Performance Improvement of Perovskite Solar Cell Design with Double Active Layer to Achieve an Efficiency of over 31%

Abstract

This research aims to optimize the efficiency of the device structures by introducing the novel double perovskite absorber layer (PAL). The perovskite solar cell (PSC) has higher efficiency with both lead perovskite (PVK), i.e., methylammonium tin iodide (MASnI₃) and Caseium tin germanium iodide (CsSnGeI₃). The current simulation uses Spiro-OMeTAD as the hole transport layer (HTL) and TiO₂ as an electron transport layer (ETL) to sandwich the PVK layers of MASnI₃ and CsSnGeI₃, which have precise bandgaps of 1.3 eV and 1.5 eV. The exclusive results of the precise modeling technique for organic/inorganic PVK-based photovoltaic solar cells under the illumination of AM1.5 for distinctive device architectures are shown in the present work. Influence of defect density (DD) is also considered during simulation that revealed the best PSC parameters with J_SC of 31.41 mA/cm², V_OC of 1.215 V, FF of nearly 82.62% and the highest efficiency of 31.53% at the combined DD of 1.0 × 10¹⁴ cm⁻³. The influence of temperature on device performance, which showed a reduction in PV parameters at elevated temperature, is also evaluated. A steeper temperature gradient with an average efficiency of −0.0265%/K for the optimized PSC is observed. The novel grading technique helps in achieving efficiency of more than 31% for the optimized device. As a result of the detailed examination of the total DD and temperature dependency of the simulated device, structures are also studied simultaneously.

1. Introduction

Over the last few decades, perovskite solar cells (PSCs) have held much attention for their exceptional optoelectrical features compared to traditional solar cell technologies [1,2]. A few properties, such as the high carrier transport phenomena, higher absorption coefficient and variable bandgap, that are excellently prioritized and attributed to longer diffusion lengths may be the cause of the higher acceptability [2,3,4]. The remarkable increase in efficiency that started in recent years, from 3.8 percent in 2009 to 25.6 percent in 2021, has shifted the attention of the researchers in the PSC’s envisioned future development [5,6,7]. The organic layer structures have also been researched in a few earlier works for the PSC devices’ potential development [8].

PSCs based on methylammonium lead tri-iodide (MAPbI₃) have successfully produced outstanding device results [9]. The toxicity of the Pb-based PVK material hampers successful commercial fabrication, even when the MAPbI₃-based PSCs offer exceptional efficiency [10]. By replacing the Pb material with environmentally friendly materials with analogous properties, one can use another perovskite material to eliminate these consequences. The performance of the device is also affected by the difficulty of the MAPbI₃ material to absorb lower frequency photons due to its larger band gap. The volatile methylammonium can be replaced by cesium (Cs), an inorganic and non-volatile material [11]. The germanium and tin material can efficiently trigger the overall absorption with more environmentally friendly perovskite material to simulate the PSC devices. It is believed that the introduction of the MASnI₃ is justified by the fact that it has a smaller band gap than the other few and, as a result, can absorb more photons in the visible spectral range [12,13]. The problem of lower absorption remains since a single PAL can only absorb a certain amount of photons. We designed and investigated a new structure by introducing double PAL for better harvesting of the incident spectrum [13]. Previously, Singh et al. found that the efficiency of the MASnI₃ is higher, which may help in an environmentally friendly nature [14]. Similarly, Raghavendra et al. designed the PSC with all-inorganic CsSnGeI₃ material, which aided in providing a less expensive and highly efficient device [15].

