Researches On Preparation And Properties Of Organic-Inorganic Hybrid Perovskite Solar Cells By Chemical Vapor Deposition

Metal-halide perovskites are the most promising next-generation photovoltaic materials as a result of extraordinary optoelectronic properties,such as high absorption coefficient,long carrier diffusion length,low exciton binding energy,tunable bandgap,and high tolerance of defects.However,commercialization of perovskite solar cells（PSCs）still face challenges in achieving large-area high-efficiency devices and stability improvement.As a mature material preparation process,chemical vapor deposition（CVD）has been widely used in the field of semiconductor photovoltaics due to its simple preparation process and the ability to prepare large-area thin films.Although the power conversion efficiency of PSCs prepared by CVD has reached 18.9%,the PSCs prepared by CVD suffer from lower PCE compared with those deposited by the solution methods.Nevertheless,there are a few studies on the performance gaps between CVD and solution method.In addition,the surface of perovskite films has many defects,which causing serious non-radiative recombination to reduce the performance of PSCs.In this thesis,perovskite film was deposited by CVD,and the impact of temperature on the performance of perovskite film was studied.Then the mechanism of efficiency gaps on PSCs between CVD and solution method was systematically investigated.Finally,interface engineering was adopted to passivate surface defects of perovskite film and suppress ion migration to improve the photoelectric performance and stability of PSCs.The specific results are listed as follows:（1）Deposition FA_xCs_1-xPbI₃ organic-inorganic PSCs by CVD,and studying the defect of perovskite.Firstly,using FAI gas source to react with Pb I₂ and Cs I mixed precursor film by CVD to prepare perovskite film,and the impact of deposited temperature on the performance of perovskite film was studied,and high-quality FA_xCs_1-xPb I₃ perovskite films was obtained by optimizing the deposition temperature and time.Results showed that high temperature can promote the reaction kinetics to improve the reaction rate,but it will accelerate the degradation of perovskite film and reduce the crystallinity of the film at a higher temperature.The optimal deposition temperature was 160°C,and the optimal deposition time was 125 min.Moreover,the thermal stability of the film in the air and the impact of post-annealing time on device performance were investigated.The film was still stable without any decomposition after continuous heating at 150°C in the air for 1 hour,which proved that the film prepared by CVD showed good thermal stability.At the same time,the film with different post-annealing time was assembled into devices,and the best efficiency of the device with post-annealing time of 20 min was 12.65%.The efficiency of the device remained almost stable with post-annealing time of an hour,which further indicated that film deposited by CVD has good thermal stability.Finally,by comparing the performance of PSCs deposited by solution method and CVD respectively,we systematically investigated the optical loss and carrier lifetime of films,and electrical loss and activation energy of ion migration of the device.It showed that the film deposited by CVD had more defects,resulting in more serious non-radiation recombination and ion migration to reduce the performance of the device.It revealed the mechanism of performance gaps between CVD and solution method.（2）Research on photovoltaic performance of PSCs,after surface passivation of FA_xCs_1-xPb I₃perovskite film.Interface engineering was adopted to passivate surface defects of perovskite films by introducing phenethylamine iodide（PEAI）.It is found that PEAI modification can reduce the roughness of surface of the film,improve the optical performance of the film,reduce the dark current of the device and the non-radiative recombination of the interface between perovskite film and hole transport layer,and passivate the defects of surface of the perovskite film,which reduces the defect density from 6.57×10¹⁵ cm^-3 to 2.26×10¹⁵ cm^-3.After PEAI passivation,the power conversion efficiency of the device increased from 12.65%to15.29%,and the activation energy of ion migration increased from 0.26 eV to 0.35 eV,which further showed that PEAI modification suppressed ion migration.The passivated PSCs showed good stability,and the unencapsulated device was stored at 5-10%humidity for 120 h to maintain83%of the initial efficiency,while the control only maintained 77%.