Weakening Solvent‐Solute Interactions for High‐Efficiency Screen‐Printed Perovskite Solar Cells

Screen printing has emerged as a leading candidate for industrial‐scale fabrication of perovskite photovoltaics. However, strong solvent‐solute interaction in conventional formulations accelerates the preferential crystallization of perovskites at points, hindering the progressive phase evolution from point to line to plane. In this work, we introduced halogen ions to weaken solvent‐solute interactions, achieving the reduced Pb···O coordination strength counterbalanced by enhanced Pb‐I bonding interactions. This weakened interaction delays formamidinium iodide participation in rapid phase transitions to α‐formamidinium lead iodide, enabling controlled crystallization kinetics. The optimized screen‐printed perovskite solar cells demonstrate remarkable power conversion efficiencies (PCE) of 21.8% for 0.05 cm² devices and 18.95% for 5 cm × 5 cm mini‐modules (active area: 12.60 cm²). Furthermore, this strategy exhibits broad process compatibility, achieving 23‐24% PCEs for both blade‐coating and spin‐coating devices fabricated under ambient conditions (25‐30 °C, 35‐50% relative humidity). These breakthroughs highlight the universal potential of coordination engineering for scalable perovskite photovoltaics.