Extracting ammonium halides by solvent from the hybrid perovskites with various dimensions to promote the crystallization of CsPbI3 perovskite

The suitable optical bandgap and high chemical stability have made inorganic CsPbI3 perovskite become a promising light absorber in perovskite solar cells (PSCs). However, it is still a great challenge to obtain a high-quality CsPbI3 perovskite film because of its phase instability, let alone composition manipulation. Herein, we report a new and general strategy, extracting ammonium halide by solvent (EAH-S), to solve the above problems. During the EAH-S process, ammonium halide is introduced into the traditional precursor solution to form a transitive compound (e.g. 3D, 2D and 1D hybrid perovskites). Then, the transitive compound is soaked in a solvent with moderate polarity (e.g. ethanol, methanol, isopropanol), during which ammonium halide would be extracted to promote the crystallization of CsPbI3 perovskite. The extraction of ammonium halide is proved to be the vital process, which could release PbI2 and prompt the nucleation of p-CsPbI3 at the interface with the assistance of ammonium ions. By combining the EAH-S method with a conventional annealing process, the composition of CsPbI3 perovskite film could be finely manipulated, and the film quality is well improved. More promisingly, the carbon-based CsPbI3 PSCs without hole transporter achieve a efficiency of 15.35%, a new record for inorganic C-PSCs.