The effectiveness of photoelectrochemical (PEC) water splitting is significantly restricted by insufficient light harvesting, rapid charge recombination, and slow water reduction kinetics. Since the presence of amorphous phases in the interfaces hinders the overcome of these inherent limitations, a photoelectrode must be built strategically. Herein, we artificially controlled the crystallographic orientation of indium tin oxide (ITO) to determine the orientation with the smallest lattice mismatch at the Cu₂O interface, thus significantly reducing the amorphous phase in the early stage of electrodeposition nucleation. The [222]/[400] mixed orientation ITO primarily exposed the {400} surface planes and accelerated charge transfer by forming an optimal interface with preferentially grown (111) oriented Cu₂O and minimized amorphous region. In addition, the ITO surface energy was calculated using density functional theory to theoretically verify which plane is more active for growing the photoactivation layer. The rationally designed ITO/Cu₂O/Al-dope ZnO/TiO₂/Rh-P device, with each layer serving a specific purpose, achieved a photocurrent density of 8.23 mA cm⁻² at 0 V_RHE under AM 1.5 G illumination, providing a standard method for effective solar-to-hydrogen conversion photocathodes.