cell materials. By simulating exciton dissociation,
charge carrier generation, and transport processes, researchers can optimize material
properties and device architectures to improve overall solar cell performance.
Computational chemistry assists in predicting the stability and degradation mechanisms
of hybrid materials and devices. By simulating degradation pathways, such as chemical
reactions, photochemical degradation, and environmental factors, researchers can design
hybrid solar cells with improved stability and longevity (Cui et al., 2020).

1.14.2 Bio hybrid solar cells

Dye-sensitized solar cells (DSSCS) are seen as a prospective substitute for

traditional p–n junction devices and were initially developed as an economically viable

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photovoltaic technology. Because they have already proven their value to society by
offering power conversion efficiencies (PCE) of over 13% at the laboratory size and 10%
in small solar modules. Because of their outstanding performance in a range of irradiation
situations, DSSCS are regarded as the best option for artificial light, shadowy, or dim
environments. Their manufacturing process is very easy to use, economical, safe for the
environment, and able to meet industrial demands for producing large-area devices
(Musazade et al., 2018)

Bio hybrid solar cells integrate biological components, such as photosynthetic

proteins or enzymes, with synthetic materials to harness solar energy. While
computational chemistry isn't directly involved in the biological aspects of biohybrid
solar cells, it can contribute to understanding and optimizing the synthetic components
and interfaces. Here's how computational chemistry can aid in the development of
biohybrid solar cells (Ravi and Tan, 2015) .

Computational chemistry techniques can be used to design and screen synthetic

materials that interact effectively with biological components. By simulating the
electronic and structural properties of materials, researchers can identify candidates that
promote efficient charge transfer and compatibility with biological molecules.
Computational chemistry allows for the modeling of interfaces between synthetic and
biological components in biohybrid solar cells. This includes understanding the energetics
and dynamics of charge transfer processes at the interface, which is crucial for efficient
energy conversion. Computational simulations help optimize the properties of synthetic
materials used in biohybrid solar cells. This includes optimizing the electronic structure,
absorption properties, and stability of materials to enhance their performance in
conjunction with biological components.Understanding exciton dynamics at the interface
between synthetic and biological components is essential for efficient energy transfer in
biohybrid solar cells. Computational chemistry techniques can model exciton generation,
migration, and dissociation processes, providing insights into how to design interfaces for
optimal energy conversion.: Computational modeling of complete biohybrid solar cell
devices allows researchers to optimize device architectures and operating conditions. This
includes predicting device performance metrics such as efficiency, voltage, and current
under different illumination conditions and guiding experimental efforts towards optimal
device configurations (Lin et al., 2020).

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 Computational chemistry allows researchers to model the molecular structure of
the biological and synthetic components of Bio hybrid solar cells. Quantum chemistry
methods can be employed to study the electronic structure, bonding interactions, and
optical properties of the molecules involved, providing insights into their behavior within
the solar cell. By employing density functional theory (DFT) or other quantum
mechanical methods, computational chemistry can elucidate the electronic properties of
the materials used in Biohybrid solar cells. This includes calculating band gaps, electron
affinities, and ionization potentials, which are crucial for understanding charge transfer
processes within the solar cell.: Computational chemistry can aid in the optimization of
biohybrid solar cell materials and device architectures. Through molecular dynamics
simulations and Monte Carlo methods, researchers can explore the conformational
dynamics of biological molecules and the self-assembly behavior of hybrid materials,
aiming to design structures that maximize light absorption and charge separation
(Musazade et al., 2018).

Motivation

Understanding charge transport mechanisms is essential for improving the

efficiency of solar cells. Computational chemistry can model electron and hole transfer
processes within biohybrids solar cells, helping to identify factors that influence charge
mobility and recombination rates. Computational chemistry techniques such as time-
dependent DFT (TD-DFT) can simulate the absorption and emission spectra of
biohybrids solar cell materials. These simulations provide valuable information about the
light-harvesting capabilities and photophysical properties of the materials, guiding
experimental efforts to enhance solar cell performance. The interfaces between biological
and synthetic components play a crucial role in biohybrid solar cell performance.
Computational chemistry can investigate the molecular interactions at these interfaces,
including protein-pigment interactions or dye-semiconductor interfaces, to optimize
interfacial properties and enhance charge transfer efficiency. By integrating
computational chemistry with experimental techniques, researchers can gain a
comprehensive understanding of biohybrid solar cells and accelerate the development of
next-generation renewable energy technologies (Lu et al., 2019).

Objective

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 As dye-sensitizers in DSSCs, natural cyanidin, crocetin and phycocyanobilin have
been studied using density functional theory (DFT) at the B3LYP/6-31G(d) and
B3LYP/6-31+G(d) levels. Ground state geometries, electronic transition energies
and oxidation potentials are reported. The HOMO → LUMO transition describes
all lowest singlet excited states. The ground state oxidation potentials are
calculated to be 0.86 V, 1.72 V and 1.14 V (vs. a normal hydrogen electrode,
NHE), respectively, and the excited state oxidation potentials are −1.86 V, −2.6 V
and −1.6 V (vs. NHE), respectively. Deprotonation order is determined by
calculating proton affinities at different sites.

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CHAPTER 2

REVIEW OF LITERATURE

This article presents a theoretical investigation of the optoelectronic properties of

eight novel donor-π-acceptor organic dyes, designated M1–M8. The M1–M8 were
created by structurally altering the π-conjugated bridge of the previously published
reference molecule IC2. The end-capped cyanoacrylic acid serves as the acceptor unit and
the core donor unit of the suggested molecules is indolo[3,2,1-jk]carbazole. To assess the
photophysical and photovoltaic capabilities, DFT and TDDFT calculations were carried
out using the B3LYP, CAM-B3LYP, ωB97XD, and M062X functional. The findings
show that M1–M8's HOMO–LUMO energy gaps are less than IC2's. M7 has the lowest
energy gap of all 2.61 Ev and the redshifted absorption wavelength value 436 nm (Janjua
et al., 2021).

DSSCS, which replaced p-n junction photovoltaic devices, were introduced during
a period of intense search for alternate energy sources. Because the two roles of light
absorption and charge transport are performed separately in the DSSC, as opposed to in
traditional systems, this makes it distinctive. Metal-free organic sensitizers can achieve
power conversion efficiencies of up to approximately 11.65% by using organic sensitizers
to capture a significant portion of sunlight from the UV to the near infrared spectrum.
Currently, light sensitizers used in DSSCS are analyzed experimentally using a trial-and-
error method that is costly and time-consuming due to chemical synthesis. Generally
speaking, unsatisfactory outcomes from advanced (Gong et al., 2012).

With the goal of determining which dye has the best qualities for usage as a
sensitizer in dye-sensitized solar cells (DSSCS), systematic theoretical studies of a few
canthaxanthins from the flavone and flavanol families are pursued. Density-Functional
Theory (DFT) provides a fully optimized ground-state geometry for these dyes in the gas
phase. Predictions of the vertical electron excitation energy, maximal absorption
wavelength, oscillator strengths, light harvesting efficiency (LHE), free energy change of
electron injection, and dye regeneration are made using Time-Dependent Density
Functional Theory (TDDFT) with Polarizable Continuum Model (PCM) for solvent
effects. Identification is also made of the dyes' ground state charge regeneration and
excited state charge transfer. In the gas phase, each of these computations was carried out

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using. For a future energy supply, dye-sensitized solar cells (DSSC) offer an effective and
simple-to-implement technology. It has a similar power conversion efficiency (PCE) to
traditional silicon solar cells with less expensive production and material prices. Materials
for DSSCS, like titanium oxide (TiO2), are widely available, reasonably priced, and
environmentally safe. Roll-to-roll printing could be used to print DSSCS on a mass
manufacturing line because DSSC materials are less contaminated and can be processed
at room temperature. Because they function better in reduced light conditions, DSSCS are
a great option for interior applications. Transparent and colored thin films have been
produced to improve aesthetic values as a result of molecular engineering advancements.
Thus far, these advantages have drawn a great deal of attention from researchers and
commercialization teams (Li et al., 2021).

Emerging technologies like DSCs must attain greater stability and efficiency
while keeping production costs low in order to effectively compete with conventional
photovoltaics. Researchers have examined material properties that can enhance device
performance or stability, and many of the advancements in the field of DSC have been
based on the computational design and screening of new materials. Appropriate modeling
techniques provide researchers with the ability to view the previously unobservable but
vital heterointerfaces that govern DSC performance, providing a chance to create new,
more effective materials and streamline procedures. In this report, we provide an
overview of current computational modeling work on DSCs, showing how the concepts
and simulation instruments applied to these systems can also be applied to the study of
perovskite solar cells, a relatively new topic (Baxter, 2012).

The energy conversion efficiency of dye-sensitized solar cells (DSSCS) based on

organic dyes 1 and 2 differing only in their π spacer was observed. To explain this,
density functional theory (DFT) and time-dependent DFT calculations of the organic
dyes' geometries, electronic structures, and absorption spectra before and after binding to
titanium oxide were performed. By using these, we are able to measure metrics like light
harvesting efficiency and electron injection efficiency related to the short-circuit
photocurrent density (JSC), as well as determine factors like dipole moments linked with
the open-circuit photovoltage (10Voc). The findings show that 1 with a thiophene spacer,
as opposed to 2 with a thiazole spacer, could induce a red shift in the absorption
spectrum, boost the oscillator's strength, and There has been a lot of experimental and
theoretical interest in dye-sensitized solar cells (DSSCS) since they emerged as viable

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low-cost substitute for conventional silicon-based solar cells. Since DSSCS employ
distinct components for the light-harvesting and transport activities than silicon-based
solar cells do, researchers may fine-tune each component and, in the best-case scenario,
maximize the material's overall performance in constructed devices. This work provides
experimental obstacles due to the variety of basic components found in these cells and
their numerous potential combinations. Despite substantial experimental efforts devoted
to its development, the photoconversion efficiencies achieved to date remain modest.
Creating an affordable and effective computational approach that might discover the
prospective dyes, semiconductors, and more qualitatively or even quantitatively (Li et al.,
2019).

