University of Jammu

(Department of Electronics)

Project Report
on
Simulation study of fullerene and non-fullerene Organic Solar Cells
using Scaps-1D
Submitted to the University of Jammu

In Department of Electronics

For the fulfillment for the award of MSc. Electronics session 2023-25

Submitted by:

Vipin Mishra 007ELE23

 CERTIFICATE

It is certified that the project entitled “ simulation study of fullerene and non-
fullerene organic solar cells using scaps-1D” has been undertaken by Vipin
Mishra, students of 4th semester M.Sc. Electronics program in the Department of
Electronics, University of Jammu, has been submitted for the partial fulfillment of
the requirement for Master of Science in electronics.

Countersigned

PROF. SUSHEEL K SHARMA Dr. ROCKEY GUPTA

(Head of Department) (Supervisor)

 Declaration
We Vipin Mishra and student of MSc. Electronics session 2023-25 in the Department of
Electronics, University of Jammu hereby, declare that the project report entitled
“simulation study of fullerene and non- fullerene organic solar cells using scaps-1D”
submitted for the partial fulfillment for the award of Degree of Master of Science in
Electronics, is a record of the research work carried out by us in the Department of
Electronics, University of Jammu, under the guidance Dr. ROCKEY GUPTA.

We also ascertain that no part of this project report is presented elsewhere for the award
of any degree or diploma of any University of Institution.

Vipin Mishra

Roll no. 0007ELE23

Date: 09/06/2025

Place: University of Jammu

 Acknowledgement
First and foremost, we are thankful to the “The Almighty God” for giving us strength and
endurance to carry out our project work successfully.

We offer our sincere thanks to our project supervisor, Dr. ROCKEY GUPTA, for his
excellence, guidance, encouragement, esteemed supervision and moral support in
compilation of this work. His balance mixture of a humor, remarkable patience and
wisdom helped us to make continuous progress during our study period.

We express our courteous gratitude to Prof. Susheel Kumar Sharma, Head of

Department of Electronics, University of Jammu for providing necessary research
environment and facilities. We also thank individually all the teaching and non-teaching
staff of the department.

We would like to extend our warm gratitude to our research scholar Miss Mehak
Sharma & Heena Thakur of Department of Electronics for her continuous
encouragement and timely suggestion at every stage of work.

Perhaps, the most difficult moments in one’s life are those when one wishes to express
ones heartily feeling for one’s parents in shape of words. We express our profound
regards to our parents, for the love, attention, encouragement and the moral values, which
they have ingrained in us.

Vipin Mishra
 CONTENT
Chapter 1: INTRODUCTION
1.1 World energy requirement
1.2 Limitations of fossil fuels
1.3 Renewable energy resources
Chapter 2: SOLAR CELL
2.1 Parameters of solar cell
2.2 Generations of solar cell
2.3 Organic Solar cells
Chapter 3: Simulation study of fullerene and non-fullerene Organic
Solar Cells using Scaps-1D.
3.1 Introduction of the PTB7PC70BM, PM6Y6 and P3HTPCBM absorber
layers.

3.2 Device Structure and Computational Details

3.3 Result and discussions
3.4 Conclusion
Chapter 4: Performance investigation of Cs3Bi2I3 and Cs3Bi2AgI6
based Perovskite solar cell using various charge transport layers.
4.1 Introduction
4.2 Device Structure and Computational Details.
4.3 Result and discussions
4.4 Conclusion
Chapter 1: INTRODUCTION
The escalating demand for energy worldwide, propelled by a growing global population
and continuous economic development, presents a critical juncture for humanity [1]. This
surge in energy consumption necessitates a fundamental shift away from traditional
energy systems towards more sustainable alternatives. The environmental consequences
associated with the prevailing reliance on fossil fuels, most notably the accelerating threat
of climate change and widespread pollution, underscore the imperative for this transition
[5]. This report aims to provide a comprehensive analysis of the global energy landscape,
critically examining the limitations of fossil fuels and exploring the vast potential of
renewable energy resources. A significant portion of this analysis will be dedicated to
solar cell technology, delving into its fundamental principles, historical evolution through
different generations, and the cutting-edge advancements in perovskite solar cells, which
represent a promising frontier in sustainable energy generation.

The consistent upward trend in global energy consumption highlights the pressing need
for sustainable alternatives. Increased population directly results in a larger number of
energy consumers. Concurrently, economic development, particularly in previously less
industrialized nations, leads to higher standards of living and a subsequent increase in per
capita energy consumption [2] This dual effect creates a continuous upward pressure on
global energy demand, making the transition to sustainable energy sources not just an
environmental choice but a fundamental necessity to secure future energy supplies
responsibly. The tension between these rising energy needs and the environmental
consequences of meeting them with fossil fuels creates a significant challenge that
renewable energy technologies must address. While fossil fuels currently dominate the
energy mix, their well-documented contribution to greenhouse gas emissions and various
forms of pollution presents a clear and present danger to the planet [5]. Renewable
energy offers a cleaner alternative, but its deployment needs to accelerate dramatically to
not only meet the growing energy demand but also displace the existing reliance on fossil
fuels to mitigate the escalating environmental crisis.

The rising consumption of fossil fuels, together with increasing green- house gas
emission, threatens our secure energy supply. The price rise could lead to worldwide
recession and the negative environmental effect could cause irreversible change to the
global climate. The lack of sufficient energy supplies can also hold back the growth of
billions of people living in the developing countries. Therefore, development of clean,
secure, sustainable and affordable energy sources should be our priority in this century
2. Global Energy Demand: Current Scenario and Future Projections
2.1. Current Global Energy Consumption: Trends and Regional Analysis
Global energy demand experienced a significant growth of 2.2% in 2024, surpassing the average
annual increase of 1.3% observed between 2013 and 2023.This acceleration indicates a potential
shift in long-term trends and highlights the need for responsive energy policies. Electricity
demand surged by 4.3% in 2024, nearly doubling the average annual increase over the past
decade. This dramatic rise was driven by a confluence of factors, including increased cooling
needs due to record global temperatures, rising consumption in the industrial sector, the ongoing
electrification of transport, and the rapidly expanding energy demands of data centers and
artificial intelligence. This surge underscores the increasing importance of electricity as the
primary energy carrier in the global economy.

Emerging and developing economies were responsible for over 80% of the increase in global
energy demand in 2024. Within this group, China and India exhibited significant, though
varying, growth rates. China's energy demand growth slowed considerably in 2024, halving its
2023 rate, while India's increase alone outpaced the total increase in all advanced economies
combined, highlighting the shifting centers of energy consumption on the world stage. In
contrast, advanced economies saw a return to energy demand growth in 2024 after years of
decline.[16]. This growth, though smaller in scale compared to developing economies, suggests a
potential reversal of previous trends, possibly due to increased electricity consumption in these
regions.

Despite the increasing adoption of renewable energy, fossil fuels still constitute a significant
portion of the global energy supply. In 2022, oil, coal, and natural gas accounted for
approximately 80% of the total energy mix. This dominant share underscores the magnitude of
the challenge involved in transitioning to renewable energy sources. While renewable energy
sources are experiencing growth, their overall contribution to the total energy mix remains
comparatively smaller [5]. A more rapid and widespread expansion of renewable energy
technologies is essential to meet sustainability goals and mitigate the environmental impacts of
fossil fuel consumption.

To provide a clearer picture of the current energy landscape, the following table summarizes
global energy consumption by region and source based on available data.[5]. This consolidated
view allows for easy comparison of energy mix across different regions and highlights the
relative contribution of fossil fuels versus various renewable sources.
Region Oil Natur Coal Nucle Hydro Wind Solar Other
(%) al Gas (%) ar (%) (%) (%) Renewables
(%) (%) (%)

World 32 23 26 4 6 4 2 2
(2023)

OECD 37.8 25.5 15.4 17.7 2.4 6.1 2.5 2.6

(2022)

Non- 26.2 21.1 36.8 1.8 7.3 2.6 1.1 3.1

OECD
(2022)

Asia 29.5 12.8 45.3 2.4 6.8 1.9 0.9 0.3

Pacific
(2022)

Europe 32.1 24.4 13.7 14.6 4.6 6.5 3.5 0.6

(2022)

North 40.3 36.2 11.7 8.7 1.6 1.8 0.7 0.1

America
(2022)

Note: Percentages may not always add up to 100 due to rounding and the inclusion of other
minor energy sources.

This table clearly illustrates the continued dominance of fossil fuels in the global energy mix,
although it also highlights the increasing, albeit still relatively small, contribution of renewable
energy sources like wind and solar across different regions. The energy consumption patterns
vary significantly by region, with some areas exhibiting a higher reliance on coal while others
depend more on oil or natural gas. Understanding these regional differences is crucial for
developing effective and targeted strategies for the global energy transition.
The global energy landscape is undergoing a profound transformation, driven by a confluence of
demographic shifts, economic development, and the escalating impacts of climate change.
Projections indicate a substantial increase in global energy demand by mid-century,
fundamentally altering the existing energy paradigm. By 2050, the world population is
anticipated to reach 10 billion people, expanding at a rate of approximately 1 million individuals
every six days.1 This demographic expansion serves as a foundational driver for increased energy
consumption worldwide.

Accompanying this population growth, a projected 15% increase in overall energy use is
expected by 2050. Critically, this entire growth is earmarked for elevating living standards in the
developing world, underscoring the intrinsic link between energy access and global development
objectives.1 This emphasis on equitable development means that future energy growth must be
predominantly sourced from sustainable, low-carbon alternatives to avoid exacerbating
environmental challenges. For developing nations to achieve higher living standards without
intensifying climate change, their energy growth must be predominantly from sustainable
sources.

This places a significant imperative on accelerating the deployment of renewable energy and
lower-carbon technologies in these regions, necessitating supportive policy, technological
innovation, and market incentives.1 This transforms the energy transition from solely an
environmental concern for developed nations into a fundamental issue of global equity and
sustainable development, implying that solutions must be not only technologically viable but
also affordable and accessible to prevent developing economies from being locked into high-
carbon pathways, which would undermine global climate targets.

Sector-specific energy demands are also poised for significant increases. Global electricity
demand is projected to nearly double, while energy consumption for both transportation and
industrial activities is expected to grow by more than 20% each. 1 These figures highlight the
broad-based nature of future energy requirements across various economic sectors. Beyond these
socioeconomic factors, climate change itself is emerging as a powerful accelerator of future
energy demand. Scenarios involving vigorous warming could increase global climate-exposed
energy demand by 25–58% by 2050, a rise that is in addition to the 1.7–2.8 factor increase
already anticipated from socioeconomic developments. 2 Even under moderate warming
scenarios, an 11–27% increase in energy demand is projected.2

This reveals a critical positive feedback loop: greenhouse gas emissions from energy
consumption contribute to warming, which in turn drives further energy demand, particularly for
cooling in hotter regions. If this additional demand is met by fossil fuels, it risks accelerating
warming, creating a self-reinforcing cycle. This amplifies the urgency for decarbonization, as a
failure to mitigate climate change will not only worsen environmental conditions but also
increase the energy burden, complicating the transition. Regional impacts of climate change on
energy demand are not uniform; for instance, energy demand is projected to rise by over 25% in
the tropics and southern regions of the USA, Europe, and China due to climate-induced factors.2
The primary drivers of this escalating energy demand are multifaceted. Population expansion,
with global figures projected between 8.4 and 10 billion people by 2050 and future growth
concentrated in northern mid-to-low latitudes, directly translates to increased energy
consumption.2

Economic growth, measured by per-capita GDP, is also a potent force, projected to increase
substantially from $9,763 in 2010 to between $18,000 and $42,000 by 2050, with varying
geographic patterns.2 Energy demand exhibits greater sensitivity to income growth than to
population expansion, indicating that economic prosperity is a more significant determinant of
increased energy use.2 The pursuit of affordable and reliable energy is fundamental to economic
development and modern living standards, particularly in developing countries where a
significant energy disparity persists.1

This drive for improved quality of life is a core component of growing energy consumption.
Shifts in the sectoral composition of economies also play a role, with industry and services
identified as the most significant contributors to changes in global energy demand, both showing
net positive increases. Electricity demand, in particular, is projected to expand across all sectors,
with commercial electricity accounting for 80% of the global climate-driven energy demand
increase.2 Long-term energy assessments fundamentally rely on understanding economic trends,
technological advancements, consumer behavior, and climate-related public policy, all of which
interact dynamically to shape future demand.1

The existence of a "large energy disparity still exists between developed and developing
countries" 1 is particularly noteworthy. When combined with the understanding that all projected
energy growth is for developing nations 1 and that low-income countries, especially in the
Middle East, Africa, and Asia, are projected to experience substantial climate-induced energy
demand increases 2, a critical vulnerability becomes apparent. These regions, already energy-
poor and with lower adaptive capacity, face a double burden: they need more energy for
fundamental development, and climate change simultaneously forces them to need even more
energy (e.g., for cooling) just to maintain basic living standards.

