Solvent-engineering-processed CsPbIBr2 inorganic perovskite solar cells with efficiency of ∼11%

Recently, the cesium lead halide perovskite (CsPbIBr2) materials demonstrating the most balanced bandgap and stability among all inorganic perovskite analogs have received great attention in photovoltaic community. However, the poor quality of solution-processed CsPbIBr2 films with small grains and massive voids and defects severely impedes its further development. This obstacle issue mainly roots from the slow crystallization process of perovskites when using traditional high boiling point solvent of dimethyl sulfoxide (DMSO). Herein, a novel solvent engineering strategy, namely alcohol-induced rapid crystallization process, is originally developed. We intentionally add some low boiling point alcohols, such as methanol, ethanol, isopropanol, and n-butanol, to form a lower boiling point DMSO-alcohol azeotropic mixture, which can be volatilized quickly and effectively accelerate the crystallization process of CsPbIBr2 films. Meanwhile, we elaborately adopt some CsI additives to suppress the intrinsic self-doping and passivate the defects of perovskites. Besides, the influence of annealing temperatures on the film quality and device performance is also investigated in this study. Consequently, the pinhole-free, highly crystallized CsPbIBr2 films with large grains and a preferable (100) orientation are successfully achieved via CsI/methanol treatment recipe when annealed at the optimized temperature of 280 °C. The as-obtained perovskite solar cells (PSCs) with a superior long-term stability feature yield a highly promising power conversion efficiency (PCE) of 11.49%. To our knowledge, this is the highest reported efficiency among all CsPbIBr2 inorganic PSCs.