In photovoltaic systems like dye-sensitized solar cells, the chemical structural

engineering of photosensitizers plays a crucial role. As a result, a unique dye system was
created and manufactured that included cyan acrylic acid to enhance interaction and an
indigo group to boost light resistance. FTIR, HNMR, CHN, and UV-Visible were used to
purify and evaluate all intermediates and dyes. The outcomes demonstrated that every
anticipated dye chemical structure has been attained. The produced dye was applied to
two semiconductors, titanium dioxide and titanium dioxide doped with Na, in order to
create a photoanode. Due to the dyes' H-aggregation on the semiconductor, a blue shift in
UV visibility was observed in all produced samples. Through the use of DFT calculations
and the Cyclic Voltammetry technique, the energy level of dyes was examined. The
outcomes validated the potential for a number of porphyrin sensitizers with various
electron-donating and withdrawing substituents are studied using the density functional
theory (DFT) and time-dependent DFT approach in order to find effective sensitizers for
dye-sensitized solar cells (DSSCS). Comparing the developed dyes to the best sensitizer
to date (YD2-o-C8), we discovered that the absorption bands are moved to longer
wavelengths and the highest occupied molecular orbital to lowest unoccupied molecular
orbital (HOMO–LUMO) energy gap values are reduced. Crucially, our created dyes
improve the electron injection process by having higher anchoring group contributions to
the LUMOs. Our computations showed that because of their enhanced optical qualities,
the novel systems ought to perform better than the efficient dyes that are currently on
market (Hosseinnezhad et al., 2020).

As one of the third-generation solar cell technologies to help meet the world's
energy needs the twenty-first century, dye-sensitized solar cells (DSSCS) have generated

PAGE \* MERGEFORMAT 29
a lot of interest. Prominent benefits of DSSCS are low cost, simple construction, and
environmental friendliness. A few constraints, including as limited long-term stability, a
narrow absorption spectrum, transportation and collecting losses of charge carriers, and
an inadequate charge transfer mechanism for dye molecule regeneration, have prevented
DSSC advancement during the past 20 years from being substantially faster than average.
Developing new electrode materials with appropriate nanoarchitectures, metal quantum
dot fluorescent dyes, and dyes with compositions that contain promising semiconductors
are some of the strategies the scientific community is utilizing to increase the
performance of DSSCS(Rahman et al., 2023a).

As one of the third-generation solar cell technologies to help meet the world's
energy needs in the twenty-first century, dye-sensitized solar cells (DSSCS) have
generated a lot of interest. Prominent benefits of DSSCS are low cost, simple
construction, and environmental friendliness. A few constraints, including as limited
long-term stability, a narrow absorption spectrum, transportation and collecting losses of
charge carriers, and an inadequate charge transfer mechanism for dye molecule
regeneration, have prevented DSSC advancement during the past 20 years from being
substantially faster than average. Developing new electrode materials with appropriate
nanoarchitectures, metal quantum dot fluorescent dyes, and dyes with compositions that
contain promising semiconductors are some of the strategies the scientific community is
utilizing to increase the performance of DSSCS(Shaikh et al., 2018).

The quantum dot sensitized solar cell (QDSSC) has garnered significant interest
owing to its distinct features, including ease of manufacture, robustness, and the
possibility for multiple electron generation. Its structure and operating principle are
similar to those of the dye sensitized solar cell. To improve QDSSCS' overall
performance, a lot of work has gone into optimizing their many parts. The performance of
the device can be significantly impacted by the counter electrode (CE), which is widely
recognized to have a crucial role in sensitized solar cells. As excellent counter electrode
materials for QDSSCS, metal chalcogenides have recently been investigated. A summary
of recently developed metal chalcogenide CE materials for QDSSCS, as well as carbon
and traditional noble metals, is provided in this paper. The impact of CE materials on the
2-hydroxynaphthalene-1,4-dione (henna1), 3-(5-(1E) and their electronic structures,
polarizabilities, and hyperpolarizabilitiesVinyl) thiophen-2-yl -2-(1,4-dihydro-1,4-
dioxonaphthalen-3-yloxy)Density functional theory (DFT) was utilized in the study of

PAGE \* MERGEFORMAT 29
anthocyanin dye sensitizers and -2-isocyanoacrylic acid (henna2) using the hybrid
functional B3LYP. Using a hybrid technique, i.e. TDSCF-DFT (B3LYP), which
combines the characteristics and dynamics of many-body in the presence of time-
dependent (TD) potentials, the ultraviolet-visible (UV-Vis) spectrum was studied.
Plotting and assignment of features of the electronic absorption spectra in the visible and
near-UV regions were done using TD-DFT computations. Bands of the metal–organic
complex are present because of the absorption (n → π*). The computed outcomes imply
that photoinduced electron transfer processes are responsible for the three lowest energy
excited states of the studied dye sensitizers. The transport of electrons across the interface
between the semiconductor TiO2 electrode and Population expansion and economic
development have led to a rise in global energy usage. For human use, solar energy is one
of the most significant renewable energy sources. In this study, four new organic dyes
(D2–D5) based on triphenylamine (TPA) of the D–A–π–A structure were theoretically
investigated using DFT and TD-DFT techniques in preparation for their potential
application as dye-sensitized solar cells (DSSCS). The structural, electrical, photovoltaic,
and optical properties of the D2–D5 dyes were thoroughly examined in relation to the
modifications made to the π-spacer of the reference molecule D1. Band gaps (E gap) for
D2–D5 ranged from 1.89 to 2.10 eV, whereas λabswere found to be between 508 and 563
nm. The findings indicate that altering the dye D1's π-spacer enhanced its hole injection
and to assess their suitability for use in dye-sensitized solar cells (DSSCS), a set of metal-
free organic donor-acceptor (D–A) derivatives (ME01–ME06) of the well-known dye
C281 were created using first-principles calculations. Time-dependent density functional
theory (TD-DFT) and density functional theory (DFT) were used to calculate their
electrical and physical properties. Molecular characteristics such as UV-vis absorption
spectra, light-harvesting efficiency (LHE), and driving forces of electron injection
(ΔGinj) are necessary to evaluate a dye's suitability for use in dye-sensitive solar cells
(DSSCS). The full visible spectrum is expected to be covered by the large absorption
optical spectra of ME01, ME02, and ME04, making these three dyes attractive candidates
for DSSC applications. After performing device-relevant calculations on the parent dye
and the three dyes that made the short list, the dye molecules (Rasal et al., 2022).

The ease of preparation, environmental and architectural compatibility, low cost,

and high photoelectric conversion efficiency of dye-sensitized solar cells (DSSCS) have
garnered significant interest. A semiconductor device known as a DSC generates

PAGE \* MERGEFORMAT 29
electricity by converting solar radiation into electrical energy [1, 2]. An anchored
molecular sensitizer (dye molecules), a wide band gap semiconductor (usually the wide
band gap TiO2), a redox electrolyte (usually the redox couple), a counter electrode
(usually a piece of glass coated with platinum), and a mesoporous metal oxide layerwhich
functions as a photo anode and is typically developed from TiO 2 nanoparticlesare the four
main components of a typical DSSC. When photons are absorbed by the dye molecules in
DSSCS, they get excited. Sensitizer photo absorptions produce electron injection from
dye-sensitized solar cells (DSSCS) use photosensitizers. The gas phase model and the
implicit/explicit solvent model were two of the theoretical models that were used to study
their structural, electrical, and optical characteristics at the DFT/TDDFT levels. Both the
cluster and periodic models were used to the dye/semiconductor interactions studied by
means of the complex. Following a thorough analysis of how the results varied depending
on the theoretical framework, certain fundamental ideas could be deduced from the
theoretical study of structurefunction correlations in dye–TiO 2 assemblies and isolated
dyes. Some broad recommendations can be made for the future development of dyes
intended for use in DSSCS based on these concepts. The DFT functionals, for example,
that are employed to estimate the crucial parameters for DSSCS need to be thoroughly
verified. On occasion, the performances of the (Rahman et al., 2023a).

For dye-sensitized solar cells (DSSCS), a wide variety of organic dyes have been
created. But the development of new dyes has not fully incorporated theoretical
screening. The primary causes are the infrequent use of quantitative calculations and the
imprecise estimations of open-circuit photovoltaic (VOC) and short-circuit current
density (JSC), particularly for VOC. This work involves the theoretical prediction of
VOC using two distinct models for three D-π–A organic dyes (1, 2, and 3) that have
different donors but the identical π bridge and acceptor. Despite a little variation in their
architectures, precise quantitative computations successfully distinguish their qualities
(Gong et al., 2012).

Emerging technologies like DSCs must attain greater stability and efficiency
while keeping production costs low in order to effectively compete with conventional
photovoltaics. Researchers have examined material properties that can enhance device
performance or stability, and many of the advancements in the field of DSC have been
based on the computational design and screening of new materials. Appropriate modeling
techniques provide researchers with the ability to view the previously unobservable but

PAGE \* MERGEFORMAT 29
vital heterointerfaces that govern DSC performance, providing a chance to create new,
more effective materials and streamline procedures. In this report, we provide an
overview of current computational modeling work on DSCs, showing how the concepts
and simulation instruments applied to these systems can also be applied to the study of
perovskite solar cells, a relatively new topic (Baxter, 2012).

The energy conversion efficiency of dye-sensitized solar cells (DSSCS) based on

organic dyes 1 and 2 differing only in their π spacer was observed. To explain this,
density functional theory (DFT) and time-dependent DFT calculations of the organic
dyes' geometries, electronic structures, and absorption spectra before and after binding to
titanium oxide were performed. By using these, we are able to measure metrics like light
harvesting efficiency and electron injection efficiency related to the short-circuit
photocurrent density (JSC), as well as determine factors like dipole moments linked with
the open-circuit photovoltage (10Voc). The findings show that 1 with a thiophene spacer,
as opposed to 2 with a thiazole spacer, could induce a red shift in the absorption
spectrum, boost the oscillator's strength, and There has been a lot of experimental and
theoretical interest in dye-sensitized solar cells (DSSCS) since they emerged as viable
low-cost substitute for conventional silicon-based solar cells. Since DSSCS employ
distinct components for the light-harvesting and transport activities than silicon-based
solar cells do, researchers may fine-tune each component and, in the best-case scenario,
maximize the material's overall performance in constructed devices. This work provides
experimental obstacles due to the variety of basic components found in these cells and
their numerous potential combinations. Despite substantial experimental efforts devoted
to its development, the photoconversion efficiencies achieved to date remain modest.
Creating an affordable and effective computational approach that might discover the
prospective dyes, semiconductors, and more qualitatively or even quantitatively (Li et al.,
2019).

In photovoltaic systems like dye-sensitized solar cells, the chemical structural

engineering of photosensitizers plays a crucial role. As a result, a unique dye system was
created and manufactured that included cyan acrylic acid to enhance interaction and an
indigo group to boost light resistance. FTIR, HNMR, CHN, and UV-Visible were used to
purify and evaluate all intermediates and dyes. The outcomes demonstrated that every
anticipated dye chemical structure has been attained. The produced dye was applied to
two semiconductors, titanium dioxide and titanium dioxide doped with Na, in order to

PAGE \* MERGEFORMAT 29
create a photoanode. Due to the dyes' H-aggregation on the semiconductor, a blue shift in
UV visibility was observed in all produced samples. Through the use of DFT calculations
and the Cyclic Voltammetry technique, the energy level of dyes was examined. The
outcomes validated the potential for a number of porphyrin sensitizers with various
electron-donating and withdrawing substituents are studied using the density functional
theory (DFT) and time-dependent DFT approach in order to find effective sensitizers for
dye-sensitized solar cells (DSSCS). Comparing the developed dyes to the best sensitizer
to date (YD2-o-C8), we discovered that the absorption bands are moved to longer
wavelengths and the highest occupied molecular orbital to lowest unoccupied molecular
orbital (HOMO–LUMO) energy gap values are reduced. Crucially, our created dyes
improve the electron injection process by having higher anchoring group contributions to
the LUMOs. Our computations showed that because of their enhanced optical qualities,
the novel systems ought to perform better than the efficient dyes that are currently on
market (Hosseinnezhad et al., 2020).