Considering the carrier transport layers (CTLs), the influence of the appropriate HTLs also becomes significant as they affect the extraction and aid in the instantaneous flow of the light-generated holes from the perovskite absorber layer to the cathode of the PSC. The use of a highly pure HTL of Spiro-OMeTAD [2,2′,7,7′-tetrakis-(N, N-di-p-methoxyphenylamine)-9,9′-spirobifluorene] is widely accepted in the fabrication and stability factors [16]. At the same time, ETL selection is also imperative for lowering the rate of recombination as well as optimizing the efficiency of the PSC. The earlier work by Azri et al. [17] further focused on obtaining a higher efficiency with the ETL of TiO₂. Also, the report by Alam et al. shows that the TiO₂ is better ETL for the exclusive carrier mobility as well as better band alignment with the perovskite layer [18]. These results offer an opportunity to select better CTLs for the rational design of PSC devices [17]. It is also essential to declare that designing the PSC can be done using numerical simulation for better optimization strategies. This not only saves money and time but also offers a clear optimization methodology that is superior for efficient solar cell design. For this reason, the 1-dimensional solar cell capacitance simulator (SCAPS-1D) developed by ELIS, Ghent University, Belgium, which uses the drift-diffusion model, is widely adopted by researchers [3,8,19,20]. The simulator contains certain unique benefits, such as practically grading all parameters as well as the layer by layer stacking. The simulations run in both dark and illumination conditions, and their working principle is dependent on solving the continuity and Poisson equations [21]. Almost all the available solar cell simulators, such as TCAD, are equipped with basic semiconductor equations for solving the optoelectronic outputs. On the other hand, the SCAPS-1D is an open source and user-friendly, and the results are validated with the help of the extensive publications of the article with the SCAPS-1D simulator [22,23,24,25]. Therefore, SCAPS-1D is preferred in this work over other TCAD tools, such as AFORS- HET (automat for simulation of heterostructures), Lumerical and Silvaco ATLAS [26,27,28,29,30]. Optimization of the transport layers for the PSC for improved in-device carrier movement using the simulator of SCAPS-1D successfully triggers the efficiency of the PSC and can be considered one of the important scientific contributions [7,17]. Concerning the idea mentioned earlier, we investigated the impact of the PAL thickness, the total defect densities and the influence of temperature on the PSC performances. In addition, the EQE and J-V outputs for the PSC are also investigated for the superior performance of the PSC device.

The present work is organized as follows: Introduction in Section 1 is followed by Section 2 of the device design, which provides a comprehensive overview of the device arrangement and the material parameters utilized in the simulations. The results and discussion in Section 3 of the article give the results related to unique HTLs, ETLs and DD. The work is accomplished in the final Section 4, with the future scope.

2. Device Architecture of the PSC

This section is further subdivided into two parts: Firstly, Materials and Simulative Inputs, and secondly, Mathematical Methods are described.

2.1. Materials and Simulative Inputs

As the conventional PSC structural design consists of three distinct layers, Figure 1a depicts the simulated PSC with an n-i-p configuration. Firstly, the double absorbing layer (AL) is kept between the electron transport layer (ETL) and the hole transport layer (HTL). The present work is designed on methylammonium tin tri-iodide (MASnI₃) and Cesium tin germanium iodide (CsSnGeI₃) functioning as PAL. The ETL of, i.e., TiO₂ and HTL of Spiro-OMeTAD are confirmed with superior outcomes of the previous literature reports [31], which results in high efficiency. The use of TiO₂ is obvious for two reasons. First, the carrier mobility is high, and second the suitable band alignment with the PAL as compared to the other ETLs, such as MoO₃, and WO₃ [32]. The ETL of TiO₂ has a homogenous layer with a small grain structure enhancing the surface area of the under-layer and improving the total efficiency of the PSC device. Apart from that, the TiO₂ gives a better performance compared with other ETL layers.

The working mechanism of the PSC device (CsSnGeI₃/MASnI₃) is presented in Figure 1b. The absorption coefficient α is shown from SCAPS-1D utilizing the factor of α = A_α (h𝜈-E_g)^1/2 [33]. E_g is the material’s bandgap simultaneously. The input parameters used in the current simulation are provided in Table 1, and the interface defect density (IDD) parameters have been listed in Table 2. The entire simulations are carried out at AM1.5 photo illumination with an integrated power of 100 mW/cm².

