LAUSR

Both phase and morphology of perovskite films are very important for high‐performance optoelectronic devices. Although a two‐step method based on CsBr ethylene glycol monomethylether (EGME) solution can prepare pure‐phase CsPbBr3 films, they have a poor morphology due to excessive Ostwald ripening. Herein, a bi‐solvent engineering strategy is demonstrated to simultaneously optimize phase and morphology of CsPbBr3 films in a two‐step solution method, which uses the bi‐solvents of EGME and isopropanol (IPA) instead of EGME for CsBr solution at the second step. Optimizing the volume ratio of bi‐solvents and immersion time can control the Ostwald ripening effectively and result in pure‐phase, compact, and smooth CsPbBr3 films. Finally, the prepared films are applied to perovskite solar cells (PSCs) with a structure of fluorine‐doped tin oxide (FTO)/compact TiO2 (c‐TiO2)/CsPbBr3/carbon. In comparison with EGME, the champion power conversion efficiency (PCE) of devices from EGME/IPA bi‐solvents increases from 3.57% to 7.29% owing mainly to higher coverage, smoother surface, and lower trap density of CsPbBr3 films from EGME/IPA bi‐solvents. This work provides a simple and efficient method for the preparation of high‐quality CsPbBr3 films.