As one of the third-generation solar cell technologies to help meet the world's
energy needs the twenty-first century, dye-sensitized solar cells (DSSCS) have generated
a lot of interest. Prominent benefits of DSSCS are low cost, simple construction, and
environmental friendliness. A few constraints, including as limited long-term stability, a
narrow absorption spectrum, transportation and collecting losses of charge carriers, and
an inadequate charge transfer mechanism for dye molecule regeneration, have prevented
DSSC advancement during the past 20 years from being substantially faster than average.
Developing new electrode materials with appropriate nanoarchitectures, metal quantum
dot fluorescent dyes, and dyes with compositions that contain promising semiconductors
are some of the strategies the scientific community is utilizing to increase the
performance of DSSCS (Rahman et al., 2023a).

As one of the third-generation solar cell technologies to help meet the world's
energy needs in the twenty-first century, dye-sensitized solar cells (DSSCS) have
generated a lot of interest. Prominent benefits of DSSCS are low cost, simple
construction, and environmental friendliness. A few constraints, including as limited
long-term stability, a narrow absorption spectrum, transportation and collecting losses of
charge carriers, and an inadequate charge transfer mechanism for dye molecule
regeneration, have prevented DSSC advancement during the past 20 years from being
substantially faster than average. Developing new electrode materials with appropriate

PAGE \* MERGEFORMAT 29
nanoarchitectures, metal quantum dot fluorescent dyes, and dyes with compositions that
contain promising semiconductors are some of the strategies the scientific community is
utilizing to increase the performance of DSSCS (Shaikh et al., 2018).

The quantum dot sensitized solar cell (QDSSC) has garnered significant interest
owing to its distinct features, including ease of manufacture, robustness, and the
possibility for multiple electron generation. Its structure and operating principle are
similar to those of the dye sensitized solar cell. To improve QDSSCS' overall
performance, a lot of work has gone into optimizing their many parts. The performance of
the device can be significantly impacted by the counter electrode (CE), which is widely
recognized to have a crucial role in sensitized solar cells. As excellent counter electrode
materials for QDSSCS, metal chalcogenides have recently been investigated. A summary
of recently developed metal chalcogenide CE materials for QDSSCS, as well as carbon
and traditional noble metals, is provided in this paper. The impact of CE materials on the
2-hydroxynaphthalene-1,4-dione (henna1), 3-(5-(1E) and their electronic structures,
polarizabilities, and hyperpolarizabilities Vinyl) thiophen-2-yl -2-(1,4-dihydro-1,4-
dioxonaphthalen-3-yloxy). Density functional theory (DFT) was utilized in the study of
anthocyanin dye sensitizers and -2-isocyanoacrylic acid (henna2) using the hybrid
functional B3LYP. Using a hybrid technique, i.e. TDSCF-DFT (B3LYP), which
combines the characteristics and dynamics of many-body in the presence of time-
dependent (TD) potentials, the ultraviolet-visible (UV-Vis) spectrum was studied.
Plotting and assignment of features of the electronic absorption spectra in the visible and
near-UV regions were done using TD-DFT computations. Bands of the metal–organic
complex are present because of the absorption (n → π*). The computed outcomes imply
that photoinduced electron transfer processes are responsible for the three lowest energy
excited states of the studied dye sensitizers. The transport of electrons across the interface
between the semiconductor TiO2 electrode and Population expansion and economic
development have led to a rise in global energy usage. For human use, solar energy is one
of the most significant renewable energy sources. In this study, four new organic dyes
(D2–D5) based on triphenylamine (TPA) of the D–A–π–A structure were theoretically
investigated using DFT and TD-DFT techniques in preparation for their potential
application as dye-sensitized solar cells (DSSCS). The structural, electrical, photovoltaic,
and optical properties of the D2–D5 dyes were thoroughly examined in relation to the
modifications made to the π-spacer of the reference molecule D1. Band gaps (Egap) for

PAGE \* MERGEFORMAT 29
D2–D5 ranged from 1.89 to 2.10 eV, whereas λabs were found to be between 508 and
563 nm. The findings indicate that altering the dye D1's π-spacer enhanced its hole
injection and to assess their suitability for use in dye-sensitized solar cells (DSSCS), a set
of metal-free organic donor-acceptor (D–A) derivatives (ME01–ME06) of the well-
known dye C281 were created using first-principles calculations. Time-dependent density
functional theory (TD-DFT) and density functional theory (DFT) were used to calculate
their electrical and physical properties. Molecular characteristics such as UV-vis
absorption spectra, light-harvesting efficiency (LHE), and driving forces of electron
injection (ΔGinj) are necessary to evaluate a dye's suitability for use in dye-sensitive solar
cells (DSSCS). The full visible spectrum is expected to be covered by the large
absorption optical spectra of ME01, ME02, and ME04, making these three dyes attractive
candidates for DSSC applications. After performing device-relevant calculations on the
parent dye and the three dyes that made the short list, the dye molecules (Rasal et al.,
2022).

The dye-sensitized solar cell (DSSC) community often uses density functional
theory (DFT) and time-dependent DFT as helpful computational techniques to evaluate
experimental data and elucidate the fundamental mechanisms behind the operation of
these devices. Nevertheless, these techniques can offer insights much beyond a strictly
descriptive goal, particularly if appropriate computing tools and mechanisms for
evaluating and validating the computational outputs are created. This is true even in spite
of their noteworthy contributions. The performance of three new TiO 2-based DSSCS that
use organic dyes and are all members of the expanded pyridinium family is studied in this
contribution to show how recently developed computational approaches can be used to
design and interpret the macroscopic behavior of DSSCS(Le Bahers et al., 2013).

A set of dyes derived from coumarin was examined; these dyes were made up of
nine molecules and were manufactured using a very similar process to dye sensitized
solar cells (DSSCS). Through theoretical calculations, optimized geometries, energy
levels of the highest occupied molecular orbital and the lowest unoccupied molecular
orbital, and ultraviolet-visible spectra were obtained; these results were then compared
with experimental conversion efficiencies of the DSSC. An analysis of an excited state in
terms of natural transition orbitals (NTOs) was conducted; chemical reactivity parameters
were computed and correlated with the experimental data related to the efficiency of the

PAGE \* MERGEFORMAT 29
DSSC. A novel proposal was obtained to design new molecular systems and forecast their
possible use as a dye in DSSCS(Choi et al., 2007).

To determine the nature of electronic transitions in the visible region and

understand how the substituent influences the metalloporphyrin's electronic structure, a
combination of electronic absorption, resonance Raman spectroscopy, and density
functional theory calculations have been applied to a series of β-substituted zinc
porphyrins. When conjugated β substituents are used, the border molecular orbitals'
energy and nature are greatly perturbed, and new molecular orbitals are produced from
the parent metalloporphyrin species. An expansion of Goutermans' four-orbital model
explains the observed complex electronic absorption spectra. Resonant Raman
spectroscopy has been used to determine the excitations involved in the visible
transitions. This has demonstrated how much of the B band's original character still
(Clark and Dines, 1986).

Dyes-sensitized solar cells (DSSCS) were first proposed by O'Regan and Grätzel
in 1991 for the purpose of harvesting solar energy and photoconversion to electrical
current. Since then, due to the potential benefits of easy manufacture, low costs, and
transparency compared to traditional crystalline silicon solar cells, dye-sensitized solar
cells (DSSCS) have garnered ever-increasing attention in scientific study and practical
applications. I−I−3 redox couple-containing electrolyte, dye-adsorbed wide band gap oxide
semiconductor (like TiO2), and a platinum counter electrode are the components of a
typical DSSC. The sensitizer plays a crucial role in the semiconductor process by
absorbing light and introducing electrons into the conduction band. Therefore, achieving
a desirable photo-to-current conversion efficiency (η) requires modifying the dye-
sensitizer (Chen et al., 2007).

Experimental and computational techniques are used to study the spectral

characteristics of lawsone (2-hydroxy-1,4-naphthoquinone), the active ingredient of
henna, a natural color, in ethanol. The time-dependent density functional theory (TD-
DFT) approach yields a predicted UV-Vis absorption spectrum. It is contrasted with the
experimental results to enable a comprehensive molecular orbital-based assignment of the
UV-Vis spectral characteristics. Furthermore, we have examined the electrochemical
impedance spectrum and light intensity-dependent J-V properties of a dye-sensitized solar
cell made with lawsone and a ZnO photoanode. A respectable power conversion

PAGE \* MERGEFORMAT 29
efficiency of 0.68% at 26 mW cm −2 light intensity was demonstrated by the photovoltaic
data of the sensitizer adsorbed on ZnO films (Nandi and Das, 2022).

A study using density functional theory was conducted to design a new All-Solid-
State dye-sensitized solar cell (SDSC) using a donor-acceptor conjugated polymer in
place of a liquid electrolyte. The narrow band gap, hole transporting material (HTM) is
used in place of the typical redox mediator (I -1I-3), and the electronic and optical
properties predict that the donor and acceptor moieties in the polymeric body have
increased the ability to absorb visible light and transport charges, relative to their parent
polymers. Packing N3 between HTM and TiO 2 creates a unique “upstairs”-like band
energy diagram. When light is applied to the proposed configuration, electrons will move
simultaneously from the dye to TiO2 and from HTM to dye (to regenerate dye). Our
theoretical simulations demonstrate that this is the case (Marchioro, 2014).

Designing heterocyclic azo dyes for dye-sensitized solar cells was the goal of this
investigation. Quantification of factors including light harvesting efficiency and electron
injection efficiency related to the short-circuit photocurrent density (JSC) were also done
by quantum chemistry calculations. The open-circuit photovoltage (VOC) was also
calculated. In the visible range (502–521 nm), all of the dyes exhibited strong oscillator
strength (f) (0.473–0.961) and light harvesting efficiency (LHE) (0.663–0.891). After
attaching to titanium oxide, all dyes exhibited enhanced light harvesting efficiency (LHE)
(0.733–0.898) and slightly red-shifted absorbance (521–527 nm). Because these dyes
have a high driving force for electron injection, there's a good chance they will display
bigger JSC. Additional high VOC (1.037–1.128 eV) was observed with these dyes (Rana,
2014).

