Intermediate Phase Assisted Sequential Deposition For The A-site Cation Engineering Of Perovskite Film

The A-site cation engineering of the perovskite film is an important technology,which had been applied to improve the photovoltaic performance and the stability of perovskite solar cell（PSC）devices.In most cases,the one-step deposition method was used to achieve the A-site cation engineering of the perovskite film,with the assistance of anti-solvent and hot-casting technology.However,this method is not compatible with the large-scale industrialization,due to the complex procedures and environmental problems.The sequential deposition has also been developed to prepare high quality perovskite film.Because it does not need to use anti-solvent and hot-casting technology,it is more competitive for the large-scale industrialization.However,the A-site cation engineering is retarded in sequential deposition,owing to the secondary nucleation reaction of the Pb I₂layer is special.There is no effective strategy to control the type and amount of A-site cation into final perovskite film by sequential deposition.Thus,it is necessary to develop a simple and efficient strategy,which is based on sequential deposition,to achieve high-quality multi-cation perovskite films and low-dimension perovskite films.In this thesis,the intermediate phase assisted sequential deposition（IPASD）strategy is developed to promote the sequential deposition,and the high Cs triple cation perovskite films can be achievd via this strategy.This strategy can not only control the amount Cs into final perovskite films,but also enlarge the grain size,adjust the crystallinity,band gap and photoelectric characteristics of the final perovskite films.The long-term working stability of PSC devices based on IPASD strategy is improved dramatically,and the power conversion efficiency（PCE）is increased to 20.45%.Then,the electron transport layer（ETL）of the triple cation PSC devices is optimized.Sn O₂-ethylene diamine tetraacetic acid（EDTA）acylamide compound（SEAC）is synthesized by a special reaction between Sn O₂ solution and EDTA ammonia solution.By changing the amount of EDTA ammonia solution in final mixture,the size of nanoclusters in SEAC solution can be adjusted,leading to higher light transmittance and smoother surface morphology on FTO conductive glass.The stability of the triple cation PSC devices using SEAC ETL is further improved,and the best PEC is up to 21.29%,due to the cluster size induced enhancement of electrical conductivity,the EDTA molecules passivated surface oxygen defects,and the construction of rational interfacial chemical interaction.The IPASD strategy is further explored to produce low dimension perovskite films.It shows that the amount of intermediate phase is the key to acquire MA-free quasi-two dimentional（2D）perovskite films via sequential deposition.The width of quantum well can be regulated by changing the mass ratio of GAI in GAI/FAI solution.The quasi-2D perovskite films prepared by IPASD strategy has the reverse-graded quantum well distribution and highly vertical orientation.In general,the composition and concentration of A-site cations in final perovskite films can be controlled by using IPASD strategy.This thesis shows that IPASD strategy can not only be used to prepare high-quality multiple cation perovskite films,but also can be applied to produce high-quality quasi-2D perovskite films,wihic is worthy of further research and promotion.