‫اﻟﺟﻣﮭورﯾﺔ اﻟﺟزاﺋرﯾﺔ اﻟدﯾﻣﻘراطﯾﺔ اﻟﺷﻌﺑﯾﺔ‬

People's Democratic Republic of Algeria

‫وزارة اﻟﺗﻌﻠﯾم اﻟﻌﺎﻟﻲ و اﻟﺑﺣث اﻟﻌﻠﻣﻲ‬
Ministry of Higher Education and Scientific Research

Mohamed Khider Biskra University

Faculty of Exact Sciences and Life Sciences

Department of Material Science

Sector: Physics
Option: Physics of materials and photonic components
Ref:…………

Thesis presented with a view to obtaining

the diploma of:
DOCTORATE

Study of hybrid organic-inorganic solar cells based

on perovskite materials
(Etude de cellules solaires hybrides organiques-inorganiques à base de matériaux
pérovskites)

Presented by

Azri Faiza
February 3rd, 2022
Date: ………………
In front of the board of examiners composed of:

Ms MEFTAH Amjad Professor , University of Biskra Chair

Mrs MEFTAH Afak Professor , University of Biskra Supervisor

Mr DEHIMI Lakhdar Professor, University of Batna Examiner

Mr LAKHDAR Nacereddine Professor , University of El Ouad Examiner

Mr SENGOUGA Nouredine Professor , University of Biskra Co-supervisor

A CKNOWLEDGMENTS

All the thanks is for god, who gave me the force and the will to accomplish this work.

In this occasion, I would like to give special thanks, to my

teacher and supervisor Pr. Meftah Afak, not only for the
invaluable input and suggestions but also for being patient with
me.

Many thanks to all my teachers at the University of

Mohamed Khider Biskra.

And finally I would like to thank my little family and my big

family who were always by my side for supporting me.

AZRI Faiza
Abstract

In this work two perovskite solar cells in n-i-p and p-i-n configurations were studied
using SCAPS simulator. The two primary solar cells’ structures are / /
/ : / and / : / / / . The
achieved power conversion efficiencies were 13.94% and 10.99%, for n-i-p and p-i-n
PSCs, respectively. In order to enhance its performance, several materials were
suggested as electron and hole transport layers (ETL and HTL). For both configurations,
it was found that Zinc oxide ( ) and titanium dioxide ( ) are the most adequate
materials as ETL and Copper (I) thiocyanate ( ) forms the appropriate HTL. Also,
performances of n-i-p and p-i-n PSCs were improved by optimizing the absorber
thickness which was found to be 1 . With these considerations the power conversion
efficiency reached 25.02% and 25.11% for conventional (n-i-p) and inverted PSCs,
respectively .In addition, the detrimental effect of defects at the /
interface on our PSCs performance is also presented. Furthermore, the effect of
temperature on PSCs were studied.

Key words: Simulation, Solar cell, Perovskite, conventional PSC, inverted PSC.

‫اﻟﻣﻠــﺧـص‬

‫ ﺑﺈﺳﺘﻌﻤﺎل ﺑﺮﻧﺎﻣﺞ اﻟﻤﺤﺎﻛﺎة‬p-i-n ‫ و‬n-i-p ‫ ﺗﻤﺖ دراﺳﺔ ﺧﻠﯿﺘﯿﻦ ﺷﻤﺴﯿﺘﯿﻦ ﻟﻠﺒﯿﺮوﻓﺴﻜﺎﯾﺖ ذات اﻟﺒﻨﯿﺘﯿﻦ‬،‫ﻓﻲ ھﺬا اﻟﻌﻤﻞ‬
‫و‬ / / / : / ‫ھﻤﺎ‬ ‫اﻷوﻟﯿﺘﯿﻦ‬ ‫اﻟﺨﻠﯿﺘﯿﻦ‬ .SCAPS
‫ و‬13.94 % ‫ ﻣﺮدود اﻟﺘﺤﻮﯾﻞ اﻟﻤﺘﺤﺼﻞ ﻋﻠﯿﮫ ﻛﺎن‬. / : / / /
‫ ﺗﻢ إﻗﺘﺮاح اﻟﻌﺪﯾﺪ ﻣﻦ اﻟﻤﻮاد‬،‫ ﻣﻦ أﺟﻞ ﺗﺤﺴﯿﻦ أداء ھﺎﺗﯿﻦ اﻟﺨﻠﯿﺘﯿﻦ‬.‫ ﻟﻠﺨﻠﯿﺘﯿﻦ اﻟﻌﺎدﯾﺔ و اﻟﻤﻘﻠﻮﺑﺔ ﻋﻠﻰ اﻟﺘﻮاﻟﻲ‬10.99%
‫ ُوﺟﺪ أن أﻛﺴﯿﺪ اﻟﺰﻧﻚ و ﺛﻨﺎﺋﻲ أﻛﺴﯿﺪ اﻟﺘﯿﺘﺎن ھﻤﺎ أﻧﺴﺐ ﻣﺎدﺗﯿﻦ‬،‫ ﻣﻦ أﺟﻞ ﻛﻼ اﻟﺨﻠﯿﺘﯿﻦ‬.‫ﻛﻄﺒﻘﺎت ﻧﺎﻗﻠﺔ اﻻﻟﻜﺘﺮوﻧﺎت و اﻟﺜﻘﻮب‬
‫ ﺗﺤﺴﯿﻦ أداء اﻟﺨﻠﯿﺘﯿﻦ ﺑﺠﻌﻞ‬،‫ أﯾﻀﺎ‬.‫( ھﻮ اﻟﻤﺎدة اﻟﻤﻨﺎﺳﺒﺔ ﻟﻨﻘﻞ اﻟﺜﻘﻮب‬ ) ‫ﻟﻨﻘﻞ اﻹﻟﻜﺘﺮوﻧﺎت و أن ﺛﯿﻮﺳﯿﺎﻧﺎت اﻟﻨﺤﺎس‬
‫ ﻓﻲ اﻟﺨﻠﯿﺔ اﻟﻌﺎدﯾﺔ و‬25.02% ‫ ﺑﺈﻋﺘﺒﺎر ھﺬه اﻟﺘﺤﺴﯿﻨﺎت ﻣﺮدود اﻟﺘﺤﻮﯾﻞ وﺻﻞ إﻟﻰ‬. ‫ﺳﻤﻚ اﻟﻤﺎدة اﻟﻔﻌﺎﻟﺔ ﯾﺴﺎوي‬
ُ
‫ ﺗﻤﺖ دراﺳﺔ اﻟﺘﺄﺛﯿﺮ اﻟﮭﺪام ﻟﻠﻌﯿﻮب ﻓﻲ اﻟﺴﻄﺢ اﻟﻔﺎﺻﻞ ﺑﯿﻦ‬،‫ ﺑﺎﻹﺿﺎﻓﺔ إﻟﻰ ذﻟﻚ‬.‫ ﻓﻲ اﻟﺨﻠﯿﺔ اﻟﻤﻘﻠﻮﺑﺔ‬25.11% ‫اﻟﻰ‬
.‫اﻟﺒﯿﺮوﻓﺴﻜﺎﯾﺖ و ﺛﻨﺎﺋﻲ أﻛﺴﯿﺪ اﻟﺘﯿﺘﺎن و ﻛﺬﻟﻚ ﺗﺎُﯾﺮ درﺟﺔ اﻟﺤﺮارة ﻋﻠﻰ أداء اﻟﺨﻠﯿﺘﯿﻦ‬

‫ ﺧﻠﯿﺔ ﺑﯿﺮوﻓﺴﻜﺎﯾﺖ ﻣﻘﻠﻮﺑﺔ‬،‫ ﺧﻠﯿﺔ ﺑﯿﺮوﻓﺴﻜﺎﯾﺖ ﻋﺎدﯾﺔ‬،‫ ﺑﯿﺮوﻓﺴﻜﺎﯾﺖ‬،‫ ﺧﻠﯿﺔ ﺷﻤﺴﯿﺔ‬،‫ ﻣﺤﺎﻛﺎة‬:‫اﻟﻜﻠﻤﺎت اﻟﻤﻔﺘﺎﺣﯿﺔ‬
Table of content
ACKNOWLEDGMENTS ................................................................................................................... iii
Abstract ................................................................................................................................................iv
List of figures ........................................................................................................................................ i
List of tables ....................................................................................................................................... iii
List of abbreviations .........................................................................................................................iv
Introduction ........................................................................................................................................ i
Motivation ........................................................................................................................................... 2
Aims and objectives ......................................................................................................................... 2
Structure of the thesis ..................................................................................................................... 3
Chapter 1 ............................................................................................................................................. 1
Fundamentals of Solar Cells .......................................................................................................... 1
1.1Introduction ............................................................................................................................................ 5
1.2 Evolution and History of Solar Cells ............................................................................................. 6
1.2.1 First generation ............................................................................................................................... 6
1.2.2 Second generation .......................................................................................................................... 6
1.2.3 Third generation ............................................................................................................................. 7
1.2.4Fourth generation ............................................................................................................................ 7
1.3 Working principle of typical silicon Solar Cell ............................................................................ 8
1.3.1 Absorption of photons .................................................................................................................. 9
1.3.2 Conversion of photon energy to an electric energy........................................................... 9
1.3.3 Collection of charges ................................................................................................................... 10
1.4 Electrical parameters of the solar cell ..................................................................................... 10
1.4.1 Equivalent electrical circuit ..................................................................................................... 10
1.4.2 Short circuit current ................................................................................................................ 12
1.4.3 Open circuit voltage .................................................................................................................... 13
1.4.4 Fill Factor ..................................................................................................................................... 13
1.4.5 Power conversion efficiency ................................................................................................ 13
Chapter 2 .............................................................................................................................................. 5
Perovskite materials and Solar cells design .................................................................................. 5
2.1 Evolution and History of Perovskite Solar Cells ....................................................................... 15
2.2 Perovskite Crystal Structure ........................................................................................................ 17
2.3 Electronic Structure of Perovskites .............................................................................................. 18
 2.4 Tuning the band gap with composition .................................................................................. 19
2.5 Doping of perovskite materials ................................................................................................... 21
2.5 Properties of organic-inorganic hybrid perovskites ........................................................... 22
2.6 Deposition methods of perovskite films .................................................................................. 24
2.6.1 One step solution process ......................................................................................................... 24
2.6.2 Sequential two steps solution process ................................................................................ 25
2.6.3 Vapor Assisted Solution Process ............................................................................................ 26
2.6.4 Thermal Vapor Deposition ....................................................................................................... 26
2.7 Applications of organometal halide perovskites .................................................................. 27
2.7.1 Solar cells ........................................................................................................................................ 28
2.7.2 Multi-junction photovoltaics ................................................................................................... 28
2.7.3 Building-integrated photovoltaics ........................................................................................ 30
2.7.4 Light emitting diodes .................................................................................................................. 31
2.7.5 Solar water-splitting ................................................................................................................... 33
2.7.6 Space applications ....................................................................................................................... 34
2.8 Perovskite Solar Cell Device Architecture .................................................................................. 35
2.9 Working mechanisms of perovskite solar cells..................................................................... 36
2.10 Excitonic effects .............................................................................................................................. 37
2.10.1 Wannier-Mott excitons ........................................................................................................... 37
2.10.2 Frenkel excitons ......................................................................................................................... 38
2.11 Challenges in perovskite solar cells ........................................................................................ 38
2.11.1 Hysteresis of perovskite solar cells .................................................................................... 38
2.11.1.1 Trapping of electronic carriers at the perovskite interfaces......................... 39
2.11.1.2 Ion migration ................................................................................................................... 39
2.11.1.3 Ferroelectric polarization ........................................................................................... 40
2.11.1.4 Capacitive effects ............................................................................................................ 40
2.11.2 Degradation of perovskite materials ................................................................................. 41
Chapter 3 .......................................................................................................................................... 15
Study and optimization of MAPbI perovskite solar cell ................................................... 15
3.1 Introduction ........................................................................................................................................ 44
3.2 The basics of SCAPS-1D .................................................................................................................. 45
3.2.1 Definition of the problem.......................................................................................................... 45
3.2.2 Define the working point .......................................................................................................... 46
 3.2.3 Selection of the measurement(s) to simulate ................................................................... 47
3.2.4 Starting the calculation(s) ........................................................................................................ 47
3.2.5 Displaying the simulated curves ............................................................................................ 47
3.3 Solar cell definition .......................................................................................................................... 48
3.3.1 Editing a solar cell structure .................................................................................................... 49
3.3.2 Reference Conventions for Illumination, Voltage and Current .................................. 49
3.3.3 Contacts ........................................................................................................................................... 50
3.3.4 The optical absorption constant a(l) or a( n) of a layer............................................ 50
3.4 Principal of Numerical Simulation ............................................................................................. 51
3.4.1 Poisson’s equation ....................................................................................................................... 51
3.4.2 Continuity equations .................................................................................................................. 52
3.5.3 Carrier transport equations ..................................................................................................... 52
3.6 Device structure ................................................................................................................................ 53
3.7 Absorption coefficient of MAPbI perovskite material ........................................................ 53
3.8 The layers input parameters ........................................................................................................ 54
3.9 MAPbI Perovskite Solar cell performance .............................................................................. 55
3.9.1 The band gap energy diagram at equilibrium .................................................................. 55
3.9.2 The Current density-Voltage characteristic ...................................................................... 56
3.10 Effect of electron transport layer ............................................................................................. 60
3.10.1 Input parameters of ETL materials .................................................................................... 60
3.10.2 Current density- Voltage characteristic............................................................................ 61
3.11 Effect of the hole transport layer ............................................................................................. 65
3.11.1 Input parameters of HTL materials .................................................................................... 66
3.11.2 Current density-Voltage characteristic ............................................................................. 66
3.12 Optimization of perovskite solar cell...................................................................................... 70
3.13 Optimization of perovskite thickness .................................................................................... 72
3.14 Effect of interfacial defects ......................................................................................................... 76
3.15 Effect of temperature .................................................................................................................... 81
3.16 Conclusion ......................................................................................................................................... 83
Conclusion ........................................................................................................................................ 85
References ........................................................................................................................................ 86
List of figures
Figure 1. 1: Conventional solar cell structure. ..................................................................................... 8
Figure 1.2: Absorption phenomena in semiconductors. .................................................................. 9
Figure 1. 3: Functioning principle of the solar cell. ......................................................................... 10
Figure 1. 4: J-V characteristic in dark and under illumination of a solar cell. ....................... 11
Figure 1. 5: The equivalent circuit of a real solar cell..................................................................... 12
Figure 2. 1: Evolution of solar cell efficiencies………………………………………………………………………………16
Figure 2. 2: Perovskite cubic crystal structure. ................................................................................ 17
−4
Figure 2. 3: (a) Bonding diagram of a [ 6 ] cluster, (b)The bottom shows the band
gap structure for the quasiparticle self-consistent GW approximation . ................................ 19
Figure 2. 4: The versatility of hybrid perovskite materials
and their absorption tunability. .............................................................................................................. 20
Figure 2. 5: Doping materials in halide perovskites . ..................................................................... 22
Figure 2. 6: Photograph shows a large plastic film perovskite device ..................................... 23
Figure 2. 7: Perovskite film deposition by one step procedure. ................................................. 25
Figure 2. 8: Perovskite film deposition by two steps procedure. .............................................. 25
Figure 2. 9: Perovskite film deposition by vapor assisted solution process. ........................ 26
Figure 2. 10: (a) dual source evaporation, (b) chemical vapor deposition, and (c) flash
evaporation. .................................................................................................................................................... 27
Figure 2. 11: Schematics of several perovskite/silicon tandem architectures..................... 30
Figure 2. 12: Picture of semitransparent perovskite solar cells without (left) and with
(right) D102 dye. .......................................................................................................................................... 30
Figure 2. 13: A flexible, ultrathin, ultralight and semitransparent perovskite film ……….31
Figure 2. 14: Green and red perovskite LEDs. ................................................................................... 32
Figure 2. 15: Photograph of near infrared flexible PeLED with large-area . ......................... 32
Figure 2. 16: Water splitting system structure based on perovskite solar cells . ................ 33
Figure 2. 17: Perovskite solar cells for space applications .......................................................... 34
Figure 2. 18: Regular perovskite solar cell structures. .................................................................. 35
Figure 2. 19: Working mechanisms of perovskite solar cells. ..................................................... 37
Figure 2. 20: Types of excitons in crystalline materials……………………………………………... 38
Figure 2. 21: (A) The current–voltage (I-V) response with hysteresis; and (B) negligible
hysteresis of PSCs . ....................................................................................................................................... 39
Figure 2. 22: Hysteresis factors of perovskite materials............................................................... 42
Figure 3. 1: The SCAPS start-up panel: the Action panel or main panel.....................................45
Figure 3. 2: (a) Defining problem panel and (b) selecting an example. .................................. 46
Figure 3. 3: Define the working point. .................................................................................................. 46
Figure 3. 4: Select the measurement(s) to simulate. ...................................................................... 47
Figure 3. 5: Results panels. ....................................................................................................................... 48
Figure 3. 6: Simulation procedure using SCAPS software. ........................................................... 48
Figure 3. 7: Definition solar cell structure panel. ............................................................................. 49
Figure 3. 8: Reference Conventions for illumination, voltage and current. ........................... 49
Figure 3. 9: Contact properties panel. .................................................................................................. 50