2.2. Mathematical Methods

The substantial parameter that influences the PSCs outputs can be achieved using the numerical simulator of SCAPS-1D (Solar Cell Capacitance Simulator) that was discovered by Burgelman et al. [21] Specifically, the 1D-equation manages the semiconductor materials at the steady-state condition. The correlation between the charge density and electric fields (E) for the p-n junction could be represented as follows [10]:

(1)$\frac{{\partial }^2\phi }{{\partial }^{2}x}=-\frac{\partial E}{\partial x}=-\frac{\rho }{{\epsilon }_s}=-\frac{q}{{\epsilon }_s}\left[p-n+N_D^{+}\left(x\right)-N_A^{-}\left(x\right)\pm N_{\mathrm{def}}\left(x\right)\right]$

Here, the electrostatic potential is represented as $\phi$; the charge is represented as $q$; and the static relative permittivity of the medium is depicted by ${\epsilon }_s$. The electrons and the hole are shown as n and $p$, respectively, while the density of the donor and acceptor is represented as $N_D^{+}$ and $N_A^{+}$. The defect density of both the acceptor and donor is symbolized with $N_{\mathrm{def}}\left(x\right)$.

Similarly, the carrier continuity equation for the PSC can be represented as depicted below [36]:

(2)$-\frac{\partial j_p}{\partial x}+G-U_p\left(n,p\right)=0$

(3)$\frac{\partial j_n}{\partial x}+G-U_n\left(n,p\right)=0$

The electron and hole current densities are $j_n$ and $j_p$; the carrier generation rate is presented by $G$; and the rate of recombination for the electron and hole are $U_n\left(n,p\right)$ and $U_p\left(n,p\right)$, respectively.

Concurrently, the current density of the carrier is also attained from the following equation [37]:

(4)$j_p=qn{\mu }_{p}E-q{D}_p\frac{\partial p}{\partial x}$

(5)$j_n=qn{\mu }_{n}E+q{D}_n\frac{\partial n}{\partial x}$

where the charge is presented as $q \mathrm{and}$ the carrier mobilities are shown as ${\mu }_p$ and ${\mu }_n$ while the carriers’ diffusion coefficients are $D_p$ and $D_n$. It is worth mentioning that the software SCAPS-1D (version 3.8) extracts all the fundamental equations of the perovskite solar cell: the current density, the generation, as well as the rate of recombination. Lastly, the SCAPS-1D also uses certain other fundamental equations to understand and optimize the defect-related recombination losses whose information is provided in a prior publication.

3. Results and Discussion

The Results and Discussion section is distributed into five subsections that explore the effect of PAL thickness, temperature, mass defect density and the comparison of single and dual PAL-based PSCs. Results are shown in Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6.

3.1. Effect of the Combined Thickness of the PALs in PSC

The proportional investigation of the distinct thicknesses for the CsSnGeI₃- and MASnI₃-based active layers is plotted on the x- and y-axis. Contour plotting reported in Figure 2a–d offers a more innovative way to check thickness compatibility. The PV parameters for the PSC are investigated for obtaining the optoelectronic characteristics of the PSC under the AM1.5 photo illumination. It can be observed that the V_OC is maximum for smaller thickness PAL combination offering a value of 1.27 V. The value decreases with increasing the thickness for the higher possible recombination values. As far as the J_SC is concerned, the MASnI₃ thickness of 1.6 µm and 0.2 µm provides a better J_SC value offering up to 31.84 mA/cm². A minimal value is obtained for a smaller thickness combination of CsSnGeI₃ and MASnI₃ layers due to inability of photon absorption inside the PALs, obtaining a value of 26.40 mA/cm², which further contributes to attaining a smaller efficiency value. In Figure 2c, the dual PAL offers the highest FF of 83.44% at a smaller value of the thicknesses. At last, the effect of the combined thickness over the efficiency is depicted in Figure 2d, as the highest value of efficiency is 31.53% at the thickness of 1 µm and 0.2 µm of MASnI₃ and CsSnGeI₃, respectively. This is due to the high value of J_SC at the thickness level of 1 µm, as the efficiency is directly proportional to the efficiency of the PSC. The contour study further provides the efficiency range for simulating further parameters of the PSC device.

3.2. Impact of Temperature on PSC

The effect of the temperature is studied with a detailed comparison of the solar cell parameters. Figure 3 shows the impact of temperature on the J_SC, V_OC, FF and PCE. As the dependency on the temperature for the J_SC is evident that it keeps decreasing from 31.41 mA/cm² at 300 K to 31.32 mA/cm², the V_OC also reduces from 1.215 V to 1.18 V; on the contrary, the FF value also decreases with increasing the value of the 82.5% to 77.5%. Lastly, the efficiency value offers the highest efficiency value of 31.53% to 27.9%, as shown in Figure 3a. Additionally, a steeper temperature gradient with an average efficiency of −0.0265%/K for the optimized PSC can be observed.