A range of chemical dyes with a core unit of phenothiazine were produced and
successfully applied in the production of dye-sensitized solar cells (DSSCS). The
phenothiazine was modified by attaching a cyanoacrylate moiety at position C(3) to act as
an electron acceptor and a triarylamine moiety at position Cto act as an electron donor.
Under AM 1.5 sunlight conditions (100 mW cm−2), the dye-based DSSCS demonstrated
impressive quantum efficiency, ranging from 4.2% to 6.2%. To maximize the incident
photon-to-current conversion efficiency, a range of substituents, including methyl, hexyl,
and triphenyl amino groups, were introduced at the Nof phenothiazine. To investigate the
impact on device properties, a thiophenylene group was added at various points along the
primary chromophore (Luo et al., 2016).

PAGE \* MERGEFORMAT 29
 One effective method for examining and describing the optical, electrical, and
structural characteristics of dye-sensitized solar cells (DSCs) is theoretical and
computational modeling. The major objective of this work is to model the dye-
semiconductor electron injection process, which is the primary charge generating step in
DSCs. To that end, we describe the ground and excited state features of both freestanding
and TiO2-adsorbed metallorganic and completely organic dyes. We want to critically
examine the possibilities and constraints of the existing DFT and TDDFT computational
approaches to simulate DSCs by evaluating earlier data from our lab combined with fresh
computations. Although typical DFT approaches provide an accurate description of
ruthenium dyes, exchange-correlation functionals specifically tuned to strongly
conjugated organic dyeswhich are characterized by significant charge transfer excited
states—are needed (Pastore and De Angelis, 2014).

With the use of Density Functional Theory (DFT) and Time-Dependent Density
Functional Theory (TD-DFT), six new D-π-A organic dyes with an indenothiophene unit,
based on the 3D triphenylamine derivative (IDTTPA), have been created and theorized.
D-π-A dye-based dye-sensitized solar cells (DSSCS) can have their efficiency further
increased by varying the anchoring group. This work examined the impact of various
acceptor groups on the electron injection to surface capabilities of D-π-A dyes (A1-A6)
both before and after they bound to the TiO2 cluster (Slimi et al., 2020).

In order to serve as photosensitizers for dye-sensitized solar cells (DSCs), we

designed and synthesized novel organic dyes of the double electron acceptor type based
on the phenothiazine framework. The photovoltaic properties of the dyes were estimated
during the design stage using density functional theory (DFT) and time-dependent density
functional theory (TD-DFT) calculations. The molecular structure with two electron
acceptors on both sides of the phenothiazine moiety provided the efficient electron
extraction paths from the electron donor part, as evidenced by the analysis of the
electronic structures on the donor and acceptor as well as the excitations between
HOMOs and LUMOs. Consequently, the measurements of photovoltaic properties of the
DSCs prepared in the laboratory scale showed that the organic dyes of this type (Slodek
et al., 2019).

Over the last ten years, DSSCS have been the subject of much research, and the
quest for more effective DSSC dyes continues. We use density functional theory (DFT)
and time-dependent DFT approaches to analyze the effects of rigidifying dithiophene and

PAGE \* MERGEFORMAT 29
elongating π-spacers on the performance of dithiafulvenyl (DTF)-based organic dyes. The
light-harvesting efficiency of DTF-2P-T and DTF-2P-2T can be enhanced by
systematically elongating the π-spacer of the dye by increasing the amount of thiophene
groups. This results in a broadening of the absorption range and a redshift of the
absorption peak. DTF-2P-T also performs well on the important characteristics, such as
the shift of the TiO2 conduction, the electron injection driving force (D), and the light-
harvesting efficiency (LHE), making it the most effective dye out of the three (Bera et al.,
2021).

For many organic donor-π-bridge-acceptor (D-π-A) dyes, strong electron-donating

functionality is desirable. Planarization of nitrogen substituents and the usage of aromatic
ring-substituted nitrogen atoms with low resonance-stabilized energy are two techniques
for boosting the electron-donating strength of typical nitrogen-based donors. Dyes-
sensitized solar cell (DSC) sensitizers are made using organic donor motifs that are
derived from the planar nitrogen-containing heterocycle indolizine. We investigate
computationally and empirically resonance active substitutions at multiple places on
indolizine in conjugation with the D-π-A π-system. Measurements of oxidation potential,
UV/Vis, and IR absorptions show that the indolizine-based donors contribute electron
density with strengths stronger than triarylamines and diarylamines. Understanding the
performance of indolizine-based dyes in DSC devices can be gained through fluorescence
lifetime tests conducted in solution and on TiO2(Wu and Zhu, 2013).

The distinct characteristics of dye-sensitized solar cells (DSSCS) have garnered

significant interest. The current study has examined and examined the potential suitability
of molecularly designed triphenylamine-based dyes with donor-bridge-acceptor
architecture for use in dye-sensitive solar cells (DSSCS). The device's long-term stability
has been enhanced by the introduction of hydantoin anchoring group, which has replaced
the widely utilized cyanoacrylic acid. Interpretation of the results regarding the effects of
different anchoring groups and pi-spacers has been done from the perspective of
DFT/TD-DFT calculations. Sensitizers that have been designed have appropriate light-
harvesting efficiencies, lifetimes in the excited state, electron injection, and regeneration
capabilities. Three hydantoin dyes have red-shifted electronic spectra when compared to
other members of the same family (Basheer et al., 2014).

The cis-[Ru(4,4′-COOH-2,2′-bpy)2(NCS)2]/TiO2 system has been studied using

density functional theory (DFT) in conjunction with a periodic approach and a hybrid

PAGE \* MERGEFORMAT 29
functional in order to better describe the phenomena occurring at the dye/semiconductor
interface in dye-sensitized solar cells and to comprehend the interfacial electron transfer
from the excited dye to the semiconductor. The analysis at this theoretical level has
focused on the interplay between the geometrical and electronic coupling between the
semiconductor and dye, as well as the viability of interfacial electronic transfer. With the
dye's LUMO being substantially higher in energy than the semiconductor's conduction
band, our findings demonstrate that the electronic transfer is extremely advantageous
from a thermodynamic perspective. Furthermore, the theoretical injection duration (Preat,
2010).

As sensitizers for dye-sensitized solar cells (DSSCS), three anthraquinone dyes

with carboxylic acid as an anchoring group are created and produced. Although these
anthraquinone dyes exhibit broad and powerful absorption spectra in the visible range (up
to 800 nm), preliminary photophysical and photoelectrochemical tests indicate that they
perform very poorly on DSSC applications. The reason for these dyes' poor DSSC
performance is examined using density functional theory (DFT) calculations,
fluorescence lifetime measurements, and transient absorption kinetics. The outcomes
indicate that the low performance could be caused by the two carbonyl groups on the
anthraquinone framework's strong electron-withdrawing characteristic, which would
inhibit the dye's effective electron injection into TiO2's conduction band (Li et al., 2007).

To determine the nature of electronic transitions in the visible region and

understand how the substituent influences the metalloporphyrin's electronic structure, a
combination of electronic absorption, resonance Raman spectroscopy, and density
functional theory calculations have been applied to a series of β-substituted zinc
porphyrins. When conjugated β substituents are used, the border molecular orbitals'
energy and nature are greatly perturbed, and new molecular orbitals are produced from
the parent metalloporphyrin species. An expansion of Goutermans' four-orbital model
explains the observed complex electronic absorption spectra. Resonant Raman
spectroscopy has been used to determine the excitations involved in the visible
transitions. This has demonstrated how much of the B band's original character (Clark
and Dines, 1986).

Dyes-sensitized solar cells (DSSCS) were first proposed by O'Regan and Grätzel
in 1991 to harvest solar energy and photoconversion to electrical current. Since then, due
to the potential benefits of easy manufacture, low costs, and transparency compared to

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traditional crystalline silicon solar cells, dye-sensitized solar cells (DSSCS) have garnered
ever-increasing attention in scientific study and practical applications. I −I−3 redox couple-
containing electrolyte, dye-adsorbed wide band gap oxide semiconductor (like TiO 2), and
a platinum counter electrode are the components of a typical DSSC. The sensitizer plays a
crucial role in the semiconductor process by absorbing light and introducing electrons
into the conduction band. Therefore, achieving a desirable photo-to-current conversion
efficiency (η) requires modifying the dye-sensitizer (Chen et al., 2007).

Experimental and computational techniques are used to study the spectral

characteristics of lawsone (2-hydroxy-1,4-naphthoquinone), the active ingredient of
henna, a natural color, in ethanol. The time-dependent density functional theory (TD-
DFT) approach yields a predicted UV-Vis absorption spectrum. It is contrasted with the
experimental results to enable a comprehensive molecular orbital-based assignment of the
UV-Vis spectral characteristics. Furthermore, we have examined the electrochemical
impedance spectrum and light intensity-dependent J-V properties of a dye-sensitized solar
cell made with lawsone and a ZnO photoanode. A respectable power conversion
efficiency of 0.68% at 26 mW cm −2 light intensity was demonstrated by the photovoltaic
data of the sensitizer adsorbed on ZnO films (Nandi and Das, 2022).

A study using density functional theory was conducted to design a new All-Solid-
State dye-sensitized solar cell (SDSC) using a donor-acceptor conjugated polymer in
place of a liquid electrolyte. The narrow band gap, hole transporting material (HTM) is
used in place of the typical redox mediator (I -1I-3), and the electronic and optical
properties predict that the donor and acceptor moieties in the polymeric body have
increased the ability to absorb visible light and transport charges, relative to their parent
polymers. Packing N3 between HTM and TiO 2 creates a unique “upstairs”-like band
energy diagram. When light is applied to the proposed configuration, electrons will move
simultaneously from the dye to TiO2 and from HTM to dye (to regenerate dye). Our
theoretical simulations demonstrate that this is the case (Marchioro, 2014).

Designing heterocyclic azo dyes for dye-sensitized solar cells was the goal of this
investigation. Quantification of factors including light harvesting efficiency and electron
injection efficiency related to the short-circuit photocurrent density (JSC) was also done
by quantum chemistry calculations. The open-circuit photovoltage (VOC) was also
calculated. In the visible range (502–521 nm), all of the dyes exhibited strong oscillator
strength (f) (0.473–0.961) and light harvesting efficiency (LHE) (0.663–0.891). After

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attaching to titanium oxide, all dyes exhibited enhanced light harvesting efficiency (LHE)
(0.733–0.898) and slightly red-shifted absorbance (521–527 nm). Because these dyes
have a high driving force for electron injection, there's a good chance they will display
bigger JSC. Additional high VOC (1.037–1.128 eV) was observed with these dyes (Rana,
2014).

