Boosting Near‐Infrared Utilization in PbS Quantum Dot Solar Cells via a Back‐Interface Chemical‐Bonding Molecular Buffer

Abstract PbS quantum dots (QDs) offer a promising near‐infrared (NIR) light‐harvesting material platform for high‐efficiency broadband photovoltaics. However, efficient carrier extraction at the solar cell back‐contact remains challenging due to the severe trap‐induced recombination and insufficient carrier delocalization. Herein, a chemical‐bonding molecular buffer, (2‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)ethyl)phosphonic acid (MeO‐2PACz) is introduced, at the QD/Au back contact for high‐performance quantum dot solar cells. Unlike conventional unbonded buffers, MeO‐2PACz forms stable covalent bonds on QDs surface, enabling an orientated molecular arrangement that promotes photogenerated carrier delocalization and interfacial energy alignment. This approach yields up to an 18.1% enhancement in NIR carrier collection efficiency over unmodified devices, significantly surpassing the 8.0% gain achieved by unbonded buffers, while achieving a power conversion efficiency (PCE) of 13.3% that outperforms the reference device (11.5%). Additionally, MeO‐2PACz device shows excellent operational stability, retaining 93% of initial PCE after 10 h continuous illumination due to suppressed interfacial photooxidation. This study develops an oriented bonding interface engineering to address interfacial carrier loss in NIR QDs optoelectronic devices, guiding the further molecular design of bonding buffers.