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

Cu2O is a model p-type semiconductor for photocathodes in photoelectrochemical (PEC) water splitting cells. However, major challenges remain in controlling its deposition into thin and homogeneous semitransparent films. Herein, we report a new route to construct thin homogeneous Cu2O layers on transparent fluorine doped tin oxide (FTO) substrates via the in situ electroconversion of CuSCN to Cu2O. We highlight the morphology control of the resulting converted Cu2O thin films while demonstrating that they maintain promising performance for solar-driven hydrogen production with a maximum incident photon to current efficiency (IPCE) reaching 60% (at 0 V vs RHE and 450 nm) for a 180 nm thick film and integrated solar photocurrents up to 4 mA cm–2. In addition, altering the deposition conditions (e.g., applied potential, electrolyte compositions, and pH) gives important insight into the mechanism and operation of the electroconversion process.