This exacerbates existing inequalities, signifying that the energy transition is not merely an
environmental or economic challenge but a profound issue of global social justice and human
development. Sustainable energy solutions must therefore be not only technically viable and
cost-effective but also equitable and accessible to ensure that climate action does not
inadvertently deepen existing disparities or hinder the development aspirations of the Global
South.
 Table 1: Global Energy Demand Projections to 2050

Metric Projection by 2050 Source

1
Projected Global Population 10 billion people

1
Overall Increase in Energy Use 15% (all for developing
world)

1
Projected Increase in Global Nearly double
Electricity Demand

1
Projected Increase in >20%
Transportation Energy Demand

1
Projected Increase in Industry >20%
Energy Demand

2
Climate Change Induced 25–58% (on top of
Energy Demand Increase socioeconomic growth)
(Vigorous Warming Scenario)

1
Projected Carbon Emissions Projected to fall for the first
Decline (by 2030) time

1
Projected Carbon Emissions 25% decline
Decline (by 2050)

1
Projected Growth of Solar and >4x increase
Wind in Total Energy Mix

1
Projected Share of Oil and >50%
Natural Gas in Total Energy
Mix

1.2 Limitations of Fossil Fuels

The continued reliance on fossil fuels presents a complex array of limitations, encompassing
severe environmental degradation, the inherent constraint of resource depletion, and significant
geopolitical ramifications. These challenges collectively underscore the urgent global imperative
to transition towards alternative energy sources.

The environmental impacts of fossil fuels are extensive and well-documented. The combustion
of coal, oil, and natural gas is unequivocally identified as the primary contributor to greenhouse
gas emissions, directly driving climate change. 3 Coal, in particular, generates the highest amount
of CO2 compared to other fossil fuels.3 The Intergovernmental Panel on Climate Change (IPCC)
highlights that human activities have already led to a 1°C increase in global temperatures above
pre-industrial levels, with a further 1.5°C warming likely between 2030 and 2052. 4 Beyond
climate change, air pollution resulting from natural gas and coal combustion poses a significant
public health crisis, causing severe respiratory diseases, cardiovascular problems, and
contributing to an estimated 4.2 million premature deaths annually due to outdoor air pollution,
as reported by the World Health Organization (WHO, 2022). 3 The combustion of oil in
transportation and power generation also releases harmful atmospheric pollutants that
detrimentally impact air quality and human health. 3 This strong link between fossil fuel use and
human health elevates the energy transition to a major public health imperative.

The extraction and use of fossil fuels also lead to extensive habitat destruction and
contamination. Coal mining and extraction practices result in deforestation, habitat destruction,
and the removal of topsoil.3 Oil extraction, through practices such as dredging, and incidents like
spills, tank leaks, and improper disposal, cause widespread contamination of soil and freshwater,
leading to ecological disturbances.3 Specifically, heavy metal discharge from oil extraction
negatively impacts marine and coastal habitats. 3 The overarching reliance on non-renewable
fossil resources contributes to broader ecological issues, including biodiversity loss, further
habitat destruction, population decline of species, and even extinction. 3 This comprehensive
environmental degradation highlights that fossil fuel dependence is not merely an environmental
problem but a systemic threat to public health, national security, and global stability.

Resource depletion is an inherent limitation of fossil fuels, as they are finite energy sources.
Their continuous exploitation leads to inevitable scarcity. 3 The case of Uzbekistan, facing
depleting gas reserves and increasing reliance on imports, illustrates how resource scarcity can
pose serious threats to both environmental and economic stability for nations heavily dependent
on these fuels.4

Furthermore, the geopolitical implications of fossil fuel dependence are profound. Geopolitical
risks are intimately intertwined with environmental concerns, as distant issues can generate
instability and conflict.3 Climate change, exacerbated by fossil fuel use, can intensify conflicts
between nations, often over access to increasingly scarce natural resources. 3 Political instability
and armed conflicts have a direct and significant impact on global supply chains, leading to
inadequate resource acquisition and the depletion of key resources vital for individuals and
groups.3 In contexts of political instability and violence, governments may prioritize immediate
economic benefits over long-term environmental sustainability, perpetuating a cycle of resource
exploitation and environmental harm.3 Globalization, while offering economic benefits, can
paradoxically harm environmental quality by incentivizing the relocation of pollution-intensive
industries to developing countries that offer lower production costs and potentially weaker
environmental regulations.4 This practice effectively shifts the environmental burden rather than
resolving it. The Environmental Kuznets Curve (EKC) hypothesis suggests that environmental
degradation initially surges with economic development before declining. 3 This is particularly
relevant for developing nations, which may experience increased environmental impact in their
early stages of economic growth due to prioritizing economic expansion and industrialization. 3 If
developing nations, which are projected to drive the majority of future energy demand increase
for rising living standards 1, follow this traditional EKC trajectory, they will initially rely heavily
on fossil fuels and increase their environmental footprint. This directly contradicts the urgent
global need for rapid decarbonization to meet climate targets. 1 The tension between immediate
economic benefits and long-term sustainability 3 becomes a critical policy challenge, implying
that a business-as-usual development model is incompatible with climate goals. This highlights
the critical need for developing countries to "leapfrog" the high-carbon industrialization phase
that developed nations underwent, requiring access to affordable and reliable renewable energy
technologies, significant international support, technology transfer, and policy frameworks that
enable sustainable industrialization. The global energy transition is therefore not just about what
energy sources are used, but how development pathways are structured to avoid locking in future
environmental degradation.

1.3 Renewable Energy Resources: Potential and Characteristics

The imperative to rapidly scale renewable electricity generation is paramount for effectively
addressing climate change and other pressing environmental challenges. 5 These energy sources
are poised to play a crucial role in shaping the future global energy mix.

Major categories of renewable energy sources include utility-scale and rooftop solar
photovoltaics (PV), concentrated solar power (CSP), onshore and offshore wind, hydropower,
geothermal electricity, and various ocean energy technologies such as wave, tidal, ocean thermal
energy conversion (OTEC), and salinity gradient energy. 5 These sources are fundamentally
regarded as low-carbon alternatives, capable of meeting burgeoning energy needs while
simultaneously reducing ecological footprints, primarily because they produce electricity without
releasing greenhouse gases (GHGs) that contribute to air pollution.4

The global potential of these renewable resources is assessed across three key metrics: technical,
economic, and feasible potential. Technical potential defines the maximum amount of
electricity that could be produced using current technologies, accounting for geographical and
technical limitations, as well as conversion efficiencies. 5 Four key renewable technologies
demonstrate exceptionally high technical potentials, each exceeding 100 PWh/year: utility-scale
solar PV, concentrated solar power, onshore wind, and offshore wind. 5 Hydropower, geothermal
electricity, and ocean thermal energy conversion (OTEC) also show substantial potential, each
above 10 PWh/year.5 Rooftop solar PV, wave, and tidal energy contribute with technical
potentials above 1 PWh/year.5 Salinity gradient energy, though smaller in scale, still holds a
technical potential above 0.1 PWh/year.5 It is important to note that reported technical potential
estimates vary widely, often spanning several orders of magnitude, a variability attributed to
different methodologies and assumptions.5

The economic potential incorporates the cost of each renewable resource in addition to technical
limitations. Critically, the literature suggests that the global economic potential of renewables is
significantly higher than both current and projected near-future electricity demand, indicating
their cost-effectiveness.5 The feasible potential is the most restrictive category, accounting for
societal and environmental constraints (e.g., land use, public acceptance, ecological impact).
Fewer studies have quantified this potential, and while all these potential ranges are valuable for
assessing available energy sources, they may not fully capture the complex challenges inherent
in deploying large-scale renewable portfolios.5 This highlights that the challenge of the global
energy transition is less about the inherent availability or even cost-effectiveness of renewable
energy resources, and more about the complex socio-technical and political-economic aspects of
integrating these resources into existing energy systems at scale. This underscores the need for
comprehensive policy frameworks, significant infrastructure investment, and continuous
innovation in areas beyond just energy generation, such as grid management, energy storage, and
demand-side management.

Table 2: Global Technical Potential of Key Renewable Electricity Sources

Renewable Energy Source Global Technical Potential Source

(PWh/year)

5
Utility-scale Solar PV >100

5
Concentrated Solar Power >100
(CSP)

5
Onshore Wind >100
 5
Offshore Wind >100

5
Hydropower >10

5
Geothermal Electricity >10

5
Ocean Thermal Energy >10
Conversion (OTEC)

5
Rooftop Solar PV >1

5
Wave Energy >1

5
Tidal Energy >1

5
Salinity Gradient >0.1

Renewables are projected to be the fastest-growing energy type in the global energy mix. 1
Specifically, solar and wind energy are anticipated to increase more than fourfold in the total
energy mix by 2050, signifying their role as primary drivers of change in the energy landscape. 1
Electricity generation from solar and wind is projected to grow the fastest across all sectors,
contributing significantly to the doubling of global electricity demand. 1 Increased renewable
energy consumption is consistently shown to improve environmental quality by reducing both
ecological footprint and CO2 emissions. The positive impact on CO2 mitigation becomes even
more pronounced at higher levels of existing environmental degradation. 4 Despite the rapid
growth of renewables, projections indicate that oil and natural gas will still meet over 50% of
energy demand in 2050 under any credible scenario, remaining an essential, albeit declining, part
of the global energy mix.1 This projection suggests that the energy transition by 2050 is not a
complete displacement of fossil fuels but rather a significant shift in the composition of the
energy mix and a reduction in carbon intensity. The decline of coal implies a shift towards
natural gas (a lower-emission fossil fuel compared to coal) alongside renewables. Crucially, the
report notes that "hard-to-decarbonize commercial transportation and industrial activity will
account for nearly half of the world's emissions in 2050" 1, indicating persistent demand for
liquid and gaseous fuels in sectors where electrification or renewable alternatives are currently
challenging or prohibitively expensive. This underscores that the "transition" is a complex,
multi-decade transformation involving all energy vectors and sectors, requiring a portfolio of
solutions beyond just renewable electricity generation.

