Energy Band Architecture of a Hierarchical ZnO/Au/Cu<i>_x</i>O Nanoforest by Mimicking Natural Superhydrophobic Surfaces

Abstract

The ZnO/Cu₂O heterojunction promises high efficiency in photocurrent conversion and other light-driven processes, but the lattice mismatch between ZnO and Cu₂O leads to slow electron transfer and low conversion efficiency. In addition, the stability of Cu₂O is still the main challenging and limiting factor for device applications in real environments. Cu<i>_x</i>O is a mixed semiconductor of CuO and Cu₂O, which is a promising alternative to Cu₂O in device fabrication due to its better stability and photocatalytic efficiency. In this work, Cu<i>_x</i>O nanorods were attached to vertically aligned gold-decorated ZnO nanorods, creating a hierarchical ZnO/Au/Cu<i>_x</i>O nanoforest. In addition, the hierarchical surface shows superhydrophobicity, which can prevent Cu₂O degradation by water and oxygen. Femtosecond time-resolved transient absorption spectroscopy was employed to investigate the electron transfer dynamics in the ZnO/Au/Cu<i>_x</i>O heterojunction. The nanoforest demonstrates enhanced electron mobility, increased lattice match, and higher photocurrent conversion efficiency compared with bare ZnO, Cu<i>_x</i>O, or ZnO/Cu<i>_x</i>O.