Surface restoration of polycrystalline Sb₂Se₃ thin films by conjugated molecules enabling high-performance photocathodes for photoelectrochemical water splitting

Achieving both high onset potential and photocurrent in photoelectrodes is a key challenge while performing unassisted overall water splitting using tandem devices. We propose a simple interface modification strategy to maximize the performance of polycrystalline Sb₂Se₃ photocathodes for photoelectrochemical (PEC) water splitting. The para-aminobenzoic acid (PABA) modification at Sb₂Se₃/TiO₂ interface enhanced both the onset potential and photocurrent of the Sb₂Se₃ photocathodes. The surface defects in the polycrystalline Sb₂Se₃ limited the photovoltage production, lowering the onset potential of the photocathode. Surface restoration using the conjugated PABA molecules efficiently passivated the surface defects on the Sb₂Se₃ and enabled the rapid photoelectron transport from the Sb₂Se₃ to the TiO₂ layer. The PABA treated Sb₂Se₃ photocathode exhibited substantially improved PEC performance; the onset potential increased from 0.35 to 0.50 V compared to the reversible hydrogen electrode (V_RHE), and the photocurrent density increased from 24 to 35 mA cm⁻² at 0 V_RHE.