2. SOLAR CELL

2.1 Parameters of Solar Cells

A solar cell, also known as a photovoltaic (PV) cell, is an electronic device specifically
engineered to convert the energy of light directly into electricity through the photovoltaic effect. 6
Its electrical characteristics, including current, voltage, or resistance, are inherently altered when
exposed to light.6 The operational behavior of a PV cell is comprehensively characterized by its
current-voltage (I-V) relationship, which is intrinsically dependent on the cell's equivalent circuit
parameters.7 Accurate estimation of these parameters is crucial for the effective modeling,
control, and economic viability of photovoltaic systems.

Key performance parameters define a solar cell's output and efficiency:

● Short-Circuit Current (Isc or Jsc): This parameter represents the maximum current that
flows through the solar cell when the voltage across its terminals is zero, effectively when
the cell is short-circuited.8 It signifies the largest current that can be drawn from the solar
cell.8 Isc is directly influenced by several factors: the physical area of the solar cell (often
normalized to current density, Jsc, to remove area dependence), the number of incident
photons (i.e., the intensity of the light source), and the spectrum of the incident light
(typically standardized to the AM1.5 spectrum for measurement consistency). 8 Furthermore,
it depends on the collection probability of light-generated carriers, which is chiefly
governed by surface passivation and the minority carrier lifetime within the cell's base
material.8 For an ideal PV cell with minimal resistive losses, Isc is essentially identical to
the light-generated current.8
● Open-Circuit Voltage (Voc): Voc represents the maximum voltage available from a solar
cell, occurring when the net current flowing through the cell is zero (i.e., when the solar cell
is open-circuited).8 This voltage corresponds to the amount of forward bias induced across
the solar cell junction by the light-generated current. 8 A crucial underlying parameter is the
"dark saturation current" (I0), which quantifies recombination within the device. A higher I0
indicates greater recombination, leading to a lower Voc.8 I0 itself increases with temperature
and decreases with improvements in material quality.8
● Fill Factor (FF): The FF is a dimensionless parameter defined as the ratio of the maximum
power (Pmax) obtainable from the solar cell to the theoretical maximum power, which is the
product of Voc and Isc (FF = Pmax / (Voc * Isc)).8 Graphically, it serves as a measure of the
"squareness" of the solar cell's I-V curve and corresponds to the area of the largest rectangle
that can be inscribed within the I-V curve.8 In conjunction with Voc and Isc, the Fill Factor
is instrumental in determining the actual maximum power output from a solar cell. 8 A
higher FF signifies a more ideal, "square" I-V curve, indicating lower internal losses and
more efficient power extraction from the cell.
● Efficiency (PCE - Power Conversion Efficiency, or η): Efficiency represents the overall
 effectiveness of a solar cell in converting incident light energy into electrical power. 8 It is
calculated as the ratio of the electrical power output at the maximum power point (Vmp,
Imp) on the I-V curve to the total incident light power, typically measured under a standard
AM1.5G simulated solar spectrum.8 PCE is the most widely recognized and critical metric
for assessing the overall performance of a solar cell. It directly quantifies the fraction of
incoming solar energy that is successfully converted into usable electricity. 8 Various
external factors, including temperature, intrinsic material properties, prevailing weather
conditions, and solar irradiance, significantly influence the actual output power and thus the
efficiency of solar cells.6 For example, Perovskite Solar Cells (PSCs) have demonstrated
impressive performance metrics, with a reported Voc of 1.18 V, FF of 82.24%, Jsc of 27.12
mA/cm², and a PCE of 27.90% for an incident solar spectrum from the electron transport
layer (ETL) side.9

The precise and accurate estimation of solar photovoltaic (PV) cell parameters is paramount for
comprehensive analysis and effective control of PV systems.7 The current-voltage relationship,
which dictates PV cell behavior, is inherently dependent on these parameters. 7 This capability is
crucial for understanding their performance under various conditions and for optimizing the
design of PV systems.7 Accurate parameter estimation is vital for modeling and simulation,
enabling the creation of reliable models that simulate the electrical behavior of PV devices. It is
also essential for performance evaluation, allowing for the assessment of efficiency and overall
performance. Furthermore, precise parameter knowledge is necessary for developing effective
control strategies, such as Maximum Power Point Tracking (MPPT), which aims to extract the
maximum possible power from the PV system under varying environmental conditions. 7
Accurate models based on estimated parameters can serve as a reference for diagnosing module
failures and monitoring the PV power plant's performance, allowing for quick responses to
potential faults and minimizing losses.7 Finally, unrealistic assumptions in modeling due to
inaccurate parameters can lead to inaccurate predictions of economic returns, highlighting the
importance of precise estimation for realistic financial assessments. 7 In summary, accurate
parameter estimation provides the foundational data needed for comprehensive analysis, efficient
design, and optimal operation of solar PV systems, ultimately contributing to their reliability,
efficiency, and economic viability.

2.2 Generations of Solar Cells

The development of photovoltaic technology has progressed through distinct generations, each
characterized by different materials, structures, and performance targets, aiming for higher
efficiency, lower cost, and broader applicability.

6.1. First-Generation Solar Cells: Crystalline Silicon and Beyond

First-generation solar cells are predominantly based on crystalline silicon, which includes both
monocrystalline and polycrystalline forms.70 Monocrystalline silicon cells, characterized by their
highly ordered single-crystal structure, offer the highest efficiencies among first-generation
technologies, reaching up to 24.2%.55 However, their production is more expensive due to the
energy-intensive process of growing large, pure silicon crystals. Polycrystalline silicon cells,
made from melting multiple silicon crystals together, are less expensive to manufacture but
exhibit slightly lower efficiencies, typically up to 19.3%. 55 Another significant material in this
generation is gallium arsenide (GaAs), which offers high efficiencies in the range of 28-30% and
good stability. However, the high cost of materials and specialized manufacturing processes limit
its use to niche applications, such as in space exploration. 72 First-generation solar cells have
dominated the market since their emergence in the 1950s and continue to hold a substantial share
due to their well-established reliability and performance.

6.2. Second-Generation Solar Cells: Thin-Film Technologies

Second-generation solar cells are characterized by the use of thin layers of semiconductor
materials, typically only a few micrometers thick, deposited onto a substrate. 70 This approach
requires less semiconductor material compared to the wafer-based crystalline silicon cells of the
first generation. Key materials in this category include amorphous silicon (a-Si), cadmium
telluride (CdTe), and copper indium gallium selenide (CIGS). 48 Generally, second-generation
solar cells are cheaper to produce than their first-generation counterparts 48, making solar energy
more accessible to a wider range of applications. Their efficiencies typically range from 10% to
20% 70, which is generally lower than the highest efficiencies achieved by monocrystalline
silicon cells but still suitable for many applications, particularly where cost and flexibility are
important factors. Thin-film solar cells also offer the advantage of flexibility 70, allowing them to
be used in applications such as portable electronics and building-integrated photovoltaics.

6.3. Third-Generation Solar Cells: Emerging Concepts and Materials

Third-generation solar cells represent a departure from traditional semiconductor junction-based
technologies, aiming to overcome the Shockley-Queisser limit, which defines the theoretical
maximum efficiency for single-junction solar cells. 72 This generation encompasses a diverse
array of emerging concepts and materials, including dye-sensitized solar cells (DSSCs), organic
solar cells (OSCs), quantum dot solar cells, and perovskite solar cells. 70 These technologies
utilize novel materials and device designs to enhance efficiency and reduce production costs 72,
often focusing on solution-processed materials and the exploration of non-toxic alternatives.
Among the third-generation technologies, perovskite solar cells have garnered significant
attention due to their rapid and impressive increases in efficiency, already surpassing 25% in a
relatively short period of research.70 These cells also offer the potential for flexible and even
transparent solar energy harvesting, opening up new avenues for their application.48

● Dye-Sensitized Solar Cells (DSSCs): DSSCs are photochemical solar cells that utilize an
electrolyte to convert sunlight into electricity. 11 They are known for their semi-transparency,
low manufacturing cost, easy fabrication procedures, and acceptable performance in low-
light conditions.11 Natural dyes extracted from plants can be used to reduce toxicity and
pollution, though these are generally less stable and efficient than synthetic dyes. 11 A DSSC
typically involves a semiconductor layer like TiO2, where a photon of sunlight is absorbed
by a dye and passed to this layer. 11 DSSCs offer high potential for integration with
 buildings, indoor energy harvesting, and smart farming. 11 Their adaptability for fenestration
(window design) in buildings is a key advantage, as their transparent nature makes them
suitable for outdoor applications like windows in building-integrated photovoltaic systems. 11
They are cost-effective, producing reasonably priced electricity. 11 DSSCs can be transparent
with varying degrees of transparency, allowing for investigation into both energy efficiency
and the efficiency of the DSSCs themselves when integrated into window systems. 11 They
can also adjust light transmission through color changes and reversal, which helps control
heat and light transfer, thereby reducing energy consumption and heating loads. 11 However,
the efficiency of DSSCs strongly depends on their morphology, composition, and
thickness.11 The highest reported efficiency for DSSCs is 14%.11
● Organic Solar Cells (OSCs): OSCs are thin films made of organic semiconductors, either
polymers or molecules, typically around 100 nm thick. 11 They are recognized for their
potential as a low-cost, lightweight, and easily processed alternative to inorganic solar cells,
with less environmental impact.12 Semi-transparent OSCs can be effectively used in
buildings as electricity-generating windows and ceilings. 11 Despite these advantages,
commercialization of OSCs has historically faced challenges due to stability issues and
relatively lower power conversion efficiencies (PCEs) and shorter lifetimes compared to
traditional inorganic cells.12
Recent progress in OSCs has been significant. Breakthroughs in non-fullerene acceptors and
advanced polymer donors have led to PCEs exceeding 20% in laboratory settings, closing
the gap with traditional technologies.12 Recent advances show a 16.5% PCE in single-
junction devices and 17.3% in tandem devices, representing more than a threefold
improvement over PCEs from about 15 years ago.13 These improvements are attributed to
new non-fullerene electron acceptors with broader absorption, low loss in charge separation
driving force, optimized film morphology, and advancements in interfacial layer and device
engineering.13 All-Polymer OSCs (APSCs), where both electron donor and acceptor
materials are polymers, have seen a tenfold increase in publications, with PCEs reaching
10.3%.13 Advantages of APSCs include large and tunable light harvesting, robust film
morphology, compatibility for large-area device manufacturing, and long-term device
stability.13 As laboratory-scale devices approach the 20% PCE target, large-area modules are
being developed, with a PCE of 5.6% for a module with an active area of 216 cm² (16
elementary cells connected) achieved, demonstrating impressive stability for 60 days—a
significant milestone for large-scale applications. 13 Improvements have also been made to
enhance device lifetimes in various application environments, with devices now designed
for use under atmosphere, greater than one-sun illumination, indoor low-light illumination,
and even underwater.13 This involves optimizing intrinsic active-layer morphology and
packaging to prevent degradation. Indoor devices are designed to capture an optimized
number of photons for less power-demanding operations, benefiting from the flexibility and
partial transparency of organic materials.13 Despite progress, challenges remain, including
the historical issue of low PCEs and short device lifetimes for large-scale
commercialization.13 A mismatch often exists in the optimal conditions for different steps in
OSCs (light absorption, exciton splitting, charge carrier migration, and charge collection). 13
 For instance, while broad absorption spectra of polymers are good for light harvesting, they
can lead to increased nonradiative decay of excitons, causing significant loss in open-circuit
voltage.13 Tremendous engineering research is still needed to match fabrication conditions
to the intrinsic potentials of large-area devices, and there is a need for green chemistry in
syntheses to minimize environmental impact and lower production costs. 13 Nevertheless, the
recent results raise hope for reaching PCEs of over 20% for OSCs in the next few years,
indicating a bright future for large-scale applications and a substantial impact on the global
energy landscape.13
● Perovskite Solar Cells (PSCs): Perovskite solar cells are among the most rapidly
expanding type of solar cells due to their high device performance, ease of synthesis, high
open-circuit voltage, and affordability.9 These materials offer excellent light absorption,
charge-carrier mobilities, and lifetimes, resulting in high device efficiencies with
opportunities for low-cost, industry-scalable technology. 14 PSCs have demonstrated
remarkable advancement in power conversion efficiency (PCE), increasing from 3.5% to a
certified 25.8% in just ten years.15 They possess a higher absorption coefficient, a longer
diffusion length, a lower rate of recombination, and a higher degree of defect tolerance, all
contributing to increased PCE by enhancing both Voc and Jsc. 15 NREL regularly attains
efficiencies of >20% for PSCs, with high-efficiency devices at 1 cm² and larger. 14 Dual-
junction thin-film tandem solar cells using low-cost polycrystalline halide perovskites for
both top and bottom cells have been developed, with certified efficiencies reaching 22% in
2016.14 Research has also focused on the ultrafast dynamics of excited states, revealing
ultraslow carrier cooling and very slow surface recombination in perovskite materials,
which are advantageous properties.14 Despite these advantages, the development of
perovskite-based solar cells continues to be impeded by issues with perovskite stability
under ambient conditions and the utilization of the hazardous heavy element lead (Pb). 9
Current research focuses on developing tin-based PSCs to overcome challenges associated
with lead-based perovskites and enhancing mechanical stability for flexible PSCs. 15
Achieving the full potential of PSCs will require overcoming barriers related to stability and
environmental compatibility, but if these concerns are addressed, perovskite-based
technology holds transformational potential for rapid terawatt-scale solar deployment. 14

