Heterojunction engineering enables more versatile and higher-performance systems than single components. In parallel with heterojunction engineering, defect engineering has emerged as a means of tailoring the optoelectronic properties of photoelectrodes. However, constructing effective, visible-light responding, and stable hybrid semiconductor heterojunctions is a challenging task under the strict requirements of band alignment, vacancy characteristics, and interface properties. In this study, the photoelectrochemical (PEC) reduction of CO 2 to methanol is augmented by a novel approach explored by modeling the Fermi level in a multi-interface architecture.