Transparency and Morphology Control of Cu2O Photocathodes via an in Situ Electroconversion

Cu2O is a model p-type semiconductor for photocathodesin photoelectrochemical (PEC) water splitting cells. However, majorchallenges remain in controlling its deposition into thin andhomogeneous semitransparentfilms. Herein, we report a new route toconstruct thin homogeneous Cu2O layers on transparentfluorine dopedtin oxide (FTO) substrates via thein situelectroconversion of CuSCN toCu2O. We highlight the morphology control of the resulting convertedCu2O thinfilms while demonstrating that they maintain promisingperformance for solar-driven hydrogen production with a maximumincident photon to current efficiency (IPCE) reaching 60% (at 0 V vsRHE and 450 nm) for a 180 nm thickfilm and integrated solarphotocurrents up to 4 mA cm-2. In addition, altering the depositionconditions (e.g., applied potential, electrolyte compositions, and pH)gives important insight into the mechanism and operation of theelectroconversion process.