i
Figure 3. 10: Optical absorption constant of a layer. ...................................................................... 51
Figure 3. 11: Solar cell structures (n-i-p at left and p-i-n at right). .......................................... 53
Figure 3. 12: Absorption coefficient of perovskite. ................................................ 54
Figure 3. 13: Energetic band diagram of: (a) conventional n-i-p and (b) inverted p-i-n;
perovskite solar cell..................................................................................................................................... 56
Figure 3. 14: Current density- Voltagecharacteristic of conventional PSC. ........................... 57
Figure 3. 15: Device quantum efficiency characteristic of conventional PSC. ...................... 58
Figure 3. 16: Current density- Voltage characteristic of inverted PSC. ................................... 59
Figure 3. 17: Device quantum efficiency characteristic of inverted PSC................................. 59
Figure 3. 18: Effect of ETL layer on Current density-Voltage characteristic for n-i-p PSC.
............................................................................................................................................................................. 62
Figure 3. 19: Effect of ETL on quantum efficiency for n-i-p PSC. ............................................... 63
Figure 3. 20: Effect of ETL layer on Current density-Voltage characteristic for p-i-n PSC.
............................................................................................................................................................................. 64
Figure 3. 21: Effect of ETL on quantum efficiency for p-i-n PSC. ............................................... 64
Figure 3. 22: Bands alignment between ETL materials and perovskite.................................. 65
Figure 3. 23: Effect of HTL on J-V characteristic using as an ETL of n-i-p PSC. .......... 68
Figure 3. 24: Effect of HTL on quantum efficiency using as an ETL of n-i-p PSC. ...... 68
Figure 3. 25: Effect of HTL on J-V characteristic using as an ETL of p-i-n PSC. .......... 69
Figure 3. 26: Effect of HTL on quantum efficiency using as an ETL of p-i-n PSC. ...... 69
Figure 3. 27: Bands alignment between HTL materials and perovskite. ................................ 70
Figure 3. 28: Energetic band diagram of / / / / cell. ........... 70
Figure 3. 29: Energetic band diagram of / / / / cell. .......... 71
Figure 3. 30: Effect of perovskite thickness on J-V characteristic of n-i-p PSC..................... 73
Figure 3. 31: Effect of perovskite thickness on output parameters for n-i-p PSC. .............. 73
Figure 3. 32: Effect of perovskite thickness on J-V characteristic of p-i-n PSC..................... 74
Figure 3. 33: Effect of perovskite thickness on output parameters for p-i-n PSC. .............. 75
Figure 3. 34: Effect of defects on J-V characteristic for n-i-p PSC. ..................................... 77
Figure 3. 35: Effect of defects on J-V characteristic for n-i-p PSC. ........................................ 78
Figure 3. 36: Effect of and on open circuit voltage ( ). ................................................. 78
Figure 3. 37: Effect of and on power conversion efficiency ( ) for n-i-p PSC. .......... 79
Figure 3. 38: Effect of defects on J-V characteristic for p-i-n PSC. ...................................... 79
Figure 3. 39: Effect of defects on J-V characteristic for p-i-n PSC. ........................................ 80
Figure 3. 40: Effect of A and on open circuit voltage ( ) for p-i-n PSC. .................... 80
Figure 3. 41: Effect of and on power conversion efficiency ( ) for p-i-n PSC. ......... 81
Figure 3. 42: Effect of temperature on J-V characteristic for n-i-p PSC. .................................. 82
Figure 3. 43: Effect of temperature on J-V characteristic for p-i-n PSC. .................................. 82
Figure 3. 44: Effect of Temperature on Voc and eta for conventional and inverted PSCs.
............................................................................................................................................................................. 83

ii
List of tables
Table 3. 1: Device parameters used in simulation. .......................................................................... 55
Table 3. 2: Electron transport materials parameters for simulation. ...................................... 61
Table 3. 3:Effect of ETLs on output parameters for n-i-p PSC. ................................................... 63
Table 3. 4: Effect of ETLs on output parameters for p-i-n PSC. .................................................. 65
Table 3. 5: Input parameters of the proposed HTL materials. .................................................... 66
Table 3. 6: Effect of the different HTL proposed materials on output parameters for n-i-p
PSC. ..................................................................................................................................................................... 67
Table 3. 7:Effect of the different HTL proposed materials on output parameters for p-i-n
PSC. ..................................................................................................................................................................... 67
Table 3. 8: The output parameters of conventional PSC in case of then as ETL71
Table 3. 9:The output parameters of inverted PSC in case of then 2as ETL. ........ 71
Table 3. 10: Energy position and types of interfacial defects...................................................... 76

iii
List of abbreviations

Perovskite Solar Cell

Photo Voltaic

Organic Photo Voltaic

Current density

Current

Voltage

Elemantary charge

Photogenrated current

Diode Current

Dark saturation current

Boltzmann constant

Absolute temperature

Ideality factor

Series resistance

Shunt resistance

Short circuit current

Open circuit voltage

Fill factor

Maximum produced power

Maximum voltage

Maximum current

Power conversion efficiency

iv
Incident power

National Renewable Energy Laboratory

Hole transport layer

Electron transport Layer

Valence band

Conduction band

Methyl Ammonium

Formamidinium

Hybrid Organic Inorganic perovskite

Dimethylformamide

Gamma-butiloractone

dimethyl sulfoxide

Silicon heterojunction

interdigitated back contact solar cell

Light Emitting Diode

Perovskite Light Emitting Diode

Electron Transport Material

Hole Transport Material

Transparent Conductive Oxide

Power conversion efficiency

Highest Occupied Molecular Orbital

Lowest Unoccupied Molecular Orbital

v
Introduction
 Introduction

Energy is necessary for humankind’s existence and continuance. This energy needs
technology to be produced and utilized. The resource of energy is one of the main factors
that characterize the production process of energy. Furthermore, the energy sources can
be divided into two categories according to the duration of its existence; the non-
renewable energy includes all the sources of energy that can be exploited in a finite
quantity, among them: Coal, natural gases, petroleum and its derivatives, radioactive
elements. The quantity of energy obtained from non-renewable energy is high [1]. The
renewable energy sources with an immediate regeneration includes: Solar, wind, tides,
geothermal and hydroelectricity... etc. But the energy amount obtained from these
sources is lower compared to the first category.

The sun produces energy in form of light. The idea of converting sunlight into usable
form of energy is inspired from photosynthesis. This concept is used in solar cells basing
on photovoltaic effect. The field of solar cells has witnessed great development over the
years.

One of the most promising and most “talked-about” solar cells is hybrid organic-
inorganic perovskite solar cells. The rapid growth in renewable energy and solar cells
technology made perovskite solar cells (PSC) a specular star in photovoltaics industry.
This relatively new technology requires huge researches because it promises excellent
energy future; it also holds immense potential for better engineering, more efficient
solar cells. PSCs composed of organic-metal-halide materials have made impressive
progress in just a few years with maximum power conversion efficiencies (PCEs)
evolving from 3.8 % in 2009 to a certified 22.1 % in 2016 [2] and today they exceeded
25 % in power conversion efficiency [3]. Hybrid organic–inorganic halide perovskite
solar cells (PSCs) have risen to stardom owing to the unusual characteristics of the
halide perovskite absorber such as high charge carrier mobility, large and strong optical
absorption, long free carrier diffusion length, low exciton binding energy, cost, as well as
their low processing temperature [4].

1
 Introduction

Motivation

Recently, perovskite materials are considered as promising candidates for hybrid solar
cells due to their ease of fabrication, strong absorption of light, and low non-radiative
recombination rates, plus its ability to exploit on over 20 years of development of
related dye-sensitized and organic photovoltaic cells [5]. Perovskite cells are less costly
to produce than their silicon counterparts and are flexible, lightweight, ultra-thin and
semi-transparent according to their components and thickness [6]. The dramatically
success of PSCs has attracted the experts of inorganic thin-films and organic PV
materials to the field of PSC research. Perovskite solar cell includes a perovskite
structured compound, such as hybrid organic-inorganic lead halide-based material as
the absorption layer. This cell is more efficient than both thin-film technologies and the
single-crystalline silicon solar cell. Furthermore, advances in the design of device
architecture are one of the most important factors that drove the evolution of PSCs.
Planar heterojunction structures in the n-i-p and p-i-n configurations are proposed as
conventional and inverted structures, respectively. Furthermore, perovskite cells are
able to produce energy from artificial light. Also they can be efficient even with incident
sunrays from other angles in addition to 90 degrees angles unlike silicon panels [6].

Current deposition methods of perovskite materials made perovskite solar cells

scaling up to be market competitors. Spin coating and Ink-Jet printer methods could be
implemented to mass produce these cells at a very low production cost [7]

Aims and objectives

The major challenge of photovoltaic is to produce more efficient solar cells with
less prices and long lifetime. One of the promising methods to enhance the performance
of hybrid solar cells is to determine best candidate materials working as electron and
hole transport layers. The aim of this work is to study the effect of changing electron and
hole transport materials in order to achieve best efficiencies and to specify a bunch of
options for charge transport layers. Also, studying and examining the performance of
both conventional and inverted perovskite solar cells and determining the most efficient
one. Using numerical simulation, two different configurations of perovskite solar cells

2
 Introduction

were investigated to determine which one is more efficient. Moreover, effects of electron
and hole transport layers for n-i-p and p-i-n structures were studied by alteration them
every time using its potential replacements.

Structure of the thesis

This thesis is organized into three chapters. Chapter one is a background on solar cells in
general. The history and evolution of solar cells will be touched upon small paragraphs
describing different generations of solar cells. Also, working principals of solar cell
devices were explained leading to its electrical parameters and how to calculate them.

Chapter two is an overview on perovskite materials. In this chapter we will talk

about history and evolution of perovskite materials then their crystal and electronic
structure. Also, properties and deposition methods of perovskite materials will be
discussed. Then, we will mention applications of perovskite based solar cells in some
different fields and its possible architectures. Later, the hysteresis process of perovskite
materials and its causes will be discussed briefly.

Chapter three is about simulation of perovskite solar cells. We will start by

describing the utilized simulation software which is SCAPS 1D and its working basics
such as the manner to define a problem and how to run it; also the most important steps
for achieving a successful simulation as our study requires. After that, we will present
the structure of modeled solar cell which is in planar configuration and results of
simulating conventional and inverted perovskite solar cells. And make a comparison
between their extracted output parameters.

Then, we will study the effect of charge transport layers on both solar cells in
conventional and inverted configurations. This is in order to specify the suitable
materials for transporting electrons and holes from both sides n and p, respectively.
After that, we will enhance solar cells performance by improving thickness of absorber
layer. Furthermore, we will present defects which may be present at perovskite/
titanium dioxide interface and studying the impact of these defects on solar cells
performance. Finally, we will study the effect of temperature on PSCs’ performance.

3
 Chapter 1

Fundamentals of Solar Cell

 Chapter 1 Fundamentals of Solar Cells

1.1 Introduction

The safer and cleaner renewable energy sources are required to compensate the limited
sources of conventional nonrenewable energy such as gas, coal and petroleum even the
nuclear power generation. For many years, photovoltaic (PV) technologies offered such
solutions and already have been used [8]. Initially, the use of PVs was for power
generation on satellites and space craft [9] and later also for terrestrial applications
[10].

Another factor favoring the development of PV industry, which is the growth of

population in off-grid rural areas not connected to the state electrical networks (about
2.5 billion worldwide) [11]

Also, social concerns about modern improved living norms as well as the high
human desire to economize spending money drove to relying on solar cells as an
alternative energy source for terrestrial applications. In addition, there is a necessity to
protect our health and environment. The use of environmentally-benign PV technology
instead of the conventional fossil fuels is the lone way to reduce producing
environmentally-harmful greenhouse gases [12].

Global energy deficiencies led to increasing research interests on PV technology

[13]. In addition to improvement of the silicon solar cells efficiencies [14] with reduction
of solar energy cost, a new PV materials and novel solar cells devices have developed.
The increase in production volume and new cost efficient solar cell technologies
rendered this achievement possible. Presently, a number of promising options for future
developments of PV technology are available. The high cost of solar cell modules
hindered the commercialization of these technologies. Improved performance, lower
cost and reliability of PV systems remain major concerns even though efforts made by
researchers over the years [15].

The base concept of the solar cell is converting sunlight into a usable form of energy.
Where, the solar cell is an optoelectronic device able to convert light into electric
current, both the direct sun light and also artificial or ambient light. The term light is

5
 Chapter 1 Fundamentals of Solar Cells

referred here as the electromagnetic radiation emitted by the sun on to the surface of
the earth.

1.2 Evolution and History of Solar Cells

The best replacement of fossil fuel for energy generation is solar cells technology which
is advanced in order to produce cheap, efficient and a long life time (stable) solar cells.
In order to meet these ultimate goals in photovoltaic technology which has led to
discoveries of new materials and new techniques in solar cells fabrication, research has
been going on [16].

Today, four generations of solar cells are available, thus, enabling the use of
different types of solar cells according to our needs and preferences.

1.2.1 First generation

Silicon solar cells are the most widely used of all solar cells, and they are also the most
efficient in terms of single crystalline cell photovoltaic devices. These solar cells based
on silicon wafer are considered as first generation solar cells. Bell Laboratories
developed the first silicon solar cell in 1954 [16-17], with an efficiency of 6%. This type
of solar cell is the most widely used with the highest reported cell efficiency (single
crystal cell) of ~ 28% [18]. In this generation of solar cells, there are three types of
silicon: single crystalline silicon ( − ), multicrystalline silicon and amorphous silicon
(a-Si). However, − is expensive and involves high cost of fabrication. This has
increased recent research interests into the next generation of thin film solar cells.

1.2.2 Second generation

The second generation materials had been developed to reduce production costs of solar
cells without threatens their energy efficiency [16]. This second generation materials
had been developed to reduce production costs of solar cells without jeopardizing their
energy output [16]. Thin film materials have been the subject of intensive research to

6
 Chapter 1 Fundamentals of Solar Cells

reduce the fabrication costs of the technology based on silicon, and to increase material
utilization. The main materials emerged as the most promising candidates for this
generation are: hydrogenated amorphous silicon ( − : ), cadmium telluride ( )
as well as copper indium diselenide ( ) and its related alloys like Copper Indium
Gallium diselenide ( ) [19-20]. The highest recorded efficiencies of
and thin film single cells are as high as 23.4% and 22.1%, respectively [21].
Most of materials consisting these cells are rare and expensive (indium) or highly toxic
(cadmium). Because of these drawbacks, a different generation of solar cells has been
inspired [19].

1.2.3 Third generation

The third generation of solar cells is the cheapest type of solar cells. The efficiencies
gotten so far for dye-sensitized and organics single cells are ~ 11.9 % and 16.5%
respectively [21]. This indicates that the efficiency of organic solar cell generation is
generally very low. Furthermore, organic photovoltaic is technologically immature and
its wide spread applications are limited by several instabilities issues such as cells
degradation mechanisms in different environments. Hence, OPV and dye-sensitized
technology are relatively low to make these cells competitive in a commercial market
[19]. With the relentless effort of researchers in photovoltaics, a new type of solar cell
which is based on organic-inorganic hybrid solar cell known as perovskite solar cells
emerged as promising technology.

1.2.4 Fourth generation

The fourth-generation solar cells are hybrid, which combine the low cost and flexibility
of conducting polymer films (organic materials) with the lifetime stability of novel
nanostructures (inorganic materials).

Fourth-generation approaches to photovoltaics (PVs) aim to achieve high efficiency

devices but still use thin films deposition methods. Also, in common with Si-based thin-

7
 Chapter 1 Fundamentals of Solar Cells

film technologies, these will use materials that are both nontoxic and not limited in
abundance.

This type of solar cells consist of p-n junctions in different semiconductor materials
with increased bandgap are placed on top of each other, to absorb different sections of
the solar spectrum. Where, the highest bandgap intercepts the sunlight first [22].

1.3 Working principle of typical silicon Solar Cell

The basic property common to all photovoltaic cells is that they convert sunlight into
electrical power by the photovoltaic effect, which is the generation of a potential
difference at the junction of two different materials when the device is illuminated by
the sun radiation. Where, the device works as a diode in the dark and generates
photovoltage under illumination. The conventional silicon solar cell structure is
illustrated in Figure 1.1.

Figure 1. 1: Conventional solar cell structure.

The transformation of solar energy to an electric energy is based on three mechanisms:

8
 Chapter 1 Fundamentals of Solar Cells

1.3.1 Absorption of photons

Photons with energy more than gap energy are absorbed by the active material where
these photons transferred to an electron-hole pairs. Electron moves to the conduction
band leaving a hole at the valence band (Figure 1.2). The excess of photon energy
compared with gap width is transferred to heat. While, photons with energy inferior
than gap width go through the material without being absorbing [23].

Figure 1.2: Absorption phenomena in semiconductors.

1.3.2 Conversion of photon energy to an electric energy

A zone of charge space is formed by depopulating the area between n and p materials
leading to creation of an electric field, which is the responsible on electron-hole pairs
separation at the p-n junction [24]. If the light-generated minority carrier reaches the p-
n junction, it is swept across the junction by the electric field at the junction, where it is
now a majority carrier as presented in Figure 1.3.

9
 Chapter 1 Fundamentals of Solar Cells

Figure 1. 3: Functioning principle of the solar cell.

1.3.3 Collection of charges

Charges are collected by metallic electrodes at front and rear surfaces of the cell. So, an
electric current is generated by the solar cell [25].

1.4 Electrical parameters of the solar cell

The electrical behavior of the solar cell can be best described by its current-voltage
characteristic curve ( − ) (Figure 1.4). Variations of current ‘ ’ (or current density ‘ ’)
in function of voltage ‘ ’ in dark and under illumination allow to evaluate the device
performance [26].

1.4.1 Equivalent electrical circuit

The electrical behavior of an ideal device can be modeled using the Shockley diode
equation (Equation 1.1) [27]:

( )= − = − exp ( )− 1 1.1

Where,

10
 Chapter 1 Fundamentals of Solar Cells

: Photogenerated current ( ).

: Diode current( ).

: Dark saturation current (current density flowing through the diode under reverse
bias in the dark),

: Boltzmann constant (1.38066 × 10 ⁄ = 8.61400 × 10 ⁄ ).

: Absolute temperature ( ).

∶ Absolute charge of an electron (1.60281 × 10 ).

Figure 1. 4: J-V characteristic in dark and under illumination of a solar cell.

In reality, no device is ideal and so the equation must be modified to account for
potential losses that may arise [28]. In case of real solar cell, the solar cell is modeled as
presented circuit in Figure 1.5.

11
 Chapter 1 Fundamentals of Solar Cells

Figure 1. 5: The equivalent circuit of a real solar cell.

I-V characteristic is presented by Equation

E 1.2 [28]:

( )
= − exp ( )− 1 − 1.2

Where:

: Ideality factor of diode.

: Series resistance (Ω).

∶ Shunt resistance (Ω).

