Improving the photovoltage of Cu2O photocathodes with dual buffer layers

Abstract Cuprous oxide (Cu 2 O) is a promising oxide material for photoelectrochemical water splitting (PEC), and increasing its photovoltage is the key to creating efficient overall PEC water-splitting devices. Previous reports are mostly focused on optimizing the energy band alignment between Cu 2 O and the n-type buffer layer to improve the photovoltage of Cu 2 O photocathodes. However, the band alignment between the n-type buffer layer and the protective layer is often ignored. In this work, Cu 2 O photocathodes with a single buffer layer (Ga 2 O 3 ) and dual buffer layers (Ga 2 O 3 /ZnGeO x ) are fabricated, and their PEC performances are compared. Results show that after inserting the second buffer layer (ZnGeO x ), the onset potential of the Cu 2 O photocathode increases by 0.16 V. Operando electrochemical impedance spectroscopy measurements and analysis of the energy-level diagrams of each layer show that an energy level gradient between Ga 2 O 3 and TiO 2 is created when ZnGeO x is introduced, which eliminates the potential barrier at the interface of Ga 2 O 3 /TiO 2 and improves the photovoltage of the Cu 2 O photocathode. Our work provides an effective approach to improve the photovoltage of photoelectrodes for solar water splitting by introducing dual buffer layers.