Harnessing Molecular Tautomerism to Tune Precursor Coordination Chemistry for Efficient and Stable Perovskite Solar Cells

ABSTRACT Homogeneous crystallization remains a critical challenge for high‐performance perovskite photovoltaics, as conventional molecular additives typically exhibit fixed coordination characteristics that limit precise regulation of precursor evolution. Here, we demonstrate molecular tautomerism as an effective design principle for tuning precursor coordination chemistry by employing purine as a prototype coordination modulator. The intrinsic tautomerism of purine redistributes electron density among multiple nitrogen sites, enabling tautomer‐dependent Pb–N coordination and hydrogen‐bonding interactions with different precursor species. Density functional theory calculations reveal distinct interaction strengths of purine tautomers toward precursor species, establishing the fundamental basis for tautomerism‐enabled tunable coordination. Such tunable molecular interactions modulate the precursor coordination network and regulate intermediate‐state evolution, thereby retarding nucleation and promoting homogeneous crystal growth. Consequently, the resulting perovskite films exhibit enhanced crystallinity and a more homogeneous energetic landscape. The optimized solar cells achieve a champion power conversion efficiency of 27.05% (certified 26.51%), and the corresponding mini‐module delivers an aperture‐area (12.95 cm 2 ) efficiency of 21.52%. This work establishes molecular tautomerism as a design principle for tunable precursor coordination, providing a molecular‐level approach to controlling perovskite crystallization for efficient and scalable photovoltaics.