Tuning the anisotropic facet of Cu₂O single-crystals for photocarrier spatial segregation

Precise design of anisotropic facets is a key strategy for modulating semiconductor photoelectrochemical (PEC) performance, but it still faces significant challenges. In this work, we proposed an approach to modulate Cu₂O photoelectrodes based on triple engineering, including morphology, defect state, and crystal facet engineering, which promoted photocarrier separation through rational design of anisotropic facets. By controlling the precursors, six Cu₂O photoelectrodes with anisotropic facet structures and different oxygen vacancy (O_V) contents were obtained. The prepared Cu₂O photoelectrodes exhibited significant negative photocurrent responses to H₂O₂ catalyzed by the sandwich immunoenzyme, which enabled the development of a PEC immunoassay for the sensitive detection of carcinoembryonic antigen (CEA). The anisotropic separation of photocarriers and the highly selective recognition of target molecules could be effectively achieved by optimizing the ratio of facets exposed and the facets with characteristic adsorption. Combined with density functional theory (DFT) calculations, the electronic structure characteristics and photocarrier transfer behavior of anisotropic facets have been investigated, elucidating the critical role of crystal facet engineering in promoting the anisotropic separation of photocarriers and modulating the kinetics of surface reactions. This work provides an innovative engineering strategy for the development of PEC sensors with high photoelectric conversion efficiency.