The SCAPS-1D simulator exclusively solves the three distinct equations to investigate the influence of temperature on material properties. Referencing both Equations (6) and (7), the density of states in the valence/conduction band [N_V(T)/N_C(T)] fluctuates with the temperature. The thermal velocity V_th(T) is also influenced by the temperature, as shown in Equation (8), while the other important parameters are expected to remain consistent, regardless of temperature fluctuations. The diffusion coefficient is temperature dependent and that can be given by D = μkT/q. Lastly, the default temperature, T₀, is set to 300 K in the SCAPS-1D and should be defined at this temperature [38].

(6)$N_C(T)=N_C(T_0){\left(\frac{T}{T_0}\right)}^{1.5}$

(7)$N_V(T)=N_V(T_0){\left(\frac{T}{T_0}\right)}^{1.5}$

(8)$V_{th}(T)=V_{th}(T_0){\left(\frac{T}{T_0}\right)}^{1.5}$

An increasing temperature further increases all the remaining three parameters, such as N_C(T), N_V(T) and V_th(T), and the observed performance can be associated with the same. An increasing density of states provides more states for the electrons and holes to conquer. The solar cell performance can also be impacted by the temperature-dependent thermal velocity as it influences the diffusion of carriers of the material. An increasing temperature results in an increase in thermal velocity (Equation (8)), which can lead to a reduction in the carrier lifetime and an increase in the recombination rate. This further leads to higher reverse saturation current and reduces the device performance, particularly in terms of V_OC and FF, as shown in Figure 3a,b. The temperature decreases the overall Voc linearly as the open-circuit voltage declines with the temperature because of the temperature dependency of I₀. The current work describes a lesser temperature gradient compared with the previous report value by Sobayel et al. [20].

Figure 3b also depicts the J-V characteristics at various temperatures, which offers precise information on the impact of temperature. The maximum parameters with the optimized conditions of temperature are listed below in Table 3. PV parameters are compared with the earlier works by Raghhavendra et al. where CsSnGeI₃ based absorber is utilized to enhance the efficiency. The PSC with the single PAL of wider bandgap perovskite material of CsSnGeI₃ is employed, which reaches up to 13.29% [15]; that is why the efficiency is lower for employing the higher bandgap material in the PSC. Similarly, the single PAL materials by Singh et al. reach an efficiency up to 20.58%, which included the extensive optimization approach [11], while Noel et al. obtained an efficiency up to 6.4% using the MASnI₃ layer in the PSC [39] that is also listed in Table 3.

3.3. Influence of the Total Defect Density (DD) of the Optimized PSC Devices

The combined influence of MASnI₃ and CsSnGeI₃ layer DD on the PSC outputs, namely J_SC, V_OC, FF and efficiency, are illustrated in Figure 4. The current work is simulated under the fluctuating DD range of the MASnI₃ layer and CsSnGeI₃ layer from 1.0 × 10¹⁴ cm⁻³ to 1.0 × 10¹⁵ cm⁻³, respectively. The simulation results are attaining the best PSC parameters with J_SC of 31.41 mA/cm², V_OC of 1.215 V, FF of nearly 82.62% and the highest efficiency of 31.53%, at the combined DD of 1.0 × 10¹⁴ cm⁻³ due to the optimized photo-absorption at less defective MASnI₃/CsSnGeI₃ active material. The combined study of defect density provides reasonable detail about the PSC for obtaining a more efficient PSC device having double PAL.

3.4. EQE and J-V Parameters Comparison of the Simulated PSC Devices

In Figure 5a, the single PAL of CsSnGeI₃ shows a marginally lower QE than the double PAL of CsSnGeI₃/ MASnI₃ as the double PAL absorbs higher value of wavelengths for the combined low and high bandgaps. The single PAL of CsSnGeI₃ only absorbs the photons with an energy level higher than the bandgap of the PAL. As a result, the smaller energy photons cannot be absorbed in the single PAL. The second layer in double PAL also absorbs the transmitted photons through the first layer. This leads to an offering of a substantially larger value, up to 85%, than the earlier finding by Azri et al. [17].

