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Optimization of lead-free CsSnI3-based perovskite solar cell structure

Optimization of lead-free CsSnI3-based perovskite solar cell structure 1IntroductionSolar cell technology has evolved since its inception through three generations, the first is based on thick wafers of silicon semiconductor material, which despite their high manufacturing costs continue to dominate [1]. The second generation cells is based on amorphous nanocrystalline or polycrystalline semiconductor thin films deposited on cheap substrates [2].Perovskite cells, which belong to the third generation of solar cells, are currently the focus of interest and exploitation of scientists and research groups specialized in this field. Power conversion efficiencies of solar cells utilizing these materials expanded from ∼3.8% in 2009 to ∼25.5% in 2020 [3]. The Perovskite material is typically composed of three parts according to the ABX3 stoichiometry. A represents, in most cases, the organic part like methylammonium CH3NH3+, MA, or formamidinium HC(NH2)2+, FA, but can also be inorganic like cesium Cs. B is a metal ion, bivalent in the conventional composition, usually lead Pb2+, or one of its substitutes like germanium Ge2+, selenium Se2+, etc. B can also be trivalent or tetravalent like bismuth Bi4+, antimony Sb4+ or titanium Ti4+. X is a halide anion such as the chlorine anion Cl−, the bromine anion Br−, or the iodine anion I− [4] Photovoltaic devices based on the absorber Perovskite MAPbI3 are still the most efficient and most widely studied Perovskite solar cells. However, the instability of the Methylammonium MA cation hinders their commercialization [5]The conversion record achieved so far is 25.6% for the FAPbI3-based Perovskite cell, in which the more stable Formamidinium FA replaces MA [6]. Several methods have been detailed in the literature to address the instability problem and to increase efficiency, such as the additive engineering-based approach [7].Lead Pb2+ is still essential to ensure excellent photoelectric properties of Perovskite films. However, lead can be toxic to the environment, humans, and other species. For this reason, lead-free Perovskites have attracted much attention recently. Several non- or less toxic elements can replace lead in the composition of Perovskite, tin Sn is one of them. It has even been reported that tin-containing Perovskites have equally good optoelectronic properties. However, tin has a tendency to oxidize to Sn4+, so it is recommended to use encapsulation in the manufacture of tin-based Perovskite cells [8]. Cesium tin iodide CsSnI3, with a band gap of 1.3 eV, is one of the candidates to replace the conventional lead-based Perovskite material. The latter is completely inorganic, has similar optoelectronic properties to its lead-based counterpart, and can be deposited using low-cost processes [9]. In addition, several authors have reported the excellent mechanical and electronic properties of cesium-based perovskite films [10,11].In this article, we have presented a work that consists in modeling and simulating, then optimizing the structure of a single solar cell whose absorber material is the lead-free and inorganic Perovskite CsSnI3. We have particularly focused on the impact of the increase of the defect density at the interfaces between the absorber layer and the neighboring layers. We have then simulated the performance of the structures with alternative ETL and HTL layers.The goal of the study is the optimization of the structure that leads to the best performance and photovoltaic parameters with minimum interface recombination rate and appropriate bandgap energy shifts at the absorber boundaries, and this with minimal fabrication cost, in addition to adapting to a tandem configuration as a bottom cell in combination with an appropriate top sub-cell.2Simulation modelA drift–diffusion model was considered to express the