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.