First-principles Study On Photoelectric Properties Of All Inorganic Tin-based Perovskite Materials

With the development of human society,the problem of environmental pollution has become increasingly prominent and people need to find clean energy.Solar cells based on perovskite materials are popular because of their low cost and high efficiency in converting light to electricity.Although the conversion efficiency of lead based perovskite material is high,it is toxic and restricts development.The element tin,which is in the same main group as lead,can form non-toxic perovskite materials.However,the optoelectronic properties of tin-based perovskite still need to be enhanced and tuned.Strain engineering can effectively modulate the material properties,which is important for regulating the performance of tin-based perovskite materials.Therefore,based on the all inorganic tin-based perovskite materials,we use first principles and strain engineering to study its photoelectric properties.The main achievements are as follows:（1）The band structure,carrier mobility and optical absorption of Cs Sn X₃（X=Cl,Br,I）cubic phase,tetragonal phase and orthorhombic phase are studied by HSE06 hybrid functional calculation.The results show that Cs Sn X₃（X=Cl,Br,I）is a direct bandgap semiconductor,and the bandgap is decreasing from Cl to I.The density of states plot shows that the contribution of the bottom of conduction band comes from the superposition of Sn s,p orbitals with Cl p,Br p and I p,respectively,forming partial hybrid bonds Sn-Cl,Sn-Br and Sn-I,while the contribution of the top of valence band comes from Sn p orbitals.The hole mobility of Cs Sn X₃（X=Cl,Br,I）is always greater than that of electron.The carrier mobility of all three phases of Cs Sn I₃ was better than that of Cs Sn Cl₃ and Cs Sn Br₃.The light absorption coefficient of Cs Sn X₃（X=Cl,Br,I）is 10⁵cm^-1in infrared,visible and ultraviolet.They are good choices for solar cells.（2）The band structure,carrier mobility and optical absorption of Cs₂Sn X₆（X=Cl,Br）under different strain conditions were studied by HSE06 hybrid functional calculation.The results show that the band gaps of Cs₂Sn Cl₆ and Cs₂Sn Br₆ under strain-free conditions are 3.984 e V and2.491 e V and they direct band gap semiconductors.The band gap decreases under compressive strain and increases under tensile strain.For strain-free Cs₂Sn Cl₆,the electron mobility is 288.33 cm²V^-1s^-1and the hole mobility is 0.007 cm²V^-1s^-1.For strain-free Cs₂Sn Br₆,the electron mobility is 611.31cm²V^-1s^-1,and the hole mobility is 0.02 cm²V^-1s^-1.Under compressive strain,the localization of the charge is weakened,leading to a great enhancement of the Cs₂Sn X₆（X=Cl,Br）carrier mobility.Besides,the compressive strain causes the band gap to become smaller,making the absorption edge of Cs₂Sn X₆（X=Cl,Br）red shifted.