Ideally for an efficient solar cell,

cel should be minimized ( → 0) and should be
maximized ( → ∞) [29].

1.4.2 Short circuit current

The short circuit current is the maximum photo-generated

photo generated current delivered by a solar
cell when the terminals of the solar cell are short-circuited.
shor It yields information about
the charge separation and transport efficiency in the cell. is related to illumination
intensity, illuminated surface, wave lengths of radiation, charges mobilities and
temperature[27].
( = 0) = = 1. 3

12
 Chapter 1 Fundamentals of Solar Cells

1.4.3 Open circuit voltage

At zero current ( = 0), the voltage reaches the maximum value ( ) (i.e. when the
terminals of the solar cell are not connected to each other) [27].

= ( + 1) 1.4

1.4.4 Fill Factor

The fill factor ( ) is defined as the ratio between the maximum produced power
( ) and the product of short circuit current and open circuit voltage. is used to
characterize the non-ideality or in other words the "squareness" of the − curve [30].
×
= ×
= ×
1.5

1.4.5 Power conversion efficiency

It is one of most important parameters, which is used to evaluate solar cells

performance. The power conversion efficiency ( )is defined as the ratio between the
generated power by the cell ( ) and the incident power from the sun radiation
( ).The efficiency depends on the spectrum and intensity of the incident sunlight and
the temperature of the solar cell [27].
= 1.6

13
 Chapter 2

Perovskite materials and Solar cells

design
 Chapter 2 Perovskite materials and Solar cells design

2.1 Evolution and History of Perovskite Solar Cells

Recent type of solar cells has gained a major interest which is perovskite solar cells
(PSCs) as “third and even fourth generation solar cells”. The compounds with formula of
(originated from the mineral name of calcium titanate [31] generally
belong to a perovskite-type compound; which was discovered in 1839 by German
mineralogist Gustav Rose, and was named in honor of the Russian mineralogist Lev
Perovski (1792-1856) [32].

Inorganic perovskite oxides (e.g., , , , etc.) and halides

( , , etc.),have gained a big attention due to their divers applications in
optics, magnetics, electronics and superconductors [32]. Hybrid organic-inorganic
perovskites which contains an organic ammonium cation ( , = , etc.),
a divalent metal cation ( , , , , , , etc.), and halide ions
( , ), has attracted attention of scientific community [32].

The first perovskite solar cell was reported by Kojima et al. in 2009 [33]. They used
methylammonium lead iodide ( , ‘ ’) and methylammonium lead
bromide ( , ‘ ’) as solid sensitizers in dye-sensitized solar cells
(DSSCs) with liquid electrolyte [13]. This DSSC showed low power conversion efficiency
of 3.13% and 3.81% for and solar cells, respectively [32-33].

In 2012, Michael M. Lee et al. reported a meso-Superstructured organometal halide

perovskites solar cell with power conversion efficiency of 10.9% [21-34] by replacing
the liquid electrolyte by a solid hole transport material (HTM). Due tremendous efforts
by scientific researchers, power conversion efficiency reached 25.2% according NREL
[3] (Figure 2.1).

15
Chapter 2 Perovskite materials and Solar cells design

Figure 2. 1: Evolution of solar cell efficiencies.

16
 Chapter 2 Perovskite materials and Solar cells design

Perovskite solar cells have much architecture that has evolved over time. First cell
was based on the design of the liquid electrolyte DSSC configuration, which reported in
2009. In 2012, the first step to development of the mesoscopic and meso-
superstructured architectures, when the liquid electrolyte was replaced by a solid state
hole transport material (HTM) [32].

During 2013-2014, a “regular” structure was developed using penetrated perovskite

materials into mesoporous metal oxide layer, and was capped by another layer on the
top. Since then, the regular structure has been widely used to fabricate high-efficiency
PSCs [32].

2.2 Perovskite Crystal Structure

As mentioned before, "Perovskite" originates from the mineral name of calcium titanate
( ) and the compounds with formula of generally belong to a perovskite-
type compound, where the A is a divalent and B is a tetravalent metal ions [32].

Figure 2.2 illustrates the perovskite structure, where the A cation is coordinated
with twelve X ions and the Β cation with six. Thus, the A cation is normally found to be
somewhat larger than the cation [35]. In addition to the oxide perovskites, halide-
based perovskites are also well known.

Figure 2. 2: Perovskite cubic crystal structure.

By replacing the cationic component with an organic ammonium at the A site, the
resulting compound is called an "organic-inorganic perovskite compound". The metal

17
 Chapter 2 Perovskite materials and Solar cells design

ion component usually is tin or lead. The general formula of perovskite compounds
is [( ) ], in which modifications of metal ( ), halide (X) and organic groups
(R) precisely control the physical properties. Among them, the tin perovskite is
relatively better for electrical conduction, and the lead one is better for optical
properties [36].

In next sections, we will concentrate on materials because much of the

high efficiency solar cells have focused on as light absorber.

2.3 Electronic Structure of Perovskites

In the hybrid perovskite structure of , the metal has an occupied s orbital

(lone pair) whose electrons interact strongly with the in-plane anion p states forming an
anti bonding state as the top of the VB with mostly s-orbital character. The CB minimum
is constituted from anti-bonding Pb(6p)-I(5p) states with a p orbital character (Figure
2.3.a) [37].

The substitution of the monovalent A cation does not directly affect the electronic
band structure in halide perovskites [32].

Both VB and CB are formed by anti-bonding orbitals. The anti-bonding structure

contributes to suppression of charge recombination leading to superior photovoltaic
property such as high voltage generation. Figure 2.3.b, shows a high symmetry of band
structure, which enables direct p-p electron transition from VB to CB [40].

18
 Chapter 2 Perovskite materials and Solar cells design

Figure 2. 3: (a) Bonding diagram of a [ ]− cluster, representing the perovskite

[38] and (b) The bottom shows the band gap structure for the quasiparticle self-
consistent GW approximation [39].

2.4 Tuning the band gap with composition

The composition of the perovskite has been altered by incorporating other

monovalent cations [formamidinium ( ) and ], divalent cation ( ), and
halide ions ( and ), which results in optical absorption tunability [4] as shown
in figure 2.4. This make their band gap can be tuned widely from the blue to the red
spectral regions [41]. As mentioned before, the valence and conduction bands of
perovskites are determined by the inorganic octahedron. The organic cation does not
contribute to these bands but modulates the band gap by modifying the lead-halide bond
distance [41].

However, the tolerance factor affected by the A cation size, changes the spacing of
[ ] octahedra, leading to altering the band gap. The decreased ionic sizes of ,
, and cations (253, 217 and 181 , respectively) led to increasing band gaps
1.48, 1.52 and 1.67 for ( ), ( ),) and ( ),), respectively [3]. While
the ionic size of the halide decreases, the band gap increases and for single crystals it is
found to be 2.97, 2.24, and 1.53 for the , , and perovskite, respectively [42].

19
 Chapter 2 Perovskite materials and Solar cells design

The full tunability of the band gap for has been demonstrated for
– compositions and strongly recommended for – compositions from UV–visible
absorption spectroscopy and PL measurements [41]. From a photovoltaic perspective,
is thus suitable for single band gap absorbers and could be
interesting for tandem applications whereas is relevant to light emitting
devices [42].

Using perovskites with mixed cations and halides is an important theme because the
pure perovskite compounds suitable for PV applications come with numerous
disadvantages [42]. For instance, some stabilizes the perovskite structure and
prevents it from transforming into the yellow polymorph known for the perovskites.
Introducing allows tuning the band gap, which is favorable for tandem applications,
and some appears to be favorable for the device performance [42]. Moreover,
incorporation of the inorganic stabilizes the perovskite phase of and
reduces the defect density [4].

Figure 2. 4: The versatility of hybrid perovskite material and

their absorption tunability. Schematics of some investigated perovskites closely related to
. The insets show (a) single crystal of , (b) single crystal of , (c) colloidal
solutions of ( = , , ) perovskites, (d) solar cells of 49 different compositions in
the / − − / compositional space, (e) single crystal of , (f) single crystal of
and (g) colloidal nanocrystals of ( = , , ) perovskites [4].

20
 Chapter 2 Perovskite materials and Solar cells design

2.5 Doping of perovskite materials

Doping is regarded as intentional introduction of a small amount of ‘impurities’ into an

otherwise pure material (host) to tune its electronic properties (e.g. hole or electron
transport) [43].

Certainly, dopants engineering has emerged as one powerful strategy to tailoring

the properties of halide perovskites, making this prominent material even more
attractive for practical applications.

Doped halide perovskites exhibit diverse optical and electronic properties with
respect to undoped counterparts, with principal characteristics including enhanced
stability, high quality thin films with enlarged grain size, improved photoluminescence
quantum yields, new emission characteristics, reduced defect state density, thus leading
to excellent optoelectronic performance of devices that were constructed by using the
doped perovskites as active layers.

Various dopants, including main group metals (e.g., , , , , ), transition

metals (e.g., , , ), and rare earth metals (e.g., , , ), have been successfully
doped into halide perovskite polycrystalline films, single crystals, and nanocrystals,
giving rise to a wide variety of exotic properties different from those of the mother
compounds. Also, Mojtaba abdi-jalebi et al. found that , , and in ,
(or ), and cation halide based salts, respectively, have ionic radii similar to
and can be doped into the perovskite absorption layer to regulate the morphology and
photophysical properties of perovskite to improve the photovoltaic performance of
perovskite thin films [44].

The metallic elements, including main group metal cations, transition metal cations,
and rare earth metal cations that have been doped in halide perovskites, are marked in
the periodic table (Figure 2.5). The orange, blue, green, and yellow colors denote the
metal dopants for optoelectronic performance control, crystal growth control, structural
stability control, and light conversion in halide perovskites, respectively [45].

21
 Chapter 2 Perovskite materials and Solar cells design

Figure 2. 5: Doping materials in halide perovskites [39].

Furthermore, Yin et al. and Wang et al. [46] showed experimentally and
theoretically, respectively, that HOIPs may be possibly self-doped as a result of crystal
defects engineering [43]. It has been proposed recently that perovskite solar cells
represent p-i-n devices where p-type doping is induced by the presence of lead and
methyl ammonium vacancies ( and ), while n-doping results from the presence of
iodide vacancies ( ) as it follows from the theoretical calculations. It is believed that
doping can be achieved in by using different and ratios in the
precursor solutions [47].

2.5 Properties of organic-inorganic hybrid perovskites

Perovskite materials have many advantages as light absorber, such as:

 Strong absorption coefficients, low non-radiative carrier recombination rates and

small effective masses of electrons and holes [38]
 The perovskites are direct band gap semiconductors [39].

22
 Chapter 2 Perovskite materials and Solar cells design

 The electron/hole diffusion lengths are observed to be longer than 100 . and
low energy loss [39].
 Low temperature solar cell processing preferably
preferably via the printing techniques
[31], which makes it possible to be deposited on a flexible substrate (Figure 2.6).
 Low payback time due to the low cost of production and the high performance
[48].

Figure 2. 6: Photograph showss a large plastic film perovskite device (left: perovskite side, right:
gold electrode side) fabricated by the low temperature coating methods.

 Photovoltaic properties of perovskite are benign to defect formation. Because,

ionic vacancies form trap states that reside within VB and CB or exist as
shallow defects near VB and CB. Carriers trapped by very shallow defects can
be detrapped easily and can contribute to current generation [40]
[40].
 Mobility of carriers in is ambipolar, exhibiting
hibiting similar effective
mass for both electron and hole (0.23
( and 0.29,, respectively) which agrees
with the concept that the perovskite is an intrinsic semiconductor unlike Si
and GaAs [40].

Moreover, perovskite materials have been attracted attention due to their

interesting characteristics of the inorganic components, which include: thermal stability
and the high degree of structural order and also due to the properties of the organic
component such as the functional versatility, mechanical flexibilit
flexibility and low-cost
processability [48].

23
 Chapter 2 Perovskite materials and Solar cells design

2.6 Deposition methods of perovskite films

Many scientific researches and potential applications concerning organic-inorganic

hybrid materials strongly depend on accessibility and reliability of simple fabrication
techniques. Fabrication of hybrid materials faces some difficulties such as
decomposition of the organic components and finding an appropriate solvent because
the chemical and physical properties of organic and inorganic components, in addition
the unfavorable characteristics of some substrates make the deposition inhomogeneous
[49]. Despite these difficulties, preparation of perovskite layers became essential for
fabricating high efficiency devices. Generally, accurate control of the stoichiometry,
crystallographic phase, and grain structure of the perovskite material is required to
fabricate high efficiency perovskite solar cells [4]. These parameters can be controlled
by four primary deposition methods: one-step solution process, two- steps solution
process, vapor-assisted solution process and thermal evaporation process.

2.6.1 One step solution process

The one-step solution process was the first used method to fabricate perovskite films.
And now it is the most used and adopted technique in preparing perovskite materials
due to its simplicity. In this method, methylammonium iodide ( ) and lead
iodide ( ) are taken in 3:1 molar ratio, and dissolved in an aprotic polar solvent, such
as dimethylformamide ( ), gamma-butyrolactone ( ), dimethyl sulfoxide (DMSO),
N-2- methyl pyrrolidone, or a mixture of them to form a homogenous precursor solution.
The solution is then spin coated on the substrate and dried and heated at mild
temperatures (70 ℃ − 100 ℃) until the film turns into black color which indicates that
film is formed [50-51], the method is illustrated in figure 2.7. Films
prepared using the single-step solution method exhibited highly porous morphologies
consisting of perovskite crystallites in spherical and polygonal shapes (with GBL) or
needle shape (with DMF) [4]. The spinning rate, drying process, and temperature are
expected to affect the morphology [51]. Additionally, the environmental
conditions (e.g., oxygen and humidity), morphology of the substrates, can also influence
the uniformity, crystallinity, phase purity, surface morphology, and interface properties
of the perovskite films [4]

24
 Chapter 2 Perovskite materials and Solar cells design

Figure 2. 7: Perovskite film deposition by one step procedure.

2.6.2 Sequential two steps solution process

Devices prepared by one step solution process exhibited a poor surface coverage of
perovskite films [4]. To surmount this, Burschka et al. developed the two steps solution
deposition method to prepare uniform on a mesoporous layer. The two
steps method is illustrated in Figure 2.8. In this technique, salt is dissolved in
and is deposited on a glass substrate using vacuum evaporating or spin coating method
followed by dipping the slide into ( ) solution or spin coating the
solution on film. The films then are dried in mild temperature for while. The black
color of the films gives a visual confirmation of the thin film formation [40-
4]. The films prepared by the two-step method were dense and conformal [4]. The
dipping time and concentration of the precursor solution were found to affect
photovoltaic performance [51].

Figure 2. 8: Perovskite film deposition by two steps procedure.

25
 Chapter 2 Perovskite materials and Solar cells design

2.6.3 Vapor Assisted Solution Process

Developing the two steps solution deposition to vapor deposition of is known as

vapor assisted solution process. A uniform and conformal films with high phase
purity was fabricated by Chen et al. using this method [4]. In vapor assisted solution
process presented in Figure 2.9, the germ layer of is spin coated than exposed to
vapor generated from heating powder at 150 ° in an inert environment. This
method produces perovskite films with a full conversion of and a conformal,
uniform and smooth film with large sized grains up to the micrometer scale. In the other
hand, vapor assisted solution process is limited by the slow incorporation process of
into framework which needs a several hours to complete conversion [4].

Figure 2. 9: Perovskite film deposition by vapor assisted solution process.

2.6.4 Thermal Vapor Deposition

Smooth, conformal and uniform perovskite films were resulted from co-
evaporation of and then annealing by Snaith et al. in 2013 [4]. Alternative
vapor deposition methods were developed such as the layer-by-layer vacuum
evaporation, chemical vapor deposition and flash evaporation. Vapor deposition method
results uniform and pinhole-free perovskite films compared to solution processed films
(Figure 2.10). The benefits of this technique are that it is possible to precisely control the
thickness and smoothness of the thin-film surfaces [49]. However, only few research

26
 Chapter 2 Perovskite materials and Solar cells design

groups have fabricated high efficiency devices using this method, because it is difficult to
control temperature during deposition due to the low thermal stability of both the
precursor and the products.

Figure 2. 10: (a) dual source evaporation, (b) chemical vapor deposition, and (c) flash
evaporation.

2.7 Applications of organometal halide perovskites

Optical and electrical properties as well as low processing cost of organic-inorganic

perovskites have got researches attention due to its electronic structure. These properties
could to adapt the new requirements of scientific studies and technical developments [49]. A
variety of technologies can benefit from the special properties of these promising
materials.

27
 Chapter 2 Perovskite materials and Solar cells design

2.7.1 Solar cells

Because of promising potential to transfer renewable solar energy to electric energy,

solar cells based on perovskites are one of the most attractive optoelectronic
applications. Advances in the design of device architecture are one of the most
important factors that drove the evolution of perovskite solar cells [4]. The first solar
cells based on lead iodide based perovskite sensitizers were reported by kojima et al. in
2009. Where, they constructed a / ( : ) liquid sensitized solar
cell. The obtained power conversion efficiency were found to be 3.13% and 3.81% for
and based solar cells, respectively [33]. Also, they
concluded that using a series of hybrid perovskite materials
( : , ; :ℎ ) with a different energy gaps can optimize the perovskite solar
cell performance [33]. Replacing the liquid electrolyte with a solid hole transport
material overcame the instability issue associated with the liquid electrolyte [4]. Hybrid
organic inorganic perovskites are ideal candidates for tandem solar cells due to their
tunable bandgap that ranges of 1.2 − 2.3 and versatility in the device configurations
[4].

Furthermore, perovskites based solar cells can be optimized by using appropriate

contacts to make photogenerated charges efficiently extracted [41]. In current designs,
as it will be more detailed in the next paragraphs, the perovskite is sandwiched between
two different materials; the electron and the hole transport layers.

