Donor–Acceptor Pair‐Mediated Carrier Dynamics Optimization Boosts Photocatalytic Hydrogen Evolution of Cu‐In‐S/ZnIn ₂ S ₄ Heterojunctions

Ternary I–III–VI group quantum dots (QDs), featuring unique donor–acceptor (D–A) pair energy levels, have demonstrated great promise in the trapping and separation of photogenerated carriers, and are highly promising candidates for photocatalytic hydrogen evolution. However, the further enhancement of their photocatalytic hydrogen evolution performance is fundamentally restricted in the absence of a directional driving force to guide the efficient migration of carriers stored in the D–A pairs. In this work, Cu‐In‐S QDs with high‐density D–A pair energy levels were fabricated via nonstoichiometric regulation, followed by partial ZnS coating to passivate the surface defects of the quantum dots. On this basis, Type‐II‐like heterojunctions were constructed using the as‐prepared QDs and layered ZnIn 2 S 4 (ZIS) nanosheets rich in sulfur vacancies (V S ). Various characterizations including 3D fluorescence spectroscopy, X‐ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and photoelectrochemical measurements verify that the built‐in electric field formed at the heterojunction interface and the well‐matched staggered band structure can provide sufficient driving force for the directional migration of charge carriers, thus realizing efficient spatial separation of photogenerated electrons and holes. Under 100 W xenon lamp irradiation, the optimal heterojunction catalyst achieves a maximum hydrogen evolution rate (HER) of 29.25 mmol·g −1 ·h −1 , which is over 70 times higher than that of pristine Cu‐In‐S QDs, and also exhibits excellent cycling stability. This work provides systematic theoretical guidance for the defect energy level regulation and carrier dynamics optimization of I–III–VI group semiconductors and offers new insights into the design and construction of high‐efficiency photocatalytic energy conversion systems.