Solvent‐Actuated Self‐Assembly of Amphiphilic Hole‐Transporting Polymer Enables Bottom‐Surface Passivation of Perovskite Film for Efficient Photovoltaics

Abstract Bottom‐surface defect passivation of perovskite film, lagging far behind easily conducted bulk and top‐surface passivations in perovskite solar cells (PSCs), remains rather challenging because most passivation molecules/groups can be eroded by polar solvents used for the subsequent perovskite deposition. In this work, an effective bottom‐surface passivation is enabled for enhanced performance of inverted PSCs by covalently attaching a passivation group (hydroxyl) to a hole transporting polymer. A short linker (methylene) between the hydroxyl and the conjugated backbone bearing hydrophobic long alkyl chains is adopted to improve the resistance of the resultant amphiphilic polymer to polar solvents. A solvent evaporation‐induced self‐assembly of the amphiphilic hole transporting polymer is developed to enrich hydroxyl groups on the film surface, passivating defects of the upper perovskite layer via interactions with undercoordinated Pb²⁺ and I^– sites. Inverted PSCs based on this hole transporting film are superior in efficiency (20.12%), reproducibility, large‐area fabrication, and stability to its classical poly(bis(4‐phenyl)(2,5,6‐trimethylphenyl)amine) counterpart. This work demonstrates that rational introduction of passivation groups into the hole transporting layer combined with self‐assembly‐modulated component distributions is useful to realize bottom‐surface passivation of the perovskite layer for improved photovoltaic performance.