2.7.2 Multi-junction photovoltaics

The efficiency of a single-junction solar cell is limited by the Shockley– Queisser limit,
which includes losses from transmitted below-band-gap photons and from
thermalization of hot photogenerated carriers [41]. The tandem design can better utilize
the solar energy so that high-energy photons are absorbed by the upper wide bandgap
subcell, while those in longer wavelength region are harnessed by the bottom narrow
bandgap subcell [52]. The designs of the multi-junction concept can be divided into four
configurations: two-terminal (2-T) monolithically integrated (two stacked cells that are
connected electrically in series) and four-terminal (two mechanically stacked cells that
are electrically independent represented in Figure 2.11.a), the spectral splitting systems
and four-terminal reflective tandem [41-52-53].
28
 Chapter 2 Perovskite materials and Solar cells design

The monolithically integrated two-terminal perovskite/silicon tandem architecture

consists of a perovskite top cell, which is deposited onto the silicon bottom cell. The two
subcells are then electrically connected in series, through a recombination layer or
tunnel junction.

The four-terminal tandem (Figure 2.11.b) is the most simple tandem device
architecture. The two subcells are fabricated independently, mechanically stacked on
top of each other and contacted individually.

A four-terminal spectral splitting tandem device consists of a dichroic mirror, which

splits the light toward the high and low bandgap cells, as illustrated in Figure 2.11c. In
four-terminal reflective tandem configuration, the PV Mirror concept is used which is a
concentrating mirror, spectrum splitter, and light-to-electricity converter all in one: It
consists of a curved arrangement of cheapest subcells that absorb part of the solar
spectrum and reflect the remainder to their shared focus, at which a second solar
converter is placed illustrated in Figure 2.11.d [53].

Stacking perovskite cells on well-established photovoltaic cells, such as those made

from crystalline ( − ), , , or could maintain high efficiencies.
Where, the perovskite cell can be used as the top cell because its band gap can be tuned
to transmit sufficient light to the bottom cell. Also, producing perovskite cells on top of
other cells does not damage them because of low-temperature processing of the hybrid
perovskite cells [41].

In 2017, a power conversion efficiency is obtained for the monolithically integrated

two-terminal solar cell / (SHJ: Silicon heterojunction) reached
23.6 % and 26.4% for mechanically stacked four-terminal /
(IBC: interdigitated back contact solar cell) [53]. A 23.4% conversion efficiency is
achieved for the / PERL system in spectral splitting configuration [54].

29
 Chapter 2 Perovskite materials and Solar cells design

Figure 2. 11: Schematics of several perovskite/silicon tandem architectures: a) 44-terminal

mechanically stacked; b) 2-terminal
terminal monolithically integrated; c) 4-terminal
terminal optical spectral
splitting; d) 4-terminal reflective
flective tandem.

2.7.3 Building-integrated
integrated photovoltaics

Building-integrated
integrated photovoltaics are an attractive concept for economic generation of
solar power [41-55].
55]. Neutral color tinted windows with controllable levels of
transparency is more demanded for novel applications in windows, cladding of buildings
and vehicles [55-56];and
56];and combination between tunable semi-transparency
semi transparency and high
high-
power-conversion
conversion efficiency could be delivered by perovskites
pe [41].

Giles et al. fabricated microstructured perovskite solar cells with a discontinuous

active layer. The perovskite layer was formed as islands with the spiro
spiro-OMeTAD
infiltrating the spaces between and also coating the islands with a thin laye
layer. They found
that, incorporation of a dye or pigment into the regions where light passes through
modifies optically the semitransparent cells as shown in Figure
igure 2.12[55]
2.12[55].

Figure 2. 12:: Picture of semitransparent perovskite solar

solar cells without (left) and with (right)
D102 dye included in the spiroOMeTAD layer, with 10 nm gold electrodes [55].

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 Chapter 2 Perovskite materials and Solar cells design

Recently, a 1.3 × 0.9

9 perovskite photovoltaic panel made by Construction
company Skanska’s Warsaw contains 52 modules and seeks to cover the energy needed
to light one employee’s workspace for eight hours [57]. Saule uses ink
ink-jet printing. The
inks were formulated so that every layer of different material in the cell has the right
properties to produce and transport electrons when light is shone on them (Figure 2.13)
[57].

Figure 2. 13:: A flexible, ultrathin, ultralight and semitransparent

semitransparent perovskite film produced by
Saule Technologies [57].

2.7.4 Light emitting diodes

Light-emitting
emitting diodes (LEDs), a kind of solid-state
solid state lighting device based on inorganic
semiconductors could provide highly efficient and convenient light point sources o
of
different colors. Organometal halide perovskites have the potential to produce highly
efficient light emission spanning the visible spectrum and exceptional color quality at
low cost, resulting from their extraordinary optical property and compatibility with roll-
to-roll
roll solution processed techniques [58]. Most recently, high brightness perovskite
LEDs (PeLEDs) with panchromatic colors covering the entire visible spectra has been
realized from organometal halide perovskites ( = or ,
= , or ) at room temperature, which potentially opening up a wide range of
optoelectronic applications in addition to solar cells [59].
[59]

At 2014, a green and red electroluminescence from and

based PeLEDs, respectively were reported by Tan et al. as showed in
Figure 2.14 [60]. The green PeLED achieved a luminance of 364 at a current
density of 123 , giving external
external quantum efficiency of 0.1%, while a luminance

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 Chapter 2 Perovskite materials and Solar cells design

of 16.2 was achieved at a current density of 55 and external quantum

efficiency of 0.018% or 0.03 was achieved at 5.7 for red PeLED [60].

Also, Nana et al. have reported

reported a green perovskite light emitting diode based on
perovskites, with a low turn-on
turn voltage of 2 and an external quantum
efficiency of 0.43% at a brightness of 5000 [61].

Figure 2. 14: Green and red perovskite LEDs [60].

Most recently, Zhao, X and Zhi-Kuang

Zhi Kuang Tan has developed high
high-efficiency, near-
infrared LEDs that can cover an area of 900 using low-cost
cost solution
solution-processing
methods. Using perovskite, they reported a 799 near-infrared
infrared PeLED that
operates with an external quantum efficiency (EQE) of 20.2%. (Figure
igure 2.15). Note that,
infrared LEDs are useful for optical communications and convert
co vert illumination, and are
commonly found in remote controls and security camera
cam setups [62].

Figure 2. 15: Photograph

hotograph of near infrared flexible PeLED with large-area
large area [62].

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 Chapter 2 Perovskite materials and Solar cells design

2.7.5 Solar water-splitting

The conversion of sunlight directly into chemical fuels is a process called artificial
photosynthesis using a splitting solar cell. Perovskite solar cells have already been used
to split water into and .Generally the output voltage for solar cells at
maximum power point is around 0.9 , so tandem cells are needed in water photolysis
[56]. The structure of solar water-splitting is based on two perovskite solar cells
connected in series as illustrated in figure 2.16. Perovskite tandem solar cell is used to
achieve the photovoltage necessary to overcome the thermodynamically required
minimum voltage of 1.23 for splitting water and the additional 0.1 and 0.3 for
kinetically driving the and evolution reactions [41].

Luo et al. connected two solar cells (outside the electrolyzer vessel) in
series to split water and achieved a solar-to-hydrogen conversion efficiency of
12.3% [56], which is close to the most notable example of water-splitting using
GaInP/GaAs tandem cells that achieved 12.4% [41].

Most recently, Mohite, A. et al. developed a water splitting system for fuel
production using low-cost abundant materials (Figure 2.16). The Device was
constructed of > 20% efficient perovskite solar cells with > 1500 hrs stability in
operation [63].

Figure 2. 16: Water splitting system structure based on perovskite solar cells [63].

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 Chapter 2 Perovskite materials and Solar cells design

2.7.6 Space applications

Solar cells for space applications have to be resistant to harsh environmental conditions
(Figure
igure 2.17). Especially, tolerance against radiation and charged particles is mandatory
[64].

Low-energy
energy protons can cause higher performance degradation th
than high-energy
protons because they are more likely to be stopped in shallower regions. Nevertheless,
flexible perovskite cells exhibited exceptional resistance (equating several years in
space) and showed significant potential for power generation in spac
space-related
applications [64].

Recently, Olga et al. fabricated a flexible perovskite solar cells with / /

: / / / / . The solar cell irradiated
with 100 protons (fluence from ~ 3 × 10 to ~ 3 × 10 protons
protons/cm , equating
several years in space). Flexible PSCs
PSCs exhibited a good radiation tolerance and did not
show color center formation, revealing their outstanding resistance against low
low-energy
proton radiation. They denoted that this can be credited to the combined effect of
intrinsically large carrier diffusion
diffusion length exceeding the thin absorber film thickness and
the defect tolerance of perovskite crystals [64].

Figure 2. 17:: Perovskite solar cells for space applications [64].

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 Chapter 2 Perovskite materials and Solar cells design

2.8 Perovskite Solar Cell Device Architecture

Perovskites solar cells have two main structures. In general, the most adopted structure
by researchers all around the world is the “regular” structure. The regular perovskite
solar cell is formed of a mesoporous oxide layer (as a wide band gap window layer), a
lead halide layer penetrated into the porous of the oxide layer (as a light absorbing
layer), hole transport material HTM (an efficient hole conductor) and an ohmic contact
(as a hole collector) (Figure 2.18.a) [31].

Getting the mesoporous oxide layer thinner in regular structure until removing it
eventually, led to another architecture of perovskite solar cells. Similar to inorganic thin
film solar cells, the planar n-i-p heterojunction structure is comprised of a TCO cathode,
an n type ETM, an intrinsic perovskite layer, a p type HTM and a metal anode ( Figure
2.18.b).

Figure 2. 18: Regular perovskite solar cell structures.

An opposite sequence of HTM and ETM configuration is used in planar p-i-n

heterojunction structure (inverted structure).The p-i-n structure is comprised of a TCO
anode, a p type HTM, an intrinsic perovskite layer, an n type ETM and a metal cathode.
The p-i-n heterojunction structure exhibited excellent photon to electron conversion
rate and enhanced device stability maintained ~90 % in PCE after 30 days of exposure
to ambient condition [32].

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 Chapter 2 Perovskite materials and Solar cells design

2.9 Working mechanisms of perovskite solar cells

Both mesoscopic and regular structures contain generally a thin compact layer,
where photo-generated electrons in perovskites were injected through it. The balanced
electron and hole diffusion lengths made material appropriate in p-n and
p-i-n (or n-i-p) planar structures.

Certainly, perovskite provides electron and hole path-ways planar structure, while
in the mesoscopic structure it provides electron and hole path-ways in both of
perovskite and oxide layers (see Figure 2.19) [51].

Minemoto et al. [65] and Tanaka et al. [66-36] have observed that the dominant
charge carrier in lead halide perovskite is a typical Wannier- type exciton. This is similar
to the type of charge carriers observed in inorganic materials [65-66]. Therefore, lead
halide perovskite solar cells (thin film and/or inert mesoporous configuration) operate
generally as p–i–n (or n-i-p) junction [67].

The perovskite material serves as active layer (absorber), while the n-type material
serves as the electron transporting material (ETM) and the p-type material as the hole
transporting material (HTM). The photo-generated carriers at the –i- layer are then
transported towards the contacts across the n and p layers [48].

Device structure affects working mechanism of the device. Also, the solar cell
performance is dependent mainly on the quality of perovskite layer regardless on the
device structure [51].

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 Chapter 2 Perovskite materials and Solar cells design

Figure 2. 19: Working mechanisms of perovskite solar cells.

2.10 Excitonic effects

Excitons are electron-hole pairs that are bound by coulombic interactions. Excitons
existing in the semiconductors and insulators are created after absorbing photons by
inter-band transitions. Where, the electron is in the conduction band (LUMO band) and
the hole is in the valence band (HOMO band) [49]. Excitons have an important role in
optoelectronic devices because they govern some characteristics of materials. There are
two main types of excitons that have been identified in crystalline materials: Wannier-
Mott and Frenkel excitons.

2.10.1 Wannier-Mott excitons

They are found in inorganic semiconductors which the dielectric constant is relatively
large. Also, they are usually larger than single unit cells because of small coulombic
interactions. Wannier-Mott excitons have a large Bohr radius (The distance between the
electron and hole [68] ) that encompasses many atoms which make it highly delocalized
and can move freely throughout the crystal, hence they get the other name of "free"
excitons as illustrated in Figure 2.20.a).

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 Chapter 2 Perovskite materials and Solar cells design

2.10.2 Frenkel excitons

These excitons are highly localized and they are comparable to a few unit cells in size
in organic molecules (Figure 2.20.b). They have to move through the crystal by hopping
from one atom site to another [49]. The Frenkel excitons have a much smaller Bohr
radius which is comparable to the size of the unit cell.

In perovskites, because of the organic barriers, the excitons are

confined in inorganic sheets. The Bohr radius is about ~0.05 [69] and the exciton
binding energy has been calculated to be about 50 , but it could be even as low as
2 , indicating that at room temperature, and especially at the higher operating
temperatures of a solar cell, the majority of charge carriers are free electrons and holes
[70].

Figure 2. 20: Types of excitons in crystalline materials, (a) Wannier-Mott and (b) Frenkel
excitons.

2.11 Challenges in perovskite solar cells

Two of the main issues for commercialization of perovskite photovoltaic technology are
(i) strong current–voltage (J–V) hysteresis, (ii) relatively fragile stability of PSCs. These
drawbacks will be discussed in next paragraphs.

2.11.1 Hysteresis of perovskite solar cells

The so-called current (J)–voltage (V) hysteresis is a mismatch of current measured

between forward scan (voltage biased from 0 to ) and reverse scan (voltage biased
from to 0 ) [71]. Consequently, the resultant photovoltaic parameters vary
38
 Chapter 2 Perovskite materials and Solar cells design

depending on the direction and rate of the scan as shown in Figure 2.21 [72]. Therefore,
hysteresis imposes a serious problem on determination of perovskite solar cell
efficiencies and long term device operational stability [73].

Figure 2. 21: (A) The current–voltage (I-V) response with hysteresis; and (B) negligible
hysteresis of PSCs [74].

Many possible theories elucidating the origin or mechanism of hysteresis in PSCs

have been proposed. These proposed origins are discussed in next paragraphs.

2.11.1.1 Trapping of electronic carriers at the perovskite interfaces

It is known that methods used in synthesis of perovskite materials create defects states
within perovskite material. Also, migration of ions can create traps and lead to
interfacial charge accumulation. Furthermore, it was revealed that all vacancies generate
shallow traps or slightly perturbed states in the band and resonances (deep localized
states hybridized with conduction or valence band states), indicating that carriers could
still relax easily to VBM and CBM. Deep electronic states inside the band gap can be
formed by interstitials and antisites associated with Pb and I. Reports have shown that
grain boundaries and imperfections on the perovskite surface may introduce localized
states, which could serve as trap centers for photogenerated carriers [72].

2.11.1.2 Ion migration

According to Frolova et al., perovskite represents an electrochemically active

system with the mobile hydrogen (methylammonium) cations and iodine anions. Where

39
 Chapter 2 Perovskite materials and Solar cells design

the perovskite films suffer from decomposition under the applied electric field, and the
electrochemical degradation of the perovskite films is almost irreversible [68].

Migration of ions/vacancies under electric field through the perovskite layer plays
an important role in the hysteresis. It was estimated that the motion of up to 3.7% of
with diffusion coefficient of 10 cm s contributes to the hysteresis. Ion migration
can cause the device degradation by reducing the built-in electric field which cannot be
prevented by encapsulation [68].

2.11.1.3 Ferroelectric polarization

Theoretical calculations suggested the possibility of ferroelectricity of 3 where

the ferroelectric material is capable of sustaining a permanent polarization in the
absence of an applied electric field. The existence of a polar molecule (organic cation) at
the center of the perovskite cage has also been suggested to be one of the possible
causes of orientational disorder and polarization [72].

2.11.1.4 Capacitive effects

The nature of charge distribution and kinetics of the charging processes are addressed
by analyzing capacitive responses. Park and co-workers found that large CH3NH3PbI3
crystal and presence of mesoporous TiO2 significantly reduce the I–V hysteresis. They
also reported that the capacitive charges tend to get stored in smaller crystals and
planar structure. When the crystal size increases the chemical capacitance of the device
increases [72].

Kim et al. reported that the normal structure with cp-TiO2 and spiro-OMeTAD
demonstrates severe I-V hysteresis, whereas the inverted planar layout with
(PEDOT:PSS) and (PCBM) is a typical hysteresis-free structure showing almost no
capacitive current at room temperature [74]. Also, they revealed that replacing both cp-
and spiro-OMeTAD with other selective contact layers substantially reduce the
capacitance along with a considerable shift of the electrode polarization domain toward
higher frequency [74].

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 Chapter 2 Perovskite materials and Solar cells design

2.11.2 Degradation of perovskite materials

Degradation of perovskite materials is one of the most issues that affect existence,
availability and commercialization of PSCs. Stability is evaluated as per standard of
International Electrotechnical Commission damp heat test (at 85° , 85% relative
humidity). Stable devices can maintain its performance with less than 10% reduction of
PCE after 1000 ℎ of exposure while PSCs can maintain only 80% of initial efficiency after
500 ℎ [75].

The physical origin of the hysteresis was attributed to several processes which are
discussed in following paragraphs and illustrated in Figure 2.22.

Perovskite decomposition represents electrolysis process producing ,

and (Figure 2.22). Where, oxidation of anions (free or incorporated with )
liberates molecular iodine which can be trapped in the form of triodide ( ) or partially
evolve from the films (Equation 2.1). Simultaneously, reduction of hydrogen ions
(individual or incorporated with ) leads to releasing molecular hydrogen (Equation
2.2) [47].

Anode process:

2( )∗ ⟶2 + +2 2.1

Cathode process:

2( )∗ +2 ⟶2 + 2.2

Overall reaction:

2 ⎯⎯⎯⎯⎯⎯⎯ + +2 2.3

Furthermore, moisture has been proposed to be one of the most prominent factors
for perovskite degradation. perovskite films usually change color from dark
brownish to yellow when exposed to air, indicating degradation and , and
were formed; in the presence of oxygen, could further degrade to iodine ( ) and

41
 Chapter 2 Perovskite materials and Solar cells design

by a redox reaction. Other factors were examined, such as oxygen, light illumination,
and thermal stress [76].