transport of photo-generated carriers [12]. Photogenerated current density was calculated with expressions derived by using the numerical solutions of the Poisson equation and the continuity equations for holes and electrons [13]Equation (1) represents the expression of photogenerated current density [14](1)Jph=q∫λminλmaxF(λ)·EQE(λ)dλ,{J}_{{\rm{ph}}}=q\underset{{\lambda }_{{\rm{\min }}}}{\overset{{\lambda }_{{\rm{\max }}}}{\int }}F(\lambda ){\rm{\cdot }}{\rm{EQE}}(\lambda ){\rm{d}}\lambda ,where λmin and λmax are minimum and maximum wavelengths, q is the electron charge, F(λ)(\lambda )is the solar spectrum, and EQE(λ)(\lambda )is the external quantum efficiency of the cell.A two model equivalent circuit was considered to evaluate the current–voltage behavior(2)J=Jph−(J0+Js)·eq·(V−JRs)2kT−1−V−J·RsRsh,J={J}_{{\rm{ph}}}-({J}_{0}+{J}_{{\rm{s}}}){\cdot }\left({{\rm{e}}}^{\frac{q{\cdot }(V-J{R}_{{\rm{s}}})}{2{kT}}}-1\right)-\frac{V-J{\cdot }{R}_{{\rm{s}}}}{{R}_{{\rm{sh}}}},where Rs and Rsh are parasitic resistances.J0 is the reverse dark saturation current density due to the radiative recombination assuming the Shockley-read-Hall recombination theory. And Js is the interface recombination contribution in current density losses reported as a function of the interface recombination velocity [15] expressed in equation (3). Minority carrier concentration and bandgap energy offsets at the boundaries of the absorber were evaluated using equations (4) and (5).(3)Sn,p=σn,p·Vth·Ntn,p.{S}_{{\rm{n}},{\rm{p}}}={\sigma }_{{\rm{n}},{\rm{p}}}{\cdot }{V}_{{\rm{th}}}{\cdot }{N}_{{\rm{tn}},{\rm{p}}}.Here, Ntn,p is the front/back interface density, Vth is the thermal velocity, and σn,p is the electron/hole capture cross section at interfaces.Conduction band offset (CBO) and valence band offset (VBO) are given in the following equations:(4)ΔEc=χETL−χCsSnI3,{\Delta E}_{{\rm{c}}}={\chi }_{{\rm{ETL}}}-{\chi }_{{\rm{CsSn}}{{\rm{I}}}_{3}},(5)ΔEv=(χHTL+Eg,HTL)−(χCsSnI3+Eg,CsSnI3),{\Delta E}_{{\rm{v}}}={(\chi }_{{\rm{HTL}}}\left+{E}_{{\rm{g}},{\rm{HTL}}})-{(\chi }_{{\rm{CsSn}}{{\rm{I}}}_{3}}\left+{E}_{{\rm{g}},{\rm{CsSn}}{{\rm{I}}}_{3}}),where χ is the electron affinity and Eg is the bandgap energy.Equations (6) and (7) are solar cell Fill factor and power conversion efficiency [16].(6)FF=JMax·VMaxJsc·Voc,{\rm{FF}}=\frac{{J}_{{\rm{Max}}}{\cdot }{V}_{{\rm{Max}}}}{{J}_{{\rm{sc}}}{\cdot }{V}_{{\rm{oc}}}},(7)PCE=JMax·VMaxPinc,{\rm{PCE}}=\frac{{J}_{{\rm{Max}}}{\cdot }{V}_{{\rm{Max}}}}{{P}_{{\rm{inc}}}},where JMax and VMax are the current and voltage at the maximum power point. Jsc and Voc are the short circuit current density and the open circuit voltage, respectively. Pinc is the incident power.3Results and discussionIn this study, the basic structure, configured as follows: Glass/FTO/TiO2/CsSnI3/PTAA/Au, is considered [17]. Cesium–tin–iodine CsSnI3 is the studied lead-free Perovskite absorber, which has a band gap energy of 1.3 eV, while titanium oxide TiO2 and PTAA (poly-triyaril amine) are the materials used for the ETL and HTL electron and hole transport layers A schematic representation of the proposed solar cell is shown in Figure 1. The data of the physical parameters of the materials used in this simulation were carefully selected from the literature [18,19,20].Figure 1Schematic representation of the basic device.3.1Investigation of the interface density of defectsThe density of defects at the interfaces between the Perovskite absorber and the neighboring ETL and HTL layers has a profound influence on the collection of carriers since they are considered as obstacles that prevent their passage. This influence on the photovoltaic parameters, especially on the conversion efficiency, has been studied by varying their value from 1012 to 1020 cm−3. Figure 2 shows the behavior of the photovoltaic parameters as a function of the above-mentioned defect density increase.Figure 2Effect of interface density of defects on the photovoltaic