Fine–Tuning Interfacial Band Edge Energetics at Sb2S3/TiO2 Heterojunction via Phase Control and Defect Engineering for Enhanced Solar Water Splitting Performance

Abstract

Upon pairing with wide band gap semiconductors, the high–lying conduction band minimum (CBM) of antimony sulfide (Sb₂S₃) results in a large conduction band offset (CBO = ~0.7 eV) to reduce the energy gap between its valence band maximum (VBM) and CBM of its counterpart, leading to the back flow of the photoexcited electrons to severely limit its photocurrent density. To address this issue, a phase control over the semiconductor, which is exemplified herein by rutile–structured titanium dioxide (r–TiO₂), is put forward, resulting in not only reduced CBO to 0.5 eV but also enhanced energy difference between its CBM and VBM of Sb₂S₃ to successfully suppress the interfacial charge recombination. This carrier loss is further quenched after introducing oxygen vacancies (O_v) into r–TiO₂, which serve as the active sites to allow Sb₂S₃ strongly bound to r–TiO₂ to facilitate the electron transfer. Their synergistic effect renders the photoexcited charge carriers of Sb₂S₃/O_v–r–TiO₂ contributing mostly to its photocurrent density, which thereby turns on at an early potential of 0.2 V_RHE and rapidly increases to 1.9 mA cm^-2 (at 1.23 V_RHE), leading to its half–cell solar–to–hydrogen (HC–STH) efficiency achieving 0.408% that is among the highest performance reported for the Sb₂S₃–based photoelectrode in the literature.