Managing Crystallization in Tin‐Lead Perovskite Solar Cells via Differential Chelating Coordination

All‐perovskite tandem solar cells (TSCs) have emerged as a promising platform for exceeding the Shockley–Queisser limit in photovoltaics, but their advancement is constrained by issues related to the narrow‐bandgap tin‐lead (Sn–Pb) perovskite subcell. In particular, asynchronous crystallization kinetics generates trap states and expedites degradation, posing a key challenge. To address this issue, we introduce a bidentate ligand (1,10‐phenanthroline (phen)) that have stronger coordination with Sn 2+ than with Pb 2+ , slowing down its crystallization to synchronize with that of Pb 2+ for improving crystallinity. Through targeted molecular regulation, improved crystallinity, enlarged grain size, and substantially reduced defect densities are achieved in the resulting perovskite films. Consequently, the optimized devices deliver an open‐circuit voltage ( V OC ) of 0.887 V, a high fill factor (FF) of 81.27%, and a PCE of 23.63%. Additionally, the all‐perovskite TSCs attained a PCE of 29.08% after the introduction of phen. These results highlight an effective molecular approach for controlling perovskite crystallization kinetics and enhancing photovoltaic performance.