Study On The Vapor-deposited Inorganic Perovskite Solar Cells And Their Optoelectronic Properties

Perovskite solar cells（PSCs）have become a research hotspot in the field of photovoltaics in recent years.So far,the highest power conversion efficiency（PCE）of PSCs has reached 25.7%.However,due to the volatility of organic components,it is inferior for long-term operational stability of organic-inorganic hybrid PSCs.Because of the high chemical stability,all-inorganic perovskites have gradually attracted the attention of researchers and the PCE of Cs Pb I₃ PSCs rapidly developed to 21%by a multi-strategy-assisted solution method.However,organic by-products were easily introduced during this process.Vapor deposition,as a deposition method which can manufacture uniform,compact and solvent-free thin films,exhibits unique advantages in the fabrication process of component-purified all-inorganic perovskites.Meanwhile,the phase of the Cs Pb I₃perovskite is extremely unstable at room temperature due to the small structural tolerance factor（about 0.8）.However,the phase stability optimization strategy of traditional co-evaporation Cs Pb I₃ is currently lacking,and materials prepared by the method have many defects.These problems result in a phenomenon that the photovoltaic performance development of co-evaporation Cs Pb I₃ lags behind.Therefore,it is an important and difficult task for the development of inorganic perovskites to improve the phase stability optimizing strategy of traditional co-evaporation Cs Pb I₃.This work focuses on the problem of improving the phase stability of traditional vapor-deposited inorganic lead-iodide perovskites.And based on the composition control strategy,accurate doping of halogen anions was realized by co-evaporation doping process Compared with traditional co-evaporation Cs Pb I₃,the prepared Cs Pb I₂Br mixed halogen perovskite optimized the perovskite structure tolerance factor and inhibited the torsion of lattice structure at room temperature,thus improving the phase stability of the material.Based on this,the incorporation amount of Br^-in mixed halogen perovskite was gradient adjusted by high-throughput evaporation.Combined with the X-ray diffraction phase analysis and scanning electron microscope morphology analysis of the film,it was found that the Br^-content has a significant effect on the formation and distribution of non-conductive zero-dimensional phase Cs₄Pb I_6-xBr_x in the film.Furthermore,the phase stability and photovoltaic performance of the material were balanced by optimizing the incorporation amount of Br^-.Furthermore,this work focuses on breaking through the problem of poor phase stability of Cs Pb I₃fabricated by traditional vapor deposition,taking the simultaneous improvement of phase stability and photovoltaic performance into account,and develops a new vapor deposition process named“co-evaporation+co-evaporation”.Through this process,Cs Pb I_2.85Br_0.15 perovskite was prepared.Specifically,the new process is used to form complete Cs Pb I_2.85Br_0.15 perovskite by co-evaporation Cs Pb I₂Br film once and Cs Pb I₃ film twice and combining with high-temperature annealing process.Compared with Cs Pb I₃ prepared by traditional co-evaporation,a small amount of Br^-introduced by the new process has a bottom-up thermal diffusion,which optimizes the content and distribution of zero-dimensional Cs₄Pb I_6-xBr_x in the final Cs Pb I_2.85Br_0.15 film,and realizes the optimization of crystallization orientation and formation energy.Based on this,the phase stability of the material is improved.Also the PCE of the device was improved to 16.16%.