Simultaneous Optimization of Phase and Morphology of CsPbBr3 Films via Controllable Ostwald Ripening by Ethylene Glycol Monomethylether/Isopropanol Bi-Solvent Engineering

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 CsPbBr 3 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 CsPbBr 3 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 CsPbBr 3 films. Finally, the prepared films are applied to perovskite solar cells (PSCs) with a structure of fluorine-doped tin oxide (FTO)/compact TiO 2 (c-TiO 2 )/CsPbBr 3 /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 CsPbBr 3 films from EGME/IPA bi-solvents. This work provides a simple and efficient method for the preparation of high-quality CsPbBr 3 films.