6.4. Fourth-Generation Solar Cells: Nanotechnology and Advanced Architectures

Fourth-generation solar cells, also known as nano-photovoltaic cells, represent the cutting edge
of solar technology research.70 This generation focuses on combining the advantages of both
organic and inorganic materials at the nanoscale to achieve high efficiency and stability. 58 Key
examples of fourth-generation technologies include tandem solar cells, which involve stacking
different types of solar cells to absorb a broader range of the solar spectrum, and quantum dot
solar cells, which utilize semiconductor nanocrystals to enhance light absorption and energy
conversion.48 The primary aims of this generation are to achieve even higher conversion rates
than previous generations and to develop solar cells with enhanced flexibility for a wider variety
of applications.58 While showing significant promise, fourth-generation solar cell technologies
are still largely in the research and development phase 70, with ongoing efforts to overcome
challenges related to stability and scalability for mass production.

Several types of high-efficiency multi-junction solar cells exist:

● Lattice Matched GaInNAs Multi-Junction Solar Cell: Uses GaInNAs as a direct band-
gap semiconductor material whose band-gap can be adjusted while maintaining lattice
constant matching with GaAs and Ge substrates. Challenges include epitaxial growth
difficulties and low internal quantum efficiency, but improvements have been made through
p-i-n structures, annealing, and doping.16

● Mechanically Stacked Solar Cell: Allows stacking of III-V compound materials regardless
of bandgap energy and lattice constants, potentially reducing production costs and cell
weight. Challenges include substrate removal and interconnecting subcells.16

● Wafer Bonded Multijunction Solar Cell: Physically integrates different materials,

overcoming lattice dislocations from mismatch during epitaxial growth. This allows for
monolithic multi-junction structures without electrical and optical losses. The main
challenge is preparing the bonding surface for high electrical conductivity.16

● Inverted Metamorphic (IMM) and Upright Metamorphic (UMM) Solar Cells: These
methods use a compositionally graded buffer layer to distribute strain relaxation between
lattice-mismatched subcells, aiming for current matching and higher conversion efficiency.
IMM cells can reduce weight and enable flexible solar cells, while UMM cells have
potential for widespread application due to their similar fabrication process to lattice-
matched cells.16

The highest conversion efficiency achieved by solar cells is 47.1% for six-junction inverted
metamorphic (6J IMM) solar cells under 143 suns concentration. 16 Research-grade efficiencies
include 35.8% for five-junction direct bonded solar cells and 33.7% for monolithically grown 6J
IMM multi-junction solar cells.16 GaInP/GaAs/Ge lattice-matched triple-junction cells are well-
established with efficiencies over 30%.16

Theoretical efficiency limits for single-junction, triple-junction, and four-junction solar cells are
33.5%, 56%, and 62%, respectively, with N-junction cells theoretically reaching 68.2%. 16
Radiation resistance is a critical factor for space solar cells due to high-energy protons and
electrons. Radiation-induced displacement damage degrades performance, but methods like
protective covers, back-surface fields, and annealing can improve resistance. 16 The development
trends for III-V multi-junction solar cells are focused on achieving low-cost, high efficiency,
high radiation resistance, and simpler fabrication methods.16
2.3 Organic Solar Cells (OSCs)
This section is integrated into the "Third Generation Solar Cells" discussion within Section 2.2
for comprehensive coverage, as outlined in the detailed plan.

Organic Solar Cells: A Comprehensive Report on Advancements, Principles, and Future

Prospects
Executive Summary
Organic Solar Cells (OSCs) represent a transformative third-generation photovoltaic technology,
distinguished by their inherent flexibility, lightweight nature, and potential for semi-transparency
and low-cost, solution-processed manufacturing.1 These attributes position OSCs as a compelling
alternative and complement to traditional silicon-based photovoltaics, particularly for niche and
emerging applications.3

Recent breakthroughs, particularly in the development of non-fullerene acceptors (NFAs) and

advanced polymer donors, coupled with sophisticated morphology and interfacial engineering,
have propelled power conversion efficiencies (PCEs) to exceed 20% in laboratory settings. 1 This
rapid progress, with efficiencies nearly doubling from 2015 to 2023, signifies a maturation of the
field, narrowing the performance gap with conventional PV technologies.5

Despite these significant advancements, OSC technology faces critical challenges, primarily
concerning long-term device stability under diverse environmental stresses (e.g., oxygen,
moisture, heat, light, mechanical stress) and the complex process of upscaling from lab-scale
devices to cost-effective, large-area modules suitable for mass production. 1 Addressing these
stability and scalability hurdles is paramount for the widespread commercialization of OSCs.

The unique properties of OSCs unlock a broad spectrum of applications, including flexible and
wearable electronics, building-integrated photovoltaics (BIPV), smart windows, and various
components within the Internet of Things (IoT) and automotive sectors. 2 Continued research and
development focused on material innovation, advanced device architectures, and sustainable
manufacturing processes will be crucial in realizing the full potential of OSCs as a key
component of a sustainable energy future.3

1. Introduction to Organic Solar Cells (OSCs)

1.1. Definition and Fundamental Characteristics
Organic Solar Cells (OSCs), also known as Organic Photovoltaics (OPVs), constitute a class of
solar cell technology that primarily utilizes organic semiconducting materials to convert light
energy into electrical energy via the photovoltaic effect. 1 In contrast to traditional silicon-based
solar cells, OSCs are based on solution-processable semiconductors, which confers distinct
advantages in both manufacturing and application.2
The fundamental characteristics that define OSCs and distinguish them from other photovoltaic
technologies include:
● Low Cost: OSCs offer a lower production cost compared to traditional inorganic solar cells,
making them an economically attractive option for various applications. 1 This cost
advantage stems from the abundance of organic materials and the simplicity of their
processing.
● Flexibility: The inherent flexibility of organic materials allows OSCs to be integrated into
flexible and wearable electronics. This characteristic also makes them highly compatible
with high-throughput, roll-to-roll manufacturing processes, which can further reduce
production costs.1
● Lightweight: The lightweight nature of OSCs makes them highly suitable for portable
energy solutions, building-integrated photovoltaics (BIPV), and potentially specialized
applications such as aerospace technologies where weight is a critical factor. 2
● Semitransparency: OSCs can be engineered to be semi-transparent, enabling novel
applications such as photovoltaic windows, skylights, and integration into greenhouses,
where light transmission is desired alongside electricity generation.1
● Ease of Processing: The manufacturing process for OSCs is relatively simple, often
amenable to printing techniques like roll-to-roll processing, which offers high throughput
and scalability.2
● Non-toxic and Environmentally Friendly: OSCs are generally non-toxic and eco-friendly,
utilizing carbon-based materials and offering a reduced environmental impact compared to
some inorganic counterparts, particularly those involving heavy metals.1
● Broad Range of Raw Materials: The ability to utilize a wide variety of organic materials
contributes significantly to their cost-effectiveness and ensures resource abundance,
reducing dependence on scarce or geopolitically sensitive elements.2

1.2. Advantages of OSC Technology

The collective advantages of OSCs—flexibility, lightweight, semitransparency, low cost, and
ease of processing—make them uniquely suited for applications where traditional rigid, heavy,
and opaque silicon solar cells are impractical or aesthetically undesirable. 2 This positions OSCs
not as a direct replacement for silicon, but as a complementary technology that expands the
overall scope of solar energy utilization.3

The distinct physical attributes of OSCs, such as their inherent flexibility, lightweight nature, and
semitransparency, enable applications that conventional silicon photovoltaics cannot effectively
address. For instance, wearable electronics inherently demand flexibility, building-integrated
photovoltaics (BIPV) greatly benefit from transparency and adaptable form factors, and portable
devices necessitate lightweight solutions.2 This suggests that the commercial success and
widespread adoption of OSCs might not primarily stem from direct competition with silicon for
utility-scale power generation. Instead, their strategic value lies in carving out and potentially
dominating significant niche markets where their unique advantages are paramount. This
approach diversifies the solar energy market rather than simply replacing existing technologies,
contributing to a more versatile and adaptable energy infrastructure capable of meeting a broader
range of energy demands.

A comparative overview of Organic Solar Cells with traditional silicon solar cells is presented in
Table 1, highlighting their distinct characteristics.

