Congcong Wu

The organic-inorganic hybrid perovskite solar cells (PSCs) have attracted tremendous attention in both academic and industrial community. Unprecedented progress has been obtained in improving their power conversion efficiency (PCE) and in their cheap and facile production. However, the long-term stability issue remains the most critical challenge hindering the progress of PSCs. The perovskite light absorber is quite sensitive to humidity, oxygen, thermal and even continuous illumination. Here in this research, we address this issue by inventing a self-assembly process for fabrication of highly stable perovskite film. We reveal that CH3NH2 can slice the 3D CH3NH3PbI3 perovskite into 2D layered perovskite intermediates (LPI) via intercalation process. The 2D layered intermediate shows high solubility in a greener solvent acetonitrile (ACN). The hydrophobic polymer, poly (methyl methacrylate) (PMMA), is introduced into the LPI, resulting in chemical coordination and self-assembly into 3D perovskite grains with PMMA coated along the grain boundaries.1,2 The bilayer grain boundary effectively blocks the moisture corrosion thereby significantly improving the stability of CH3NH3PbI3 perovskite, as illustrated in Fig. 1. Further, PMMA is found to reduce the trap density by electronically compensating the iodide vacancy along the boundary, which decreases the charge recombination and improves the open circuit voltage of PSCs. The PSCs comprising of the CH3NH3PbI3-PMMA layer show excellent stability under high moisture conditions, exhibiting no phase change under ≈70% humidity for over 31 days (approximately 500% higher compared to state‐of‐the‐art) and excellent photovoltaic performance in 50–70% humidity for over 50 days. This advancement provides new direction towards realizing highly stable and efficient PSCs using facile and greener process.