Tuning the Optical and Photoelectrochemical Properties of Epitaxial BiVO4 by Lattice Strain

State‐of‐the‐art photoelectrodes in highly efficient photoelectrochemical (PEC) systems often comprise multilayer architectures where lattice mismatch‐imposed strain at the interfaces can perturb the material's crystalline lattice and electronic structure. Despite its inevitable presence, understanding of strain effects in semiconductor photoelectrodes is lacking, preventing rational exploitation of strain engineering to improve photoelectrode performance. In this work, we combine X‐ray structural characterization with strain tensor decomposition analysis as well as optical/photocurrent spectroscopic methods to demonstrate how volumetric lattice deformations caused by substrate‐imposed hydrostatic strain impact the optoelectronic and PEC properties of BiVO4. Utilizing single‐crystalline, epitaxial BiVO4/indium tin oxide (ITO)/yttrium‐stabilized zirconia (YSZx, x = 8% and 13% mol Y2O3) photoelectrodes as a model platform, we find that tensile hydrostatic strain that causes volumetric lattice dilation in BiVO4 results in slightly enhanced optical absorption, but it is detrimental to the internal quantum efficiencies in BiVO4. We attribute this to localization of photogenerated charge carriers, thereby leading to poor charge separation in the bulk of BiVO4 and increased recombination losses. Finally, we highlight the beneficial effects of compressive hydrostatic strain on enhancing the internal quantum efficiencies in BiVO4. Our results provide a basis for exploiting epitaxial strain engineering to optimize the performance of multilayer photoelectrodes in PEC systems.