In Figure 5b, the J-V parameter for the single PAL (CsSnGeI₃)- and double PAL (CsSnGeI₃/MASnI₃)-based PSC device is simulated under the optimized preconditions. The J-V curve for the simulated single and double PAL shows that the single PAL offers a smaller J_SC value than the other. This is due to a higher range of photon absorption in the perovskite material, which increases the excitons generation. Comparatively, the dual PAL offers a J_SC of 31.41 mA/cm² while the single PAL offers J_SC of 28.27 mA/cm^2, respectively. On the other hand, the double PAL-based PSC offers a smaller V_OC value due to higher possible recombination inside the dual PAL as the double PAL of CsSnGeI₃/MASnI₃ offers a V_OC of 1.215 V while a single PAL offers a V_OC of 1.33 V. The simulated PSC outputs for optimized PSCs are summarized in Table 3.

3.5. Influence of IDD on the Output of the PSC

Results reported in sections A to D assumed the ideal interface between all the heterojunctions, i.e., IDD and associated interfacial recombinations, are not considered. Studying the effect of IDD on the PSC is important because IDD can greatly impact the performance of the solar cell. These defects can lead to the recombination of charge carriers, reducing the efficiency of the PSC. By understanding the relationship between IDD and performance, scientists can develop strategies to minimize the formation of these defects and the efficiency improvement of the PSC. Additionally, studying the effect of IDD on perovskite solar cells can also help in understanding the underlying physics of these devices and can lead to the improvement of new materials as well as fabrication techniques. Additional simulations are done to obtain the effect of Spiro-OMeTAD/MASnI₃ (Figure 6a), MASnI₃/CsSnGeI₃ (Figure 6b) and CsSnGeI₃/ZnO (Figure 6c) IDD on the PV performance of the PSC. IDD is varied from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁶ cm⁻², and corresponding PV parameters are obtained. Spiro-OMeTAD/MASnI₃ IDD variation showed negligible effect on J_SC but significantly reduced the V_OC from 1.03 V to 0.95 V while it increased the IDD from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁶ cm⁻². FF was also reduced from 87.3% to 85.8%. IDD can create recombination centers that reduce the efficiency of charge transport in the cell, which can lead to a decrease in the V_OC and FF. The collective effect of J_SC, V_OC and FF led to a reduction in overall PCE from 28.3% to 25.7%. A similar trend is also observed for MASnI₃/CsSnGeI₃ and CsSnGeI₃/ZnO IDD, which showed a reduction in PCE from 25.5% to 10.3% and 29.2% to 23.3% while an increase in IDD from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁶ cm⁻², respectively. Further, detailed PV parameters are also tabulated in Table 4 with each combination of three different cases, i.e., No IDD, IDD at 1 × 10¹⁴ cm^−2, and IDD at 1 × 10¹⁶ cm⁻² for all three interfaces. Results showed that the MASnI₃/CsSnGeI₃ interface greatly impacted the PV performance compared to the other two interfaces. Also, Table 4 describes the detailed comparison of the IDD values of all three interfaces. From no DD to 1 × 10¹⁶ cm⁻², the variation is recorded to obtain the best combination of the IDD levels. The detailed analysis is shown in Table 4.

4. Conclusions

The double PALs, i.e., MASnI₃ and CsSnGeI₃, are used for simulating the perovskite solar cell utilizing the SCAPS-1D simulating software. Initially, the investigation includes the combined effect of the PAL thicknesses for finding suitable widths for attaining much-improved efficiency of the PSC. It can be depicted that the output parameters of the PSC are considerably enhanced by utilizing the thickness of 1 µm and 0.2 µm, respectively. The next evident outcome of the current work is that the defect density of both the PALs is the lowest value of defect density, i.e., 1.0 × 10¹⁴ cm⁻³, which offers an improvement in the efficiency of up to 31.53%. The investigation of the influence of the temperature also illustrates that the 300 K temperature can be suitable for the effective production of the PSC, and an increment in the temperature further impacts the V_oc. The current report is praiseworthy as the efficient combination of appropriate CTLs improved efficiency, approaching the Shockley-Queisser limit. Moreover, the IDD analysis of the double-graded PSC shows that the highest value of output can be obtained at the no interface defect density state. Apart from that, the QE and JV analysis is also accomplished between the single and double PAL in the designed PSC devices. The present work is a novel graded approach and achieves higher efficiency than prior reports by Raghvendra et al. for the lead-free PAL [15]. The output of the current simulation is important for the non-toxicity in the designed materials as well. So, for properly constructed PSC devices, the current work provides a better choice for obtaining cost-effective and improved device productivity.

