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 Sn²⁺, 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.