A range of chemical dyes with a core unit of phenothiazine were produced and
successfully applied in the production of dye-sensitized solar cells (DSSCS). The
phenothiazine was modified by attaching a cyanoacrylate moiety at position C(3) to act as
an electron acceptor and a triarylamine moiety at position C to act as an electron donor.
Under AM 1.5 sunlight conditions (100 mW cm−2), the dye-based DSSCS demonstrated
impressive quantum efficiency, ranging from 4.2% to 6.2%. To maximize the incident
photon-to-current conversion efficiency, a range of substituents, including methyl, hexyl,
and triphenyl amino groups, were introduced at the N of phenothiazine. To investigate the
impact on device properties, a thiophenylene group was added at various points along the
primary chromophore (Luo et al., 2016).

One effective method for examining and describing the optical, electrical, and
structural characteristics of dye-sensitized solar cells (DSCs) is theoretical and
computational modeling. The major objective of this work is to model the dye-
semiconductor electron injection process, which is the primary charge generating step in
DSCs. To that end, we describe the ground and excited state features of both freestanding
and TiO2-adsorbed metallorganic and completely organic dyes. We want to critically
examine the possibilities and constraints of the existing DFT and TDDFT computational
approaches to simulate DSCs by evaluating earlier data from our lab combined with fresh
computations. Although typical DFT approaches provide an accurate description of
ruthenium dyes, exchange-correlation functionals specifically tuned to strongly
conjugated organic dyes which are characterized by significant charge transfer excited
states—are needed (Pastore and De Angelis, 2014).

With the use of Density Functional Theory (DFT) and Time-Dependent Density
Functional Theory (TD-DFT), six new D-π-A organic dyes with an indenothiophene unit,
based on the 3D triphenylamine derivative (IDTTPA), have been created and theorized.
D-π-A dye-based dye-sensitized solar cells (DSSCS) can have their efficiency further
increased by varying the anchoring group. This work examined the impact of various

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acceptor groups on the electron injection to surface capabilities of D-π-A dyes (A1-A6)
both before and after they bound to the TiO2 cluster (Slimi et al., 2020).

In order to serve as photosensitizers for dye-sensitized solar cells (DSCs), we

designed and synthesized novel organic dyes of the double electron acceptor type based
on the phenothiazine framework. The photovoltaic properties of the dyes were estimated
during the design stage using density functional theory (DFT) and time-dependent density
functional theory (TD-DFT) calculations. The molecular structure with two electron
acceptors on both sides of the phenothiazine moiety provided the efficient electron
extraction paths from the electron donor part, as evidenced by the analysis of the
electronic structures on the donor and acceptor as well as the excitations between
HOMOs and LUMOs. Consequently, the measurements of photovoltaic properties of the
DSCs prepared in the laboratory scale showed that the organic dyes of this type (Slodek
et al., 2019).

Over the last ten years, DSSCS have been the subject of much research, and the
quest for more effective DSSC dyes continues. We use density functional theory (DFT)
and time-dependent DFT approaches to analyze the effects of rigidifying dithiophene and
elongating π-spacers on the performance of dithiafulvenyl (DTF)-based organic dyes. The
light-harvesting efficiency of DTF-2P-T and DTF-2P-2T can be enhanced by
systematically elongating the π-spacer of the dye by increasing the amount of thiophene
groups. This results in a broadening of the absorption range and a redshift of the
absorption peak. DTF-2P-T also performs well on the important characteristics, such as
the shift of the TiO2 conduction, the electron injection driving force (D), and the light-
harvesting efficiency (LHE), making it the most effective dye out of the three (Bera et al.,
2021).

For many organic donor-π-bridge-acceptor (D-π-A) dyes, strong electron-donating

functionality is desirable. Planarization of nitrogen substituents and the usage of aromatic
ring-substituted nitrogen atoms with low resonance-stabilized energy are two techniques
for boosting the electron-donating strength of typical nitrogen-based donors. Dyes-
sensitized solar cell (DSC) sensitizers are made using organic donor motifs that are
derived from the planar nitrogen-containing heterocycle indolizine. We investigate
computationally and empirically resonance active substitutions at multiple places on
indolizine in conjugation with the D-π-A π-system. Measurements of oxidation potential,
UV/Vis, and IR absorptions show that the indolizine-based donors contribute electron

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density with strengths stronger than triarylamines and diarylamines. Understanding the
performance of indolizine-based dyes in DSC devices can be gained through fluorescence
lifetime tests conducted in solution and on TiO2(Wu and Zhu, 2013).

The distinct characteristics of dye-sensitized solar cells (DSSCS) have garnered

significant interest. The current study has examined and examined the potential suitability
of molecularly designed triphenylamine-based dyes with donor-bridge-acceptor
architecture for use in dye-sensitive solar cells (DSSCS). The device's long-term stability
has been enhanced by the introduction of hydantoin anchoring group, which has replaced
the widely utilized cyanoacrylic acid. Interpretation of the results regarding the effects of
different anchoring groups and pi-spacers has been done from the perspective of
DFT/TD-DFT calculations. Sensitizers that have been designed have appropriate light-
harvesting efficiencies, lifetimes in the excited state, electron injection, and regeneration
capabilities. Three hydantoin dyes have red-shifted electronic spectra when compared to
other members of the same family (Basheer et al., 2014).

The cis-[Ru(4,4′-COOH-2,2′-bpy)2(NCS)2]/TiO2 system has been studied using

density functional theory (DFT) in conjunction with a periodic approach and a hybrid
functional in order to better describe the phenomena occurring at the dye/semiconductor
interface in dye-sensitized solar cells and to comprehend the interfacial electron transfer
from the excited dye to the semiconductor. The analysis at this theoretical level has
focused on the interplay between the geometrical and electronic coupling between the
semiconductor and dye, as well as the viability of interfacial electronic transfer. With the
dye's LUMO being substantially higher in energy than the semiconductor's conduction
band, our findings demonstrate that the electronic transfer is extremely advantageous
from a thermodynamic perspective. Furthermore, the theoretical injection duration (Preat,
2010).

As sensitizers for dye-sensitized solar cells (DSSCS), three anthraquinone dyes

with carboxylic acid as an anchoring group are created and produced. Although these
anthraquinone dyes exhibit broad and powerful absorption spectra in the visible range (up
to 800 nm), preliminary photophysical and photoelectrochemical tests indicate that they
perform very poorly on DSSC applications. The reason for these dyes' poor DSSC
performance is examined using density functional theory (DFT) calculations,
fluorescence lifetime measurements, and transient absorption kinetics. The outcomes
indicate that the low performance could be caused by the two carbonyl groups on the

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anthraquinone framework's strong electron-withdrawing characteristic, which would
inhibit the dye's effective electron injection into TiO2's conduction band (Li et al., 2007).

Non-renewable energy resources are being rapidly depleted due to the increasing
rate of energy consumption. This challenge has been addressed by adopting renewable
energy sources, particularly photovoltaic energy, which directly converts solar energy
into electrical energy without polluting the atmosphere. In recent years, various
photovoltaic devices, including hybrid and organic-inorganic solar cells, have been
developed for diverse applications. Dye-sensitized solar cells (DSSCS) present a
promising and innovative method for harnessing solar energy inspired by photosynthesis
in plants. Research has primarily focused on DSSCS for their low cost, exceptional
transparency, sustainability, and straightforward fabrication process. Moreover, DSSCS
offer the benefits of high efficiency, flexibility, and easier implementation compared to
traditional silicon-based solar cells. For approximately two decades, DSSCS have
struggled with stagnant efficiency levels despite extensive (Opeyemi, 2021).

Dye-sensitized solar cells, or DSSCS, have garnered increasing attention in recent

years because of their many benefits over traditional silicon devices, including their high
molar absorption coefficient, ease of molecular tailoring, and straightforward fabrication
procedure. One of the key requirements for large-scale commercialization is high energy
conversion efficiency. When compared to silicon devices (over 25%) and other marketed
technologies, the maximum recorded efficiency of DSSCS, at 12.3%, is still inadequate.
Metal-free organic dyes have been observed to have even lower efficiency when used as
sensitizers in DSSCS. To achieve maximum efficiency, a lot of work is therefore needed.
The academic research community and industrial applications scientists have a significant
challenge in improving the performance of metal-free DSSCS. This review's goal is to
showcase the most current (Malhotra et al., 2024).

The present study investigates the relationship between the molecular structures of
a series of azo dyes and their performance when applied to dye-sensitized solar cells
(DSSCS) through both experimental and computational analysis. Specifically, seven azo
dyes with three distinct donating groups (dimethylamino, diethylamino, and
dipropylamino) and carboxylic acid anchoring positions (ortho-, meta-, and para-
substituted phenyl rings) are examined. Single-crystal X-ray diffraction is utilized to
assess the effects of conformation and quantify the contribution of quinoidal resonance
forms to the intramolecular charge transfer (ICT), which regulates their intrinsic

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photovoltaic potential from an electronic perspective. Harmonic oscillator stabilization
energy (HOSE) calculations reveal that the para- and ortho-azo (Zhang et al., 2013).

Traditionally, careful molecular design and device level alterations have been the
key strategies used to increase the photovoltaic performance of dye-sensitized solar cells
(DSSCS). Yet, these approaches are constrained by expensive and time-consuming
synthesis processes. Here, we present the effectiveness of a different strategy based on the
in silico evolutionary de novo design of new dye structures with higher DSSC power
conversion efficiency (PCE) values. The evolutionary fitness function makes use of
predictive structure–property relationship (QSPR) models calibrated from empirical data,
as the PCE cannot yet be computed directly from basic principles. Phenothiazine-based
dye sensitizers are designed using our design methodology. A genetic algorithm is
utilized to explore the chemical structure space by methodically assembling molecules
from fragments in a synthetically tractable way (Błaszczyk, 2018).

To optimize visible light absorption, the majority of photovoltaic (PV) devices are
opaque. Nevertheless, see-through solar cells provide new opportunities for integrating
PV. This work optimizes a selective near-infrared sensitizer based on a polymethine
cyanine structure (VG20-Cx) to produce dye-sensitized solar cells (DSSCS) entirely
transparent and colorless, going beyond optimizing visible light harvesting. We do this by
taking into account the human eye photopic response. The dye was given the capacity to
reject the higher S0–Sn contributions far in the blue, where the human retina is not as
sensitive, while yet being able to absorb light beyond 800 nm (the S0–S1 transition),
giving rise to this unique property. With an aggregation-free anatase TiO 2 photoanode
connected to it, the selective NIR-DSSC can achieve 3.1% power conversion efficiency
and 76% average visual transmittance (AVT), which is close to the 78% mark (Traverse
et al., 2017).

