Preparation And Study Of Efficient And Stable MAPbI₃ Perovskite Solar Cells In Atmospheric Environment

As potential alternative to traditional photovoltaic cell,organic-inorganic lead halide perovskite solar cell（PSC）has attracted global attention due to their advantages of high light absorption coefficient,low exciton binding energy,bipolar charge transfer,high carrier mobility and low preparation cost.The power conversion efficiency（PCE）of PSC has promptly increased from the initial 3.8%in 2009 to the current 25.7%.However,most of the efficient perovskite solar cells are small area devices and prepared in an inert environment.Although great progresses have been made in the preparation of large-area cells,the long-term stability of the devices in the ambient environment is still a major challenge,which seriously hinders its industrial development.Due to the slow crystallization rate of perovskite films and the formation of high defect states in the film,it is difficult to obtain high quality air-processed film with traditional Pb I₂ lead source.In this dissertation,we regulate the crystallization process of perovskite film by Pb source engineering,assisted with additive engineering and interface engineering in atmospheric environment to obtain high quality film.From the perspective of simplicity and environmental protection,one-step deposition method is used to prepare perovskite film with eco-friendly ethyl acetate anti-solvent.The general research contents are as follows:Firstly,in order to solve the problem of poor quality of air-processed perovskite film prepared by Pb I₂ lead source,we incorporate three volatile methylamine salts into Pb I2-based perovskite precusor solutions and systematically study the effect of MACl,MASCN and MAAc additives on the perovskite crystallization process.Results show that these volatile methylamine salts all can regulate the crystal growth of perovskite to different degrees and improve the film quality with enhanced crystallinity and enlarged crystal grains.By comparison,the device with MACl additive achieves the highest PCE of 20.06%with almost no hysteresis owing to the significantly reduced defect state density in the film.Meanwhile,the device with MASCN addition delivers the second-best PCE（19.19%）.Notably,the according perovskite film exhibits the strongest crystallinity that renders excellent photovoltaic performance even in ultrashort annealing duration or without annealing,indicating a prospect for the rapid upscaling of PSCs in ambient air.Furthermore,the PSCs without encapsulation show greatly enhanced air stability after the film growth modulation.Secondly,in order to fundamentally solve the problems existed in the Pb I2-based perovskite thin film,we replace Pb I2 lead source with non-halide lead source for the preparation of perovskite film.By optimizing the ratio of Pb（SCN）2 and Pb（Ac）2 non-halide lead sources,homogeneous,dense and high quality perovskite films with large grain size and enhanced moisture resistance are obtained.The presence of Ac^-and SCN^-ions not only enables the facile formation of homogeneous and highly crystalized perovskite films,but also directs the uniform growth of the crystals along（110）direction.Through further passivation modification on perovskite film,we demonstrate a 20.55%efficiency,one of the best results for air-processed MAPb I3 PSCs,which is also the highest value achieved with non-halide lead sources.Furthermore,the unencapsulated device shows 5-fold prolonged air stability than the conventional Pb I2-based PSC.Finally,although the devices based on double non-halide Pb source have obtained the high PCE,the use of a single lead source can simplify the preparation technology and the perovskite film prepared by pure Pb（SCN）2 is theoretically more resistant to moisture.In this study,we use pure Pb（SCN）2 lead source for the preparation of perovskite film and solve the problem of poor film coverage by adding HAc.The result reveals for the first time that the introduction of HAc significantly inhibits the generation of two-dimensional perovskite intermediate phase and promotes the direct generation of three-dimensional perovskite,thus regulating the crystal dynamic growth of the perovskite film,effectively avoiding the generation of pinholes.On the other hand,the passivation of perovskite reduces the density of defect states in the film by doping KAc and further improves the quality of the film.Therefore,the co-doped device finally achieves the best PCE of 19.27%,which is the highest efficiency of the device prepared by using Pb（SCN）2 single non-halide lead source.