Synthesis of Highly Crystalline α-Formamidinium Lead Triiodide Halide Perovskite Powder via Stoichiometric Control

Generally, formamidinium (FA)-based halide perovskite thin films are fabricated using halide precursors, such as PbI 2 and FAI, but this approach often leads to stoichiometric distortions, resulting in perovskite films with structural defects and reduced crystallinities. These problems can adversely influence power conversion efficiencies and open-circuit potentials of perovskite solar cells. In this study, we propose a microcrystalline perovskite powder (MCP) synthesized by controlling the stoichiometry of the FAI precursor. We optimize the synthesis of α-FAPbI 3 powder using 1.1 equiv of FAI. Interestingly, the synthesized black powder produced an excellent crystallinity and phase stability for up to six months. Remarkably, the MCP forms large colloids in solutions that are stably cohesive, promoting spontaneous nucleation and enabling the fabrication of low-defect thin films. Consequently, perovskite solar cells fabricated using the MCP display significantly improved efficiencies of 23.12% compared to those (19.64%) of the cells fabricated using the conventional PbI 2 and FAI precursors. This approach highlights the potential of MCPs for use in enhancing the performances and stabilities of perovskite-based devices.