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Author(s): Yogesh Kumar, Sweta Minj, Naman Shukla, Sanjay Tiwari

Email(s): naman.shukla43@gmail.com

Address: School of Studies in Electronics and Photonics, Pt. Ravishankar Shukla University, Raipur-492010, C.G., India

Published In:   Volume - 35,      Issue - 1,     Year - 2022


Cite this article:
Kumar, Minj, Shukla and Tiwari (2022). Design and Device Modeling of Lead Free CsSnI3 Perovskite Solar Cell. Journal of Ravishankar University (Part-B: Science), 35(1), pp. 25-34.



Design and Device Modeling of Lead Free CsSnI3 Perovskite Solar Cell

Yogesh Kumar, Sweta Minj, Naman Shukla, Sanjay Tiwari

School of Studies in Electronics and Photonics, Pt. Ravishankar Shukla University, Raipur-492010, C.G., India

 

*Corresponding author: naman.shukla43@gmail.com

Abstract:

Research of lead-free Perovskite based solar cells has gained speedy and growing attention with urgent intent to eliminate toxic lead in Perovskite materials. The main purpose of this work is to supplement the research progress with comparative analysis of different lead-free Perovskite based solar cells by numerical simulation method using solar cell capacitance simulator (SCAPS-1D) software. The environmental friendliness and excellent thermal stability proves Cesium Tin Iodide (CsSnI3) as one of the promising materials for the commercialization of the Perovskite solar cells. However, CsSnI3 solar cells suffer from poor efficiency due to having low open-circuit voltage, VOC attributed to poor absorber film quality as well as energy level mismatch at the interfaces between different layers like transparent front contact. The architecture of the solar cell is n-i-p device structure acts as light CsSnI3 absorber active layer, TiO2 as electron transport layer and Spiro-OMeTAD as hole transport layer with device structure FTO/ TiO2/CsSnI3 / Spiro-OMeTAD /Au. The open circuit voltage Voc, short circuit current density Isc, fill factor and power conversion efficiency Voc=1.09V, Jsc=28.85mA/cm2, FF=88.65%, eta=28.09%, V_MPP=0.99V, J_MPP=28.15 mA/cm2 respectively.

 

Keywords — Perovskite Solar Cell, Lead-free, CsSnI3, SCAPS 1D

 

Introduction:

Perovskite solar cells have experienced a major leap in their power conversion efficiency (PCE) just over a decade due to their very simple manufacturing process, comparatively low processing cost, high absorption coefficient, low surface recombination rates and relatively high efficiency. It has increased from 3.8% in 2009 reported by Miyasaka and his colleagues in 2009 (Kojima et al., 2009) to 25.5% till date (NREL, Best research-cell efficiencies) in single-junction architectures, which is quite close enough to the crystalline silicon solar cells at 26.7%. The hybrid organic-inorganic perovskites have opened new doors towards more efficient light harvesting materials. Owing to the property of tunable frequency, these solar cells can be quite effective in absorbing different light frequencies by different layers which can lead to a boost in their efficiencies unlike the conventional solar cells. Despite this, lead based perovskites have two major challenges: a) poor stability which is being addressed by improved device engineering and encapsulation as well as incorporating the use of perovskites, b) high toxicity that is raising a concern on an environmental level. Lead free perovskite materials, which are non-toxic and are also being looked upon as another alternative. These lead free materials will be a preference in the solar cell market which will help in commercialization of perovskite solar cells if they do not compromise with the device performance. Ideally, Pb-free perovskites when used as light harvesting layers in solar cells, should have low toxicity, high optical absorption coefficients, low exciton-binding, narrow direct band gaps, high mobilities. Perovskites in the form of double perovskites, some Sn/Ge based halides, and also some Bi/Sb-based halides with perovskite-like structure show fascinating properties and are low-toxicity materials. Up to 2020, the highest efficiency for Sn-based perovskites has been reported to have reached 13.24%. In these Pb-free perovskite materials, comparatively only Sn-based PSCs have shown very promising performance. In Sn-based PSCs, certain factors like the poor air-stability caused due to quick oxidation of Sn2+ leading to increased recombination losses, small formation energy of vacancies, high intrinsic carrier density etc. leads to poor device performance as compared to their corresponding lead-based analogues. The anti-bonding coupling between Sn-5s and I-5p is comparatively weaker in FASnI3 (FA = CH (NH2)2) than CsSnI3 and MASnI3 as a result of the larger ionic size of FA which is also the reason behind the increase in formation energies of Sn-vacancies. Along with experiments, simulation also plays a vital role in analyzing various properties of these materials and the corresponding performance parameters for various such materials. This work aids in studying the relation of the properties with the parameters, comparing multiple materials with the help of theoretical analysis by designing a device model. Here, a comparative study of various Pb-free perovskites on a similar configuration is done which helps us know about the distinguishing properties, their impacts on device performance and further work for achieving high efficiencies for Pb-free perovskites

