Beyond Hole Transportation: Substrate-Engineered Sb ₂ Se ₃ Photocathodes

While antimony selenide (Sb 2 Se 3 ) has emerged as a promising absorber for photoelectrochemical water splitting, the critical role of the hole transport layer (HTL) for back-contact remains underexplored. We introduced solution-processed NiO x nanocrystals as noble metal-free HTL that synergistically enable: (1) Thermodynamic-stability-driven [hk1]-oriented Sb 2 Se 3 growth with the lowest interfacial formation energy and (2) Electron-blocking functionality through a 2.16 eV conduction band offset at the back contact interface. Therefore, the optimized NiO x -based photocathode achieved a photocurrent density of −17 mA cm –2 at 0 V versus reversible hydrogen electrode (RHE) and 214 mV photovoltage, outperforming Au-based and HTL-free-based counterparts. This dual functionality-crystallographic templating and hole-selective transport not only improve the crystal growth of the absorber but also suppress electron back flowing. This work establishes NiO x nanocrystals as a design paradigm for chalcogenide photoelectrodes, emphasizing concurrent interfacial lattice matching and electronic alignment optimization for solar-fuel generation.