Theoretical Study On Electronic Structure Of CH₃NH₃SnI₃,CH₃NH₃SnBr₃ And The Interface Between TiO₂/CH₃NH₃SnI₃

Solar energy,like wind,biomass,tidal power and geothermal energy,is renewable energy.Perovskite solar cells?Perovskite solar cells:PSCs?,with advantages of narrow band gap width,high photoelectric conversion efficiency,high carrier mobility,preparation of low cost and simple preparation method,are attracting much attention in recent years.Perovskite,general formula for ABX₃,acts as perovskite light absorption of solar cell materials.Different X atoms have a significant effect on the performance and efficiency of PSCs.MAPbI₃?MA:CH₃NH₃?is one of the most studied materials PSCs,which has the highest efficiency in various light absorbing materials of PSCs.However,Pb is toxic.Therefore,we select the non-toxic Sn to replace Pb.We calculated the various properties of MASnI₃ and MASnBr₃ by using the first principles method.First,mesoporous PSCs were synthesized by various ways.The efficiency of PSCs with diffident electrons transporting materials was studied.The mesoporous PSCs is composed of FTO,dense layer,mesoporous layer,photosensitive layer,hole transporting layer and electrode.We mainly explored the preparation process of mesoporous layer and photosensitive layer and found that compared to slurry method,the hydrothermal method was better.Likely,PSCs synthesized with two-step method has a higher efficiency than that with one-step method.In PSCs,two-step method can enlarge the contact area between perovskite and mesoporous.Thus,excitons transfer more easily from perovskite to the mesoporous TiO₂layer.Then,frist-principles method was employed to study the crystal structures and electronic properties of MASnI3 and MASnBr3 with different phases.It is found that their electronic properties are greatly affected by the halide atoms,and crystal structures.We show that the band gap and carrier effective mass decrease as the sizes of halide atoms increase.The tetragonal phase has the smallest band gap and lightest carrier effective mass.Especially,MASnI₃ with TETP phase may show the best performance because of the lowest band gap and the lightest effective mass.By comparing with Pb-system,we predict that Sn-based halide perovskites also exhibit potential good properties in solar-energy harvesting.Finally,we have performed first-principles calculations to study the structure and electronic properties of the interface between CH₃NH₃SnI₃ and TiO₂.We found that Anatase?001?surface has better lattice and atoms arrangement match with CH₃NH₃SnI₃.The charge transfers from CH₃NH₃SnI₃ to TiO₂ are observed for all the four systems.SnI₂/A system is more stable than other three systems.Meanwhile,SnI₂-T interface could make electron-hole pairs separate and transport more easily.Therefore,anatase TiO₂ may be a better candidate for electron transporting materials in CH₃NH₃SnI₃ perovskite solar cells.