parameters of the basic cell structure. (a) Short current density, (b) open circuit voltage, (c) fill Factor and (d) power conversion efficiency.The results revealed the degradation of the performance from the increase of the front or back interfaces defect density higher than 1014 cm−3 due to the increase of the recombination velocity at the considered interface, which favors the capture of the carriers by the trap states. The influence was more significant for the increase in the front interface defect density. It was noticed that the photocurrent density was not affected by the augmentation of the back interface defects, because it mainly comes from the photo-generated electrons. This study shows the importance of keeping the defect density at the interfaces below a value of 1015 cm−3 to achieve the best performance.3.2Investigation of appropriate ETL and HTL materialsThe dissociation of photogenerated pairs of carriers (electrons and holes) in the absorber occurs at the front and back interfaces between the ETL layer and the absorber, and the HTL layer and the absorber, respectively. For this reason, the amount of defects at these locations must be taken into account because of its relationship with the recombination rate. On the other hand, the shift of energy bands at the interfaces strongly affects the amount of collected carriers.Therefore, the choice of the materials used for ETL and HTL layers is important. In this section, several materials have been proposed for investigation to reach high performance. Zinc sulfide (ZnS), tin dioxide (SnO2), cadmium zinc sulfide (CdZnS), and 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (PCBM) were investigated as ETM. The alternative materials studied for the hole transport layers were the organic semiconductor 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD), cuprous oxide (Cu2O), nickel oxide (NiO), and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). Data and material input parameters used in the simulation are taken from the literature [13,19,20]. The conversion efficiency of the different structures is plotted in Figure 2.Figure 3(a) shows that the structure based on the SnO2-ETL material gives the best efficiency of 19.92% with a narrower conduction band offset than the base cell. However, the front interface recombination velocity value remains unchanged. While Figure 3(b) reveals that using Spiro-OMeTAD-HTL material leads to the best efficiency with a more appropriate value of valence band offset 0.3 eV and an unchanged back interface recombination velocity. A better performance of the organic-HTL materials was noted compared to the inorganic materials. However, the structure based on inorganic Cu2O-HTL still recorded a high yield of 18.31% and appropriate values of VBO and Sp. The simulation results allow us to consider the structure SnO2/CsSnI3/Spiro-OMeTAD as the optimal configuration which reaches the best performance with the most appropriate values of bandgap energy offsets and recombination velocity at the interfaces. However, in order to favor a totally inorganic cell, the SnO2/CsSnI3/Cu2O structure can be considered, although the conversion efficiency is slightly lower. The current–voltage curves of the mentioned structures are represented in Figure 4. Simulation results are detailed in Table 1.Figure 3Power conversion efficiency: (a) for different ETL materials; (b) for different HTL materials.Figure 4J–V characteristics of CsSnI3-based structures.Table 1Performance of CsSnI3-based perovskite cell structuresCell structureJph (mA/cm²)Voc (Volt)FF (%)PCE (%)CBO–VBO (eV)Sn–Sp (cm/s)TiO2/CsSnI3/PTAA (Basic)30.680.82973.3319.890.76–0.39103–103SnO2/CsSnI3/Spiro-OMeTAD (Optimal)30.680.82973.3619.920.50–0.30103–103SnO2/CsSnI3/Cu2O (Inorganic)30.460.82970.1618.310.50–0.57103–103In order to close this study, the suggested structures were simulated as bottom sub-cell in two-terminal tandem configuration in association