Epitaxial growth of B-doped Sb₂S₃ nanorod photoanode and investigation of the charge transfer mechanism by using femtosecond transient absorption spectroscopy towards photoelectrochemical water splitting

Sb₂S₃ exhibits outstanding photon harvesting capability, positioning it as a premier photoanode candidate for photoelectrochemical (PEC) water splitting, environmental friendliness, and cost-effective advantages. However, its applied implementation has been limited by slow charge separation kinetics and severe bulk recombination. In this study, boron-doped Sb₂S₃ nanorods were heteroepitaxially grown on Bi₂O₂S substrates using hydrothermal synthesis. The Bi₂O₂S nanosheets induce the preferential growth of Sb₂S₃ along the [hk1] direction, effectively reducing bulk transport barriers. Simultaneously, B doping creates shallow-level defects within the bandgap of 1D Sb₂S₃, serving as transient trapping centers for electron-hole pairs. Through femtosecond transient absorption spectroscopy (fs-TAS), we elucidated the complex photoelectrochemical mechanism and charge transfer pathways. Quantitative analysis revealed that the shallow-level trapping extends the carrier lifetime of Bi₂O₂S/Sb₂S₃: B to 253.75 ps - 53 times longer than that of pristine Sb₂S₃ (4.79 ps). Performance tests measured a photocurrent density of 11.07 mA cm⁻² at 1.23 V_RHE for the optimized photoanode, which is an 8.31-times enhancement over Sb₂S₃. This work proposes a synergistic strategy combining heterointerface design and defect-state regulation, providing an innovative solution for crystallographically oriented growth of Sb₂S₃ photoanodes and optimization of spatial carrier transport pathways.