Photoelectrochemical performance of nanoscale Cu2O by integrating ZnO thin films mimicking a 3D–2D heterojunction: experiments & first-principles analysis

Abstract

The generation of hydrogen from water using sunlight offers a promising approach for scalable and sustainable carbon-free energy production. The success of solar-to-fuel technology hinges on the design of efficient, durable, and cost-effective photoelectrochemical (PEC) cells that can absorb sunlight and drive water-splitting reactions. In this context, we present a promising heterojunction by integrating Cu₂O with a ZnO overlayer mimicking a 3D–2D heterojunction, addressing the challenges associated with copper-based metal oxides in PEC water-splitting reactions. The heterojunction thin films were deposited on ITO glass substrates using a low-cost, scalable spray pyrolysis technique. We varied the thickness of the ZnO layer by adjusting the total spray time from 30 to 120 seconds on the pre-deposited Cu₂O thin films. Our study identified 90 seconds as the optimal spray time, yielding a peak photocurrent of 1.25 mA cm⁻² and an ABPE of 0.98% at an overpotential of 270 mV. Density functional theory (DFT) studies were also conducted to elucidate the mechanism behind the improved photocurrent of the heterojunction.