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.