                                                                             

The organic-inorganic halide perovskite (ABX3) solar cells are emerging as the best contender for futuristic photovoltaic energy harvesting process, which is evident from its tremendous growth of achieving power conversion efficiency as high as 25.2% reported form single-cell till to-date. Both the natural environment and humans. Therefore, there has been growing interest in the development of alternative perovskites that use Sn instead of Pb, such as CsSnI3. Tin-based halide perovskite materials have been successfully employed in lead free perovskite solar cells. Recently, several studies have revealed that the substitution of the methyl ammonium cation by cesium (Cs) in the perovskite structure could significantly enhance its thermal stability. Notwithstanding that the high-performance perovskite cells are dominated by lead (Pb) based materials like Methyl Ammonium Lead Halide, MAPbX3 (Shukla et al., 2021 and gopal et al., 2020) or Formamidinium Lead Hallie (FAPbX3), the environmental impact of Pb as well as high bandgap of these perovskite materials have always made researchers think of its environmentally benign and low bandgap options, tin (Sn) based perovskites like MASnX3 . Apart from this, inorganic cations like Cesium (Cs) have been considering as the substitute of the organic counter parts because of the instable ambient/outdoor performance of MAPbX3 and FAPbX3 due to the fragmentation of the organic components . Thus Cesium Tin Iodide, CsSnI3 may be considered as one of the viable choices for the commercialization of perovskite solar cells. However, CsSnI3 based solar cells suffer from lower efficiency. The stable and efficient perovskite solar cells can be developed through optimization of the solar cell device through experiments supported by data which is obtained by optical and electrical simulations. In this research work, the numerical simulation of the CsSnI3 based perovskite solar cell was done by using Solar Cell Capacitance Simulator (SCAPS-1D). It is a one dimensional solar cell simulator based on the drift diffusion physical model (Burgelman et al., 2000).simulation of PSC. This software tool has executed the semiconductor equation, the continuity equation of carrier, Poisson equation, carrier transport equations etc.

The SCAPS software gives us the results by solving the basic semiconductor equations, Poisson equations, the continuity equations for electrons and holes and other carrier transport constraints (Burgelman et al.,2013). Organic metal halide perovskite is used as active layer in this simulation. Device simulations have been performed according to the parameters given in the literature summarized in Table 1 (Lin et al., 2014; Hima et al., 2019; Calado et al., 2016; Isoe et al., 2020).The n-i-p device structure is FTO/ TiO2/ CsSnI3/ Spiro-OMeTAD /Au. For optimized design of the solar cell for above structure, short circuit current density Jsc, open circuit voltage Voc, fill factor FF and efficiency are  Voc= 1.09V, Jsc=28.85mA/cm2, FF= 88.65%, eta= 28.09%, V_MPP=0.99 V, J_MPP=28.15 mA/cm2

                                                                                                         

FTO

TiO2

CsSnI3

Spiro-OMeTAD

Au

                                                                                                  

 



 

 

    

 

