Hard Lewis Base‐Driven Crystallization Control for Efficient All‐Perovskite Tandem Solar Cells

All‐perovskite tandem solar cells (APTSCs) have attracted considerable research interest in recent years due to their higher theoretical efficiencies and broader spectral coverage. Nonetheless, as the bottom narrow‐bandgap cell in APTSCs, tin‐lead (Sn‐Pb) hybrid perovskite solar cells (PSCs) still face challenges of high defect density and poor crystallization morphology, which hinder the further improvement of device performance and long‐term stability. This work proposes a Lewis hard‐basicity amplification strategy that provides additional potential hard‐acid binding sites and promotes coordination with Sn 2+ , thereby enabling defect passivation and regulating crystallization. Ultimately, we achieved a champion power conversion efficiency (PCE) of 23.71% for single‐junction Sn‐Pb PSCs. By integrating 1.77 eV wide‐bandgap perovskites with Sn‐Pb hybrid perovskites, we further fabricated APTSCs with a champion PCE of 29.44%. Both devices retain approximately 80% of their initial efficiency after 1080 h of continuous operation under one‐sun illumination.