∗
Superoxide ( ) generated through electron transfer from to attacks
the perovskite absorber leading to the formation of methylamine ( ), lead iodide,
iodine, and water as degradation products [77]
[ . Under light illumination, could
further decompose to generate [76]. Also, during annealing at 85 ℃ for a
perovskite sample, it was found that decomposed to and [76].

Despite the solutions

ns used to encapsulate and isolate the material from moisture,
the material was still degrading. These studies strongly suggest that there could be a
self-degradation
degradation pathway for perovskite solar cells [76].

Wang et al. reported that at room temperature the

the relatively high vapor pressure of
, is expected to diffuse easily to non-degraded
non degraded perovskite regions just when it is
generated. could also induce degradation of other iodide based perovskites (such as
and . . ), suggesting the generality of -induced
induced degradation [[76].

Figure 2. 22:
22 Hysteresis factors of perovskite materials.

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 Chapter 3

Study and optimization of MAPbI

perovskite solar cell
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

3.1 Introduction

Studying the behavior of real device or an imaginary system and analyzing it using
computer application is based on mathematical model adapted to the studied system.
Numerical modeling is now widely agreeable practice by scientific community. It
simplifies understanding work principles of solar cells and also helps identification of
the major parameters which affect the performance of the cell [78]. It also helps to
reduce processing cost and time spent on solar cell device fabrication by providing
useful information on how to vary the production parameters to improve the device
performance.

Over the years several modeling tools specific to thin-film PV devices have been
developed. A number of these tools have reached a mature status and are available to
the PV community. Among them:

 AMPS (Analysis of Microelectronic and Photonic Structures), It is a

one-dimensional (1D) device physics code which is applicable to any two terminal
device including photovoltaic device. AMPS was developed by Prof. Stephen
Fonash and a number of his students at The Pennsylvania State University [79].
 wxAMPS is an update of AMPS. The user interface of wxAMPS uses a cross-
platform library and provides quick data entry and improved visualization. It is designed
at the University of Illinois at Urbana Champaign, in collaboration with Nankai
University of China [80].
 PC1D (Personal Computer One Dimensional) is very used in the simulation of
solar cells. This software was developed in Australia at the university South Wales of
Sydney. It allows simulating the behavior of photovoltaic devices based on
semiconductor by respecting to one-dimensional (axial symmetry) [81].
 AFORS-HET (Automat For Simulation of Heterostructures)is a one dimensional
numerical computer program for modeling multi layer homo- or Heterojunction solar
cells as well as some common solar cell characterization methods [79].
 ASA(Advanced Semiconductor Analysis) is designed for the simulation of devices
based on amorphous and crystalline semiconductors. It has been developed by the
group of Prof. Miro Zeman at the Technical University of Delft in the Netherlands [79].

44
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

 SCAPS-1D (Solar Cell Capacitance Simulator)is a one-dimensional solar cell

simulation program developed at the Department of Electronics and Information
Systems (ELIS) of the University of Gent, Belgium [82].

3.2 The basics of SCAPS-1D

SCAPS-1D has been developed to simulate the operation of thin-film solar cells. SCAPS is
originally developed for cell structures of the CuInSe2 and the CdTe family. Several
extensions however have improved its capabilities so that it is also applicable to
crystalline solar cells (Si and GaAs family) and amorphous cells (a-Si and
micromorphous Si) [82]. SCAPS is a Windows-oriented program, which is opened with
the ‘Action Panel’ (Figure3.1).

Figure 3. 1: The SCAPS start-up panel: the Action panel or main panel.

3.2.1 Definition of the problem

By clicking the button set problem (Figure 3.2.a) in the action panel, we can chose load
in the lower right corner of the new opened panel (Figure 3.2.b) to select an example to
study which can be modified in the cell properties [82].

45
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

Figure 3. 2: (a) Defining problem panel and (b) selecting an example.

3.2.2
.2 Define the working point

The working point specifies the parameters

parameters which are not varied in a measurement
simulation, and which are relevant to that measurement (Figure 3.3). Thus:
 Temperature ( ): Necessary for all measurements. ( ), ( ), the thermal
velocities, the thermal voltage and all their derivatives are the only variables
which have anexplicit temperature dependence. These parameters must be
inserted manually for each temperature [82].
 The voltage : is unnecessary in − and − simulation, but it is taken as the
dc-bias voltage in − simulation and in (l) simulation. SCAPS always starts
at 0 , and proceeds at the working point voltage in a number of steps that also
should be specified [82
82].
 The frequency : is neglected in − , (l) and − simulation. But in −
measurement is taken into account [82].
[
 The illumination: is used for all measurements. For the (l) measurement, it
determines the
he bias light conditions. The basis settings are: dark or light, choice
of the illuminated side, choice of the spectrum. The default is one sun (
2
= 1000 / ) illumination with the ‘air mass 1.5,, global’ spectrum, but there is
a large choice of monochromatic
monochromatic light and spectra for specialized simulations
[82].

Figure 3. 3: Define the working point.

46
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

3.2.3 Selection of the measurement(s) to simulate

In the action-part
part of the Action Panel, the following measurements: − , − , −
and (l) can be simulated [82].
[ ]. Adjust if necessary the start and end values of the
argument, and the number of steps (Figure 3.4).

Figure 3. 4: Select the measurement(s) to simulate.

3.2.4 Starting the calculation(s)

ation(s)

By clicking the button calculate: single shot in the action panel. The Energy Bands Panel
opens, and the calculations start. Meanwhile, SCAPS offers a free movie how the
conduction and valence bands, the Fermi levels and the whole caboodle are evo
evolving
[82].

3.2.5 Displaying the simulated curves

After the calculation(s), SCAPS switches to the Energy band panel (or the AC
AC-band
panel) in which the band diagrams, carrier densities, current densities are shown. The
results (buttons save graphs, show data
data (the numbers are shown on screen) or save data
(the numbers are saved to a file). One of specialized output panels can be switched
(Figure 3.5) [82].

47
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

Figure 3. 5: Results panels.

Simulation procedure using SCAPS software

software can be summarized by the scheme
presented in Figure 3.6.

Figure 3. 6:
6 Simulation procedure using SCAPS software.

3.3 Solar cell definition

Definition of the solar cell structure is done using

using graphical user interface (F
(Figure 3.7.a).
Layer, contact and interface properties can be edited in solar cell definition panel.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

3.3.1
.1 Editing a solar cell structure

The ‘Solar cell definition’ panel resulting in setting problem panel allows to create or
edit solar cell structures and to save or load those from definition files [[82].Layer
properties are defined in layer panel where, it is impossible to define unrealistic
situations (Figure 3.7.b).

Figure 3. 7: Definition solar cell structure panel.

3.3.2 Reference
ference Conventions for Illumination, Voltage and Current

The illuminated side and the applied voltage and current are optional as it is shown in
Figure
igure 3.8.Internally in SCAPS, only the default reference is used (voltage applied at the
left contact, current
nt reference arrow from left to right, resulting in a reference as a
consumer) [82].

Figure 3. 8: Reference Conventions for illumination, voltage and current.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

3.3.3 Contacts

The front and back contacts properties can be set by ‘contact properties panel’ (Figure
3.9). The metal work function Φ (for majority carriers) can be inputted. However, the
option “flat bands” can be chosen.
chosen In this case, SCAPS calculates for every temperature
the metal work function Φ in such a way that flat band conditions prevail. At the
contacts a (wavelength dependent) reflection/transmission can be set
set. These can be set
either as a constant value (wavelength independent) or as a filter file. These filter files
are standards provided with SCAPS
SCAPS installation or can be constructed [[82].

Figure 3. 9: Contact properties panel.

3.3.4
.4 The optical absorption constant a(l) or a( n) of a layer

The optical absorption constant determines to what extent a particular wave length
penetrates into material. Light is poorly absorbed in the material when the absorption
coefficient is low and vice versa. Since the absorption coefficient cu
curve of
semiconductors has a sharp edge, the light with energy below the band gap will not be
absorbed and the electron can’t be excited to the conduction band [5].
[

The absorption of such layer can be set from a file or from a model used by SCAPS
simulator (Figure 3.10). When it is set from a model, the absorption coefficient a(l) is
given by Equation 3.1

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

1
(ℎ ) = 1 + 1 . −1 3.1
1

ℎ is the photon energy and the band gap. 1 and 1

are the model parameters (have
the dimension of absorption constant (1/
( or 1/ ) regardless of the value of the
exponent ) [83].

Figure 3. 10: Optical absorption constant of a layer.

3.4 Principal of Numerical Simulation

Researches in physics of devices based on semiconductors led to the realization of a

mathematical model. This model is capable to operate in virtually any device based on
semiconductor. It consists of a fundamental caboodle of equations which gather the
electrostatic potential and density of charge carriers in well specified d
domain of
simulation [28].
]. These equations are derived from Maxwell equations [[84].

3.4.1 Poisson’s equation

Poisson equation which presents the relationship between electric field of a p

p-n junction
( ) and the space charge density (ρ) is given by Equation 3.2:

( E) = 3.2

Where, the electric field is given

give by:

=− ( ) 3.3

From Equations 3.2 and 3.3:

2
+ −
2 =− =− =− [ − + ( )− ( )± ( )] 3.4

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

Where, is the electrostatic potential, is elementary charge, is the electric

permittivity ( = 0 , 0 is the vacuum permittivity and is the substance
+ −
permittivity), (p) is the electron (hole) density, ( ) is the density of ionized donors
(acceptors) and is the possible defect (Acceptor or donor) density [85].

3.4.2 Continuity equations

The continuity equations describe the variation speed of density of carriers in function
of time. These equations are in two folds, electrons and holes equations. And they are
given by Equation .3.5 and 3.6 [28]:
For electrons:
1
= + − 3.5

For holes:
1
=− + − 3.6

and are generation rates of electrons and holes by external agents. and are
recombination rates (interne) of electrons and holes, respectively. and are current

density of electrons and holes [85].

3.5.3 Carrier transport equations

There are two main carrier transport mechanisms in semiconductor devices which are
Drift and Diffusion. This movement of charge carriers generates current in the device.
Drift current is the current generated by the movement of charge carriers due to an
applied electric field (first term in Equations 3.7 and 3.8), and diffusion current is due
the diffusion of charge carriers (second term in Equations 3.7 and 3.8) [28]:

= + 3.7

= − 3.8

Where, , , and are the coefficient of diffusion and mobilities of electrons and

holes, respectively [28].

In this study, a one-dimensional modeling of conventional and inverted perovskite

solar cells was performed using SCAPS simulator (version 3.3.07).This work is focused
on designing a 3 3 3 perovskite based solar cell and extracting its output
52
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

parameters. Moreover, it studied the effect of changing electron and hole transport
layers (ETL and HTL, respectively), on the performance of the cell. We did not take into
account the effects of reflection on the front and back surfaces, series resistance and
shunt resistance. The simulation is performed at AM1.5G solar spectrum with an
2
incident power density of 100 / at room temperature (300 ).

3.6 Device structure

The designed solar cell using SCAPS simulator is illustrated in Figure 3.11. Where the
chosen structures are n-i-p and p-i-n planar architectures, and the input parameters of
each layer are summarized in Table1. With 0.05 µm of n type electron transport layer
(Indium tin oxide ) and 0.05µm of p type hole transport layer [ :
(Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate))] and 0.4 µm of intrinsic
perovskite ( 3 3 3 ). The conventional (n-i-p) and converted (p-i-n) solar cells are
represented in Figure 3.11with FTO/ITO/Perovskite/PEDOT:PSS/Au and
FTO/PEDOT:PSS/Perovskite/ITO/Au configurations, respectively.

Figure 3. 11: Solar cell structures (n-i-p at left and p-i-n at right).

3.7 Absorption coefficient of MAPbI perovskite material

According to P. Löper and co-workers [86], the most prominent feature in the optical
spectra of MAPbI perovskite materials is the well known absorption edge at ∼ 1.55 ,
seen as a sharp drop in transmittance at a wavelength of ∼ 800 . The absorption
coefficient of perovskite material was extracted from [86] and plotted in Figure 3.12.

53
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

a (x107m-1) 4

0
300 400 500 600 700 800 900 1000
l (nm)

Figure 3. 12: Absorption coefficient of perovskite.

3.8 The layers input parameters

The input parameters of ITO are extracted from the work of Pandey et al.[87] while, the
perovskites and PEDOT:PSS parameters are taken from the work of Minemoto et al. [88]
and Mandadapu et al. [89], respectively. These parameters are summarized in Table 3.1:

Parameter Term ETM (ITO)[87] Perovskite[88] HTM (PEDOT:PSS)[89]

d(µm) Thickness 0.05 0.4 0.05

Eg(eV) Band gap 3.65 1.55 2.20

χ (eV) Affinity 4.8 3.9 2.9

r Permittivity 8.9 6.5 3.00

Effective density of
Nc (cm-3) 5.8 ×1018 2.2 ×1018 2.2 ×1015
states at CB
Effective density of
Nv (cm-3) 1 ×1018 1.8 ×1019 1.8 ×1018
states at VB
µn (cm2/V s) Mobility of electrons 10 2 2 ×10−2
µp (cm2/V s) Mobility of holes 10 2 2 ×10−4
Density of n-type
Nd (cm-3) 1 ×1020 5.21 ×109 0.0
doping
Na (cm-3) Density of p-type 0.0 5.21 ×109 3.17 ×1014

54
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

doping

Nt (cm-3) Density of defects 1 ×1019 2.5 ×1013 1 ×1015

Table 3. 1: Device parameters used in simulation.

3.9 MAPbI Perovskite Solar cell performance

As mentioned in the previous section, the one-dimensional modeled n-i-p and p-i-n
planar perovskite solar cells were simulated under AM1.5G solar spectrum with an
2
incident power density of 100 / at room temperature (300 ). The extracted
current-voltage characteristic was calculated from 0 to 1.3 and the quantum
efficiency from 360 to900 . Effects of reflection on the front and back surfaces,
series resistance and shunt resistance were neglected.

3.9.1 The band gap energy diagram at equilibrium

The band diagrams of the n-i-p and p-i-n PSC at equilibrium are shown in Figures3.13. In
the conventional PSC, an energy barrier of 0.9 is present between the conduction
band minimum ( ) of the ITO and the lowest unoccupied molecular orbital (LUMO) of
the absorber CH3NH3PbI3 material, and an offset about 0.35 between the highest
occupied molecular orbitals (HOMO) of both absorber material and HTL. However, in
inverted PSC, an offset about 0.34 formed between of HTL and HOMO of the
absorber material and an energy barrier of 0.76 is between of ETL and LUMO of
the absorber.These bands alignment led to poor performance of the modeled solar cells.

55
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

2 (a)

ETL HTL
1
Ef
Energy (eV)
0
Ec

PEDOT:PSS
-1
MAPbI-Perovskite
ITO
-2

-3

-4 Ev

0.0 0.1 0.2 0.3 0.4 0.5

Position (mm)

2 Ec (b)
1 HTL
ETL
Energy (eV)

Ef
0
Ev
-1
PEDOT:PSS

ITO

MAPbI-Perovskite
-2

-3

-4

0.0 0.1 0.2 0.3 0.4 0.5

Position (mm)

Figure 3. 13: Energetic band diagram of: (a) conventional n-i-p and (b) inverted p-i-n;
perovskite solar cell.

3.9.2 The Current density-Voltage characteristic

The obtained current density-voltage characteristic curves and external quantum

efficiency are shown in Figures 3.14 and 3.15, respectively. The extracted electrical

56
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

output parameters of the conventional solar cell are inserted in Figure 3.15. The cell
exhibited a lightly low fill factor (~50.09 %)but a good short circuit current
2
=21.87 / and a remarkable open circuit voltage =1.27 (compared to the
band gap energy 1.55 of the absorber layer). These extracted parameters gave a
power conversion efficiency of ~13.94 %.

A suitable quantum efficiency of ~70 − 87 % is obtained in the visible range and is

2
related to the good current density =21.87 / .

20
Current density (mA/cm )
2

15 Voc 1.27 V
2
Jsc 21.87 mA/cm
FF 50.09 %
10  13.94 %

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Voltage (V)

Figure 3. 14: Current density- Voltage characteristic of conventional PSC.

57
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

100

Quantum efficiency (%) 80

60

40

20 Visible light range

0
400 500 600 700 800
Wave length (nm)

Figure 3. 15: Device quantum efficiency characteristic of conventional PSC.

For the inverted perovskite solar cell, the extracted electrical output parameters are
inserted in Figure 3.16. Also, this cell exhibited a low fill factor (~39.57 %) but a good
2
short circuitcurrent =21.83 / and a notable open circuit voltage =1.27 .
These extracted parameters gave a power conversion efficiency of ~10.99 %.

Particularly striking in both solar cells is the remarkably high open-circuit voltage
(up to 1.27 ) compared with its bandgap (∼ 1.55 ). Quite generally, the
bandgap-voltage offset {( / )− }, where is the elementary charge, is a useful
measure to assess the electronic quality of the absorber in the solar cell [90]. The small
difference between / of the absorber material and of the corresponding solar cell
indicates a low non-radiative recombination and long diffusion lengths of charge
carriers due to the low exciton bounding energy [32].

An acceptable quantum efficiency of ~62 − 74 % is obtained in the visible range

(Figure 3.17).

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

25

Current density (mA/cm2)

20

15
Voc 1.27 V
10 Jsc 21.83 mA/cm2
FF 39.57 %
5  10.99 %

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Voltage (V)

Figure 3. 16: Current density- Voltage characteristic of inverted PSC.

80
Quantum efficiency (%)

70

60

50

40

30

20

10 Visible light range

0
400 500 600 700 800
Wavelength (nm)

Figure 3. 17: Device quantum efficiency characteristic of inverted PSC.

The low doping density of : (1014 −3

) lead to an increased depletion
region at HTL of the device (which is a thin layer).This phenomena produces a bulk
resistance of the p type material and an interfacial contact resistance between rear
contact and the p type layer.