with the top sub-cell having the following structure: PCBM/CsSnGeI3/Spiro-OMeTAD with an absorber bandgap energy of 1.5 eV [21]. The results of the simulation are shown in Table 2. In literature, it is possible to find many simulation works which were done using different code for different purposes [22,23,24,25,26,27,28,29,30,31].Table 2Performance of CsSnI3-based perovskite cell structures2T-tandem cell structureJph (mA/cm²)Voc (Volt)FF (%)PCE (%)Top: PCBM/CsSnGeI3/Spiro-OMeTAD18.631.59391.731.68Bottom: TiO2CsSnI3/PTAA (basic)Top: PCBM/CsSnGeI3/Spiro-OMeTAD18.711.46191.429.22Bottom: SnO2/CsSnI3/Spiro-OMeTAD (optimal)Top: PCBM/CsSnGeI3/Spiro-OMeTAD18.861.46291.429.20Bottom: SnO2/CsSnI3/Cu2O (inorganic)4ConclusionIn this work, a Perovskite solar cell structure based on the lead-free Perovskite absorber CsSnI3 was simulated and optimized. The effect of defect density on the solar cell performance at the front ETL/Perovskite and back Perovskite/HTL interfaces was studied. Different cell structures with various alternative ETL and HTL materials were simulated, and the obtained results were presented. An optimal structure with selected ETL and HTL materials with appropriate values of interface recombination velocity and band gap shift at the absorber boundaries was suggested based on the obtained results. An efficiency of 19.92% was achieved with the optimal structure: SnO2/CsSnI3/Spiro-OMeTAD, and 18.31% with the fully inorganic and non-toxic structure: SnO2/CsSnI3/Cu2O. An improvement was observed over the baseline device. The structure was simulated as a bottom cell in a two-terminal tandem solar cell, and an efficiency of 29.22% was achieved. The results of this study can provide useful information before proceeding to the manufacturing stage. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Rheology de Gruyter

Optimization of lead-free CsSnI3-based perovskite solar cell structure

Applied Rheology , Volume 33 (1): 1 – Jan 1, 2023

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Publisher
de Gruyter
Copyright
© 2023 the author(s), published by De Gruyter
eISSN
1617-8106
DOI
10.1515/arh-2022-0138
Publisher site
See Article on Publisher Site

Abstract

1IntroductionSolar cell technology has evolved since its inception through three generations, the first is based on thick wafers of silicon semiconductor material, which despite their high manufacturing costs continue to dominate [1]. The second generation cells is based on amorphous nanocrystalline or polycrystalline semiconductor thin films deposited on cheap substrates [2].Perovskite cells, which belong to the third generation of solar cells, are currently the focus of interest and exploitation of scientists and research groups specialized in this field. Power conversion efficiencies of solar cells utilizing these materials expanded from ∼3.8% in 2009 to ∼25.5% in 2020 [3]. The Perovskite material is typically composed of three parts according to the ABX3 stoichiometry. A represents, in most cases, the organic part like methylammonium CH3NH3+, MA, or formamidinium HC(NH2)2+, FA, but can also be inorganic like cesium Cs. B is a metal ion, bivalent in the conventional composition, usually lead Pb2+, or one of its substitutes like germanium Ge2+, selenium Se2+, etc. B can also be trivalent or tetravalent like bismuth Bi4+, antimony Sb4+ or titanium Ti4+. X is a halide anion such as the chlorine anion Cl−, the bromine anion Br−, or the iodine anion I− [4] Photovoltaic devices based on the absorber Perovskite MAPbI3 are still the most efficient and most widely studied Perovskite solar cells. However, the instability of the Methylammonium MA cation hinders their commercialization [5]The conversion record achieved so far is 25.6% for the FAPbI3-based Perovskite cell, in which the more stable Formamidinium FA replaces MA [6]. Several methods have been detailed in the literature to address the instability problem and to increase efficiency, such