Enhancing Low–Bias Performance of N–type Cu2O Photoanode for Solar Water Splitting Via Simultaneously Accelerated Charge Transfer Kinetics at Back Contact and Liquid Junction

Poor low–bias PEC performance of state–of–the–art BiVO4, α–Fe2O3 and WO3 photoelectrodes widely used in tandem and/or parallel PEC/PV and/or PEC/PEC devices has been reported to largely limit the cell efficiency for self–biased solar water splitting. A breakthrough of such bottleneck is put forward in this contribution by employing n–Cu2O with advantageous band edge positions straddling the HER and OER redox potentials as an alternative photoanode. The ohmic Cu/n–Cu2O back contact facilitates the interfacial photoelectron transfer while the gradient distribution of the oxygen vacancies (Vo) close to the n–Cu2O/electrolyte junction promotes the photoholes injected into water, synergistically leading to an outstanding photocurrent density of 3.5 mA cm−2, an unprecedented photocurrent–to–O2 conversion efficiency exceeding 70%, and a record ABPE of 2% at an ultralow applied potential of ∼0.6 VRHE, among the highest performance and the lowest external bias of state–of–the–art metal–oxide–based photoanodes reported to date.