59
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

This effect can be observed by the deviation of the J-V curve from the quadratic shape of
an ideal solar cell J-V characteristic.
However, the strong acidity of PEDOT:PSS used in solar cells as an (HTL)
material can cause the degradation of the close perovskite or electrode and lead to
inferior perovskite crystal quality [41-91]. Furthermore, the hygroscopic PEDOT:PSS
attracts ambient humidity and enables its diffusion under the electrodes. The release of
this absorbed water towards the highly reactive metal cathode leads to the rapid
oxidation of the cathode [92].
On the other hand, the ITO has disadvantages should be taken into the
consideration; the price, the brittleness (which is an issue for flexible devices) and the
possibility of indium’s diffusion into organic materials. These drawbacks are strong
reasons to find alternative transparent electron transport materials [93].
As a solution for these issues, alternatives of the ETL and the HTL are studied to
improve the performance of these solar cells.

3.10 Effect of electron transport layer

In this section the aim is to obtain a better performance of the perovskite solar cell with
n-i-p and p-i-n structures and to determine suitable materials working as an electron
and hole transport layers (ETL and HTL, respectively).

3.10.1 Input parameters of ETL materials

In this part, a 0.05 µ of organic fullerene derivative [6,6]-phenyl-C61-butyric acid

methyl ester ( ), indium gallium zinc oxide ( ), tin dioxide ( 2 ), titanium
dioxide ( 2) and zinc oxide ( ) are used as an ETL, respectively.; and compared to
the solar cell with window layer. The input parameters of these materials are
summarized in Table 3.2.

Parameters [94] [95] [89] [88] [87]

( ) 2 3.05 3.5 3.2 3.3
( ) 3.9 4.16 4 3.9 4.1
3.9 10 9 9 9
−
( ) 2.5 ×1021 5 ×1018 2.2 ×1017 1 ×1021 4 ×1018

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

−
( ) 2.5 ×1021 5 ×1018 2.2 ×1016 2 ×1020 1 ×1019
( / ) 0.2 15 20 20 100
( / ) 0.2 0.1 10 10 25
−
( ) 2.93 ×1017 1 ×1018 1 ×1017 1 ×1019 1 ×1018
−
( ) 0.0 0.0 0.0 1.0 1 ×105
2 ×1017
Donor,
1 ×1015
−
( ) 1 ×1015 1 ×1015 1 ×1015 uniform
neutral
1.7 above

Table 3. 2: Electron transport materials parameters for simulation.

3.10.2 Current density- Voltage characteristic

The obtained J-V characteristic and quantum efficiency of n-i-p PSC are shown in Figures
3.18 and 3.19 respectively; and the extracted output parameters are summarized in
Table 3.3.

According to the obtained results for the conventional solar cell, the material
2
presents the lowest current density ~18.47 / compared to the other materials
and lowest quantum efficiency ( ). This performance may be due to its low electron
and holes mobilities (2 ×10−1 2
/ ) which affect the charge collection. On the other
hand, the exhibited the highest fill factor ( ~ 74.98 %) and a high =
1.26 .These parameters lead to a power conversion efficiency of 17.39 %.

The indium gallium zinc oxide ( ) and tin dioxide ( 2) showed acceptable and
comparable improvement in the efficiency (19.51% and 19.88%, respectively) and a
high QE. It is known that the power conversion efficiency is defined by:

=( × × )⁄ 3.9

Where is the incident power, and both of and 2 have almost the same
values of open circuit voltage, short circuit current density and fill factor ( ~ 1.27 ,
⁄ 2
~ 21 and ~71%). These close values led to conversion efficiency of
about 19%.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

Zinc oxide ( ) and titanium dioxide ( 2) seem to be the best candidates for
ETL. With an optimum compromise between the three extracted output parameters ,
, , the and 2 ETL give a better conversion efficiency of about 20%. This is
probably due to the adequate bands alignment between the conduction band of and
2 and the LUMO of the perovskite as presented in Figure 3.22. Also, noting that some
of their input parameters seem to be similar. For example, mobility of electrons is
2 2
greater in zinc oxide than in titanium dioxide (100 / and20 / , respectively).
But, this has been compensated by the defects density which is greater in zinc oxide than
in titanium dioxide (2 ×1017 −3
and 1 ×1015 −3
, respectively).

25
Current density (mA/cm )
2

20

15 ITO
PCBM
10 IGZO
SnO2
5 TiO2
ZnO
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Voltage (V)

Figure 3. 18: Effect of ETL layer on Current density-Voltage characteristic for n-i-p PSC.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

100
Quantum efficiency (%)
80
ITO
60
PCBM
40 IGZO
SnO 2
20 TiO 2
ZnO
0
400 500 600 700 800
Wavelength (nm)

Figure 3. 19: Effect of ETL on quantum efficiency for n-i-p PSC.

Parameter ITO PCBM IGZO SnO2 TiO2 ZnO

( ) 1.27 1.26 1.27 1.27 1.27 1.27
(mA/cm2) 21.87 18.47 21.59 21.89 21.36 21.78
(%) 50.09 74.98 71.08 71.43 74.66 74.53
(%) 13.94 17.39 19.51 19.88 20.26 20.64
Table 3. 3:Effect of ETLs on output parameters for n-i-p PSC.

As for the inverted structure, all the ETL materials exhibited close values of open
circuit voltages ( ~1.27 )and current densities ( ~21.9 / 2) but different
fill factors and power conversion efficiencies (Figure 3.20). Obtained output parameters
were summarized in Table 3.4. The material showed the lowest power conversion
efficiency of 16.3%, and lowest quantum efficiency ( ) (Figure 3.21).

2, , and 2 showed acceptable and comparable improvement in the

efficiency (~19.20%) and a high .

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

25

Current density (mA/cm2)

20

15 ITO
IGZO
SnO2
10 PCBM
ZnO
5 TiO2

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Voltage (V)

Figure 3. 20: Effect of ETL layer on Current density-Voltage characteristic for p-i-n PSC.

100
Quantum efficiency (%)

80

60
ITO
IGZO
40
SnO2
PCBM
20
ZnO
TiO2
0
400 500 600 700 800

Wave lentgh (nm)

Figure 3. 21: Effect of ETL on quantum efficiency for p-i-n PSC.

Figure 3.20 shows a decline in quantum efficiency at wave lengths < 400
for the conventional solar cell. This may be explained by a considerable recombination
at the front surface (i.e. high defects density 1017 −3
) which affects the "violet and
ultraviolet" portion of the spectrum, where charge carriers are not able to move into an

64
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

external circuit. But this decline is not existed in inverted solar cell’s
cell’s quantum efficiency
because it is in the back of the device.

Parameter
( ) 1,27 1,27 1,27 1,27 1,27 1,27
(mA/cm2) 21,83 21,89 21,89 21,93 21,89 21,89
(%) 39,57 58,55 61,69 61,86 61,79 61,90
(%) 10,99 16,30 17,16 17,20 17,20 17,21
Table 3. 4:: Effect of ETLs on output parameters for p-i-n
p PSC.

Figure 3. 22: Bands alignment between ETL materials and perovskite.

Therefore,
erefore, in conventional and inverted PSC the appropriate materials that could be
used as an electron transport layer are titanium dioxide (TiO2) and zinc oxide (ZnO).

3.11 Effect of the hole transport layer

After determining the optimum materials working as window and electron transport
layer which are 2 and , the hole transport layer was changed to determine the
appropriate p type material working as a hole transporter. A / / /
/ and / / / / configurations using than 2 as an
ETL were optimized. A number of organic and inorganic materials are investigated as
HTL. A 0.05µ of: 3 [poly(3
[poly(3-hexylthiophène-2,5-diyl)], − (2,2’,7,7’-

65
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene)] , [Copper(I)
thiocyanate], [Copper(I) iodide] and [Nickel (II) Oxide] are used as a hole
transport materials.

3.11.1 Input parameters of HTL materials

The input parameters of these organic and inorganic materials are summarized in Table
3.5.

Parameter − [88] [96] [97] [98] [48]

( ) 3.00 1.85 2.98 3.6 3.4
( ) 2.45 3.1 2.1 1.46 1.9
3.00 3.4 6.5 11 10
−
( ) 1 ×1019 1 ×1022 2.8 ×1019 1.6 ×1019 1.7 ×1019
−
( ) 1 ×1019 1 ×1022 1 ×1019 1.1 ×1019 2.5 ×1021
( / ) 2 ×10−4 1 ×10−4 1.7 ×10−4 50 1 ×10−4
( / ) 2 ×10−4 1 ×10−3 2 ×10−4 50 1 ×10−1
− 0.0 0.0 0.0 0.0 0.0
( )
−
( ) 2 ×1018 3.17 ×1013 1 ×1018 1.8 ×1018 1 ×1018
−
( ) 1 ×1015 1 ×1014 1 ×1015 1 ×1014 1 ×1014
Table 3. 5: Input parameters of the proposed HTL materials.

3.11.2 Current density-Voltage characteristic

Since the best performance is obtained for conventional PSC based on ZnO as an ETL, the
suitable materials used for conventional and inverted PSC as an HTL are studied in this
section.

By using 0.05 µ of zinc oxide as an ETL in conventional and inverted PSC then
changing hole transport materials, the obtained J-V characteristic curves and quantum
efficiency of n-i p PSC are presented in Figures 3.23 and 3.24, respectively. The obtained
J-V characteristic curves and quantum efficiency of p-i-n PSC are presented in Figures
3.25 and 3.26, respectively.

The J-V curves show a significant improvement of the n-i-p and p-i-n PSCs
performance. Noting that the and were not affected. Also, HOMO or calculated

66
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

from ( = + ) indicate that there are good bands alignment between HOMO of
both of HTLs and absorber layer (Figure 3.27).

For the conventional PSC, the quantum efficiency is not affected by modifying HTL
because the optical absorption of the hole transport layer is negligible since it is located
in the back side of the device. Unlike the quantum efficiency of inverted PSC which is
affected by changing HTL materials. This goes back to the layer acting as a window that
controls the transmittance of light to the active layer.

parameter : −
( ) 1.27 1.27 1.27 1.27 1.27 1.27
( / ) 21.89 21.89 21.87 21.89 21.89 21.89
(%) 74.05 74.51 79.58 83.12 83.00 83.70
(%) 20.61 20.74 22.13 23.14 23.10 23.30
Table 3. 6: Effect of the different HTL proposed materials on output parameters for n-i-p PSC.

The lowest power conversion efficiency is achieved in both solar cells based on
P3HT as HTL, because of the difference between the HOMOs reached 0.5 .

It is observed that, exhibited the best efficiency ( ~ 23.30% ) even if

− exhibits the best bands alignment as shown in Figure 4.16. This is due
to being holes mobility in − is much smaller than holes mobility in
.

parameter : 3 −
( ) 1.27 1.26 1.27 1.27 1.27 1.27
( / ) 21.89 21.89 21.89 21.88 21.89 21.89
(%) 61.78 66.55 83.15 83.08 83.17 83.73
(%) 17.12 18.39 23.12 23.13 23.16 23.31
Table 3. 7:Effect of the different HTL proposed materials on output parameters for p-i-n PSC.

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Chapter 3 Study and optimization of MAPbI perovskite solar cell

25

Current density (mA/cm )

2 20

15 P3HT
PEDOT:PSS
10 Spiro-OMeTAD
CuI
NiO
5
CuSCN

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Voltage (V)

Figure 3. 23: Effect of HTL on J-V characteristic using ZnO as an ETL of n-i-p PSC.

100
Quantum efficiency (%)

80
P3HT
60 PEDOT:PSS
Spiro-OMeTAD
40 CuI
NiO
20 CuSCN

0
400 500 600 700 800
Wave length (nm)

Figure 3. 24: Effect of HTL on quantum efficiency using ZnO as an ETL of n-i-p PSC.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

25

Current density (mA/cm2)

20

15
PEDOT:PSS
P3HT
10 Spiro-OMeTAD
NiO
5 CuI
CuSCN
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Voltage (V)

Figure 3. 25: Effect of HTL on J-V characteristic using ZnO as an ETL of p-i-n PSC.

100
Quantum efficiency (%)

80

60 PEDOT:PSS
P3HT
40 Spiro-OMeTAD
NiO
20 CuI
CuSCN
0
400 500 600 700 800
Wave length (nm)

Figure 3. 26: Effect of HTL on quantum efficiency using ZnO as an ETL of p-i-n PSC.

When is used as HTL. The solar cell exhibits a conversion efficiency of

~ 23.30 % and a high fill factor of ~83.70 % as shown in Table 3.7.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

Figure 3. 27: Bands alignment between HTL materials and perovskite.

3.12 Optimization of perovskite solar cell

Since in the previous section it was found that 2 is a good candidate like as ETL
material, we replace by TiO2 while preserving as HTL. An / /
/ / and / / / / solar cells are
modeled. The band energy diagram at equilibrium of the n-i-p
n and p
p-i-n PSC sare
presented in Figures 3.28 and 3.29.
3.

3 Ec

2
MAPbI-Perovskite
Energy (eV)

1 CuSCN

0 Ef
Ev
-1 TiO2

-2

-3

0.0 0.1 0.2 0.3 0.4 0.5

Thickness (mm)

Figure 3. 28:: Energetic band diagram of / / / / cell.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

2 CuSCN
MAPbI-Perovskite
Energy (eV)
1

0 E
Efc
-1
TiO2
-2

-3 Ev
0.0 0.1 0.2 0.3 0.4 0.5
Position (mm)

Figure 3. 29: Energetic band diagram of / / / / cell.

Tables 3.8 and 3.9 summarize the resulted output parameters in case of 2 as ETL.
An enhancement in solar cells performance comparing to the case of using ZnO as ETL
about 0.06 % in power conversion efficiency and about 0.34 % in for n-i-p PSC and
0.08% in power conversion efficiency and about 0.39 % in for p-i-n PSC.

Parameter
( ) 1.27 1.27

( / ) 21.89 21.89

(%) 83.70 84.04

(%) 23.30 23.36

Table 3. 8: The output parameters of conventional PSC in case of then as ETL

Parameter
( ) 1.27 1.27

( / ) 21.89 21.89

(%) 83.73 84.12

(%) 23.30 23.38

Table 3. 9:The output parameters of inverted PSC in case of then 2 as ETL.

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 Chapter 3 Study and optimization of MAPbI perovskite solar cell

The good performance of the modeled solar cell using 2 as ETL and as
HTL is associated with the good alignment of the highest occupied molecular orbital
(HOMO)level of the with the valance band of 3 3 3. Moreover, the energy
bands of ETL satisfy the following conditions: (1) Its conduction band (CB) lies under
the CB of the active perovskite layer to extract electrons which reach the interfaces
afterward. (2) Its valence band (VB) lies much under the VB of the perovskite to reject
the holes. (3) ETL VB has a large difference compared to the perovskite VB in order to
reject holes, because ETL has a wider band gap (3.2 ). (4) The electron mobility in ETL
2
is sufficiently high (~20 / . ). Similar requirements can also be deduced for HTL.

3.13 Optimization of perovskite thickness

Thickness of a material plays a major role in solar cells performance. So, the active layer
thickness is varied from 0.3 to 1.2 for both n-i-p and p-i-n PSC. Figures 3.30 and
3.31 show J-V characteristics and output parameters affected by variation of perovskite
thickness for the n-i-p PSC. Figures 3.32 and 3.33 show J-V characteristics and output
parameters affected by variation of perovskite thickness for the p-i-n PSC.

For both solar cells, it is observed that increasing the absorber thickness leads to
increasing in short circuit current density and decreasing in both open circuit voltage
and fill factor .

As it is indicated in Figure 3.31, increasing the thickness from 0.3 to 0.9 led to
increasing in power conversion efficiency , which is related to increasing of the short
circuit current density . At the thickness 1 of perovskite layer, the power
conversion efficiency reached its highest value 25.02 % and 25.11 % for conventional
and inverted PSC, respectively. After, it started in decreasing fairly.

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Chapter 3 Study and optimization of MAPbI perovskite solar cell

25

Current density (mA/cm2)

Perovskite thickness
20 0.3 m
0.4 m
0.5 m
15
0.6 m
0.7 m
10 0.8 m
0.9 m
5 1 m
1.1 m
1.2 m
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Voltage (V)

Figure 3. 30: Effect of perovskite thickness on J-V characteristic of n-i-p PSC.

1.29
1.28 25

1.27 24
1.26
23
Voc

Jsc

1.25
1.24 22
1.23
21
1.22
1.21 20
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3
Thickness (mm) Thickness (mm)
25.5
84.5
25.0
84.0 24.5

83.5 24.0
FF

23.5
83.0
23.0
82.5
22.5
82.0 22.0

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3
Thickness (mm) Thickness (mm)

Figure 3. 31: Effect of perovskite thickness on output parameters for n-i-p PSC.

73
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

When the thickness of the absorber increases, this will allow the longer wavelength
of the illumination to be absorbed leading to increasing the absorption of light in
perovskite layer, which contributes to the generation of electron-hole pairs. The open-
circuit voltage decreases, this variation is due to the bulk recombination of the
photogenerated carriers.
Current density (mA/cm2)

0,3 m
20
0,4 m
0,5 m
0,6 m
0,7 m
0,8 m
0,9 m
1,0 m
1,1 m
1,2 m
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Voltage (V)

Figure 3. 32: Effect of perovskite thickness on J-V characteristic of p-i-n PSC.

74
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

1.29
1.28 25

1.27 24
1.26
Voc

23

Jsc
1.25
1.24 22
1.23
21
1.22
1.21 20
0.2 0.4 0.6 0.8 1.0 1.2 0.2 0.4 0.6 0.8 1.0 1.2

Thickness (mm) Thickness (mm)

25.5
84.5
25.0

84.0 24.5
24.0
83.5
FF

83.0
 23.5
23.0

82.5 22.5
22.0
82.0
0.2 0.4 0.6 0.8 1.0 1.2 0.2 0.4 0.6 0.8 1.0 1.2

Thickness (mm) Thickness (mm)

Figure 3. 33: Effect of perovskite thickness on output parameters for p-i-n PSC.

Increasing the permittivity of the material ( ~ 6.5) (leading to low electron–hole

binding energy) [99] enhanced the charge generation. The possibility of charge
separation within the absorber itself and long charge carrier diffusion lengths
( , ~1 ) can explain the good performance of perovskite solar cell. At width ( )
more than 1 ( ≥1 ) in the absorber layer, there is a bound to occur
recombination of charge carriers generated in the absorber. In that case, the charges
recombine before they get extracted at the electrodes.

