Performance optimization of all-inorganic CsGeI3 solar cells: SCAPS simulation and DFT calculation

Abstract

It is well known that conventional organic–inorganic perovskite solar cells (PSCs) have unstable performance, while inorganic perovskite solar cells are stable but have low conversion efficiency. In order to achieve the goal of improving the conversion efficiency of solar cells, we design an inorganic germanium-base perovskite solar cells (FTO/Cd0.5Zn0.5S/IDL1/CsGeI3/IDL2/CuI/Au) to enhance the performance of the cells. We have investigated and optimized the overall performance of the solar cell using SCAPS-1D software simulation and combined with DFT calculations. Through the study, we found that CsGeI3 exhibits excellent electronic properties and ionization characteristics, which makes it suitable as an efficient absorber layer. And Cd0.5Zn0.5S and CuI have suitable energy band structures to match CsGeI3. A unique phosphorus bridge is formed on the surface of Cd0.5Zn0.5S, which realizes effective charge separation, and the valence band offset of CuI is low, so this structure is designed by us to further enhance the conversion efficiency of solar cells. We derived the photovoltaic properties of CsGeI3 through DFT calculations and found that there is a strong interaction between Ge2+ and I-, which also provides a theoretical basis for us to use CsGeI3 as an absorber layer. We have further tuned the interfacial defect layer (electron affinity, thickness), Electron transport layer (ETL) and Hole transport layer (HTL) (bandgap, defect density, thickness), absorber layer (bandgap, subjected to the main doping concentration), and operating temperature of the solar cell. It is shown that IDL1 and IDL2 have asymmetry and that IDL1 plays a major role in influencing the performance of solar cells. And too high defect density will make more defects and composite centers inside the ETL, which will reduce the quality of the ETL interface. After the final optimization, we increased the Fill Factor (FF) of the solar cell to 85.77 % and Power Conversion Efficiency (PCE) to 25.83 %. Our study provides theoretical support for the development of novel all-inorganic CsGeI3 perovskite solar cells.