Multi-Step Spin-Coating with In Situ Crystallization for Growing 2D/3D Perovskite Films

Developing perovskite solar cells (PSCs) with both high performance and long-term stability remains a critical challenge and research focus in the field of photovoltaic devices. Herein, we report a multi-step spin-coating strategy for high-efficiency 2D/3D perovskite heterojunction solar cells by sequentially depositing low-concentration 3-pyridine methylamine iodine solutions onto 3D perovskite films. This approach enables controlled Ostwald ripening and forms graded 2D/3D heterointerfaces rather than insulating capping layers, yielding a champion device with a PCE of 22.7%, significantly outperforming conventional 2D/3D planar counterparts. The optimized structure exhibits enhanced carrier extraction, suppressed recombination, and exceptional humidity stability; the hydrophobic structure further enabled >85% initial efficiency retention after 800 h at 45% relative humidity (RH) for target devices. This study establishes a novel research paradigm for developing high-performance and stable 2D/3D perovskite solar cells through gradient dimensionality engineering.