So, we optimized the thickness of perovskite layer to µ in our solar cells. The
performance of modeled solar cells improved. For n-i-p PSC, the conversion efficiency
2
reached 25.02 % and short circuit current density ( ) increased to24.70 / .
While the conversion efficiency reached 25.11 % and short circuit current density ( )
2
increased to24.92 / for p-i-n PSC.

75
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

3.14 Effect of interfacial defects

In this part, we briefly introduce the effect of defects on the device performance of
perovskite solar cells. The performance of perovskite solar cells can be altered (in most
case negatively) by defect states [100]. Deposition process of perovskite solar cell can
induce a formation of defects mainly located at surface (or interface) and grain
boundaries [101]. These defects results from the interactions of the precursor solvents
with HTL and ETL, i.e. the lack of stochiometric compositions at the surfaces of grains
and the sublimation of organic molecules during the thermal annealing process could
leave defects [101]. Existence of impurities might cause point defects which could form
recombination centers.

Substitution defects (I atom occupying a ( 3 3) site)located at ca.

−0.75 below the conduction band is the main deep defect of perovskite films
fabricated by sequential deposition method [101].

Another type of defects was reported by Fan Zhang and co-workers[99], who found
that performance hysteresis of perovskite solar cells, is due defects in bulk of both of
perovskite and 2 and Perovskite/ 2 interface,which affect the electrons injection
and electron-hole recombination at the interface. The oxygen vacancies exist naturally in
commercial and no treated crystalline 2 [100-101].

Consequently in this part, we study the effect of defects on the n-i-p and p-i-n PSCs
performances; by considering the two main types of interfacial defects: substitution
defects ( ) and oxygen vacancy ( ). The defects density is varied from 1010
to 1014 −2
while theirs energy position in the band gap and charge nature are given in
Table 3.10.

Interfacial TiO2/Perovskite defects Energy below Ec Charge type

Substitution defects (IMA) 0.75 neutral
Oxygen Vacancy (Vo) 0.17 donor
Table 3. 10: Energy position and types of interfacial defects.

For conventional PSC, the effect of the and defects on the J-V characteristic is
shown in Figure 3.34 and Figure 3.35, respectively. In both cases the most sensible
parameter is (Figures 3.36 and 3.40) which exhibits a slight reduction caused mainly

76
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

by defects when it reaches 1014 −2

. Consequently, despite that 1014 −2
is
significantly high as interface density, the power conversion efficiency decreases slightly
in conventional PSC from 25.02% to 24.61 % for the IMA defects and to 24.95% for the
defects (Figure 3.37).

In inverted PSC, the effect of the and defects on the J-V characteristic is
shown in Figures 3.38 and 3.39, respectively. The power conversion efficiency decreases
from 25.11% to 24.85 % for the IMA defects and to 25.07% for the defects (Figure
3.41).

The performance of inverted PSC is less affected by interfacial defects. Substitution

defects located deeper than defects have more pronounced effect on the
performance of n-i-p and p-i-n PSCs especially if the density of the defects
exceeds 1014 −2
. These electronic states in the band gap of the semiconductor, act as
Shockley-Read-Hall (SRH) recombination centers. However the oxygen vacancy ( ) is
considered as shallow defect which leads to slowing down the injection of photo excited
electrons from perovskite to 2 [101].

25
Current density (mA/cm )
2

20 10 -2
10 cm
11 -2
15 10 cm
12 -2
10 cm
10 13 -2
10 cm
14 -2
5 10 cm

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Voltge (V)

Figure 3. 34: Effect of defects on J-V characteristic for n-i-p PSC.

77
Chapter 3 Study and optimization of MAPbI perovskite solar cell

25

)
2
Current density (mA/cm 20 10 -2
10 cm
11 -2
15 10 cm
12 -2
10 cm
10 10 cm
13 -2

14 -2
5 10 cm

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Voltage (V)

Figure 3. 35: Effect of defects on J-V characteristic for n-i-p PSC.

1.24
1.23

1.22

1.21
Voc (V)

IMA
1.20
Vo
1.19
1.18

1.17
10 11 12 13 14 15
10 10 10 10 10 10
-2
Defect density at interface (cm )

Figure 3. 36: Effect of and on open circuit voltage ( ).

78
Chapter 3 Study and optimization of MAPbI perovskite solar cell

25.1

25.0

24.9
 (%)

IMA
24.8
Vo
24.7

24.6

10 11 12 13 14 15
10 10 10 10 10 10
-2
Defect density at interface (cm )

Figure 3. 37: Effect of and on power conversion efficiency ( ) for n-i-p PSC.
Current density (mA/cm2)

25

20
1010 cm-2
15 1011 cm-2
1012 cm-2
10
1013 cm-2
1014 cm-2
5

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Voltage (V)

Figure 3. 38: Effect of defects on J-V characteristic for p-i-n PSC.

79
Chapter 3 Study and optimization of MAPbI perovskite solar cell

Current density (mA/cm2)

25

20 1010 cm-2
1011 cm-2
15 1012 cm-2
1013 cm-2
10 1014 cm-2

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Voltage (V)

Figure 3. 39: Effect of defects on J-V characteristic for p-i-n PSC.

1.23

1.22

1.21
Vo
Voc (V)

1.20 IMA
1.19

1.18

1.17
1010 1011 1012 1013 1014
Defects density (cm-2)

Figure 3. 40: Effect of A and on open circuit voltage ( ) for p-i-n PSC.

80
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

25.15

25.10

25.05 Vo
IMA
 

25.00

24.95

24.90

24.85

1010 1011 1012 1013 1014

Defects density (cm-2)

Figure 3. 41: Effect of and on power conversion efficiency ( ) for p-i-n PSC.

Defect states lie near the middle of the band gap instead of on the bottom of the
conduction band or at the top of the valence band, have more bad impact on the
properties of 3 solar cells. These results indicate that the perovskite/ 2

interface is crucial in charge separation.

3.15 Effect of temperature

In this part, the effect of temperature on conventional and inverted PSCs is studied. The
temperature was changed from 250 to 350 .

The affected J-V characteristics of both PSCs are represented in Figures 3.42 and
3.43. They show a significant decreasing in open circuit voltages. While the short circuit
currents are not affected.

81
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

Current density (mA/cm2)

25

20 250 K
270 K
15 290 K
310 K
10
330 K
350 K
5
Conventional
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Voltage (V)

Figure 3. 42: Effect of temperature on J-V characteristic for n-i-p PSC.

Current density (mA/cm2)

25

20 250 K
270 K
15 290 K
310 K
10
330 K
350 K
5
Inverted
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Voltage (V)

Figure 3. 43: Effect of temperature on J-V characteristic for p-i-n PSC.

Figure 3.44 represents the affected open circuit voltages and power conversion
efficiencies for our PSCs. The open circuit voltage of both PSCs is influenced by the same
way. When the temperature changed from 250 to 350 , the open circuit voltage
decreased from 1.30 to 1.16 V; while the power conversion efficiency was decreased

82
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

from 26.95 % to 22.81 for conventional PSC and from 27.22 % to 22.91 % for inverted
PSC.

The open circuit voltage decreases considerably with temperature as the open
circuit voltage is given by Equation 1.4. Decreasing of open circuit voltage with
temperature is dominated by the exponential increase of the reverse saturation current
with temperature. Consequentially, the conversion efficiency decreases.

28
1.30

1.28 Voc(n-i-p) 27 h (n-i-p)

Voc(p-i-n) h (p-i-n)
1.26
26
Voc (V)

1.24
 
25
1.22

1.20 24
1.18
23
1.16

1.14 22
240 260 280 300 320 340 360 240 260 280 300 320 340 360
Temperature (K)
Temperature (K)

Figure 3. 44: Effect of Temperature on Voc and eta for conventional and inverted PSCs.

3.16 Conclusion

Conventional and inverted PSCs were simulated using SCAPS simulator, using as an
ETL and : as an HTL. The conventional PSC exhibited better performance
where the power conversion efficiency was 13.94% for conventional structure and
10.99% for the inverted one. Replacing by 2 or led to an enhancement in
PSCs’ performance where the power conversion efficiency of conventional and inverted
PSCs reached 20% and 17.2%, respectively. Also, both PSCs were optimized using
CuSCN as an HTL and ZnO as an ETL where the power conversion efficiency was 23.3%
which increased to 23.36 % and 23.38% for conventional an inverted PSCs, respectively
using 2 as an ETL. Furthermore, thickness of PSCs were optimized to 1 leading to
25.02 % and 25.11% in power conversion efficiency for conventional and inverted PSCs;
respectively.

Moreover, substitution defects and oxygen vacancies showed a detrimental

effect on PSCs performance. But the inverted structure is less affected by these

83
 Chapter 3 Study and optimization of MAPbI perovskite solar cell

interfacial defects, in agreement with experimental measurements repported by many

works

Finally, when the temperature increased from 250 to 350 , the power conversion
efficiency decreased from 26.95 % to 22.81 for conventional PSC and from 27.22 % to
22.91 % for inverted PSC.

84
Conclusion
 Conclusion

Perovskite materials with its remarkable properties such as long electron diffusion length,
high optical absorption, small electron and hole effective masses, low processing temperature
and strong excitonic transitions, made them suitable for solar cell devices. These properties
make the organometallic halide perovskites based solar cells achieve comparable efficiencies
to the single crystal silicon and thin films counterparts. And for this, perovskite solar
cells have gained a major interest as “third generation solar cells”.

Using SCAPS software, two planar perovskite solar cells in n-i-p and p-i-n configurations
were simulated at AM1.5G solar spectrum with an incident power density of 100 / at
room temperature (300 ). The considred “n” layer was a 0.05 of , “p” layer was
0.05 of : and “i” layer was 0.4 of . Both solar cells showed
relatively poor performance. Although, the conventional solar cell exhibited a power
conversion efficiency and a fill factor better than those of inverted solar cell. The power
conversion efficiency was about 13.94% for conventional solar cell and about 10.99% for
inverted cell. The poor performance of inverted PCS was related to the low doping of
: which led to bulk resistance and interfacial contact resistance and this was
observed by deviation of J-V curve from quadratic shape.
Because of some shortcomings in using and : as an ETL and HTL,
respectively; we looked for alternatives to these materials. So, several materials were studied
for possible electron and hole transport layers (ETL and HTL). , , , and
were tested as an ETL and compared to .

We found that replacing by or improved both solar cells performance

where the power conversion efficiency exceeded 20% for conventional PSC and 17.2% for
inverted PSC. Furthermore, the hole transport layer was changed to determine the appropriate
p type material working as a hole transporter. − , 3 , , and
were examined as an HTL with preserving as an ETL. For conventional PSC,
quantum efficiency curves did not affected by modifying HTL because it located in the back
side of the deviceand the optical absorption is negligible there unlike the quantum efficiency
of inverted PSC which is affected by changing HTL materials. This goes back to the layer
acting as a window that controls the transmittance of light to the active layer. In addition, the
lowest power conversion efficiency is achieved in both solar cells based on P3HT as HTL.
PSCs based on as an HTL and as an ETL achieved power conversion efficiency

86
 Conclusion

about 23.3% for both n-i-p and p-i-n PSCs. On the other hand, by replacing by the
power conversion efficiency increased by 0.06% and 0.08% for n-i-p and p-i-n, respectively.
We considered that inverted PSC is relatively more efficient than conventional PSC.

Also, thickness of PSCs were optimized to 1 . At this thickness the absorption of

photons was optimum, leading to 25.02 % and 25.11% in power conversion efficiency for n-
i-p and p-i-n PSCs; respectively.

Moreover, deposition process affects the formation of defects especially at the surface,
interface and grain boundaries. Two main types could be existed in perovskite solar cells
which are: substitution defects when atom occupies a ( ) site and oxygen
vacancies . The effect of these defects on PSCs was studied. Results showed a significant
decreasing in solar cells’ performance for both types of defects.

When the temperature changed from 250 to 350 , the power conversion
efficiency decreased from 26.95 % to 22.81% for conventional PSC and from 27.22 % to
22.91 % for inverted PSC.

As further work, experimental and numerical studies will be done on this type of solar
cells in both conventional and inverted configurations. More researches will be achieved to
find more safe and cheap materials suitable for perovskite solar cells and to make these cells
have long duration and adequate for commercial production.

87
References
 References

[1] Michele D. B, (2016), The stability of third generation solar cells, PhD. Thesis,
University of Padua, Center for Nano-science and Technology, CNST @ PoliMi,
Italian Institute of Technology.

[2] Shi, Z., Jayatissa, A. (2018). Perovskites-Based Solar Cells: A Review of Recent
Progress, Materials and Processing Methods. Materials, 11(5), 729: DOI
https://doi.org/10.3390/ma11050729

[3] https://www.nrel.gov/pv/cell-efficiency.html visited march 1st,2021.

[4] Suneth C. W., Zhaoning S., Adam B. P., and Michael J. H, (2018)., Evolution of
Perovskite Solar Cells, University of Toledo, Toledo, OH, United States. DOI:
https://doi.org/10.1016/B978-0-12-812915-9.00003-4.

[5] Amu, T. L., (2014), Performance Optimization Of Tin Halide Perovskite

Solar Cells Via Numerical Simulation, thesis for obtaining degree of master in
science, Department of Theoretical Physics African University of Science and
Technology, Abuja.

[6] Roni P., Oct 12, 2020, Perovskite applications, Perovskite Solar, Saule Technologies,
https://www.perovskite-info.com/saule-technologies-launches-sunbreaker-
lamellas-assisted-perovskite-solar-cells

[7] Bryce S., (2018), Efficient Lead-Free Perovskite Solar Cell, Department of Electrical
and Computer Engineering, 2ECE 498 CB, University of Illinois at Urbana-
Champaign, Urbana, IL 61801, USA.

[8] Stone, J. L., (1993). Photovoltaics: Unlimited Electrical Energy from the Sun. Physics
Today, 46(9), 22–29. doi:10.1063/1.881362.

[9] Torchynska T. V. and Polupan G., (2004), High efficiency solar cells for space,
Superficies y Vacío 17(3), 21-25.

[10] Harold J. H., (1977), Solar cells for terrestrial applications, Sci. direct, vol. 19, no. 6,
pp. 605–615.

89
 References

[11] Kulkarni et al, (2014), Rural Electrification through Renewable Energy Sources- An
Overview of Challenges and Prospects, vol. 5013, no. 3, pp. 384–389.

[12] Granovskii, M., Dincer, I. & Rosen, M. (2007). Greenhouse gas emissions reduction
by use of wind and solar energies for hydrogen and electricity production: Economic
factors. International Journal of Hydrogen Energy. 32. 927-931. 10.1016.

[13] Lior N., (2010), Sustainable energy development: The present (2009) situation and
possible paths to the future,” Energy, vol. 35, no. 10, pp. 3976–3994.

[14] Ye, M., Lv, M., Chen, C., Iocozzia, J., Lin, C., & Lin, Z. (2014). Design, Fabrication, and
Modification of Cost-Effective Nanostructured TiO2 for Solar Energy
Applications.Low-Cost Nanomaterials, 9–54.doi:10.1007/978-1-4471-6473-9_2.

[15] Stone, J. L. (1993). Photovoltaics: Unlimited Electrical Energy from the Sun. Physics Today,
46(9), 22–29. doi:10.1063/1.881362.

[16] Balema, V., (2009), Alternative Energy Photovoltaics, Ionic Liquids, and MOFs,
Mateial Matters, vol. 4, no. 4, p. 1.

[17] Chapin, D. M., Fuller, C. S., & Pearson, G. L. (1954). A New Silicon p-n Junction
Photocell for Converting Solar Radiation into Electrical Power. Journal of Applied
Physics, 25(5), 676–677. doi:10.1063/1.1721711 .

[18] M. A. Green et al., (2014), Solar cell efficiency tables (version 43), pp. 1–9.

[19] Brittany L., Oliva C. A., Barron R., (2011), An Introduction to Solar Cell Technology.
Open Stax CNX. 11, http://cnx.org/contents/dd0537a2-fb5d-439d-8feb
bf2e50656dae@1

[20] R. G. Nrel, (2010), Renewable Energy Data Book, no. 2010,pp. 1–132.

[21] NREL, Solar cell efficiency chart, (2019), https://www.nrel.gov/pv/assets/images/

efficiency-chart.pngi accessed august 2019.

[22] Conibeer G., (2007), Third-generation photovoltaics, ARC Photovoltaics Centre of

Excellence, School of Photovoltaic and Renewable Energy Engineering, University
of New South Wales , Sydney, NSW 2052, Australia, VOLUME 10, NUMBER 11.

90
 References

[23] Equer B., (1993), Energie solaire photovoltaïque”, physique et technologie de la

conversion photovoltaïque, 1ère édition, ELLIPES, Paris.

[24] Sato H., Minami T., Takata S., and Yamada T., (1993), Transparent conducting p-type
NiO thin films prepared by magnetron sputtering, Thin Solid Films 236, 27–31.

[25] A. Faiza, (2015), Etude d’une cellule solaire a-IGZO(n)/μ-Si(p), thesis of Master,
University Med KhiderBiskra.

[26] Nelson J., (2003), The Physics of Solar Cells. Imperial College Press: London, pp. 1–
325.

[27] Zeman M., Introduction to photovoltaic solar energy. pp. 1–139.

[28] Sze S. M., Kwok K. Ng, Physics of Semiconductor Devices, third edition. 0-471-
14323-5.

[29] Liao K.-S., Yambem S. D., Haldar A., Alley N. J., and Curran S. A., (2010), Designs and
architectures for the next generation of organic solar cells," Energies, vol. 3, pp.
1212-1250.

[30] Loreta A. T.,(2014), Performance optimization of tin halide perovskite solar cells via
numerical simulation, A Thesis presented to the Department of Theoretical
Physics, African University of Science and Technology, Abuja..

[31]Yadav P., Pandey K., Bhatt P., Raval D., Tripathi B., Chandra K. P. ,Pandey M. K. and
Kumar M., (2015), Exploring the performance limiting parameters of perovskite
solar cell through experimental analysis and device simulation. Solar Energy
122,773–782.

