Strain-Induced Distortions Modulate the Optoelectronic Properties of Epitaxial BiVO₄ Films

Transition metal oxide (TMO) photoabsorbers are expected to play an important role in the development of renewable solar-to-fuel devices. Modest efficiencies have been demonstrated with devices based on TMO photoabsorbers, and further progress will likely rely on material property control beyond conventional bulk chemistry or nanostructuring strategies. To this end, model TMO photoabsorbers such as single crystalline monoclinic bismuth vanadate (BiVO₄) are beneficial to advance the understanding of structure-functionality relationships with minimal convoluted effects inherent in polycrystalline systems. Here, the authors reveal for the first time the effects of strain modulation strategies on the optoelectronic properties of epitaxial BiVO₄ films synthesized by alternate-target layer-by-layer pulsed laser deposition. Through a combination of high-resolution X-ray diffraction methods and optical and photoluminescence spectroscopies, the correlation between anisotropic, uniaxial strain-driven bandgap widening and deviatoric strains associated with volume-preserving lattice distortions is established. Broad polaronic photoluminescence signals are detected in epitaxial BiVO₄, and its redshift is attributed to the structural distortion in BiO₈ dodecahedra. Overall, the relationship between the structural and optoelectronic properties revealed in this study suggests that strain modulation and engineering of local distortion in complex transition metal oxides may be exploited as a viable strategy for the development of efficient photoabsorbers.