First Principles Study Of Lead-Free Perovskite Used In Photovoltaic Devices

Since the organic-inorganic hybrid perovskite solar cell was first proposed in 2009,its photovoltaic efficiency has jumped to over 23% after several decades,close to the maximum efficiency of crystalline silicon solar cells.Represented by CH₃NH₃PbI₃,they have the advantages of long carrier diffusion lengths from hundred nanometer to micrometer,low exciton binding energy,shallow main defect energy level,and high light absorption.In a modern society where the demand for sustainable clean energy is growing,the development of better solar energy utilization devices has become an important scientific research and industry.Based on first-principles theoretical calculations based on density functional theory,we studied the electronic properties,optical properties,and stability of lead-free perovskites CH₃NH₃SnI₃ and A₂SiX₆（A=K、Rb、Cs,X=Cl、Br、I）.The following results have been achieved:A hexagonal structure of CH₃NH₃SnI₃ has a larger band gap value than the cubic phase and tetragonal phase due to its special structure.The hexagonal phase of CH₃NH₃SnI₃ has strong ultraviolet light absorption and visible light transmittance,showing the application potential of ultraviolet filter layer in tandem photovoltaic devices or photovoltaic devices containing TiO₂.The hexagonal CH₃NH₃SnI₃ still maintains strong ultraviolet light absorption under the strain of-5%-5%.Among the nine compounds of A₂SiX₆（A=K、Rb、Cs,X=Cl、Br、I）,K₂SiI₆、Rb₂SiI₆、Cs₂SiI₆ have direct band gap values suitable for solar cells.And all three have small effective masses of carriers.The optical property calculation results show that K₂SiI₆、Rb₂SiI₆ and Cs₂SiI₆ have characteristic absorption peaks in the visible light region,and the absorption covers the entire visible light region.The stability results reveal that K₂SiI₆、Rb₂SiI₆、Cs₂SiI₆ all have structural and thermodynamic stability.Among them,Rb₂SiI₆ and Cs₂SiI₆ also have dynamic stability at 400 K,revealing their potential for development in lead-free perovskite solar cells.