Table 1: Comparison of Organic Solar Cells (OSCs) with Traditional Silicon Solar Cells

Feature Organic Solar Cells Traditional Silicon Solar

(OSCs) Cells (c-Si)

Flexibility High (inherently flexible) 1 Low (rigid, brittle) 12

Weight Lightweight 2 Heavy

Transparency Can be semi-transparent 1 Opaque

Cost Potentially lower production Higher material and

cost 1 production cost 2

Manufacturing Process Solution-processable, High-temperature

amenable to printing (e.g., production, silicon wafer-
roll-to-roll) 2 based 2

Efficiency (Current Lab) Exceeding 20% (single- Above 33%

junction) 3 (silicon/perovskite tandem)
3

Efficiency (Commercial) Approaching 19% (module) 15%-22% (mono-

5
crystalline), 13%-18%
2
(poly-crystalline)

Lifetime/Stability Improving, but long-term Established, 25-year

3
stability under warranty common
 environmental stress
1
remains a challenge

Environmental Impact Non-toxic, eco-friendly, Raw material extraction,

decreased pollution energy-intensive production,
potential 1 waste management concerns
12

Raw Materials Broad range of organic Requires high-purity silicon

materials 3 2

1.3. Historical Context and Evolution

The field of organic solar cells has experienced remarkable progress since the invention of bulk
heterojunction (BHJ) devices by Heeger and his research team in 1995. 1 This seminal
development laid the groundwork for modern OSC architectures. Early materials utilized in these
devices included MDMO-PPV and P3HT as electron donors, paired with fullerene derivatives as
electron acceptors.1

Initial efficiencies for OSCs were quite modest. For instance, early bilayer organic solar cells
achieved power conversion efficiencies (PCEs) of approximately 1%. 3 By 2015, laboratory-scale
OSCs had barely surpassed 10% efficiency.5 However, a pivotal turning point occurred around
2015-2016 with the introduction of non-fullerene acceptors (NFAs).3 These novel materials
offered significant advantages over fullerenes, including tunable absorption profiles and higher
open-circuit voltages, which rapidly propelled OSC efficiencies from approximately 10% to 15%
and beyond.3 This rapid improvement, with efficiencies nearly doubling from 2015 to 2023,
underscores the accelerated pace of research and development in the field, demonstrating a
significant maturation of organic photovoltaics as a scientific discipline.5

2. Fundamental Working Principles of Organic Solar Cells

2.1. Device Structure and Components
A typical Organic Solar Cell device is constructed from several functional layers sandwiched
between two conducting electrodes: a transparent electrode, typically serving as the anode, and a
metal electrode, which acts as the cathode.1

The central and most critical component of the OSC is the active layer. This is where the
fundamental process of light conversion into electrical energy occurs, and its composition and
morphology are decisive for the overall energy conversion efficiency of the device. 1 The active
layer is primarily composed of a blend of an electron donor material and an electron acceptor
material.1
In addition to the active layer, OSCs frequently incorporate interlayers, such as electron
transport layers (ETLs) and hole transport layers (HTLs). These layers are strategically placed to
facilitate the selective transport of charge carriers to their respective electrodes and to minimize
charge recombination, thereby enhancing the device's efficiency.1

Common device structures found in organic solar cells include:

● Monolayer Organic Solar Cells: Representing the simplest configuration, these cells
consist of a single conjugated polymer layer positioned between two conducting electrodes. 1
● Bilayer Organic Solar Cells: In this design, two distinct organic layers are placed in direct
contact. Exciton separation predominantly occurs at the interface formed between the
acceptor and donor layers.1 Historically, early bilayer cells exhibited very low PCEs, often
around 1%.3
● Bulk Heterojunction (BHJ) Solar Cells: This is the most prevalent and successful
architecture in OSCs. It involves blending electron donor and acceptor polymers to create a
nanoscale interpenetrating network within the active layer. 1 The morphology of this active
layer, particularly the intimate mixing and phase separation of donor and acceptor domains,
is paramount for efficient exciton dissociation and subsequent charge carrier transport.1
● Ternary Organic Solar Cells: This advanced architecture incorporates a third component
into a conventional binary blend active layer. The addition of this third material is designed
to enhance light-harvesting capabilities, facilitate exciton dissociation, optimize the film
morphology, and improve charge transport characteristics. 1 This strategy has led to
significant improvements in PCEs.3
● Tandem Organic Solar Cells: These devices involve stacking two or more sub-active
layers, each engineered to absorb different portions of the solar spectrum. By capturing a
broader range of sunlight, tandem architectures can achieve very high PCEs, surpassing the
theoretical limits of single-junction devices.1

2.2. Light Absorption and Exciton Generation

The operation of an OSC commences with the absorption of light by the electron donor material
within the active layer.19 When incident photons possess energy greater than the band gap of the
organic semiconductor, their energy is transferred to electrons residing in the valence band. This
energy input promotes these electrons to a higher energy state, specifically the lowest
unoccupied molecular orbital (LUMO) level.1

This energy transfer process results in the formation of tightly bound electron-hole pairs, known
as excitons.1 The efficiency of this initial exciton generation step is directly dependent on the
light absorption properties of the active layer materials. Ideally, these materials should exhibit
broad absorption spectra, extending into the near-infrared region, to maximize the utilization of
available sunlight.19

2.3. Exciton Diffusion and Dissociation

Following their generation, excitons are electrically neutral and must diffuse through the active
layer to reach the interface between the electron donor and electron acceptor materials. 19 At this
critical interface, exciton dissociation takes place. This process involves the transfer of the
electron from the LUMO level of the donor material to the LUMO level of the acceptor material.
Simultaneously, the corresponding hole is transferred in the opposite direction, from the
acceptor's highest occupied molecular orbital (HOMO) level to the donor's HOMO level.1

For efficient charge transfer and subsequent dissociation, a precise alignment of energy levels is
required. Specifically, the donor material must possess higher HOMO and LUMO energy levels
than the corresponding levels of the acceptor material. 14 An energy level offset of approximately
0.2-0.3 eV between the donor's HOMO and the acceptor's LUMO is considered optimal for
facilitating efficient charge separation. 20 Furthermore, the morphology of the active layer,
particularly the ideal mixing and phase separation between the donor and acceptor materials, is
crucial. A well-controlled nanomorphology ensures efficient exciton dissociation and provides
effective pathways for charge carrier transport, thereby minimizing detrimental recombination
losses.1

2.4. Charge Transport and Collection Mechanisms

Once excitons have successfully dissociated at the donor-acceptor interface, the separated
electrons and holes become free charge carriers. The subsequent charge transport mechanism
involves these free electrons moving through the acceptor material towards the cathode
electrode, while the holes migrate through the donor material towards the anode electrode. 13
Efficient charge transport is intricately linked to the energy level alignment of the materials and
the overall morphology of the active layer.19 High charge carrier mobility in both the donor and
acceptor materials is essential to ensure that these separated charges can reach the electrodes
before recombining.20

Finally, charge collection occurs at the respective electrodes. The electrons are collected by the
negative electrode (cathode), and the holes are collected by the positive electrode (anode),
thereby generating an electrical current in the external circuit. 13 The work functions of the
electrodes must be appropriately matched with the energy levels of the adjacent active layer
materials to optimize charge collection and minimize energy losses at these interfaces. 19 To
further enhance this process, electron transport layers (ETLs) and hole transport layers (HTLs)
are strategically employed. These interlayers boost the selective transport of their respective
carriers while simultaneously blocking the transport of the opposite carrier towards the wrong
electrode, effectively reducing recombination near the electrodes.2

The overall power conversion efficiency (PCE) of an OSC is not determined by a single "best"
component but rather emerges from a highly synergistic and interconnected system. Every step
in the working principle, from light absorption to charge collection, is intimately linked to
specific material properties and aspects of the device architecture. For example, the tunable
energy levels of new non-fullerene acceptors (NFAs) can have a profound effect across multiple
stages. Improved light absorption by NFAs directly leads to more exciton generation. An
optimized active layer morphology, achieved through precise fabrication control, then enhances
the efficiency of exciton dissociation and subsequent charge transport. Furthermore, tailored
interlayers can reduce recombination losses and improve charge collection at the electrodes. This
intricate web of dependencies implies that significant PCE improvements are a result of the
synergistic optimization of multiple interacting components. This highlights that advancements
in OSCs are rarely isolated scientific discoveries but rather a complex outcome of
multidisciplinary research, requiring close collaboration among material chemists, physicists,
and engineers to design and optimize these intricate systems. The emphasis on an "enhanced
understanding of device morphology" 3 is a critical recognition of this complex interplay, as the
morphology dictates the efficiency of exciton dissociation and the pathways for charge transport.

3. Key Materials and Device Architectures

3.1. Active Layer Materials: Electron Donors (Polymers, Small Molecules)
The active layer of OSCs primarily relies on electron donor materials, which are responsible for
absorbing incident light and initiating the photovoltaic process by forming excitons. 19 These
donor materials are broadly classified into conjugated polymers and small molecular compounds,
each offering distinct advantages and properties.

Conjugated Polymers: These macromolecular materials have been extensively studied and
developed for their ability to form films and transport charge.
● Poly(phenylene vinylene)s (PPV) and Polythiophenes (PTs): These represent early and
widely investigated classes of polymer donors. Specific examples include MEH-PPV and
MDMO-PPV, which are derivatives of PPV, and P3HT (poly(3-alkylthiophene)), a
prominent polythiophene derivative.1 P3HT, in particular, offered significant improvements
over earlier PPVs, exhibiting a lower band gap, broader absorption, and superior hole
mobility. When paired with PCBM, P3HT-based systems achieved PCEs exceeding 4%.20
● Donor-Acceptor (D-A) Copolymers: A major advancement in polymer design involves the
alternating copolymerization of electron-donating (D) and electron-deficient (A) building
blocks. This molecular engineering strategy enhances molecular chain rigidity, promotes
extensive π-electron delocalization, and effectively reduces the material's energy gap. This
approach also allows for precise regulation of the HOMO and LUMO energy levels, leading
to broader light absorption and consequently higher efficiencies. 20 Examples of such
polymers include those incorporating 2,1,3-Benzothiadiazole (BT) and Benzo[1,2-b;4,5-
b0]dithiophene (BDT) units.20
● Wide Bandgap Polymer Electron Donors: Recent trends show an increased utilization of
wide bandgap polymer electron donors, particularly in conjunction with non-fullerene
organic polymer solar cells. This development has spurred substantial research interest in
all-polymer solar cells, aiming for robust and stable devices.7
Small Molecule Donors: These materials offer unique advantages due to their well-defined
molecular structures.
● Small molecule donors are appealing for commercial applications due to their ease of
purification, precise chemical structures, and excellent batch reproducibility, which
contribute to consistent device performance.21
● While many small molecule versions of polymer donors have been explored, their PCEs
were historically lower than their polymeric counterparts. 21 However, recent innovations
have overcome some of these limitations. For instance, the A-D-A-type small molecule
SM1, synthesized in 2017, achieved a PCE of 10.11% when paired with the acceptor IDIC,
demonstrating high light absorption in the visible region that complemented the acceptor's
absorption profile.21 Star-shaped small molecules have also shown promise, with studies
demonstrating the impact of their core type on solubility, thermal, optical, and
electrochemical properties, leading to improved photovoltaic performance in both single-
component and bulk-heterojunction OSCs.9

3.2. Active Layer Materials: Electron Acceptors (Fullerene and Non-Fullerene)

Electron acceptors play a critical role in OSCs by receiving electrons from excitons, thereby
facilitating charge separation and enabling the flow of current. 19 The evolution of acceptor
materials has been central to the significant efficiency gains observed in OSCs.

