Designing Atomic Interface in Sb₂S₃/CdS Heterojunction for Efficient Solar Water Splitting

In the emerging Sb₂S₃-based solar energy conversion devices, a CdS buffer layer prepared by chemical bath deposition is commonly used to improve the separation of photogenerated electron-hole pairs. However, the cation diffusion at the Sb₂S₃/CdS interface induces detrimental defects but is often overlooked. Designing a stable interface in the Sb₂S₃/CdS heterojunction is essential to achieve high solar energy conversion efficiency. As a proof of concept, this study reports that the modification of the Sb₂S₃/CdS heterojunction with an ultrathin Al₂O₃ interlayer effectively suppresses the interfacial defects by preventing the diffusion of Cd²⁺ cations into the Sb₂S₃ layer. As a result, a water-splitting photocathode based on Ag:Sb₂S₃/Al₂O₃/CdS heterojunction achieves a significantly improved half-cell solar-to-hydrogen efficiency of 2.78% in a neutral electrolyte, as compared to 1.66% for the control Ag:Sb₂S₃/CdS device. This work demonstrates the importance of designing atomic interfaces and may provide a guideline for the fabrication of high-performance stibnite-type semiconductor-based solar energy conversion devices.