Study On Optimization Of Perovskite Crystal Sizes And Corresponding Device Performance

Perovskite solar cells(PSCs)have attracted wide attention in the past few years.Due to the rapid rise in efficiency,it is currently considered as the most promising next-generation photovoltaic technology.In terms of efficiency alone,it has met the requirements for moving forward to commercialization.Planar PSCs have been continuously researched and optimistic because of their simple craft and low cost.Although its highest certification efficiency is still lower than the efficiency of porous PSCs,it has recently certified a power conversion efficiency(PCE)of 21.5%,which has shown broad application prospects in terms of efficiency.However,PSCs still suffer from batch-to-batch variation and instability,especially when subjected to the high air humidity.In present stage of PSCs,achieving further improvements in long-term stability and efficiency are key issues.The film morphology and crystal quality of perovskites are critical factors influencing cell efficiency and long-term stability.Many methods,including anti-solvents,vacuum-assisted flash solution process,and compositional engineering,have been developed to improve PCE and long-term stability of PSCs.Here,based on the two-step spin coating method,we propose a new method that can improve the crystal size and film morphology of perovskite,namely the dropwise addition method.Under the action of this method,using(FAPbl3)0.97(MAPbBr3)0.03 as a perovskite material is deposited on the SnO2 layer treated only with low temperature,and the crystal size can be up to 3 ?m.The correspondingly formed film has less grain boundaries and pinholes,lower roughness,higher crystallinity,etc.The photoelectric properties of the film show strong light absorption,smaller internal defects of film and carrier recombination rate,longer carrier lifetime,thus reflecting its higher photoelectric quality.From the performance of the planar device produced by this method,the corresponding best device exhibits a higher PCE of 19.73%and a smaller hysteresis characteristic,meanwhile,exhibiting better repeatability and reliability.Based on the above new method,we have introduced DMSO additive,which are combined into an optimized way of synergy.In this optimized mode,using the same perovskite material successfully prepared well-packed flat crystals with a maximum crystal size of 5 ?m.The formed film has further improvement in the number of grain boundaries,pinholes,roughness and crystallinity,exhibiting ultra-dense,smooth,pinhole-free,large-grain film,which is further optimized crystal size and film morphology.The optimized film showed further promotion in photoelectric performance.In addition,the same application in planar devices successfully achieved 20.63%of outstanding PCE and showed hysteresis characteristics that can be almost ignored.It also has good repeatability and reliability.Finally,by studying the stability of the light and humidity for the optimized device,on the one hand,it has good light stability according to the maximum power point tracing.On the other hand,after 500 hours of storage in an unpackaged device in a 40%humidity environment,it was found that 93%of the initial efficiency was maintained,while the non-optimized device under the same conditions remained only 20%of the initial efficiency after 360 hours,and thus the optimized device also has excellent humidity stability.Therefore,the planar PSCs of the high-quality thin films produced by such optimized large crystals can achieve high PCE and high moisture resistance,which provides a new idea for the future research and commercialization of PSCs.