[32] Suneth, C. W., Song, Z., Phillips, A. B., and Heben, M. J., (2018), Evolution of
Perovskite SolarCells. University of Toledo, Toledo, OH, United States, Elsevier Inc.

[33] Kojima A., Teshima K., Shirai Y., and Miyasaka T. (2009), Organometal Halide
Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. AM. CHEM.
SOC.131, 6050–6051.

91
 References

[34] Lee M. M., Teuscher J., Miyasaka T., Murakami, T.N., and Snaith H.J. (2012), Efficient
hybrid solar cells based on meso-superstructured organometal halide perovskites.
Science 338 643647.

[35] Rodríguez B. O. A. (2015), A characterization on hybrid lead halide perovskite solar

cells with TiO2 mesoporous scaffold, Master Thesis, university of Jaume, November
2015.

[36] Organic-Inorganic Perovskite Precursors, www.TCIchemicals.com. Accessed august

18th, 2016.

[37] Selina O. (2016), Research Update: The electronic structure of hybrid

perovskite layers and their energetic alignment in devices, APL MATERIALS 4,
091502.

[38] Bertrand P., Jesper T. J, Juan P. C-B., Naresh K. J., Amitava B, Sudip C., Ute B. C.,
Rajeev A., Anders H., Michael O., and Hakan R., (2017), Valence Level Character in
a Mixed Perovskite Material and Determination of the Valence Band Maximum
from Photoelectron Spectroscopy: Variation with Photon Energy; J. Phys. Chem. C
2017, 121, 26655-26666.

[39] Brivio F., Butler K. T., Walsh A., Schilfgaarde M., (2014), Relativistic quasiparticle
self-consistent electronic structure of hybrid halide perovskite photovoltaic
absorbers Phys. Rev. B 2014, 89, 155204.

[40] Tsutomu M., (2018), Lead Halide Perovskites in Thin Film Photovoltaics:
Background and Perspectives, Bull. Chem. Soc. Jpn. 2018, 91, 1058–1068.

[41] Brittman S., Adhyaksa G. W. P., & Garnett E. C. (2015). The expanding world of
hybrid perovskites: materials properties and emerging applications. MRS
Communications, 5(01), 7–26.doi:10.1557/mrc.2015.6.

[42] Correa-Baena J.-P., Abate A., Saliba M., Tress W., Jesper Jacobsson T., Grätzel M., and
Hagfeldt A., (2017), The rapid evolution of highly efficient perovskite solar cells.
Energy & Environmental Science, 10(3), 710–727. doi:10.1039/c6ee03397k.

92
 References

[43] Zhou, Y., Zhou, Z., Chen, M., Zong, Y., Huang, J., Pang, S., &Padture, N. P. (2016).
Doping and alloying for improved perovskite solar cells. Journal of Materials
Chemistry A, 4(45), 17623–17635. doi:10.1039/c6ta08699c.

[44] Abdi-Jalebi, M., Dar, M. I., Sadhanala, A., Senanayak, S. P., Franckevičius, M., Arora, N.
Friend, R. H. (2016). Impact of Monovalent Cation Halide Additives on the
Structural and Optoelectronic Properties of CH3NH3PbI3Perovskite. Advanced
Energy Materials, 6(10), 1502472. doi:10.1002/aenm.201502472.

[45] Zhou, Y., Chen, J., Bakr, O. M., & Sun, H.-T. (2018). Metal-doped lead halide
perovskites: synthesis, properties, and optoelectronic applications. Chemistry of
Materials. doi:10.1021/acs.chemmater.8b02989.

[46] Chang, C., Zou, X., Cheng, J., Yang, Y., Yao, Y., Ling, T., &Ren, H. (2019). NaI Doping
Effect on Photophysical Properties of Organic-Lead-Halide Perovskite Thin Films
by Using Solution Process. Advances in Materials Science and Engineering, 2019,
1–9. doi:10.1155/2019/2878060.

[47] Frolova, L. A., Dremova, N. N., &Troshin, P. A. (2015) , The chemical origin of the p-
type and n-type doping effects in the hybrid methylammonium–lead iodide
(MAPbI3) perovskite solar cells. Chemical Communications, 51(80), 14917–14920.
doi:10.1039/c5cc05205j.

[48] Nanduri, S. N. R. (2017), Numerical simulation and performance optimization of

perovskite solar cell. University Of Missouri-Kansas City.

[49] Yi W. (2012), Synthesis and optical properties of self-assembled 2D layered

organic-inorganic perovskites for optoelectronics. École normale supérieure de
Cachan - ENS Cachan, 2012.

[50] Amrita M. B., Dan R. W., and Thomas U., (2018), High efficient perovskite solar cell
material CH3NH3PbI3: Synthesis of films and their characterization, AIP
Conference Proceedings 1942, 140038.

[51] Lee J-W and Park N-G, (2015), Two-step deposition method for high-efficiency
perovskite solar cells, MRS BULLETIN, Materials Research Society. VOLUME 40.

93
 References

[52] Heping S., The D., Yiliang W., Jun P., Daniel J., Nandi W., Klaus W., Tom W. and ,Kylie
C., (2018), Metal halide perovskite: a game-changer for photovoltaics and solar
devices via a tandem design, Science and Technology of advanced MaTerialS, vol.
19, no. 1, 53–75.

[53] Qamar W., Naveen K. E., Yaseen I., Ashraf U., Rajan J., (2018), Tandem perovskite
solar cells, Renewable and Sustainable Energy Reviews 84, 89–110.

[54] Rui S., Anita W. Y., Ho B., Shujuan H., Mark K., Xiaojing H., Liangcong J., Yi-Bing C.,
and Martin A. G., (2015), Four-Terminal Tandem Solar Cells Using CH3NH3PbBr3
by Spectrum Splitting, J. Phys. Chem. Lett. 2015, 6, 3931-3934. DOI:
10.1021/acs.jpclett.5b01608.

[55] Eperon, G. E., Burlakov, V. M., Goriely, A., &Snaith, H. J. (2013). Neutral Color
Semitransparent MicrostructuredPerovskite Solar Cells. ACS Nano, 8(1), 591–598.
doi:10.1021/nn4052309.

[56] ChuantianZuo , Henk J. Bolink , Hongwei Han , Jinsong Huang , David Cahen ,* and
Liming Ding, Advances in Perovskite Solar Cells, Adv. Sci. 2016, 150032,

[57] Andy Extance, 7 January 2019, First building-integrated deployment shows

perovskite solar’s growing maturity, Chemistry world,
https://www.chemistryworld.com/news/first-building-integrated-deployment-
shows-perovskite-solars-growing-maturity/3009953.article

[58] Chen, J., Zhou, S., Jin, S., Li, H., & Zhai, T. (2016). Crystal organometal halide
perovskites with promising optoelectronic applications. Journal of Materials
Chemistry C, 4(1), 11–27. doi:10.1039/c5tc03417e.

[59] Minhuan W., Yantao S., Jiming B., Qingshun D., Hongjun S., Hongzhu L., Yingmin L.,
Yuzhi Z., (2016), Electroluminescence from perovskite LEDs with the structure of
Ag/Spiro-OMeTAD/CH3NH3PbI3/TiO2/FTO Chemical Physics Letters 662 (2016)
176–181.

94
 References

[60] Tan, Z.-K., Moghaddam, R. S., Lai, M. L., Docampo, P., Higler, R., Deschler, F., Price, M.,
Sadhanala, A., Pazos, L. M., Credgington, D., Hanusch , F., Bein, T., Snaith, H.J. and
Friend, R. H. (2014). Bright light-emitting diodes based on organometal halide
perovskite. Nature Nanotechnology, 9(9), 687–692. doi:10.1038/nnano.2014.149.

[61] Nana W., Lu C., Junjie S, Xiaoyong L., Yizheng J., Jianpu W., and Wei H., (2016),
Morphology control of perovskite light-emitting diodes by using amino acid self-
assembled monolayers, APPLIED PHYSICS LETTERS 108, 141102.

[62] Zhao, X., & Tan, Z.-K. (2019). Large-area near-infrared perovskite light-emitting
diodes. Nature Photonics.doi:10.1038/s41566-019-0559-3.

[63] Mohite, A., Chhowalla, M., Gupta, G., (2018), Efficient Solar Water Splitting with
5,000 Hours Stability Using Earth-abundant Catalysts and Durable Layered 2D
Perovskites, Los Alamos National Laboratory.

[64] Malinkiewicz, O., Imaizumi, M., Sapkota, S.B. et al. Radiation effects on the
performance of flexible perovskite solar cells for space applications. emergent
mater.(2020). doi:10.1007/s42247-020-00071-8.

[65] Minemoto et al, (2014), Device modeling of perovskite solar cells based on
structural similarity with thin film inorganic semiconductor solar cells, J. Appl. Phys.,
vol. 116, no. 5, p. 05450.

[66] Tanaka et al, (2003), Comparative study on the excitons in lead-halide-based

perovskite-type crystals CH3NH3PbBr3 CH3NH3PbI3,” Sci. direct, vol. 127, pp. 619–
623, 2003.

[67] Edri et al, (2014), Elucidating the charge carrier separation and working
mechanism of CH3NH3PbI(3-x)Cl(x) perovskite solar cells., Nat. Commun., vol. 5, p.
3461.

[68] Farzaneh A. R., Najmeh A., Vahid A., Aldo D-C., Karim O. A., Ali S-Z. T., Farzaneh S. G.,
Masoud P., Nasibeh M. R. F., (2018), Bulk heterojunction polymer solar cell and
perovskite solar cell: Concepts, materials, current status, and opto electronic
properties,. Solar Energy 173 407–424.

95
 References

[69] Zhyrair G., Vladimir G., and Yurii L., (2016), Large diffusion lengths of excitons in
perovskite and TiO2 heterojunction, Applied Physics Letters 108, 051109.

[70] Ibn-Mohammed T., Koh S.C.L., Reaney I.M., Acquaye A., Schileo G., Mustapha K.B.,
Greenough R., (2017), Perovskite solar cells: An integrated hybrid lifecycle
assessment and review in comparison with other photovoltaic technologies
Renewable and Sustainable Energy Reviews 80 (2017) 1321–1344

[71] Kang, D.-H., & Park, N.-G. (2019). On the Current-Voltage Hysteresis in Perovskite
Solar Cells: Dependence on Perovskite Composition and Methods to Remove
Hysteresis. Advanced Materials, 1805214.doi:10.1002/adma.201805214

[72] Elumalai, N. K., & Uddin, A., (2016),.Hysteresis in organic-inorganic hybrid

perovskite solar cells. Solar Energy Materials and Solar Cells, 157, 476 509.
doi:10.1016/j.solmat.2016.06.025.

[73] Elumalai, N., Mahmud, M., Wang, D., & Uddin, A. (2016). Perovskite Solar Cells:
Progress and Advancements. Energies, 9(11), 861. doi:10.3390/en9110861

[74] Kim, H.-S., Jang, I.-H., Ahn, N., Choi, M., Guerrero, A., Bisquert, J., & Park, N.-G.
(2015). Control of I–V Hysteresis in CH3NH3PbI3 Perovskite Solar Cell. The Journal
of Physical Chemistry Letters, 6(22), 4633–4639. doi:10.1021/acs.jpclett.5b02273.

[75] Unni K., Manjot K., Manjeet K., Akshay K., (2019), Factors affecting the stability of
perovskite solar cells: a comprehensive review,” J. Photon. Energy 9(2), 021001.

[76] Wang, S., Jiang, Y., Juarez-Perez, E. J., Ono, L. K., & Qi, Y. (2016). Accelerated
degradation of methylammonium lead iodide perovskites induced by exposure to
iodine vapour. Nature Energy, 2(1), 16195. doi:10.1038/nenergy.2016.195.

[77] Aristidou, N., Sanchez-Molina, I., Chotchuangchutchaval, T., Brown, M., Martinez, L.,
Rath, T., & Haque, S. A. (2015). The Role of Oxygen in the Degradation of
Methylammonium Lead Trihalide Perovskite Photoactive Layers. Angewandte
Chemie, 127(28), 8326–8330. doi:10.1002/ange.201503153.

96
 References

[78] Sylla, A., Touré, S., and Vilcot, J. P. (2017). Numerical Modeling and Simulation of
CIGS-Based Solar Cells with ZnS Buffer Layer. Open Journal of Modelling and
Simulation, 5, 218-231..

[79] Nadia, M., (2016). Study Of The Effect Of Grading In Composition On The
Performance Of Thin Film Solar Cells Based On AlGaAs And CZTSSe, A Numerical
Simulation Approach, Doctorat Thesis In Énergétique, Université Med Kheider
BISKRA, June

[80] Liu, Y., Sun, Y., & Rockett, A. (2012). A new simulation software of solar cells -
WxAMPS. Solar Energy Materials and Solar Cells, 98, 124-128.

[81] M. Belarbi, A. Benyoucef , B. Benyoucef, (2014). Simulation Of The Solar Cells With
Pc1d, Application To Cells Based On Silicon, Advanced Energy: An International
Journal (Aeij), Vol. 1, No. 3.

[82] Burgelman, M., Decock, K., Niemegeers, A., Verschraegen, J., and Degrave, S. (2018).
SCAPS manual , Version: 23 January 2018.

[83] Marc Burgelman, (2018). Models for the optical absorption  ()of materials in
SCAPS, 20-1-2018, Correspondence address: Dept. of Electronics and Information
Technology (ELIS), University of Gent, ‘Belgium’. E-mail:
Marc.Burgelman@elis.ugent.be

[84] Singh Surjeet. (2017). Mathematical Modeling of a P-N Junction Solar Cell using the
Transport Equations. Browse all Theses and Dissertations. 1775.(2017).

[85] Atlas User’s Manual, Device simulation software, Santa Clara, California 95054,
November 7, 2014.

[86] Löper, P., Stuckelberger, M., Niesen, B., Werner, J., Filipic, M., , Moon, S., Yum, J.,
Topic, M., De Wolf, S., Ballif, C., et al. (2015). Complex refractive index spectra of
CH3NH3PbI3 perovskite thin films determined by spectroscopic ellipsometry and
spectrophotometry. Journal of Physical Chemistry Letters 6, pp. 66–71.

[87] SCAPS data base 2018. Version sacps3307.

97
 References

[88] Minemoto,T., Murata, M. (2014). Impact of work function of back contact of

perovskite solar cells without hole transport material analyzed by device
simulation. Current Applied Physics 14. 1428e1433.

[89] Mandadapu,U.,Vedanayakam, S. V., and Thyagarajan,K. (2017). Simulation and

Analysis of Lead based Perovskite Solar Cell using SCAPS-1D. Indian Journal of
Science and Technology.Vol 10(11).

[90] Wolf,S. D.,Holovsky,J., Moon,S. J., Lö per, P., Niesen, B.,edinsky, M, Haug, F. J., Yum, J.
H., and Ballif,C. (2014). Organometallic Halide Perovskites: Sharp Optical
Absorption Edge and Its Relation to Photovoltaic Performance. J. Phys. Chem. Lett.
5, 1035−1039.

[91] Yi, M., Jang, W., & Wang, D. H. (2019).Controlled pH of PEDOT:PSS for Reproducible
Efficiency in Inverted Perovskite Solar Cells: Independent of Active Area and
Humidity. ACS Sustainable Chemistry &
Engineering.doi:10.1021/acssuschemeng.8b06619

[92] Voroshazi, E., Verreet, B., Buri, A., Müller, R., Di Nuzzo, D., &Heremans, P. (2011).
Influence of cathode oxidation via the hole extraction layer in polymer:fullerene
solar cells. Organic Electronics, 12(5), 736–744.doi:10.1016/j.orgel.2011.01.025

[93] Meiss, J., Uhrich, C. L., Fehse, K., Pfuetzner, S., Riede, M. K., & Leo, K. (2008).
Transparent electrode materials for solar cells. Photonics for Solar Energy Systems
II.doi:10.1117/12.781275 .

94<91 Wang,Y.,Xia,Z., Liang, J., Wang, X.,Liu, Y.,Liu, C.,Zhang, S., andZhou, H. : Towards
printed perovskite solar cells with cuprous oxide hole transporting layers: a
theoretical design. Semicond. Sci. Technol. 30 054004 (7pp).(2015).

[95] Azri,F.,Labed,M., Meftah,A. F.,Sengouga,N.,Meftah, A. M. (2016). Optical

characterization of a-IGZO thin film for simulation of a-IGZO(n)/l-Si(p)
heterojunction solar cell. Opt Quant Electron 48:391, (2016).

98
 References

[96] Chen,A.,Zhu,K.,Shao, Q. (2016). Understanding effects of TCO work function on the

performance of organic solar cells by numerical simulation. Semicond.Sci. Technol.
31 065025 (6pp).

[97] Haider,S. Z.,Anwar,H., and Wang, M. (2018). A comprehensive device modelling of

perovskite solar cell with inorganic copper iodide as hole transport
material.Semicond. Sci. Technol. 33, 035001 (12pp).

[98] Sajid, A.,Elseman, M.,Ji, J.,Dou, S.,Huang, H.,Cui, P.,Wei, D.,Li, M. (2016). Novel hole
transport layer of nickel oxide composite with carbon for high-performance
perovskite solar cells”, Chin. Phys. B. 25(9): 097303.

[99] Miyata, A., Mitioglu, A., Plochocka, P., Portugall, O., Wang, J. T.-W., Stranks, S. D., …
Nicholas, R. J. (2015). Direct measurement of the exciton binding energy and
effective masses for charge carriers in organic–inorganic tri-halide perovskites.
Nature Physics, 11(7), 582–587. doi:10.1038/nphys3357

[100] Fan, Z., Wei, M., Haizhong, G., Yicheng, Z., Xinyan, S., Kuijuan, J., He, T., Qing, Z.,
Dapeng, Y., Xinghua, L., Gang, L. and Sheng, M. (2016). Interfacial Oxygen Vacancies
as a Potential Cause of Hysteresis in Perovskite Solar Cells.
acs.chemmater.5b04019.

[101] Feng, W., Sai, B., Wolfgang, T., Anders, H. and Feng, G. (2018). Defects engineering
for high-performance perovskite solar cells. npj Flexible Electronics 2:22.

99