Synergistic Surface Under‐Coordinated Sites and Ligand Engineering of Colloidal Quantum Dots for High‐Efficiency Bifunctional Photoelectrochemical Devices

Abstract Colloidal quantum dots (QDs) have demonstrated great potential as building blocks in various photoelectrochemical (PEC) devices that enable highly efficient optical‐electrical‐chemical conversion. However, the photogenerated electrons and holes in most of the QDs are generally confined to cause inefficient charge carrier separation and extraction for limited PEC performance. Herein, a two‐step surface engineering technique is developed to manipulate the photoinduced charge carrier kinetics in a classical InP/ZnSeS QD system through the construction of Zn vacancies (V Zn )‐related under‐coordinated (UC) Se/S sites and subsequent Cl − ligand exchange. It is revealed that the introduced V Zn ‐UC Se/S sites can act as hole‐trapping centers to facilitate the charge separation, and the Cl − ligands further induced a local internal electric field in QDs to drive a more efficient carrier extraction. As a result, the optimized QDs‐based PEC device delivers a maximum photocurrent density of 12.1 mA cm −2 in PEC hydrogen evolution (1 sun, AM 1.5G) and an exceptional responsivity of 1.22 A W −1 in self‐powered PEC photodetection. This study deepens the understanding of the intricate interplay between surface modulation and optoelectronic properties in QDs, offering a universal strategy to design cost‐effective and high‐performing QDs‐based PEC devices for solar energy conversion and light detection applications.