Rational Design of Perovskite Precursor Inks for Dip-Coated Perovskite Solar Cells

Dip-coating is a simple yet versatile deposition method inherently compatible with complex, non-flat surfaces. Unlike conventional horizontal coatings, its vertical withdrawal configuration demands precise control over viscosity, surface tension, evaporation, and gravity to achieve uniform thin films. However, the performance of dip-coated perovskite solar cells (PSCs) has remained limited because commonly used volatile-solvent-dominated precursor inks provide inadequate morphological control. Also, conventional dip-coating strategies for rheological control are unsuitable for PSCs, as polymeric binders or high precursor concentrations can impair crystallization and charge transport. Here, by reversing the conventional DMF-dominant formulation, we identify an NMP-dominant DMF:NMP (= 7:93 (vol%/vol%)) solvent system that enables uniform, pinhole-free perovskite films via dip-coating. The resulting devices exhibit power conversion efficiencies exceeding 25%, representing the highest reported performance for dip-coated PSCs. Moreover, the ink enables conformal coating on textured, curved, and three-dimensionally complex surfaces. This work establishes an ink-design strategy for high-performance dip-coated PSCs, opening a practical pathway toward perovskite photovoltaics on nonplanar and structurally diverse substrates.