as the additive engineering-based approach [7].Lead Pb2+ is still essential to ensure excellent photoelectric properties of Perovskite films. However, lead can be toxic to the environment, humans, and other species. For this reason, lead-free Perovskites have attracted much attention recently. Several non- or less toxic elements can replace lead in the composition of Perovskite, tin Sn is one of them. It has even been reported that tin-containing Perovskites have equally good optoelectronic properties. However, tin has a tendency to oxidize to Sn4+, so it is recommended to use encapsulation in the manufacture of tin-based Perovskite cells [8]. Cesium tin iodide CsSnI3, with a band gap of 1.3 eV, is one of the candidates to replace the conventional lead-based Perovskite material. The latter is completely inorganic, has similar optoelectronic properties to its lead-based counterpart, and can be deposited using low-cost processes [9]. In addition, several authors have reported the excellent mechanical and electronic properties of cesium-based perovskite films [10,11].In this article, we have presented a work that consists in modeling and simulating, then optimizing the structure of a single solar cell whose absorber material is the lead-free and inorganic Perovskite CsSnI3. We have particularly focused on the impact of the increase of the defect density at the interfaces between the absorber layer and the neighboring layers. We have then simulated the performance of the structures with alternative ETL and HTL layers.The goal of the study is the optimization of the structure that leads to the best performance and photovoltaic parameters with minimum interface recombination rate and appropriate bandgap energy shifts at the absorber boundaries, and this with minimal fabrication cost, in addition to adapting to a tandem configuration as a bottom cell in combination with an appropriate top sub-cell.2Simulation modelA drift–diffusion model was considered to express the transport of photo-generated carriers [12]. Photogenerated current density was calculated with expressions derived by using the numerical solutions of the Poisson equation and the continuity equations for holes and electrons [13]Equation (1) represents the expression of photogenerated current density [14](1)Jph=q∫λminλmaxF(λ)·EQE(λ)dλ,{J}_{{\rm{ph}}}=q\underset{{\lambda }_{{\rm{\min }}}}{\overset{{\lambda }_{{\rm{\max }}}}{\int }}F(\lambda ){\rm{\cdot }}{\rm{EQE}}(\lambda ){\rm{d}}\lambda ,where λmin and λmax are minimum and maximum wavelengths, q is the electron charge, F(λ)(\lambda )is the solar spectrum, and EQE(λ)(\lambda )is the external quantum efficiency of the cell.A two model equivalent circuit was considered to evaluate the current–voltage behavior(2)J=Jph−(J0+Js)·eq·(V−JRs)2kT−1−V−J·RsRsh,J={J}_{{\rm{ph}}}-({J}_{0}+{J}_{{\rm{s}}}){\cdot }\left({{\rm{e}}}^{\frac{q{\cdot }(V-J{R}_{{\rm{s}}})}{2{kT}}}-1\right)-\frac{V-J{\cdot }{R}_{{\rm{s}}}}{{R}_{{\rm{sh}}}},where Rs and Rsh are parasitic resistances.J0 is the reverse dark saturation current density due to the radiative recombination assuming the Shockley-read-Hall recombination theory. And Js is the interface recombination contribution in current density losses reported as a function of the interface recombination velocity [15] expressed in equation (3). Minority carrier concentration and bandgap energy offsets at the boundaries of the absorber were evaluated using equations (4) and (5).(3)Sn,p=σn,p·Vth·Ntn,p.{S}_{{\rm{n}},{\rm{p}}}={\sigma }_{{\rm{n}},{\rm{p}}}{\cdot }{V}_{{\rm{th}}}{\cdot }{N}_{{\rm{tn}},{\rm{p}}}.Here, Ntn,p is the front/back interface density, Vth is the thermal velocity, and σn,p is the electron/hole capture cross section at interfaces.Conduction band offset (CBO) and valence band offset (VBO) are given in the following equations:(4)ΔEc=χETL−χCsSnI3,{\Delta E}_{{\rm{c}}}={\chi }_{{\rm{ETL}}}-{\chi }_{{\rm{CsSn}}{{\rm{I}}}_{3}},(5)ΔEv=(χHTL+Eg,HTL)−(χCsSnI3+Eg,CsSnI3),{\Delta E}_{{\rm{v}}}={(\chi }_{{\rm{HTL}}}\left+{E}_{{\rm{g}},{\rm{HTL}}})-{(\chi }_{{\rm{CsSn}}{{\rm{I}}}_{3}}\left+{E}_{{\rm{g}},{\rm{CsSn}}{{\rm{I}}}_{3}}),where χ is the electron affinity and Eg is the bandgap energy.Equations (6) and (7) are solar cell Fill factor and power conversion efficiency [16].