Fullerene Derivatives: For over three decades, fullerene derivatives have been the most
successful and widely utilized electron acceptor materials in organic photovoltaics. 1 Their three-
dimensional conjugated electronic structures provide excellent electron mobility and electron-
accepting capabilities.
● PC60BM and PC70BM: Phenyl-C61-butyric acid methyl ester (PC60BM) and its C70
analogue, PC70BM, have been the dominant fullerene acceptors since their introduction in
1995.20 PC70BM, in particular, offers stronger absorption in the visible range compared to
PC60BM, leading to higher short-circuit current density (Jsc) and improved PCEs in
devices, although its purification process makes it more expensive.20
● Bisadducts and Multiadducts (e.g., ICBA): To address limitations such as the relatively
low open-circuit voltage (Voc) associated with fullerene acceptors, researchers developed
bisadducts and multiadducts like Indene-C60 Bisadduct (ICBA) and Indene-C70 Bisadduct
(IC70BA).20 These derivatives are designed to achieve higher LUMO levels, which directly
translates to higher Voc values in OSCs. For instance, bis-PCBM has a LUMO level 0.1–
0.15 eV higher than PCBM, and P3HT/IC60BA systems achieved PCEs of 5.44%.20

Non-Fullerene Acceptor (NFA) Materials: The emergence of NFAs around 2015-2016 marked
a paradigm shift in OSC research, overcoming many of the limitations of fullerene derivatives. 5
NFAs are typically designed organic molecules, often based on fused-ring electron acceptors,
offering significant advantages.
 ● Tunable Properties: NFAs provide highly tunable absorption profiles and energy levels,
allowing for more precise optimization of the active layer to maximize light absorption and
open-circuit voltage.5 This tunability enables the utilization of a more extensive portion of
the solar spectrum than traditional fullerene acceptors.19
● Enhanced Morphological Stability: NFAs generally exhibit improved morphological
stability compared to fullerenes, which contributes to better device performance and
longevity.19
● Key NFA Types: Successful NFA designs often incorporate electron-deficient units, such
as diketopyrrolopyrrole (DPP) or perylene diimide (PDI), combined with electron-rich units
to create D-A-D (Donor-Acceptor-Donor) or A-D-A (Acceptor-Donor-Acceptor)
structures.19 This structural engineering not only allows for energy level tuning but also
enhances light absorption and charge carrier mobility.19
● ITIC and Y6 Derivatives: The synthesis of ITIC-like molecules in 2015 by Xiaowei
Zhan's group was a breakthrough, leading to significant PCE improvements. 21 Subsequent
ITIC derivatives pushed PCEs to 14% by 2018. 3 A major milestone was achieved in 2019
with the small-molecule NFA Y6, which, when combined with the polymer PM6, achieved
15% PCE in single-junction OSCs.3 Y6 and its derivatives have since propelled PCEs to
over 20% for single-junction devices. 3 Recent examples include L8-BO-F (2021) and L8-
ThCl (2024), which have demonstrated impressive efficiencies by optimizing molecular
packing, light absorption, and reducing voltage loss through homogeneous mixtures and
tighter π-π stacking.4
● Benefits as Third Components: NFAs are also frequently introduced as third components
in ternary OSCs, where they can form nanofiber structures that provide more interfaces for
exciton dissociation, adjust material properties through chemical modification, and offer
good light absorption in the NIR region, along with improved thermal and light stability.15

3.3. Interfacial Layers (ETLs and HTLs)

Interfacial layers, specifically Electron Transport Layers (ETLs) and Hole Transport Layers
(HTLs), are crucial components in OSC device architectures. Their primary role is to facilitate
the selective transport of charge carriers (electrons to the cathode via ETLs, holes to the anode
via HTLs) and to block the transport of the opposite carrier, thereby significantly reducing
recombination losses at the electrodes and enhancing overall power conversion efficiency. 2 The
meticulous design and optimization of these layers are vital for high-performance and stable
devices.

Advancements in Interfacial and Morphology Engineering via Self-Assembled Monolayers

(SAMs):

Self-assembled monolayers (SAMs) have emerged as a vital class of nanomaterials offering a

unique and effective strategy for tailoring interfacial electronic and chemical properties in
OSCs.6 Their ability to form crystalline domains with long-range order through facile film
formation is a key advantage. A typical SAM molecule comprises an anchoring group, a spacer,
and a terminal functional group. The anchoring group binds to the substrate surface, while the
terminal group electronically couples with the overlying active layer, influencing its morphology
and determining the energetic alignment at the interface. The spacer group, often an alkyl chain
or aromatic group, controls electronic isolation and molecular arrangement.6 The spontaneous
self-assembly of SAMs from solution or vapor provides a straightforward method to introduce
high-quality interlayers at various scales.6

SAMs play diverse roles in OSCs, impacting charge generation, transport, and extraction,
particularly in high-efficiency, non-fullerene acceptor (NFA)-based devices.6
1. SAM as a Charge Transport Layer (CTL): SAMs are excellent candidates for robust and
efficient alternative charge transport layers due to their ultra-low thickness, which
eliminates concerns about bulk CTL properties.6
○ Hole Transport Layer (HTL) SAMs: Carbazole-based SAMs with phosphonic acid
anchoring groups, such as 2PACz, have become crucial in high-performance NFA-
based OSCs for their efficacy in hole transport. 2PACz-SAMs have enabled PCEs
exceeding 20% without the need for traditional polymeric HTLs like PEDOT:PSS. 6 The
synthesis of 2PACz is straightforward and cost-effective. These SAMs bind strongly
and stably to indium tin oxide (ITO) surfaces, and π–π interactions between adjacent
carbazole moieties promote intrinsic stabilization and ordering, facilitating efficient
hole extraction with minimal material consumption and reduced parasitic absorption. 6
The use of 2PACz SAMs can eliminate the need for acidic and hygroscopic
PEDOT:PSS, offering significant stability advantages. 6 Modifications to 2PACz with
different functional groups (e.g., F-2PACz, Cl-2PACz) allow for fine-tuning of the ITO
work function, leading to improved ohmic contact and efficient hole extraction.6
○ Electron Transport Layer (ETL) SAMs: Fullerene-based SAMs can tune the work
function of ZnO to match the LUMO level of the acceptor molecule, reducing energy
barriers and segregating acceptor components near the ETL. SAMs on ZnO can also
suppress photocatalytic reactions, improving photostability.6
2. SAM as an Additional Interfacial Modifier: SAMs can be introduced atop existing HTL
or ETLs to simultaneously modify the morphology of both the CTL and the active layer,
thereby enhancing charge generation and transport.6 For example, the MPA2FPh-BT-BA
SAM (2F-SAM), when mixed with PEDOT:PSS, improved the aggregation morphology of
both PEDOT:PSS and the active layer in PM6:Y6 OSCs, boosting PCEs above 17% and
significantly enhancing Jsc.6 The interfacial dipole formed by the 2F-SAM molecule at the
anode enhances the electrical conductivity of the HTL and modifies the work function of
ITO, promoting efficient hole extraction.6
3. SAM as a Third Component in the Donor–Acceptor Blend: The solubility of certain
SAM-polar organic molecules in common solvents allows for their integration into ternary
blend systems. This enables the design of SAM-based ternary blends with optimal phase
segregation.6 For instance, C60-SAM can be incorporated into D18:Y6 BHJ OSCs to tune
the active layer morphology, improving charge carrier lifetime and minimizing
recombination losses. This effectively creates a pseudo-ZnO/SAM/BHJ configuration,
 acting as a passivation layer and inducing a favorable face-on molecular orientation, which
enhances charge carrier mobility and collection efficiency.6
4. SAM as a Hole Extraction Layer in Single-Material OSCs: SAM-HTLs are excellent
choices for intrinsically charge-generating single-material OSCs, which are vital for
increasing reliability and commercial viability. The tunability of ITO work function by
modifying functional groups in carbazole-based SAMs (2PACz) could effectively separate
and extract charges from 'Y6-like' acceptor materials.6

The impact of SAMs on performance metrics is multifaceted. They effectively modify the work
function of ITO, enabling tailored energy level alignment for efficient carrier extraction and
inducing Fermi-level pinning near the hole transport level. 6 Their ultra-thin nature (∼1–3 nm)
can also facilitate tunneling of separated charge carriers. SAMs influence thin-film formation
kinetics by acting as a template, modifying wettability, and influencing the morphology of
subsequent layers. When incorporated as a third component, SAMs can optimize device
performance by influencing morphology, phase segregation, and molecular orientation. 6
Furthermore, SAMs have demonstrated a superior ability to passivate defects, particularly
oxygen vacancies in metal oxide transport layers and in hybrid perovskite layers. In NFA-based
OSCs, SAMs show promising potential for trap passivation, suppressing undesirable
photocatalytic reactions.6 Hole-selective SAMs with tuneable energy levels can also act as
'donor-like' components, facilitating exciton dissociation in small molecule acceptor-based
single-material devices.6

Regarding stability, SAMs play a crucial role in mitigating rapid performance degradation in
OSCs. They offer an intrinsically stable and chemically inert alternative to conventional HTLs
like PEDOT:PSS, which are known for their acidic and hygroscopic nature that can induce
degradation.6 The thermodynamic-driven growth processes of ultra-thin SAM formation lead to
uniform and stable layers. Strategies like pre-heating the substrate and solvent washing can
minimize micelle formation and improve layer quality, enhancing stability under ambient
storage.6 Composite HTLs combining SAMs with polyoxometalates have resulted in remarkably
high thermal and photostability.6 ITO/SAM electrodes are exceptionally stable compared to
ITO/PEDOT:PSS due to the inert behavior of SAMs, and phosphonic acid linkers in 2PACz
HTLs reduce detrimental reactions with active layer components. 6 In inverted architectures,
SAMs can significantly enhance photostability by passivating surface traps on the ZnO layer,
suppressing photocatalytic reactions that impair charge transport.6

3.4. Electrode Materials (Transparent and Flexible)

Electrode materials are fundamental to the operation and practical application of OSCs,
particularly for achieving transparency and flexibility. They serve to collect the separated charge
carriers and transmit light into or out of the device.

Transparent Conductive Electrodes (TCEs):

● Indium Tin Oxide (ITO): Historically, ITO has been the most widely used transparent
 electrode due to its high transparency and conductivity. 17 However, ITO has limitations,
particularly its rigidity, high cost, and scarcity of indium, which hinder its use in flexible
and low-cost applications.17 Flexible ITO electrodes also tend to have higher sheet
resistance (40–60 Ω/□) compared to rigid ones (10 Ω/□) and are not mechanically robust.17
● Alternatives to ITO: Significant research efforts have focused on developing alternative
TCEs that are flexible, low-cost, and maintain high transparency and conductivity. These
include:
○ Thin Metal Films and Nanowires: Ultrathin metal films (e.g., silver) and metal
nanowires (e.g., AgNWs, CuNWs) are promising alternatives. 11 Nanoporous silver thin
films, combined with molybdenum oxide (MoOx), have achieved sheet resistances of
~9 Ω/sq and ~70% transparency, offering advantages of low cost, large-area processing,
and room-temperature fabrication.25 Silver nanowire (AgNW) networks, deposited by
scalable methods like dip coating, can achieve conductivity and transmittance values
comparable to ITO, with sheet resistances typically 10–20 Ω/□ and transmittance as
high as 85%–92%.17
○ Metal/Dielectric/Metal (MDM) Structures: Multilayer structures, such as
oxide/silver/oxide (e.g., MoO3/Ag/MoO3), are employed as semi-transparent top
electrodes. These structures not only improve stability and lifetime but also enhance
charge extraction and reduce electrode series resistance by modifying the morphology
of the ultrathin metal layer.11
○ Carbon-Based Materials: Materials like graphene, carbon nanotubes (CNTs), and
graphite are regarded as potential alternatives due to their excellent properties, including
low cost, solution processability, high conductance, and good chemical stability. 11
Graphene, a two-dimensional material, can be used as an electrode or conductive
additive.18 Flexible OSCs with polyimide-integrated graphene electrodes have achieved
over 15% PCE with high optical transmittance (>92%) and good mechanical
robustness.18 Free-standing multi-wall carbon nanotube (f-CNT) sheets have also been
successfully used as transparent top electrodes for semi-transparent n–i–p OSCs,
showing high fill factors and improved long-term stability compared to metal
electrodes.24
○ Conducting Polymers: Certain conducting polymers like PEDOT:PSS (though facing
stability issues due to acidity and hygroscopicity 3) are also explored for their use as
transparent electrodes or interlayers.11

