Properties Research And Optimiztion For (CH₃NH₃)₃Bi₂I₉ And CsPbIBr₂ Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells(PSCs)have attracted considerable attention owing to their tunable bandgap,longer carrier diffusion distance and lower exciton binding energy.Those prefect peculiarities have motivated the development of PSCs.Due to the optimization of preparation method and materials,the PSCs obtained increasing power conversion efficiency(PCE)from 3.8%to 25.2%in just a few years.It's on a par with monocrystalline silicon solar cells.However,the commercialization processes of PSCs are still restricted by its toxicity and long-term instability.Therefor,perovskite solar cell devices with low toxicity and stable have become a major development trend.In this paper,we have introducted two new additives strategy to improve the instability of PSCs and reported a new method to fabricate(CH₃NH₃)₃Bi₂I₉(MBI)film.(1)A two-stage electric-field-assisted reactive deposition method has been introduced to prepare MBI films for the first time.PSCs based on MBI films were fabricated and characterized.The influences of electric parameters(applied voltage mode,pulse and time,etc.)on the morphology and crystal structure of MBI film correlated with the photovoltaic performance of PSCs have also been investigated systematically in detail.Through adjusting the voltage mode,crystal growth can be completely controlled,leading to a compact MBI film with large grain size.Moreover,the MBI film prepared by electrochemical deposition required no annealing.This work determined that the optimal performance of PSCs is based on the MBI film deposited by square-wave(AC)voltage mode(-7.3 V/+1 V,5 Hz,5 min).All devices exhibited long-term stability in ambient air(humidity of>50%)for more than 300 h.This study will inspire further research on the application of electrochemical deposition technique for other lead-free PSCs.(2)Excellent power conversion efficiency and stability are the primary forces that propel the all-inorganic cesium-based halide perovskite solar cells toward commercialization.However,the intrinsic high density of trap-state and internal non-radiative recombination of Cs Pb IBr₂ perovskite film are the barriers that limit its development.In this paper,we introduced a facile additive strategy to fabricate highly efficient Cs Pb IBr₂ PSCs by incorporating sulfamic acid sodium salt(SAS)into the perovskite layer.The additive can control the crystallization behaviors and optimize morphology,as well as effectively passivate defects in the bulk perovskite film,thereby resulting in a high-quality perovskite.In addition,SAS in perovskite has possibly introduced an additional internal electric field effect that favors electron transport and injection due to inhomogeneous ion distribution.A champion PCE of10.57%(steady-output efficiency is 9.99%)was achieved under one sun illumination,which surpassed that of the contrast sample by 16.84%.The modified perovskite film also exhibited improved moisture stability.The unencapsulated device maintained over 80%initial PCE after aging for 198 h in air.The results provide a suitable additive for inorganic perovskite and introduce a new conjecture to explain the function of additives in PSCs more rationally.(3)We introduced a facile additive strategy to fabricate highly efficient Cs Pb IBr₂PSCs by incorporating cupric bromide(Cu Br₂)into the perovskite layer.The additive can control the crystallization behaviors and enhance the absorbance for visible light,thereby resulting in a high-quality perovskite.A champion PCE of 10.61%(FF is 77%)was achieved under one sun illumination,which represents a high level for Cs Pb IBr₂-based devices.