Robust Fully Screen‐printed Perovskite Solar Cells Based on Synergistic Ostwald Ripening

Fully screen‐printed process for low‐cost manufacturing significantly enhances the commercial competitiveness of perovskite solar cells (PSCs). However, the controllable crystallization in screen‐printed perovskite thin films using high ‐ viscosity ionic liquids has been suggested to be difficult, which hampers further development of fully screen‐printed perovskite devices in terms of application expansion and performance improvement. Here, we report a synergistic ripening strategy to fully control crystallization by employing methylamine propionate (MAPa) ionic liquid and water (H2O, moisture in the air). We found that a reversible and sustainable ripening process was activated by integrating MAPa/H2O in both externally and internally into perovskite crystals. MAPa effectively prevents the loss of organic salts and maintains the dispersion of Pb‐I framework, preventing the perovskite component loss and decomposition. H2O and organic salts trends to form hydration complexes, which lowers the energy barrier and enhances the reactivity of the humidity‐induced Ostwald ripening reaction. These improvements allow the perovskite films achieve controlled secondary growth, reducing defects and optimizing energy level alignment. The resulting fully screen‐printed PSCs exhibits a record power conversion efficiency of 19.47% and an operational stability over 1,000 h with maintaining 91.6% of the highest efficiency under continuous light stress at maximum power point.