Preparation And Properties Of CsPbBr₃ And Cs₂SnI₆ Perovskite Films By Vapor Deposition Method

In recent years,organic-inorganic hybrid lead halide-based perovskite materials have attracted significant attention due to their excellent photoelectric properties,and the conversion efficiency（PCE）of perovskite solar cells constructed with this material as an absorber layer has exceeded 25%,showing great commercialization potential.But there are still many issues which needs to be alleviated urgently:1)The presence of organic components in hybrid perovskites results in poor moisture and thermal stability of the material,and the device performance is prone to decline;2)The material contains lead,which is highly toxic and can cause damage to the environment and organisms;3)The conventional solution method uses the large amount of toxic organic solvents,which does not meet the requirements of green environmental protection.Vapor deposition methods such as evaporation and chemical vapor deposition（CVD）are commonly used thin film preparation methods,which have the advantages of uniform film formation,compactness,cleanness,and large area deposition.Therefore,in this thesis,the electron beam evaporation method and the CVD method were selected to prepare the wide band gap Cs Pb Br₃ material with high humidity and thermal stability and the tin-based double perovskite Cs₂Sn I₆ material,and the influence of the preparation process on the film characteristics and device performance was systematically studied.The main research contents are as follows:1)Electron beam evaporation preparation and performance study of Cs Pb Br₃ thin film:（1）When a simple ground mixed powder is used as a target to deposit the film,the resulting film is a mixture of Cs Pb Br₃ and Cs Pb₂Br₅.When the film is annealed,its grain size will gradually increase with the increase of annealing temperature;when the annealing temperature reaches 350^oC,the Cs Pb₂Br₅ phase will disappear after thermal decomposition,and a pure Cs Pb B_r3 film can be obtained;When the temperature reaches450 ^oC,the film appears lots of holes.The film annealed at 400 ^oC was used to construct an FTO/Cs Pb Br₃/C structure cell,and an efficiency of 5.37%was obtained.（2）When the thermally reacted powder is used as the target to deposit the film,since the main component of the target is Cs Pb Br₃,the Cs Pb₂Br₅ phase in the film is effectively suppressed.At the same time,the grain size increases with the increase of the annealing temperature;when the annealing temperature is higher than 300^oC,a large number of holes appear in the film.The content of Cs Pb₂Br₅ phase increases with the increase of annealing temperature;When the annealing temperature reaches 400 ^oC,the Cs Pb₂Br₅phase disappears and the film is pure Cs Pb Br₃.Applying the thin film to solar cells,it is found that the efficiency of the cells is the highest after annealing at 300 ^oC.2)CVD preparation and performance study of Cs₂Sn I₆ thin film:First,the Cs I film is deposited by electron beam evaporation,and then reacted with the high-purity Sn and I₂ mixed powder to form the Cs₂Sn I₆ film.When a closed system is used for experiments,the thermal decomposition of the film can be effectively suppressed,and the temperature range of the reaction can be widened.The band gap of the prepared Cs₂Sn I₆ film is 1.35 e V,and the highest carrier mobility is 339 cm²·V^-1·s^-1.When an open system is used for the reaction,an excessively high temperature will cause the film to thermally decompose.3)Theoretical simulation of Cs₂Sn I₆ based PSCs:The prepared Cs₂Sn I₆ film is used in solar cells,and the efficiency is extremely low.In order to explain the reason,a theoretical analysis of the working mechanism of the device is carried out,and it is found that the performance of the device is strongly dependent on the matching condition of its energy band.The implementation of energy band engineering can effectively reduce interface recombination,enhance carrier transport,and improve battery performance.