Fast Solidification and Slow Growth Strategy for High‐Performance Quasi‐2D Perovskite Solar Cells

Abstract Smooth perovskite film with high crystallinity and vertical orientation is highly favored for high‐performance quasi‐2D perovskite solar cells (PVSCs), yet limited by the critical balance between nucleation and crystal growth. To address this issue, here a fast solidification and slow growth (FSSG) strategy is developed to effectively optimize the film morphology. The fast solidification enables a smooth, pinhole‐free film, while slow growth allows it to further ripen into high‐crystallinity film. This process is enabled by the low‐boiling point solvent system, that is, acetonitrile, with high‐boiling point additives, that is, NH 4 SCN and CH 3 NH 3 Cl. Compared to the traditional method, uniform film with a larger grain/crystallite size as well as better crystallinity can be easily fabricated through this FSSG strategy. As a result, the quasi‐2D PVSCs based on (GA) 2 (MA) 4 Pb 5 I 16 processed with the FSSG strategy show a champion power conversion efficiency of 20.44%, as well as 19.08% for large‐area (1 cm 2 ) devices, which suggest the capability of the FSSG strategy for up‐scaled PVSC fabrication. Therefore, this work opens a new avenue toward morphology control of PVSCs for practical applications.