Formation of Large Grain and Compact CH3NH3Pb(I $_{\rm 1\hbox{--}x}$ Br x )3 Film by Multisteps Solvent Postannealing for High-Efficiency Perovskite Solar Cells

The reaction toward MAPb(I1-xBrx)3by the perovskite precursor is difficult to form a continuous film over a large area. In this paper, we develop a multisteps solvent-postannealing method based on a high-coverage MAPbI3film a template for preparing uniform and compact MAPb(I1-xBrx)3film with film-through large grain and uniform distribution of Br elements. The formed MAPbI3film must be annealed in the mixture vapor of dimethyl sulfoxide and aqueous HBr to achieve the simultaneous modification of composition and crystallinity, and then it has to be repaired further using CH3NH2vapor annealing to eliminate the defects of the film surface and crystal grain boundaries. The corresponding perovskite solar cells (PSCs) yield a maximum power conversion efficiency of 17.23% with an open-circuit voltage (Voc) of 1.025 V, a short-circuit current (Jsc) of 20.88 mA·cm-2, and a fill factor (FF) of 80.54%, based on a structure of ITO/PEDOT:PSS/MAPb(I1-xBrx)3/PC61BM/Bphen/Ag, with an enhancement of 18% compared with that of the optimized MAPbI3PSCs because of the simultaneous increase in Voc, Jsc, and FF. This paper provides a feasible and effective method to fabricate high-quality MAPb(I1-xBrx)3films for high-efficiency solar energy conversion devices.