The photovoltage and photocurrent of dye-sensitized solar cells (DSCS) are

mostly determined by redox mediators. The oxidized dye must be reduced by the redox
mediator much more quickly than the electrons return from TiO 2 to the oxidized dye in
order to sustain the photocurrent. In order to get high photovoltages during dye
regeneration using the redox mediator, the driving power needs to be low enough. The
introduction of our novel copper complexes as potential redox mediators in DSCs
satisfies both requirements, improving power conversion efficiency. Two copper
bipyridyl complexes are presented as new redox couples for DSCs in this study: Cu(II/I)

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(tmby)2TFSI2/1 (0.87 V vs SHE, tmby = 4,4′,6,6′-tetramethyl-2,2′-bipyridine) and
Cu(II/I)(dmby)2TFSI2/1 (0.97 V vs SHE, dmby = 6,6′-dimethyl-2,2′-bipyridine). Cu(II/I)
(dmp)2TFSI2/1 (0.93 V) is compared with the previously published data (Boschloo and
Hagfeldt, 2009).

An overview of the most recent advancements in the manufacture and use of

nanostructured metal oxide semiconductors for dye- and quantum dot-sensitized solar
cells is given in this review. The broad bandgap semiconducting oxide in these devices
serves as the photoanode, providing the framework for electron collection and light
harvesters (dye molecules or quantum dots). This is why properly adjusting the
photoanode's optical and electrical characteristics can greatly increase the operational
device's functionality. Modulating the photoanode's form and structure, applying various
materials (TiO2, ZnO, SnO2), and/or using composite systems—which enable precise
electronic band structure tuningare all necessary for optimizing the functional qualities
(Bartolomé et al., 2020).

The primary constraint limiting dye-sensitized solar cells' (DSSCS') ability to

perform better has always been charge recombination. From the perspective of the dye
structure, one of the often employed methods to improve the blocking effect of dye
molecules at the interface between TiO 2 and the electrolyte/hole conductor is the
introduction of substituents such as alkoxy/alkyl chains with a substantial steric
hindrance. Consequently, the performance of the solar cells can be enhanced by
successfully impeding the charge recombination. Here, we provide an overview of the
latest developments and molecular designs in the field of organic sensitizers utilizing
bulky donor groups based on o,p-dialkoxyphenyl (DAP). For the absorption spectrum,
charge recombination, and dye regeneration, the benefits and drawbacks of the bulky
donor groups are explored (Li et al., 2006).

Because of its simple production, low weight, and excellent weavability, the fiber-
shaped dye-sensitized solar cell is a promising flexible power conversion technology for
next-generation wearable electronics. The low power conversion efficiency and limited
flexibility of fiber-shaped dye sensitized solar cells, however, severely restrict their usage.
By progressively growing polyaniline layers and Co0.85Se nanosheets on the surface of
carbon fibers as the counter electrodes and TiO 2 nanotubes grown on the Ti wire as the
photoanode, a flexible Pt-free fiber-shaped dye sensitized solar cell with a high-power
conversion efficiency of 10.28% is created in this instance. In addition to acting as

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nucleation sites for the subsequent Co0.85Se nanosheet deposition, the polyaniline layer
can also function as catalytic sites with a large specific surface area (Zhang et al., 2019a).

Due to their unique characteristics, including their low processing costs, ability to
control a broad range of the light absorption spectrum, and potential for multiple electron
generation with a theoretical conversion efficiency of up to 44%, quantum dot-sensitized
solar cells (QDSCS) have garnered a lot of attention as promising candidates for
affordable photoelectrochemical solar cells. The architecture of QDSCs and dye-
sensitized solar cells are similar. Both involve semiconductor photoanodes that have been
sensitized with quantum dots (QDs), redox electrolytes, and counter electrodes (CEs).
Optimizing each QDSC component for improved device performance has taken a lot of
work. This review will focus on current developments in photoanodes with different
topologies, QDs with configurable band gaps, liquid, quasi-solid, or solid state
electrolytes, and CEs with high electrocatalytic activity for QDSCS(George et al., 2024).

Effective energy-conversion technologies, such as fuel cells and photovoltaics,

have been the subject of a great deal more research in recent years. These technologies
seek to reduce the world's massive energy demand as well as the environmental pollution
they cause. Due to its low manufacturing costs, high power conversion efficiency, and
ease of use, dye-sensitized solar cells (DSCS) have drawn the most attention of these
gadgets. Because platinum is a rare and expensive material, its usage as the standard for
the counter electrode (CE) of DSCS is crucial, and its limited availability has prevented
the DSCS from being widely used. Therefore, a great deal of work has gone into finding
active CE materials that are inexpensive, have high electrocatalytic activity, and have
outstanding stability. But typically, a "trial-and-error" approach is used to do this (Tuller,
2017).

In the past 20 years, there has been a lot of research done on the technology that
uses organic photovoltaic systems to convert sunlight into electric current. Today, there is
growing industry interest in this field of study. An economically and technically sound
replacement for the widely used thin-film or p-n junction photovoltaic devices is offered
by dye-sensitized solar cells (DSSCS). Reviewing the fundamental ideas of DSSCS, we
particularly address the current theoretical work that aims to optimize the properties of
DSSCS, along with a number of hotly debated and recently developed concerns in this
field (Sun and Sariciftci, 2017).

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 A viable approach to creating high-performance dye-sensitized solar cells
(DSSCS) is to accurately estimate photoelectric conversion efficiency (PCE), one of the
key metrics to assess the overall performance of DSSCS. In this work, we deliberately
created a range of organic dyes 1–4 based on anthracene by including various π-bridge or
auxiliary acceptor groups. First-principles calculations along with the normal model and
enhanced normal model were used to investigate their photovoltaic characteristics. The
max is observed to shift blue when an electron-rich thieno[3,2-b]thiophene-based π-
spacer is added to dye 2 (Almenningen et al., 2021).

For years, scientists working in materials science have been designing and finding
new molecule structures with ideal features. Experiments led by trial-and-error methods,
which are frequently costly and time-consuming, have generally dominated this field.
Here, we explore the possibility of designing dye sensitizers based on coumarins with
enhanced characteristics for application in Grätzel solar cells using a de novo
computational design approach. The combination of chemical motifs (obtained from the
current databases of structures) is done in accordance with a user-adaptable set of rules in
a fragment-based assembly method, which attempts to solve the problem of synthetic
accessibility of the developed compounds. To screen candidate dyes, we use quantitative
structure–property relationship screening instead of computationally demanding density
functional theory (DFT)/ab initio approaches (Sanchez-Lengeling and Aspuru-Guzik,
2018).

First-principles molecular dynamics and real-time time-dependent density

functional theory simulations uncover a structure–property link in all-organic dye solar
cells, which is corroborated by experiment. Utilizing energetics, vibrational recognition,
and electronic data, an essential structural characteristic at the interfaceTi–N anchoringis
deduced for a wide range of all-organic dyes on TiO 2. This fact defies common belief, but
it contributes significantly to the reported efficiency enhancement in all-organic
cyanoacrylate dye-sensitized solar cells by optimizing electronic level alignment and
photoelectron injection kinetics (Jiao et al., 2013).

Analogously to comparable methods to control charge transport across

nanostructures, a mechanism to obstruct the charge recombination process in dye-
sensitized solar cells is proposed. An unsaturated carbon bridge connects the two subunits
in the system under study, which is the TiO 2 (anatase)–chromophore contact. The
contribution from the bridge states mediating the process is explicitly considered by

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applying a theory for nonadiabatic electron transfer. It is feasible to prevent charge
recombination if a cross-conjugated fragment is present in the bridge by negatively
interfering with any potential tunneling paths. Simulations performed on actual molecules
at the DFT level of theory demonstrate how variations in the electron-withdrawing
(donating) behavior of the groups associated with the By enhancing the catalytic activity
and charge transfer capacity of the counter electrode (CE) materials, dye-sensitized solar
cells' (DSSCS) photoelectric conversion efficiency (PCE) can be significantly increased.
In order to replace the benchmark Pt, the careful hotspots of CE catalysts for DSSCS are
to build multifunctional materials that strike a balance between fabrication cost,
environmental friendliness, PCE, and electrochemical stability. Four successful
approaches—heteroatom-doped materials, the creation of noble metal-free chalcogenides
with precisely regulated facets, the building of heterostructures, and the synthesis of
composites with a synergistic effectare emphasized in this review as ways to further
enhance the photovoltaic performance of DSSCS based on inexpensive CE materials. The
impact of these tactics on catalytic activity, charge transfer capability, and reaction in
some typical instances (Savéant, 2008).

CHAPTER 3

MATERIALS AND METHODS

3.1 Computational details

Gaussian 09 program package was used for all of the calculations. 6-31+G∗ basis
set (Labat et al., 2012)and B3LYP functional have been used to optimize the ground state
structure of the dyes in gas phase. For all calculations, an integration grid of 10−8 and a
strict SCF convergence criterion (10−8a.u.) were applied. The nature of the computed
geometries has been confirmed using frequency calculations on the optimized geometry.

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An indication of a successful geometry optimization was the absence of imaginary values
in the wave numbers computations. (Labat et al., 2012).
Using the Lee-Yang-Parr gradient-corrected correlation potential (B3LYP) density
functional theory (DFT) with the 6-31G(d,p) basis set and Becke's three parameter
gradient-corrected exchange potential, the potential ground state structures of the organic
dyes CFP1A, CFP2A, CFP1CA, and CFP2CA were fully optimized. All computations
were carried out in the dichloromethane gas phase and in solution without the use of any
symmetry constraints. For condensed-phase computations, the conductor-like polarizable
continuum model (C-PCM)31, 32 was employed. Using condensed-phased optimized
geometries, time-dependent DFT (TD-DFT) with the same B3LYP/6-31G(d,p) level of
theory in solution was used to study the excitation energies (E gs) and oscillator strengths
(f) for the 10 states. The GAUSSIAN03 computer suite was used to analyze all optical
characteristics and electrical structures.33 Molecular orbitals' contribution to the
electronic transitions was computed using (Grabarz and Ośmiałowski, 2021).

The structural and dynamic properties of the dye molecules adsorbed onto the
semiconductor surface are investigated using computational investigations that typically
begin with molecular dynamics (MD) simulations. Understanding the dye's orientation
and stability on the surface, as well as the interaction between the dye and the
semiconductor, is aided by these simulations (Duncan and Prezhdo, 2007).

3.2 Computational Screening and Optimization

High-throughput computational techniques, such as density functional theory

calculations combined with machine learning algorithms, can be used for screening large
numbers of dye and semiconductor candidates to identify materials with favorable
properties for DSSCS. Optimization algorithms can then be employed to fine-tune the
device parameters for improved efficiency.The electrochemical behavior of dye-
sensitized solar cells (DSSCS), encompassing the electric potential distribution, current
density, and charge accumulation within the apparatus, can be modeled by FEM
simulations. The performance of DSSCS under various operating situations is predicted
and their design is optimized with the aid of these simulations (Perez-Sanchez and
Wenzel, 2011).

