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

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 C₆₀ 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.