Unified Crystal Phase Control with MACl for Inducing Single‐Crystal‐Like Perovskite Thin Films in High‐Pressure Fusion Toward High Efficiency Perovskite Solar Cell Modules

Abstract Perovskite solar cells, recognized for their high photovoltaic conversion efficiency (PCE), cost‐effectiveness, and simple fabrication, face challenges in PCE improvement due to structural defects in polycrystalline films. This study introduces a novel fabrication method for perovskite films using methylammonium chloride (MACl) to align grain orientation uniformly, followed by a high‐pressure process to merge these grains into a texture resembling single‐crystal perovskite. Employing advanced visual fluorescence microscopy, charge dynamics in these films are analyzed, uncovering the significant impact of grain boundaries on photo‐generated charge transport within perovskite crystals. A key discovery is that optimal charge transport efficiency and speed occur in grain centers when the grain size exceeds 10 µm, challenging the traditional view that efficiency peaks when grain size surpasses film thickness to form a monolayer. Additionally, the presence of large‐sized grains enhances ion activation energy, reducing ion migration under light and improving resistance to photo‐induced degradation. In application, a perovskite solar cell module with large grains achieve a PCE of 22.45%, maintaining performance with no significant degradation under continuous white LED light at 100 mA cm⁻² for over 1000 h. This study offers a new approach to perovskite film fabrication and insights into optimizing perovskite solar cell modules.