Self‐Limiting Ultrathin Heterocycle‐Bridged Interface Enabling Efficient p–i–n PbS Quantum Dot Solar Cells

ABSTRACT Hole‐transporting self‐assembled monolayers (SAMs) have driven rapid efficiency gains in solution‐processed p–i–n solar cells over the past few years. By contrast, while efficient electron extraction is equally crucial for device operation, electron‐transporting SAMs remain scarcely explored, thereby constraining further improvements in device performance. Here, we present an electron‐extraction‐modulating self‐limiting ultrathin molecular layer strategy for PbS quantum dot (QD) solar cells. The designed thiophene‐based molecules feature thiol anchors that coordinate with surface Pb 2 + ions to suppress nonradiative recombination, while their electron‐rich aromatic rings engage in π–π interactions with the top C 60 layer to enhance electron extraction. Critically, their high volatility enables the removal of excess molecules during annealing, yielding a compact, ultrathin molecular modification at the interface. This interface engineering delivers a power conversion efficiency of 14.47% in p–i–n PbS QD solar cells‐the highest value reported to date. These results provide a robust and scalable pathway for applying self‐limiting ultrathin molecular layer as a powerful paradigm for interfacial design.