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

Abstract In the emerging Sb 2 S 3 ‐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 Sb 2 S 3 /CdS interface induces detrimental defects but is often overlooked. Designing a stable interface in the Sb 2 S 3 /CdS heterojunction is essential to achieve high solar energy conversion efficiency. As a proof of concept, this study reports that the modification of the Sb 2 S 3 /CdS heterojunction with an ultrathin Al 2 O 3 interlayer effectively suppresses the interfacial defects by preventing the diffusion of Cd 2+ cations into the Sb 2 S 3 layer. As a result, a water‐splitting photocathode based on Ag:Sb 2 S 3 /Al 2 O 3 /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:Sb 2 S 3 /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.