Solution-Processed Cu₂S Nanostructures for Solar Hydrogen Production

Cu₂S is a promising solar energy conversion material due to its suitable optical properties, high elemental earth abundance, and nontoxicity. In addition to the challenge of multiple stable secondary phases, the short minority carrier diffusion length poses an obstacle to its practical application. This work addresses the issue by synthesizing nanostructured Cu₂S thin films, which enables increased charge carrier collection. A simple solution-processing method involving the preparation of CuCl and CuCl₂ molecular inks in a thiol-amine solvent mixture followed by spin coating and low-temperature annealing was used to obtain phase-pure nanostructured (nanoplate and nanoparticle) Cu₂S thin films. The photocathode based on the nanoplate Cu₂S (FTO/Au/Cu₂S/CdS/TiO₂/RuO ) reveals enhanced charge carrier collection and improved photoelectrochemical water-splitting performance compared to the photocathode based on the non-nanostructured Cu₂S thin film reported previously. A photocurrent density of 3.0 mA cm^-2 at -0.2 versus a reversible hydrogen electrode (V _RHE) with only 100 nm thickness of a nanoplate Cu₂S layer and an onset potential of 0.43 V _RHE were obtained. This work provides a simple, cost-effective, and high-throughput method to prepare phase-pure nanostructured Cu₂S thin films for scalable solar hydrogen production.