New Solution Synthesis And Theoretical Study Of Inorganic Perovskite Materials Cs₂SnI₆

With the continuous increase of global energy consumption,fossil energy may be exhausted in the future.And solar energy because of its rich,clean,renewable and other advantages are more and more favored by people.Perovskite solar cells have attracted a lot of researchers’ interest in recent years due to their advantages of easy preparation,low cost and high photoelectric conversion efficiency.Although the efficiency of organic-inorganic hybrid perovskite solar cells has exceeded that of several commercial cells,its stability is not good,mainly due to the degradation and volatilization of organic groups contained in perovskite materials.Therefore,more and more researchers have turned to the study of inorganic perovskite materials.In recent years,Cs₂SnI₆ has attracted the attention of researchers.It is a variety of inorganic perovskite materials.Cs₂SnI₆ is a direct band gap semiconductor material with a band gap of 1.30～1.62 e V.Theoretically,the cell efficiency can reach 30～33%.In this paper,the traditional method of synthesizing Cs₂SnI₆ powder is more complex and high cost,and a simple synthesis method is proposed.The first principle of Cs₂SnI₆ doped with F^-,Cl^-and Br^-ion was studied.The specific research contents are as follows:（1）In order to reduce the cost and simplify the synthesis method of Cs₂SnI₆ powder,a new simple solution method was proposed to synthesize Cs₂SnI₆ powder.The synthesis method has only two steps: The first step is to dissolve Cs I and SnI₂（or SnI₄）powder into different reaction solvents;Step 2: Stir slowly at room temperature to obtain pure Cs₂SnI₆ powder.In order to obtain the optimal synthesis route,the effects of the type of reactants,reaction solvent and ratio of reactants on the purity,crystallinity,light absorption,electrical properties and stability of Cs₂SnI₆ powder were studied.The results show that When Cs I and SnI₂ are used to synthesize pure Cs₂SnI₆ powder,the best synthetic parameter is Cs I:SnI₂=1:1;When Cs I and SnI₄ were used to synthesize pure Cs₂SnI₆ powder,the best synthetic parameter was Cs I:SnI₄=3:2.If the ratio of Cs I to SnI₂ is 1:1,Cs₂SnI₆ powder crystals synthesized from acetone,acetonitrile and anhydrous ethanol have better crystallization,and Cs₂SnI₆ powder synthesized from anhydrous ethanol has better air stability and air thermal stability.When the ratio of Cs I to SnI₄ was 3:2,Cs₂SnI₆ powder crystals synthesized in acetone,isopropanol,acetonitrile and anhydrous ethanol had better crystallization.Cs₂SnI₆ powder synthesized from acetonitrile had better air stability,while Cs₂SnI₆ powder synthesized from anhydrous ethanol had better air thermal stability.We found that when Cs I:SnI₂=1:1 and Cs I:SnI₄=3:2,the optical absorption of Cs₂SnI₆ powder obtained in the solvent of anaqueous ethanol was more heat-resistant annealing,so it was more suitable to be used as the absorption layer material of actual solar cells.（2）In order to increase the stability of Cs₂SnI₆,the first principle calculation is mainly based on VASP software package.This paper studied the effects of doping with different concentrations of F^-,Cland Br^-ion on the internal energy,band gap,state density and optical properties of Cs₂SnI₆.The results show that with the increase of F^-ion concentration,the band gap gradually increases and the internal energy gradually decreases,indicating that Cs₂SnI₆ becomes more and more stable after doping F^-ion.The band gaps of Cs₂ SnI₅F and Cs₂ SnI₄F₂ are between 1.0 and 2.0 e V,which can absorb more sunlight,and the doping of a small amount of F^-ions makes them more stable than Cs₂SnI₆.Therefore,they can be used as candidate materials for the absorption layer of inorganic perovskite solar cells.With the increase of the concentration of doped Cl^-ions,the band gap gradually increased and the internal energy gradually decreased,indicating that Cs₂SnI₆ became more and more stable after doping Cl^-ions.The band gaps of Cs₂ SnI₅Cl,Cs₂ SnI₄Cl₂ and Cs₂ SnI₃Cl₃ are between 1.0 and 2.0 e V,which can be used as candidate materials for inorganic perovskite solar cell light-absorbing layer.With the increase of the doped Br^-ion concentration,the band gap and internal energy of Cs₂SnI₆ gradually became larger and smaller,which indicated that Cs₂SnI₆ became more and more stable after doping Br^-ion.Since the band gaps of Cs₂ SnI₅Br,Cs₂ SnI₄Br₂,Cs₂ SnI₃Br₃,Cs₂ SnI₂Br₄ and Cs₂ SnIBr₅ are all between 1.0 and 2.0 e V,they can be used as candidate materials for the optical absorption layer of inorganic perovskite solar cells.