Author Contributions

Conceptualization, S.B. and M.K.H.; methodology, S.B.; software, S.B.; validation, S.B., M.K.A.M., J.M., R.P., M.Z.A., A.N.Z.R. and M.K.H.; formal analysis, S.B., M.K.A.M. and M.K.H.; investigation, S.B., J.M., R.P., M.Z.A. and A.N.Z.R.; resources, S.B. and M.K.H.; data curation, S.B., M.K.A.M. and M.K.H.; writing—original draft preparation, S.B.; writing—review and editing, S.B., M.K.A.M., J.M., R.P., M.Z.A., A.N.Z.R., M.A. and M.K.H.; visualization, S.B., M.K.A.M., J.M., R.P., M.Z.A., A.N.Z.R., M.A. and M.K.H.; Funding acquisition, M.A. and M.K.H.; supervision, S.B. and M.K.H.; project administration, S.B., M.A. and M.K.H. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors have extended their appreciation to the Deanship of Scientific Research at King Khalid University, Saudi Arabia for funding this work through the Research Groups Program under grant number R.G.P.2: 219/44. The SCAPS-1D program was kindly provided by M. Burgelman of the University of Gent in Belgium. The authors would like to express their gratitude to him.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

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Figures and Tables

Figure 1. (a) Illustration of PSC device structures; (b) the working mechanism of the PSC at the AM1.5 illuminance.

Figure 2. Contour plot of electrical parameters, namely ((a) VOC (V), (b) JSC (mA/cm2), (c) FF (%) and (d) efficiency (%)) over the PAL thickness of the PSC.

Figure 3. (a) The influence of temperature on solar cell parameters and (b) J-V characteristics of the double PAL-based PSC.

Figure 4. The contour plot of electrical characteristics of (a) VOC (V), (b) JSC (mA/cm2), (c) FF (%) and (d) PCE (%) with the simultaneous arrangement of total DD of the MASnI3/ CsSnGeI3 layer.

Figure 5. (a) Effect of single PAL and Double PAL to study the QE parameters wrt the wavelength and (b) variation of J-V curve for single PAL and double PAL under photo illumination of AM1.5.

Figure 6. The impact of IDD on the outputs of the PSC; (a) Spiro-OMeTAD/MASnI3, (b) MASnI3/CsSnGeI3 and (c) CsSnGeI3/ZnO, respectively.

Table 1

The input parameters and material characteristics in CsSnGeI₃/MASnI₃-based PSCs [15,17,34,35].

Parameters	Terms	TiO2	MASnI3	CsSnGeI3	Spiro-OMeTAD
t (nm)	Thickness	100	200	800	100
Eg (eV)	Bandgap	3.2	1.3	1.5	3.0
χ (eV)	Electron affinity	3.9	4.1	3.9	2.45
ɛr	Rel. permittivity	9	8.2	28	3.0
Nc (cm−3)	Eff. DoS at CB	1 × 1021	1 × 1018	3.1 × 1018	1 × 1019
Nv (cm−3)	Eff. DoS at VB	2 × 1020	1 × 1018	3.1 × 1018	1 × 1019
µn (cm2/Vs)	e- Mobility	20	1.6	974	2 × 10−4
µp (cm2/Vs)	h+ Mobility	10	1.6	213	2 × 10−4
Nd (cm−3)	Don. density	1 × 1019	0	1 × 1014	0
Na (cm−3)	Acc. density	1.0	1 × 1015	0	2 × 1018
Nt (cm−3)	Total DD	1 × 1014(donor type)	1 × 1014(acceptor type)	1 × 1014(acceptor type)	1 × 1014(acceptor type)

Table 2

The interface simulation parameters in MASnI₃-based PSC device.

