Tailoring Mixed-Halide, Wide-Gap Perovskites via Multistep Conversion Process

Wide-band-gap mixed-halide CH₃NH₃PbI_3–XBr_X-based solar cells have been prepared by means of a sequential spin-coating process. The spin-rate for PbI₂ as well as its repetitive deposition are important in determining the cross-sectional shape and surface morphology of perovskite, and, consequently, J–V performance. A perovskite solar cell converted from PbI₂ with a dense bottom layer and porous top layer achieved higher device performance than those of analogue cells with a dense PbI₂ top layer. This work demonstrates a facile way to control PbI₂ film configuration and morphology simply by modification of spin-coating parameters without any additional chemical or thermal post-treatment.