Fine-tuning interfacial band edge energetics at Sb2S3/TiO2 heterojunction via phase control and defect engineering for enhanced solar water splitting performance

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 = similar to 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.