Figure 1. Architecture of simulated model


Table 1: Simulated Parameters

Parameter

Spiro-OMeTAD

CsSnl3

TiO2

FTO

Thickness(nm)

0.500

  0.300

0.200

0.030

Band gap (eV)

3.170

1.270

3.200

3.500

Electron affinity(eV)

2.050

4.470

4.260

4.500

Dielectric Permittivity

3.000

10.590

9.0

10

CB effective density of States(1/cm3)

2.200e+18

1.580e+19

2.200e+18

2.200e+18

VB effective density of States(1/cm3)

1.800e+19

1.470e+18

2.00e+18

1.800e+19

Electron thermal

Velocity(cm/s)

1.00e+7

1.00e+7

1.00e+7

1.00e+7

Hole thermal velocity (cm/s)

1.00e+7

1.00e+7

1.00e+7

1.00e+7

Electron mobility(cm2/Vs)

2.00e-4

4.370e+0

2.00e+1

1.00e+2

Hole mobility(cm2/Vs)

2.00e-4

4.370e+0

1.00e+1

2.500e+1

Shallow uniform donor density ND(1/cm3)

0

5.00e+19

1.00e+6

1.00e+20

Shallow uniform acceptor Density NA(1/cm3)

2.000e+19

0

0

0

Defect Density (1/cm3)

0

1.000e+15

0

0

                                                      

                     

Figure 2: V-I graph of Perovskite CsSnI3 Solar cell

Result and discussion

Numerical modeling was carried out using 1D-SCAPS software and including various material proprieties given in Table-1. Firstly, the p-i-n solar cell structure, FTO/ Spiro-OMeTAD /CsSnI3 /TiO2/Au is studied and analyzed. Figure. 2 plots the J-V characteristics of both simulated and experimental Sn-based perovskite solar cell structure measured under reverse voltage. As can be seen from the Figure. 1, the obtained simulated results are very close to experimental ones taken from literature.

FTO/ Spiro-OMeTAD /CsSnI3 /TiO2/Au, based on Sn-perovskite material and corresponds to the layer thicknesses of 0.5, 0.3 and 0.2 micrometer for HTL, PAT and ETL, respectively. Figure. 2 displays the variation of J-V characteristic of the Sn -perovskite solar cell. The photovoltaic parameters Voc=1.09V, Jsc=28.85mA/cm2, FF=88.6587%, eta=28.09%, V_MPP=0.99V, J_MPP=28.15mA/. It is necessary to carry out an optimization process of the perovskite device. This is can be down by varying the diverse layer thicknesses, absorber, HTL and ETL layers. In this context, the optimization process consists to fix two-layer thicknesses and vary the remaining one. Then, in each case we select the layer CsSnI3 thickness that gives the optimal PCE value. Figure. 3 shows the optimized J-V characteristics of the Sn -based perovskite solar cell. It is evident that the optimized perovskite device shows a noticeable enhancement in PCE from 17.24% to 29.33%. Sn-based perovskite device shows analogous photovoltaic performance comparable to Sn-based perovskite device. Using the same optimization method mentioned above, our simulation is performed on the power conversion efficiency as function of absorber layer thickness, temperature, band gap, electron affinity, defect density of absorbent layer in order to find the optimum values. The optimized value of absorber layer thickness, temperature, band gap, electron affinity gives higher PCE. Evidently, the PCE increases with increasing of absorber thickness and then decreases after reaching a specified value as shown in Figure. 3. This increasing is due to more photons absorbed by carrier concentration in this layer creating more electron hole pairs and led to high short-circuit current density in the device. In addition, PCE is measured for different temperature and it is noted that with increase band gap efficiency is decreases as shown in Figure. 4, measurement of PCE for different electron affinity is carried out and it is noted that with increase in electron affinity is increased and decreased it works well between 4-4.5 as shown in Figure. 5, measurement of PCE for different Temperature is carried out and it is noted that with increase in Temperature efficiency is decreases and it works well between 300k-375k as shown in Figure. 6, measurement of PCE for different defect density is carried out and it is noted that with increase in defect density efficiency is decreases and it works well between 1014 -1015 as shown in Figure. 7.