Parameters	Spiro-OMeTAD/MASnI3	MASnI3/CsSnGeI3	CsSnGeI3/ZnO
Defect types	Neutral	Neutral	Neutral
Cap. cross-section e (cm2)	1 × 10−12	1 × 10−12	1 × 10−12
Cap. cross-section h (cm2)	1 × 10−12	1 × 10−12	1 × 10−12
Energy distributions	Single	single	single
Ref. for defect energy level	At Ei	At Ei	At Ei
Total DD (int. over all energies) (cm−2)	Variable	Variable	Variable

Table 3

The comparison of solar cell parameters on different device structures.

Device Architectures	VOC (V)	JSC (mA/cm2)	FF (%)	Efficiency (%)
TiO2/CsSnGeI3/Spiro-OMeTAD	1.33	28.27	84.27	28.53
TiO2/MASnI3/CsSnGeI3/Spiro-OMeTAD	1.215	31.41	82.62	31.53
Raghhavendra et al. [15]	0.797	20.43	81.63	13.29
Singh et al. [11]	1.00	25.75	79.22	20.58
Noel et al. [39]	0.88	16.8	42	6.4

Table 4

PV parameters of the simulated device at different IDD values for three different interfaces.

S. No	Spiro-OMeTAD/MASnI3 (cm−2)	MASnI3/CsSnGeI3 (cm−2)	CsSnGeI3/ZnO (cm−2)	VOC (V)	JSC (mA·cm−2)	FF(%)	PCE(%)
1	No IDD	No IDD	No IDD	1.22	31.41	82.62	31.53
2	No IDD	No IDD	1 × 1014	1.20	31.42	83.04	31.37
3	No IDD	No IDD	1 × 1016	1.07	31.41	87.04	29.21
4	No IDD	1 × 1014	No IDD	0.98	30.90	84.33	25.49
5	No IDD	1 × 1014	1 × 1014	0.98	30.90	84.33	25.49
6	No IDD	1 × 1014	1 × 1016	0.98	30.89	84.27	25.44
7	No IDD	1 × 1016	No IDD	0.88	16.99	74.55	11.18
8	No IDD	1 × 1016	1 × 1014	0.88	16.99	74.55	11.18
9	No IDD	1 × 1016	1 × 1016	0.88	16.99	74.55	11.18
10	1 × 1014	No IDD	No IDD	1.03	31.42	87.33	28.27
11	1 × 1014	No IDD	1 × 1014	1.03	31.42	87.33	28.27
12	1 × 1014	No IDD	1 × 1016	1.02	31.41	87.19	28.05
13	1 × 1014	1 × 1014	No IDD	0.97	30.90	84.46	25.41
14	1 × 1014	1 × 1014	1 × 1014	0.97	30.90	84.46	25.41
15	1 × 1014	1 × 1014	1 × 1016	0.97	30.89	84.39	25.37
16	1 × 1014	1 × 1016	No IDD	0.88	16.99	74.52	11.17
17	1 × 1014	1 × 1016	1 × 1014	0.88	16.99	74.52	11.17
18	1 × 1014	1 × 1016	1 × 1016	0.88	16.99	74.52	11.17
19	1 × 1016	No IDD	No IDD	0.95	31.37	85.79	25.66
20	1 × 1016	No IDD	1 × 1014	0.95	31.37	85.79	25.66
21	1 × 1016	No IDD	1 × 1016	0.95	31.36	85.57	25.57
22	1 × 1016	1 × 1014	No IDD	0.94	30.85	84.12	24.44
23	1 × 1016	1 × 1014	1 × 1014	0.94	30.85	84.12	24.44
24	1 × 1016	1 × 1014	1 × 1016	0.94	30.84	84.05	24.40
25	1 × 1016	1 × 1016	No IDD	0.88	16.94	73.73	10.95
26	1 × 1016	1 × 1016	1 × 1014	0.88	16.94	73.73	10.95
27	1 × 1016	1 × 1016	1 × 1016	0.88	16.94	73.72	10.95

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