Enhanced Visible Light-Induced Charge Separation and Charge Transport in Cu2O-Based Photocathodes by Urea Treatment.

Carrier density, photocharge transfer kinetics, and charge transfer resistance of the anodized Cu-Cu2O-CuO photocathode were greatly improved using thermal treatment with urea. Time-correlated single-photon counting (TCSPC) results revealed the faster electron transfer kinetics from Cu2O to CuO in the urea-treated Cu-Cu2O-CuO composite photoelectrodes. Preservation of the metallic copper component via the intermediate Cu3N during the treatment facilitated higher bulk conductance of the Cu-Cu2O-CuO photocathode for improved charge transport. Higher carrier density was also observed in the urea-treated photoelectrode, which was possibly attributed to the presence of nitrogen as a dopant. Furthermore, the compact outer layer of CuO protected the underlayer Cu2O from being in direct contact with the aqueous solution. This suppressed the photocorrosion of Cu2O and resulted in the higher photostability of the Cu-Cu2O-CuO film. When these advantages were combined, the urea-treated Cu-Cu2O-CuO film showed a higher photocurrent of 2.2 mA/cm2 and improved stability versus that of the conventional Cu-Cu2O-CuO film (1.2 mA/cm2). To improve the charge transfer kinetics and carrier density, this paper provides a new strategy for synthesizing effective and stable Cu2O-based photoelectrodes by using urea treatment.