Figure 3: J-V Characteristics with different thickness of CsSnI3 Perovskite active layer

 

Figure 4: Response of J-V Characteristics with different band gap (tunable range) of CsSnI3 Perovskite active layer

 

Table 2: J-V Characteristics parameters at different thickness of CsSnI3

Thikness

Voc

Jsc

FF

eta

0.100

1.11

17.404

89.01

17.24%

0.200

1.104

25.236

88.74

24.745%

0.300

1.098

28.850

88.658

28.094%

0.310

1.097

29.071

88.657

28.291%

0.320

1.097

29.271

88.654

28.469%

0.330

1.096

29.453

88.655

28.629%

0.400

1.092

30.287

88.636

29.326%

0.500

1.087

30.504

88.441

29.339%

 

                                              

Table 3: J-V Characteristics parameters with different band gap (tunable range) of CsSnI3

Band gap

Jsc(mA/cm2)

Voc(V)

FF

PCE(%)

1.20

31.322

1.030

88.25

28.47 %

1.23

30.48

1.039

88.36

28.55 %

1.26

29.21

1.088

88.69

28.20 %

1.27

28.85

1.098

88.65

28.09 %

1.271

28.82

1.099

88.64

28.09 %

1.278

28.636

1.105

88.66

28.08 %

1.28

28.576

1.107

88.67

28.07 %

1.29

28.245

1.117

88.77

28.02 %

 

Figure 5: Recorded J-V Characteristics of the device with variation of temperature

 

Table 4: J-V Characteristics parameter at different temperature

Temperature (K)

Voc(V)

Jsc(mA/cm2)

FF

PCE

300

1.098

28.850

88.658

28.094 %

325

1.076

28.920

87.914

27.360 %

350

1.053

28.980

86.970

26.548 %

375

1.030

29.032

86.130

25.757 %

400

1.006

29.078

85.248

24.947 %

425

0.982

29.119

84.234

24.093 %

450

0.957

29.155

83.312

23.258 %

475

0.932

29.188

82.275

22.389 %

                                 

Table 5: J-V Characteristics parameters at different electron affinity value

Electron affinity(eV)

Voc(V)

Jsc(mA/cm2)

FF

PCE(%)

4.0

1.093

28.429

88.517

27.508 %

4.1

1.097

28.803

88.803

28.090 %

4.17

1.098

28.845

88.804

28.129 %

4.2

1.098

28.848

88.802

28.134 %

4.27

1.098

28.851

88.795

28.136 %

4.37

1.098

28.851

88.767

28.128 %

4.47

1.098

28.850

88.658

28.094 %

4.5

1.098

28.850

88.574

28.067 %


Figure 6: Response of J-V Characteristics at different electron affinity

 

Figure 7: The role of defect density in CsSnI3 Perovskite solar cells

 

Table 6: Recorded parameters at different defect density of CsSnI3

Defect density

Voc

Jsc

FF

PCE(%)

1E+14

1.158

29.687

89.25

30.68 %

1.1E+15

1.096

28.760

88.65

28.09 %

1.2E+16

1.032

21.454

87.56

19.38 %

1E+17

0.968

7.114

86.01

5.92 %

1.3E+18

0.887

1.154

83.14

0.85 %

1.5E+19

0.821

0.323

77.62

0.20 %

1E+20

0.771

0.142

71.64

0.07 %

1E+21

0.770

0.048

68.73

0.02 %

                             

Acknowledgement

I am thankful for research facilities provided by Photonics Research Laboratory, School of Studies in Electronics and Photonics, Pt. Ravishankar Shukla University, Raipur, Chhattisgarh, India. I would like to acknowledge Dr. Marc Burgelman and the researcher team associated with Department of Electronics and Information Systems, University of Gent, Belgium for providing the simulation software SCAPS-1D.

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