(6)FF=JMax·VMaxJsc·Voc,{\rm{FF}}=\frac{{J}_{{\rm{Max}}}{\cdot }{V}_{{\rm{Max}}}}{{J}_{{\rm{sc}}}{\cdot }{V}_{{\rm{oc}}}},(7)PCE=JMax·VMaxPinc,{\rm{PCE}}=\frac{{J}_{{\rm{Max}}}{\cdot }{V}_{{\rm{Max}}}}{{P}_{{\rm{inc}}}},where JMax and VMax are the current and voltage at the maximum power point. Jsc and Voc are the short circuit current density and the open circuit voltage, respectively. Pinc is the incident power.3Results and discussionIn this study, the basic structure, configured as follows: Glass/FTO/TiO2/CsSnI3/PTAA/Au, is considered [17]. Cesium–tin–iodine CsSnI3 is the studied lead-free Perovskite absorber, which has a band gap energy of 1.3 eV, while titanium oxide TiO2 and PTAA (poly-triyaril amine) are the materials used for the ETL and HTL electron and hole transport layers A schematic representation of the proposed solar cell is shown in Figure 1. The data of the physical parameters of the materials used in this simulation were carefully selected from the literature [18,19,20].Figure 1Schematic representation of the basic device.3.1Investigation of the interface density of defectsThe density of defects at the interfaces between the Perovskite absorber and the neighboring ETL and HTL layers has a profound influence on the collection of carriers since they are considered as obstacles that prevent their passage. This influence on the photovoltaic parameters, especially on the conversion efficiency, has been studied by varying their value from 1012 to 1020 cm−3. Figure 2 shows the behavior of the photovoltaic parameters as a function of the above-mentioned defect density increase.Figure 2Effect of interface density of defects on the photovoltaic parameters of the basic cell structure. (a) Short current density, (b) open circuit voltage, (c) fill Factor and (d) power conversion efficiency.The results revealed the degradation of the performance from the increase of the front or back interfaces defect density higher than 1014 cm−3 due to the increase of the recombination velocity at the considered interface, which favors the capture of the carriers by the trap states. The influence was more significant for the increase in the front interface defect density. It was noticed that the photocurrent density was not affected by the augmentation of the back interface defects, because it mainly comes from the photo-generated electrons. This study shows the importance of keeping the defect density at the interfaces below a value of 1015 cm−3 to achieve the best performance.3.2Investigation of appropriate ETL and HTL materialsThe dissociation of photogenerated pairs of carriers (electrons and holes) in the absorber occurs at the front and back interfaces between the ETL layer and the absorber, and the HTL layer and the absorber, respectively. For this reason, the amount of defects at these locations must be taken into account because of its relationship with the recombination rate. On the other hand, the shift of energy bands at the interfaces strongly affects the amount of collected carriers.Therefore, the choice of the materials used for ETL and HTL layers is important. In this section, several materials have been proposed for investigation to reach high performance. Zinc sulfide (ZnS), tin dioxide (SnO2), cadmium zinc sulfide (CdZnS), and 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (PCBM) were investigated as ETM. The alternative materials studied for the hole transport layers were the organic semiconductor 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD), cuprous oxide (Cu2O), nickel oxide (NiO), and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). Data