Thiol-Amine-Based Solution Processing of Cu₂S Thin Films for Photoelectrochemical Water Splitting

Cu₂S is a promising solar energy conversion material owing to its good optical properties, elemental earth abundance, and low cost. However, simple and cheap methods to prepare phase-pure and photo-active Cu₂S thin films are lacking. This study concerns the development of a cost-effective and high-throughput method that consists of dissolving high-purity commercial Cu₂S powder in a thiol-amine solvent mixture followed by spin coating and low-temperature annealing to obtain phase-pure crystalline low chalcocite Cu₂S thin films. After coupling with a CdS buffer layer, a TiO₂ protective layer and a RuO_x hydrogen evolution catalyst, the champion Cu₂S photocathode gives a photocurrent density of 2.5 mA cm⁻² at −0.3 V vs. reversible hydrogen electrode (V_RHE), an onset potential of 0.42 V_RHE, and high stability over 12 h in pH 7 buffer solution under AM1.5 G simulated sunlight illumination (100 mW cm⁻²). This is the first thiol-amine-based ink deposition strategy to prepare phase-pure Cu₂S thin films achieving decent photoelectrochemical performance, which will facilitate its future scalable application for solar-driven hydrogen fuel production.