Flexible Electrodes: The demand for flexible OSCs necessitates the development of flexible
transparent electrodes (FTEs). The materials mentioned above, such as carbon nanomaterials
(graphene, CNTs) and metal nanowires (AgNWs), are actively being studied as replacements for
rigid ITO and aluminum electrodes.3 Ultrathin metal films and metal mesh electrodes also offer
high conductivity and flexibility, crucial for devices subjected to mechanical stress during
manufacturing (e.g., roll-to-roll), installation, transportation, and operation. 3 Techniques like
gravure printing allow for the preparation of large-area patterned AgNW electrodes,
demonstrating scalability for flexible applications.17
3.5. Advanced Device Architectures
Beyond the fundamental bilayer structure, significant advancements in OSC performance have
been driven by the development and refinement of sophisticated device architectures. These
designs aim to optimize light absorption, exciton dissociation, and charge transport, ultimately
boosting power conversion efficiency.
● Bulk Heterojunction (BHJ) Solar Cells: The BHJ architecture, pioneered by Heeger's
team in 1995, revolutionized OSCs by blending donor and acceptor materials to form a
nanoscale interpenetrating network.1 This design significantly increases the interfacial area
between donor and acceptor, which is crucial for efficient exciton dissociation. This
innovation was pivotal, enabling OSCs to reach around 5% efficiency by the late 2000s. 5
The morphology of this blend, including phase separation and molecular stacking, is critical
for optimal performance, achieved through techniques like solvent additives and thermal
annealing.1
● Ternary Organic Solar Cells: Ternary OSCs represent a highly effective strategy to
further enhance device performance by incorporating a third component into a binary donor-
acceptor blend.1 This third component can serve multiple functions:
○ Broadening Absorption: It can extend the light-harvesting ability by absorbing light in
different spectral regions, similar to tandem cells but with easier fabrication. 22
○ Facilitating Exciton Dissociation and Charge Transport: The third component can
optimize film morphology, improve charge separation, and enhance charge carrier
mobility.15
○ Optimizing Film Morphology: It can regulate crystallization, improve molecular
packing, and form more uniform mixed phases, which inhibit charge recombination.4
○ Improving Stability: Polymer materials as third components can enhance the stability
and heat resistance of ternary OSCs.15 Recent research has demonstrated impressive
results with ternary systems. For instance, PM6:BTA-E3-based OSCs processed with o-
xylene achieved a certified PCE of 19.57%.4 The introduction of volatile solid additives
(VSAs) like HBT-2, incorporating internal noncovalent conformational locks, has
pushed efficiencies to 20.01% by optimizing active layer morphology. 4 Ternary and
Layer-by-Layer (LbL) strategies for active layer morphological control have led to
record PCEs of up to 19.7% and 20.8%, respectively.3
● Tandem Organic Solar Cells: Tandem designs involve stacking two or more sub-active
layers, each with distinct absorption ranges, to capture a broader spectrum of sunlight and
overcome the efficiency limits of single-junction devices. 1 This approach allows for a more
comprehensive utilization of the solar spectrum, leading to significantly higher PCEs.
Tandem structures have achieved certified efficiencies in the mid-20% range in laboratory
settings.3 These architectures can involve stacking two different bandgap OSC cells or
pairing an OSC with another solar material, such as a perovskite top cell with an OPV
bottom cell.5
● Optimized Interlayers and Electrodes: Beyond the active layer, the refinement of
interfacial layers (ETLs and HTLs) and electrodes has played a crucial role in boosting
 efficiency.5 Advanced anti-reflection coatings, custom-designed for the absorption profile of
the photoactive layer, have been shown to increase photogenerated current, contributing to
higher PCEs.5

4. Advancements, Challenges, and Future Outlook

4.1. Recent Technical Advances
Over the past decade, organic solar cells (OSCs) have undergone significant technical
transformation, evolving from devices with single-digit efficiencies and short lifetimes to
achieving certified laboratory performance approaching 19-20% and demonstrating multi-year
stability.5 These profound improvements are largely attributable to breakthroughs in new
material designs, advanced device architectures, and refined processing techniques.

New Material Designs:

● Non-Fullerene Acceptors (NFAs): The introduction of NFAs around 2015–2016 is widely
considered a pivotal moment in OSC development. 5 Prior OSCs relied on fullerene
derivatives as electron acceptors, which inherently limited optical absorption and open-
circuit voltage.5 Novel NFAs, typically engineered organic molecules such as fused-ring
electron acceptors, offer significantly improved properties, including tunable absorption
profiles and higher open-circuit voltages, leading to a cascade of efficiency gains. 5 This
advancement, supported by research, rapidly pushed OSC efficiencies from approximately
10% to 15% and beyond. By 2018, single-junction cells achieved certified efficiencies of
about 11–12%, surpassing the 10% threshold for commercial relevance. 5 Recent NFA-based
OSCs have achieved PCEs exceeding 20%.3
● High-Purity Polymers and Small Molecules: The synthesis of these materials with high
purity, which minimizes defect states that can act as charge traps, has been instrumental in
the rapid progress of OSCs.5
● Chlorinated Solvent Additives: A finely tuned morphology control strategy, involving
solvent additives, has been crucial for achieving high efficiencies. In 2023, researchers
attained a 19.3% power conversion efficiency for a binary organic solar cell by using a
chlorinated solvent additive (1,3,5-trichlorobenzene). This additive precisely regulates the
crystallization of the active layer, creating an optimal bulk heterojunction structure that
significantly lowers energy losses.5

Device Architectures:
● Bulk Heterojunction (BHJ): While developed in the mid-1990s, the BHJ architecture,
which involves blending donor and acceptor materials to form nanoscale interpenetrating
networks, remains fundamental. Its continued optimization has been critical for sustained
efficiency improvements.5
● Tandem Designs: These advanced architectures involve stacking two different bandgap
OSC cells or pairing an OSC with another solar material (e.g., a perovskite top cell with an
OPV bottom cell). Such tandem structures have achieved certified efficiencies in the mid-
 20% range in laboratory settings, pushing the boundaries of performance.1
● Optimized Interlayers and Electrodes: Continuous refinement of device layers, including
interlayers and electrodes, has also contributed to efficiency improvements. This includes
the development of self-assembled monolayers (SAMs) that can effectively modify
interfacial electronic and chemical properties, enhancing charge generation, transport, and
extraction.6
● Advanced Anti-Reflection Coatings: In 2023, a record 15.8% efficient 1 cm² cell was
achieved by introducing an advanced anti-reflection coating. This coating, custom-designed
for the specific absorption profile of the photoactive layer, effectively increases the
photogenerated current.5

Processing Techniques:
● Solution-Processing Techniques: These techniques are widely used for producing organic
solar modules. For instance, a German research team announced a 14.46% efficient module
(over 26 cm² in area, encapsulated) in late 2024, demonstrating that double-digit efficiencies
are achievable in larger, application-relevant formats.5
● Roll-to-Roll Coating and Thermal Evaporation: These processes are highly amenable to
high-throughput manufacturing of organic films, akin to printing newspapers. Companies
are already operating pilot production lines utilizing these methods, indicating a pathway to
mass production.2
● Automated Slot-Die Coating and Laser Patterning: Techniques like automated slot-die
coating and laser patterning have been employed to produce large-area transparent organic
PV coatings on glass panels, including the "world's largest fully transparent OPV window"
measuring 40”×60”.5 These methods are crucial for scaling up production while maintaining
performance.

These technical advances collectively indicate that organic solar cells are a fundamentally
different technology than they were a decade ago. They have significantly closed the efficiency
gap with conventional photovoltaics and are achieving durability levels that are no longer a
prohibitive barrier for many applications.5

4.2. Current Challenges

Despite the remarkable achievements in efficiency and the unique advantages offered by OSCs,
several significant challenges must be addressed for their widespread commercial viability.
These challenges primarily revolve around long-term device stability under environmental stress
and the complexities of manufacturing scalability.

Long-Term Device Stability under Environmental Stress:

Consistent performance throughout the device lifetime is a critical hurdle for commercialization.
Unlike commercial crystalline silicon solar cells, which typically come with a 25-year warranty
at over 20% efficiency, OSCs still face limitations in this regard.3
 ● Photostability: While some OSCs have demonstrated impressive photostability, reporting
over 35,000 hours (approximately 19 years) under certain conditions, and thermal stability
over 9,000 hours at 100°C (approximately 5 years), devices with extrapolated lifetimes
exceeding 30 years often still exhibit relatively low PCEs (<11%). 3 Operation under light
irradiation can reduce device stability due to photophysical and photochemical degradation
of various layers and interfaces, leading to reduced exciton generation and mobility, and
increased trap density.3 Molecular design of polymer donors and NFAs, including main-
chain engineering and side-chain modification, are being explored to improve resistance to
degradation.3
● Environmental Factors: Real-world applications expose OSCs to various environmental
stressors, including oxygen, moisture, light, heating, and mechanical stress, all of which can
hinder stability.3
○ Oxygen and Moisture: The presence of oxygen and moisture can damage active and
buffer layers, as well as electrodes. This issue is primarily addressed through advanced
encapsulation technology, which provides both environmental protection and
mechanical confinement for volatile materials.3
○ High Temperatures: Operation at elevated temperatures (typically 60°C and up to
85°C) introduces physical degradation, particularly to the active layer. Organic layers
can become highly unstable near their glass transition temperature (around 100°C),
leading to strong phase separation within the active layer, which degrades performance. 3
Interlayer modification is an effective strategy to enhance stability by improving
interfacial contacts and blocking degradation factors.3
○ Mechanical Stress: Flexible and wearable OSCs are inherently subjected to
mechanical stress during manufacturing (e.g., roll-to-roll processes), installation,
transportation, and operation. This stress can cause degradation in active/buffer layers,
electrodes, and interfaces, negatively affecting charge transport and extraction. 3
Research is focused on replacing common rigid electrodes like ITO and Al with flexible
transparent electrodes (FTEs) such as carbon nanomaterials (graphene, CNTs) and
metal nanowires (AgNWs).3 Ultrathin metal films and metal mesh electrodes also offer
high conductivity and flexibility.3
● HTL PEDOT:PSS Issues: The widely used hole transport layer (HTL) PEDOT:PSS faces
stability issues due to its inherent acidity and hygroscopicity. These properties can lead to
degradation of the active layer and corrosion of the ITO electrode, as well as negative
interactions with NFAs.3 Self-assembled monolayers (SAMs) are showing significant
promise as more stable and effective alternative HTLs.3

Upscaling OSCs from Lab-Scale Devices to Large-Area Modules:

Translating the high efficiencies achieved in small laboratory-scale devices (<1 cm²) to large-
area modules presents significant engineering and material science challenges, often resulting in
substantial energy losses.3
 ● Electrical and Morphological Phenomena: The most prominent energy loss mechanisms
during scaling are related to electrical and morphological phenomena. Increased series
resistance in transparent conductive electrodes due to larger solar cell area leads to losses in
short-circuit current density (Jsc) and fill factor (FF).3
● Film Homogeneity and Defects: Maintaining film homogeneity and minimizing point
defects are critical issues, especially given the extremely thin nature of organic films
(typically 80–120 nm), which demands precise control over film thickness.3
● Film Formation Dynamics: Scaling technologies often alter film formation dynamics and
morphology evolution compared to lab-scale spin-coating. This necessitates precise control
over deposition procedures, ink concentration, choice of solvents, and additives to achieve
optimal active layer morphology.3
● Processing Solvents: High-performance OSCs frequently rely on toxic, halogenated
solvents, which pose a significant challenge for sustainable and environmentally friendly
mass production.3 Non-halogenated solvents are being actively explored, but their
interaction with organic materials critically influences film morphology and device
performance.3 The choice of solvent is crucial, as solvents with extreme boiling points can
be unsuitable for high-throughput techniques like slot-die coating due to issues like
condensation or undesirable residues.3
● Printing Technologies: To achieve cost-effective scalability for mass production, various
printing technologies are under development:
○ Blade Coating: Offers control over thickness, uniform large-area deposition, and
minimal material loss, but faces challenges with non-uniform film formation due to
variations in solvent evaporation rates.3
○ Slot-Die Coating: An efficient technique for large-area fabrication, allowing controlled
film thickness. However, the shear-thinning and viscoelastic behaviors of the inks can
destabilize the meniscus, affecting film quality.3
○ Spray Coating: A rapid, scalable, and cost-effective method allowing non-contact
deposition on various surfaces. Despite these advantages, achieving film uniformity
remains challenging due to irregular aerosol droplet coalescence.3
○ Inkjet Printing: A precise, non-contact technique offering advantages such as low cost,
material saving, and high-resolution patterning. However, issues like pinhole formation
and non-uniform films persist.3

In summary, while OSCs have made significant strides in efficiency and offer unique advantages
for niche applications, their widespread commercialization hinges on overcoming challenges
related to long-term stability under various environmental stresses and achieving cost-effective,
scalable manufacturing processes using sustainable materials and methods.

