Extended Light Harvesting with Dual Cu2O-Based Photocathodes for High Efficiency Water Splitting

Abstract

Cu2O is one of the most promising light absorbing materials for solar energy conversion. Previous studies with Cu2O for water splitting usually deliver high photocurrent or high photovoltage, but not both. Here, a Cu2O/Ga2O3/TiO2/RuOx photocathode that benefits from a high quality thermally oxidized Cu2O layer and good band alignment of the Ga2O3 buffer layer is reported, yielding a photocurrent of 6 mA cm−2 at 0 V versus reversible hydrogen electrode (RHE), an onset potential of 0.9 V versus RHE, and 3.5 mA cm−2 at 0.5 V versus RHE. The quantum efficiency spectrum (incident photon to current efficiency, IPCE) reveals a dramatically improved green/red response and a decreased blue response compared with electrodeposited Cu2O films. Light intensity dependence and photocurrent transient studies enable the identification of the limitations in the performance. Due to the complementary IPCE curves of thermally oxidized and electrodeposited Cu2O photocathodes, a dual photocathode is fabricated to maximize the absorption over the entire range of above band gap radiation. Photocurrents of 7 mA cm−2 at 0 V versus RHE are obtained in the dual photocathodes, with an onset potential of 0.9 V versus RHE and a thermodynamically based energy conversion efficiency of 1.9%.