3.3 Schrodinger Equations

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 The Schrödinger equation, which describes the behavior of quantum mechanical
systems, especially electrons in molecules, is a basic equation in computational
chemistry. A partial differential equation that illustrates the evolution of a system's wave
function over time is the Schrödinger equation. The time-independent Schrödinger
equation for a single particle (like an electron) in three dimensions is:−2m ℏ2 ∇2ψ(r)
+V(r)ψ(r)=Eψ(r)
ℏ is the reduced Planck constant (m is the mass of the particle, ∇is the Laplacian operator
(which represents the sum of second partial derivatives with respect to the spatial
coordinates),ψ(r) is the wave function, which represents the quantum state of the
system,V(r) is the potential energy function, which depends on the spatial coordinates, E
is the total energy of the system (Tsutsumi, 1987).

Since precise solutions are typically only achievable for simple systems, this
equation is frequently solved approximately in computational chemistry. Using numerical
techniques like many-body perturbation theory (MBPT), density functional theory (DFT),
or the Hartree-Fock method is one popular strategy. These approaches use a variety of
computational strategies and approximations to solve the Schrödinger equation and
forecast molecular attributes like electronic structure, molecular geometry, and
spectroscopic characteristics (McArdle et al., 2020).

3.4 Density Functional Theory

Dye-sensitized solar cells (DSSCS) represent a promising avenue in renewable

energy technology, offering an innovative approach to harnessing solar energy. At the
heart of DSSCS lies the concept of light absorption by a dye molecule, typically a
photosensitive organic compound, which then transfers its excited state electrons to a
semiconductor electrode, initiating the generation of electric current. One of the key
components enabling this process is the dye molecule itself, often referred to as the
sensitizer, with the choice of dye playing a critical role in determining the efficiency and
performance of the solar cell.The Dye-Sensitized Solar Cell (DSSC) structure typically
consists of several layers. The first layer is a transparent conductive substrate, commonly
glass, coated with a thin layer of a semiconductor material like titanium dioxide (TiO 2).
This semiconductor layer serves as the electron acceptor and transporter. Next comes the
dye layer, where the photosensitive dye molecules are anchored onto the surface of the
semiconductor via chemical bonding or adsorption. The dye absorbs incident photons

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from sunlight and transfers the excited electrons to the semiconductor layer. Finally, a
counter electrode layer, typically composed of a catalyst like platinum, facilitates the
regeneration of the dye molecules by accepting the electrons from the external circuit and
completing the electron cycle.
Efforts to enhance the performance of DSSCS have led to the exploration of new dye
sensitizers and strategies to improve light harvesting and electron transfer processes. For
instance, researchers are investigating the use of metal-free organic dyes, porphyrin
derivatives, or conjugated polymers as sensitizer materials, aiming to achieve higher
efficiencies, broader absorption spectra, and improved long-term stability. Additionally,
advancements in nanostructured materials and surface engineering techniques have
enabled the design of hierarchical structures and tailored interfaces to enhance light
trapping and charge separation within the solar cell architecture (Orio et al., 2009).

3.5Dye Sensitization Process

The heart of a DSSC lies in the dye sensitization process. Organic or inorganic
dyes are chosen for their ability to efficiently absorb photons across a wide range of
wavelengths. Upon absorbing light, the dye molecules undergo an excited-state electron
transfer, injecting electrons into the semiconductor's conduction band. Typically, the
semiconductor material used in DSSCS is titanium dioxide (TiO 2) due to its excellent
stability, low cost, and high electron mobility. The TiO 2 layer, also known as the
photoanode, provides a scaffold for the dye molecules and facilitates electron transport
(Kimura et al., 2012).

3.6 Efficiency and Performance

DSSCS exhibit several advantages over conventional solar cells, including ease of
fabrication, flexibility, and the ability to perform well under low-light conditions.
However, their efficiency has historically been lower than that of silicon-based solar cells.
Efforts to enhance efficiency focus on improving the dye sensitizers, semiconductor
materials, and electrolyte compositions. Despite their potential, DSSCS face challenges
such as dye degradation, electrolyte leakage, and long-term stability issues. Additionally,
their efficiency is limited by factors such as light absorption and charge recombination
losses. Addressing these challenges is crucial for the widespread commercialization of
DSSCS(Barr et al., 2002).

3.7 Applications DSSCS

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 have found applications in niche markets where flexibility, transparency, and low-
light performance are essential, such as in building-integrated photovoltaics, portable
electronics, and wearable devices. Continued research and development may expand their
use in mainstream solar energy applications. The field of DSSCS continues to evolve
rapidly, driven by advances in materials science, nanotechnology, and device engineering.
Ongoing research efforts focus on improving efficiency, stability, and scalability to make
DSSCS a viable competitor to traditional solar cell technologies in the quest for
sustainable energy solutions (Aslam et al., 2020).

3.8 Marcus’s Theory of charge transfer

DSSCS are a type of photovoltaic device that mimic photosynthesis in plants.

They consist of a semiconductor film, typically composed of titanium dioxide (TiO 2),
coated with a dye molecule that absorbs light. When light strikes the dye molecule, it
excites an electron, initiating a series of charge transfer processes.: Marcus's theory
begins with an understanding of the energy levels involved in the electron transfer
process. The dye molecule absorbs photons, promoting an electron from its ground state
to a higher energy state. This creates an excited electron-hole pair, where the electron is
in a higher energy level than its original ground state (Taylor and Kassal, 2018).

3.9 Charge Separation

Upon absorption of light, the excited electron in the dye molecule transfers to the
semiconductor's conduction band, leaving behind a positively charged dye molecule
known as an oxidized state or dye cation. This process, known as charge separation, is
crucial for generating an electric current. Marcus's theory emphasizes the significance of
redox reactions in DSSCS. After the electron transfers to the semiconductor, a redox
reaction occurs in which an electron donor, often an electrolyte solution, replenishes the
electron deficit in the dye molecule, converting it back to its original reduced state
(Kirchartz et al., 2015).

3.10 Free Energy Change and Activation Energy

The rate at which these electron transfer processes occur depends on the free
energy change (ΔG) associated with the reaction and the activation energy barrier that
must be overcome for the reaction to proceed. Marcus introduced the concept of the
reorganization energy, which characterizes the energy required to adjust the nuclear

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coordinates of the reactants and products during the electron transfer process. Marcus
distinguished between outer sphere and inner sphere electron transfer mechanisms. In
outer sphere electron transfer, the reactants and products remain spatially separated
throughout the reaction, whereas in inner sphere electron transfer, they undergo structural
rearrangement as the electron transfers (Mamleev et al., 2004).

Outer Sphere vs. Inner Sphere Electron Transfer: Marcus distinguished between
outer sphere and inner sphere electron transfer mechanisms. In outer sphere electron
transfer, the reactants and products remain spatially separated throughout the reaction,
whereas in inner sphere electron transfer, they undergo structural rearrangement as the
electron transfers. Marcus formulated an equation relating the rate constant of the
electron transfer reaction to the reorganization energy, temperature, and the free energy
change of the reaction. This equation, known as the Marcus equation, provides a
quantitative description of electron transfer kinetics in terms of these parameters (Sutton
and Vlachos, 2012).

Application to DSSCS: Marcus's theory has been extensively applied to

understand and optimize the performance of DSSCS. By manipulating factors such as dye
structure, semiconductor morphology, and electrolyte composition, researchers aim to
minimize reorganization energy and activation barriers, thereby enhancing electron
transfer rates and overall device efficiency. Despite its utility, Marcus's theory faces
challenges in accurately describing complex electron transfer processes in DSSCS.
Factors such as interfacial charge recombination, energy loss pathways, and dynamic
disorder pose significant challenges to the simplistic assumptions underlying Marcus
theory (Van Santen et al., 2009).

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3.11 Absorption spectra

Introduction to DSSCS: DSSCS are a promising type of solar cell that mimics
natural photosynthesis to convert sunlight into electricity. They typically consist of a
semiconductor substrate coated with a dye layer, an electrolyte, and a counter electrode.
The dye absorbs photons from sunlight, exciting electrons and generating electricity
through a series of redox reactions.: Absorption spectra provide essential insights into the
dye's ability to absorb light at different wavelengths. Understanding these spectra helps
optimize the efficiency and performance of DSSCS by selecting dyes with optimal light
absorption properties (Wu and Eriksson, 2010).

3.14 Computational Approaches

Computational chemistry offers a powerful toolset for simulating absorption

spectra in DSSCS. Density functional theory (DFT) and time-dependent DFT (TD-DFT)
are commonly used methods. These techniques calculate the electronic structure of
molecules and predict their optical properties, including absorption spectra.: In
computational simulations, the first step involves modeling the dye molecule and its
surroundings, typically including the semiconductor substrate and solvent molecules.
Accurate modeling requires consideration of the dye's electronic structure, geometry, and
interactions with its environment (Kheralla and Chetty, 2021).

3.15 DFT Calculations

DFT calculations are performed to determine the ground-state electronic structure

of the dye molecule and its excited states. These calculations provide information about
the distribution of electrons and molecular orbitals, which influence the molecule's
absorption properties. TD-DFT extends DFT to predict excited-state properties, including
absorption spectra. By solving the time-dependent Schrödinger equation, TD-DFT
calculates the transition energies and oscillator strengths associated with electronic
excitations, which correspond to absorption peaks in the spectra (Bourass et al., 2016).

3.16 Solvation Effects

Solvation, the interaction of the dye molecule with solvent molecules,

significantly affects absorption spectra in DSSCS. Computational models must accurately
account for solvent effects to predict realistic spectra. Solvent models such as continuum
solvation models or explicit solvent molecules can be incorporated into simulations.
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Interactions between the dye molecule and the semiconductor substrate also influence
absorption spectra. Computational studies examine how these interactions affect the dye's
electronic structure and absorption properties, providing insights into dye-substrate
compatibility and charge transfer processes (Lian et al., 2019).

3.16.1 Spectral Analysis

Once the absorption spectra are computed, they can be analyzed to identify
absorption peaks and understand the dye's absorption behavior across different
wavelengths. Spectral features such as peak positions, intensities, and broadening provide
valuable information for comparing and selecting dye candida and Computational
simulations of absorption spectra enable researchers to screen a wide range of dye
molecules and optimize their structures for enhanced light absorption in DSSCS. By
combining computational predictions with experimental validation, researchers can
design dyes with tailored absorption properties to improve solar cell performance (Leitão
et al., 2020).

3.16.2 Time dependent density functional theory

Time-dependent density functional theory (TDDFT) has emerged as a powerful

computational tool in the field of computational chemistry, particularly in studying dye-
sensitized solar cells (DSSCS). DSSCS are a promising alternative to traditional silicon-
based solar cells due to their lower production cost and higher flexibility. However, their
efficiency is heavily dependent on the properties of the dye molecules used, making
computational methods like TDDFT invaluable in their design and optimization. At the
heart of TDDFT lies the concept of the electron density, which is a fundamental property
of a molecular system. In TDDFT, the time evolution of the electron density is described
using density functionals, which are mathematical expressions of the electron density and
its dependence on spatial coordinates and time. By solving the time-dependent
Schrödinger equation within the framework of DFT, TDDFT provides insights into the
excited-state properties of molecules, making it well-suited for studying the absorption
and emission spectra of dye molecules in DSSCS(Marques and Gross, 2004).

