Accelerated Crystallization via Phase‐Formation Promoters for Rapid‐Annealed High‐Efficiency Perovskite Solar Cells

Two‐dimensional (2D) perovskites, when integrated into formamidinium (FA)‐based absorbers, offer a compelling pathway for passivating defects and enhancing the environmental durability of perovskite solar cells (PSCs). However, critical challenges remain in controlling crystallization during competing growths of low‐dimensional and three‐dimensional (3D) phases that determine ultimate photovoltaic performance. To achieve satisfactory crystal quality, energy‐intensive, time‐consuming annealing is commonly adopted, hindering scalable manufacturing. Herein, we unravel the crystallization kinetics and phase evolution of 3D‐like domains within the 2D‐confined framework of FA‐based quasi‐2D perovskites, and develop an NH 4 PbBr 3 ‐based phase additive (PA) for 2D perovskite synthesis to achieve high crystalline quality. The results demonstrate that the NH 4 PbBr 3 PA preferentially promotes 3D‐like crystallization and minimizes growth competition between low‐dimensional components. The resultant 2D PSCs yield a record power conversion efficiency (PCE) exceeding 22% with impressive stability. Notably, we observe the evolution of an ordered 2D‐to‐3D‐like gradient structure, enabling rapid formation of highly oriented, defect‐passivated perovskite films under shortened annealing. Furthermore, we propose a comprehensive global evaluation index (CGEI) to assess the performance‐processing balance of PSCs. The CGEI results confirm our strategy reduces energy consumption and material costs without compromising crystallization and device efficiency, thus providing an energy‐saving, cost‐effective route for scalable 2D PSC fabrication.