4.3. Potential and Existing Applications

Organic Solar Cells (OSCs) are recognized as an emerging next-generation photovoltaic
technology poised for sustainable energy harvesting. Their unique combination of feasible
solution-processed fabrication, low costs, color-tuning capabilities, and lightweight, flexible
device characteristics enables a broad spectrum of potential and existing applications that are
often impractical for conventional rigid solar cells. 9 While significant progress has been made,
with certified efficiencies exceeding 18%, their widespread application and commercialization
are still evolving compared to established photovoltaic technologies like silicon solar cells. 9

The key advantages of OSCs—low cost, color-tuning, lightweight, flexibility, and transparency
—are the driving forces behind their suitability for diverse use cases:
● Wearable Electronics (e-skin) and Internet of Things (IoT): The inherent flexibility,
transparency, and lightweight nature of OSCs make them ideal for seamless integration into
wearable electronic devices, smart textiles, and various components within the Internet of
Things (IoT) ecosystem. This allows for self-powered sensors and devices that conform to
irregular surfaces.9
● Building-Integrated Photovoltaics (BIPV): OSCs offer innovative architectural
integration possibilities due to their semi-transparency and flexibility. They can be
incorporated into building elements such as colorful or colorless photovoltaic windows,
skylights, and integrated directly into rooftops and open areas, generating electricity without
compromising aesthetic or functional design.2
● Automobiles and Aero/Deep Space Travel: The lightweight and flexible properties of
OSCs present opportunities for their use in vehicles, potentially extending range or
powering auxiliary systems. Furthermore, their low weight and adaptability could make
them suitable for drones and satellites, where minimizing mass is critical for performance
and launch costs.9
● Screens and Smart Glasses: Given their transparency, OSCs can be integrated directly into
screens and smart glasses, providing a discreet power source without obstructing visual
clarity. This opens avenues for self-powered displays and augmented reality devices.9
● Charging of Laptops and Mobile Devices: The versatility and portability of OSCs make
them suitable for charging personal electronic devices like laptops and mobile phones,
offering flexible and lightweight charging solutions on the go.9
● Underwater Communication and Specialized Environments: The potential for
applications in water surfaces and underwater communication suggests their adaptability to
diverse and challenging environments, highlighting their robustness beyond typical
terrestrial solar applications.9
● Catalysis and Energy Storage: Beyond direct electricity generation, OSCs could find
broader applications in areas such as photocatalysis and integration into energy storage
systems, leveraging their ability to convert light energy into chemical or electrical potential. 9

Despite these promising applications, challenges remain, particularly concerning long-term

stability (photostability, air stability, and thermal stability) and material properties, which still
differ significantly from commercialized photovoltaic technologies. Continued fundamental
research is necessary to fully understand the factors affecting device performance, synthesize
new materials with enhanced properties, and develop robust encapsulation methods to improve
stability for real-world deployment.9

Conclusion
Organic Solar Cells (OSCs) have transitioned from a scientific curiosity to a highly promising
third-generation photovoltaic technology, exhibiting inherent flexibility, lightweight
characteristics, and the potential for semi-transparency and low-cost, solution-processed
manufacturing. Recent breakthroughs, particularly in non-fullerene acceptors and advanced
polymer donors, have dramatically propelled power conversion efficiencies to exceed 20% in
laboratory settings, a performance level once considered unattainable and now comparable to
some commercial inorganic photovoltaics. This rapid advancement, with efficiencies nearly
doubling in less than a decade, underscores a significant maturation in the understanding of
material science, device physics, and fabrication techniques.

The unique attributes of OSCs position them not as a direct competitor to traditional silicon-
based solar cells for all applications, but rather as a complementary technology capable of
addressing niche and emerging markets where silicon is impractical. Their adaptability enables a
diverse range of applications, from wearable electronics and building-integrated photovoltaics to
smart windows and components for the Internet of Things. This market diversification is crucial
for expanding the overall scope of solar energy utilization and fostering a more versatile energy
infrastructure.

However, the widespread commercialization of OSCs hinges on overcoming critical challenges,

primarily related to long-term device stability under various environmental stresses—including
oxygen, moisture, heat, light, and mechanical stress—and the complex process of cost-effective
upscaling from laboratory-scale devices to large-area modules. Issues such as film homogeneity,
defect control, and the reliance on certain toxic processing solvents require continued innovation.

The ongoing research and development efforts, particularly in advanced material design,
sophisticated device architectures (such as ternary and tandem cells), and scalable processing
techniques (like roll-to-roll printing), are steadily addressing these limitations. The advancements
in interfacial engineering, exemplified by the role of self-assembled monolayers (SAMs) in
enhancing charge transport and mitigating degradation, further illustrate the depth of scientific
inquiry in this field.

In conclusion, Organic Solar Cells represent a dynamic and evolving sector within renewable
energy. While significant hurdles remain in achieving long-term stability comparable to
conventional technologies and in perfecting mass production scalability, the remarkable progress
in efficiency and the inherent advantages of flexibility, lightweight, and transparency position
OSCs as a vital component in the future sustainable energy landscape, particularly for integrated
and specialized applications. Continued investment in fundamental research and engineering
solutions will be paramount to unlock their full commercial potential.
CONCLUSIONS
The global energy landscape is at a critical juncture, characterized by rapidly increasing demand
driven by population growth and the imperative to raise living standards in developing nations.
This escalating demand is further amplified by the effects of climate change, which
paradoxically increases energy consumption, particularly for cooling in vulnerable regions. This
creates a complex dynamic where the pursuit of equitable development must be meticulously
aligned with global decarbonization efforts to avoid exacerbating environmental and social
challenges. The persistent energy disparity between developed and developing nations highlights
that the energy transition is not merely a technological or economic shift, but a profound issue of
global social justice and human development.

The limitations of fossil fuels are stark and multifaceted, encompassing severe environmental
degradation, finite resource availability, and significant geopolitical instability. Their combustion
is a primary driver of climate change and air pollution, contributing to millions of premature
deaths annually and extensive ecological damage. The reliance on fossil fuels also fuels
geopolitical conflicts over resources and creates vulnerabilities in global supply chains.
Furthermore, the historical pattern of economic development, where environmental degradation
initially surges, presents a formidable challenge for developing nations seeking prosperity
without locking into high-carbon pathways. This necessitates a "leapfrogging" strategy,
supported by international collaboration and accessible sustainable technologies.

In contrast, renewable energy resources offer a compelling pathway forward. Technologies such
as solar photovoltaics and wind power possess vast technical and economic potentials, far
exceeding current and projected energy demands. Their rapid growth is projected to significantly
reshape the global energy mix, contributing to substantial reductions in ecological footprint and
CO2 emissions. However, realizing this immense potential extends beyond resource availability
and cost-effectiveness; it involves overcoming complex socio-technical and political-economic
barriers related to grid integration, infrastructure development, land use, and public acceptance.
Despite the rapid growth of renewables, fossil fuels are projected to retain a significant share of
the energy mix by 2050, particularly in hard-to-decarbonize sectors. This underscores that the
energy transition is a complex, multi-decade transformation requiring a portfolio of solutions,
including continuous innovation in energy storage, grid management, and decarbonization
technologies for industrial and transportation sectors.

Solar cell technology, a cornerstone of renewable energy, continues to advance across multiple
generations. First-generation silicon cells remain dominant but face cost and complexity
challenges. Second-generation thin-film technologies offer transparency and integration
potential. The third generation, including Dye-Sensitized Solar Cells (DSSCs), Organic Solar
Cells (OSCs), and Perovskite Solar Cells (PSCs), represents a paradigm shift towards lower cost,
flexibility, and diverse applications, with efficiencies rapidly approaching and, in some cases,
exceeding traditional technologies. OSCs, in particular, have demonstrated remarkable progress
in power conversion efficiencies and adaptability for various environments, including indoor and
large-area applications, despite ongoing challenges related to stability and manufacturing scale-
up. Perovskite solar cells offer exceptional performance and low-cost fabrication potential,
though stability and lead toxicity remain critical research areas. Beyond these, advanced multi-
junction III-V solar cells, often considered fourth-generation technology, achieve record
efficiencies, primarily for specialized applications like space missions, showcasing the
theoretical limits of photovoltaic conversion. The continuous evolution across these generations
highlights the dynamic and promising trajectory of solar energy as a key enabler for a sustainable
global energy future.

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Su
Sunlig

FRONT CONTACT
ETL (FTO)
(TiO2)
CsPbI3 (ACTIVE
HTL (Cu2O)
BACK CONTACT
Key features and capabilities of SCAPS-1D for OSC simulation:

 One-Dimensional Modeling: SCAPS-1D models the solar cell as a stack of layers in one
dimension (along the thickness of the device). This simplifies the calculations while still
providing valuable insights into device performance.
 Multi-Layer Device Structures: It allows users to define devices with multiple
semiconductor layers, including transparent conductive oxides (TCOs), electron transport
layers (ETLs), hole transport layers (HTLs), active layers (donor:acceptor blends), and
metal contacts.
 Material Parameter Input: Users can input a wide range of material parameters for
each layer, such as:
o Band gap (Eg)
o Electron affinity (χ)
o Dielectric permittivity (ϵr)
o Effective densities of states in the conduction and valence bands (NC, NV)
o Electron and hole mobilities (μn, μp)
o Doping concentrations (NA, ND)
o Defect densities and characteristics (trap levels, capture cross-sections)
o Optical absorption coefficients
 Recombination Mechanisms: SCAPS-1D can model various recombination
mechanisms, including:
o Band-to-band (radiative) recombination
o Shockley-Read-Hall (SRH) recombination (through defects)
o Auger recombination
o Recombination at interfaces
 Output Characteristics: It can calculate and plot key solar cell performance parameters:
o Current Density-Voltage (J-V) curves: Both in dark and under illumination,
providing Open-Circuit Voltage (Voc), Short-Circuit Current Density (Jsc), Fill
Factor (FF), and Power Conversion Efficiency (PCE).
o Quantum Efficiency (QE) / External Quantum Efficiency (EQE): Shows the
efficiency of converting photons into electrons at different wavelengths.
o Capacitance-Voltage (C-V) and Conductance-Frequency (G-f)
characteristics: Useful for understanding doping profiles, defect densities, and
carrier lifetimes.
o Band diagrams: Visualize the energy levels and band bending across the device.
o Spatial distributions: Show the distribution of electric field, charge carriers, and
recombination rates within the device.
 Optimization Studies: SCAPS-1D facilitates parametric studies where users can vary
one or more parameters (e.g., active layer thickness, defect density, mobility) and observe
their impact on device performance, enabling systematic optimization.
 User-Friendly Interface: It has an intuitive graphical user interface (GUI) that makes it
relatively easy to set up simulations and analyze results