and material input parameters used in the simulation are taken from the literature [13,19,20]. The conversion efficiency of the different structures is plotted in Figure 2.Figure 3(a) shows that the structure based on the SnO2-ETL material gives the best efficiency of 19.92% with a narrower conduction band offset than the base cell. However, the front interface recombination velocity value remains unchanged. While Figure 3(b) reveals that using Spiro-OMeTAD-HTL material leads to the best efficiency with a more appropriate value of valence band offset 0.3 eV and an unchanged back interface recombination velocity. A better performance of the organic-HTL materials was noted compared to the inorganic materials. However, the structure based on inorganic Cu2O-HTL still recorded a high yield of 18.31% and appropriate values of VBO and Sp. The simulation results allow us to consider the structure SnO2/CsSnI3/Spiro-OMeTAD as the optimal configuration which reaches the best performance with the most appropriate values of bandgap energy offsets and recombination velocity at the interfaces. However, in order to favor a totally inorganic cell, the SnO2/CsSnI3/Cu2O structure can be considered, although the conversion efficiency is slightly lower. The current–voltage curves of the mentioned structures are represented in Figure 4. Simulation results are detailed in Table 1.Figure 3Power conversion efficiency: (a) for different ETL materials; (b) for different HTL materials.Figure 4J–V characteristics of CsSnI3-based structures.Table 1Performance of CsSnI3-based perovskite cell structuresCell structureJph (mA/cm²)Voc (Volt)FF (%)PCE (%)CBO–VBO (eV)Sn–Sp (cm/s)TiO2/CsSnI3/PTAA (Basic)30.680.82973.3319.890.76–0.39103–103SnO2/CsSnI3/Spiro-OMeTAD (Optimal)30.680.82973.3619.920.50–0.30103–103SnO2/CsSnI3/Cu2O (Inorganic)30.460.82970.1618.310.50–0.57103–103In order to close this study, the suggested structures were simulated as bottom sub-cell in two-terminal tandem configuration in association with the top sub-cell having the following structure: PCBM/CsSnGeI3/Spiro-OMeTAD with an absorber bandgap energy of 1.5 eV [21]. The results of the simulation are shown in Table 2. In literature, it is possible to find many simulation works which were done using different code for different purposes [22,23,24,25,26,27,28,29,30,31].Table 2Performance of CsSnI3-based perovskite cell structures2T-tandem cell structureJph (mA/cm²)Voc (Volt)FF (%)PCE (%)Top: PCBM/CsSnGeI3/Spiro-OMeTAD18.631.59391.731.68Bottom: TiO2CsSnI3/PTAA (basic)Top: PCBM/CsSnGeI3/Spiro-OMeTAD18.711.46191.429.22Bottom: SnO2/CsSnI3/Spiro-OMeTAD (optimal)Top: PCBM/CsSnGeI3/Spiro-OMeTAD18.861.46291.429.20Bottom: SnO2/CsSnI3/Cu2O (inorganic)4ConclusionIn this work, a Perovskite solar cell structure based on the lead-free Perovskite absorber CsSnI3 was simulated and optimized. The effect of defect density on the solar cell performance at the front ETL/Perovskite and back Perovskite/HTL interfaces was studied. Different cell structures with various alternative ETL and HTL materials were simulated, and the obtained results were presented. An optimal structure with selected ETL and HTL materials with appropriate values of interface recombination velocity and band gap shift at the absorber boundaries was suggested based on the obtained results. An efficiency of 19.92% was achieved with the optimal structure: SnO2/CsSnI3/Spiro-OMeTAD, and 18.31% with the fully inorganic and non-toxic structure: SnO2/CsSnI3/Cu2O. An improvement was observed over the baseline device. The structure was simulated as a bottom cell in a two-terminal tandem solar cell, and an efficiency of 29.22% was achieved. The results of this study can provide useful information before proceeding to the manufacturing stage.

Journal

Applied Rheologyde Gruyter

Published: Jan 1, 2023

Keywords: perovskite; photovoltaic; solar cell; tandem cell; thin film

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