In DSSCS, dye molecules are responsible for absorbing sunlight and initiating the
process of electron transfer, where electrons are transferred from the dye molecule to a
semiconductor material, such as titanium dioxide (TiO2). TDDFT allows researchers to
predict the absorption spectra of dye molecules, providing crucial information about their

PAGE \* MERGEFORMAT 29
electronic structure and excited states. By simulating the excited-state dynamics of dye
molecules using TDDFT, researchers can optimize their molecular structures to enhance
light absorption and electron transfer efficiency, ultimately improving the overall
performance of DSSCS. One key advantage of TDDFT is its ability to model excited-
state phenomena, such as electron transfer and charge separation, which are critical
processes in DSSCS. By simulating these processes computationally, researchers can gain
insights into the mechanisms underlying DSSC operation and identify strategies for
improving their efficiency. Additionally, TDDFT can predict other relevant properties of
dye molecules, such as their redox potentials and electron injection rates, further aiding in
the design of high-performance DSSCS(Ullrich, 2011).

Despite its many advantages, TDDFT also has some limitations in the context of
DSSC modeling. For instance, accurate calculations often require sophisticated exchange-
correlation functionals and basis sets, which can be computationally expensive.
Additionally, TDDFT may neglect certain electron correlation effects that are important
in systems with strongly correlated electrons, although efforts are underway to address
these limitations through the development of more advanced theoretical approaches. In
conclusion, TDDFT is a valuable tool in the computational chemistry toolbox for
studying dye-sensitized solar cells. By providing insights into the electronic structure,
excited-state dynamics, and photophysical properties of dye molecules, TDDFT enables
researchers to design and optimize dye sensitizers with improved performance and
stability. As computational methods continue to advance, TDDFT is likely to play an
increasingly important role in the development of next-generation DSSCS with enhanced
efficiency and durability (Casida and Huix-Rotllant, 2012).

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CHAPTER 4

RESULT AND DISCUSSION

4.1. Geometrical properties

The geometrical parameters for the selected compounds, including bond lengths
(d1, d2) and dihedral angles (θ1, θ2, θ3), are displayed per the B3LYP/6–31 G (d,p)
technique. The findings show that, for dyes containing phenyl as the π-linker, the dihedral
angle θ1, which represents the angle between the donor (D) and acceptor (A′) units, is
between 34.92 and 36.61, and dyes have non-planar structures, which are most likely the
result of steric interactions between neighboring group donor moieties and the hydrogen
of the phenyl group. These interactions assist in preventing charge recombination and dye
aggregation problems. Contrarily, the dihedral angles θ1, δ2, and δ3 for dyes that use the
triazine ring as the acceptor are small (less than 1), indicating coplanarity between the
donors and the triazine ring, which enhances the photovoltaic characteristics of the dye-
sensitized solar cell and promotes electron delocalization and intramolecular charge
transfer (Prashant et al., 2021).

12

10

6
A1
A2
4
A3
A4
2
A5
A6
0
IP EA x η (μ) S ω
-2

-4

-6

Fig.4.1Analyzing the Geometrical Properties of Solar Panels: Impact on Efficiency and

Performance.

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 In contrast, d1 for triazine-bridged systems is 1.464 Å. The constant d2 bond
values of all compounds are around 1.458 Å, which is shorter than the ~1.530 Å length of
a C-C single bond These findings show that substantial resonance between the donor and
acceptor units is present in all colors.The findings reveal that π-linker dyes based on
phenyl are coplanar with the furan ring, with θ2 and θ3 angles being smaller than 4◦. The
compounds that are connected by phenyl have a bond length d1 of roughly 1.482 Å
(Python et al., 2009).

Table 4.1.Calculated energy (eV) and chemical reactivity descriptors of studied dyes.

Dyes IP EA x η (μ) S ω
A1 5.15 3.01 4.12 1.12 -4.12 0.25 7.25
A2 5.24 2.99 4.15 1.06 -4.07 0.45 7.35
A3 4.45 2.77 4.25 0.88 -3.53 0.57 6.34
A4 5.33 3.12 3.67 1.06 -4.25 0.51 8.78
A5 5.23 3.23 4.87 0.99 -3.45 0.63 9.35
A6 4.85 3.65 4.05 0.8 -3.25 0.41 10.35

4.2. HOMO and LUMO levels and energy gap

unoccupied the lowest molecular orbital (LUMO) and highest occupied molecular
orbital (HOMO) can provide important information about the properties of the excited
state.
For DSSC applications, an acceptable dye must have the right energy levels; the HOMO
level should be below the redox potential of the redox couple (− 4.80 eV for I -1I −3
), and
the LUMO level should be greater than the conduction band edge of the semiconductor (−
4.00 eV for TiO2). The dyes under investigation, which had different donor and π-linker
groups, had their HOMO and LUMO energies derived from gas phase optimized ground
−1
state structures. The findings show that the HOMO energies continuously fall below I
I's redox potential.
Additionally, all LUMO energies (varying from − 2.99 to − 3.26 eV) are higher than the
TiO2 conduction band edge, guaranteeing efficient electron injection from excited-state
dyes into the TiO2 photoanode When the results are analyzed, it becomes clear that even
with the identical phenyl π-linker, the triazine-based dyes show more stabilized HOMO
and LUMO energy levels. The photoelectric properties of the dyes are largely reflected
in the energy gap. The absorption spectrum shifts red as a result of the gaps gradually
changing due to changes in the donor and π-linkers. Increased short-circuit current
density and e could result from this change (Kim et al., 2013).

PAGE \* MERGEFORMAT 29
12
10
8
6 A1
A2
4 A3
2 A4
A5
0 A6
IP EA x η (μ) S ω
-2
-4
-6

Fig 4.2.Gharphical representation of HOMO and LUMO levels.

A1 A2 A3

A4 A5 A6

Fig. 4.3. The optimized structures of the studied dyes.

PAGE \* MERGEFORMAT 29
To investigate the impact of the -linker on electron distribution in FMOs, this was
calculated at the B3LYP/6-31G(d,p) level in CH2Cl2 solvent.
Molecular skeleton donors phenothiazine and phenoxazine are covered with dyes,
with a higher density and a lower density seen above phenyl and triazine. It is noteworthy
that the HOMO is greatly enhanced by the anchoring group (-CO 2H), which permits
sufficient electronic coupling and rapid charge injection However, the rate of charge
recombination between photoinjected holes and decreased dyes is slowed down by the
localization of LUMO. Propagation of the LUMO orbitals occurs via π-linkers and
molecular acceptors We can also infer that these dyes' excited states might have an
intramolecular charge transfer feature (Huang et al., 2017).

12

10

6 A1
A2
4 A3
2 A4
A5
0 A6
IP EA x η (μ) S ω
-2

-4

-6

Fig 4.4.Graphical representation of energy gap

4.3. Molecular electrostatic potential (MEP)

The molecule electrostatic potential is crucial for predicting intermolecular

interactions, such as nucleophilic and electrophilic assaults. The comprehension of this
parameter is crucial. To depict various electrostatic potentials, different colors are
utilized. navy. The molecules' electrostatic potential is shown in for both substances. The
orange-hued negative portions groups that contain sulfur in phenothiazine and nitrogen in
triazine. The favored regions are the blue-colored positive ones, which are the hydrogen
atoms (Lakshminarayanan et al., 2021).

PAGE \* MERGEFORMAT 29
 60

50

40

30
A6
A5
20
A4
A3
10
A2
A1
0
IP EA x η (μ) S ω
-10

-20

-30

Fig 4.5.Mapping Charge Distributions for Enhanced Molecular Interaction

4.4. Chemical reactivity parameters

Any number of chemical reactivity parameters can be applied to the photoelectric

properties of the dyes being studied. ionization potential, chemical potential (μ), chemical
softness (S), electrophilicity index (ω), chemical hardness (η), and electrophilicity index
in terms of electronegativity (χ), electron affinity (EA), and IP. The lowest unoccupied
molecular orbital (ELUMO) and highest occupied molecular orbital (EHOMO) of a
molecule have energies that are related to their respective ionization potential (IP) and
electron affinity (EA), according to Koopmann's theorem. Particularly, the EA is the
negative of the ELUMO energy and the IP is the negative of the EHOMO energy
(Karickhoff et al., 1991).

PAGE \* MERGEFORMAT 29
12

10

6
A1
4 A2
A3
A4
2 A5
A6
0
IP EA x η (μ) S ω
-2

-4

-6

Fig 4.6.Key Factors Influencing Reaction Rates and Mechanisms.

PAGE \* MERGEFORMAT 29
CHAPTER 5
SUMMARY

Molecular structureDFT allows researchers to model the molecular structure of dye

molecules used in DSSCS and their interactions with semiconductor surfaces. By
calculating the electronic structure and geometry optimization of dye molecules,
researchers can predict their absorption spectra, molecular orbital energies, and binding
configurations on the semiconductor surface. DFT provides insights into the electronic
properties of dye molecules and semiconductor materials in DSSCS. Through
calculations of band structures, density of states, and charge distribution, researchers can
evaluate the energy levels and charge transfer processes at the dye-semiconductor
interface, essential for efficient electron injection and transport. DFT studies the
adsorption and desorption processes of dye molecules on semiconductor surfaces,
elucidating the factors influencing dye coverage, stability, and binding strength.
Understanding these interactions helps optimize dye molecule design and surface
functionalization strategies to enhance light harvesting and charge separation in DSSCS.
DFT can model the electronic structure and redox properties of electrolyte components,
such as redox mediators and counter ions, used in DSSCS. By simulating redox reactions
and charge transfer kinetics, researchers gain insights into the electrochemical processes
occurring in the electrolyte solution, crucial for efficient regeneration of oxidized dye
molecules and transport of charge carriers.: DFT studies the mechanisms of charge
transport in DSSCS, including electron injection from dye molecules to semiconductor
nanoparticles and subsequent electron diffusion through the mesoporous scaffold to the
electrode. By calculating electronic coupling strengths and transition rates, researchers
can optimize material interfaces and device architectures to minimize charge
recombination and improve overall device efficiency. Integrating insights from DFT
studies, researchers can model the overall performance of DSSCS, including photovoltaic
parameters such as open-circuit voltage, short-circuit current, fill factor, and power
conversion efficiency. By correlating computational predictions with experimental
measurements, researchers can validate theoretical models and guide the rational design
of DSSCSwith improved performance and stability.

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