Strengthened absorption of ultra-thin film bismuth vanadate using a motheye-structured triple-deck photoanode

Bismuth vanadate (BiVO₄) is one of the most promising materials used in photoelectrochemical cells (PEC cells), which are significant generators of clean energy. As with many promising materials used as photoanodes, the main problem limiting the efficiency of BiVO₄-based photoanodes is the trade-off between their large light penetration depth and small diffusion length. To reduce this gap, various methods have been investigated to improve the absorption efficiency of ultra-thin BiVO₄ layers, including template-assisted nanostructuring. In this study, we have implemented a densely packed sub-wavelength-scale nanocone array inspired by the motheye morphology using a direct printing method. Subsequently, we fabricated a series of triple-deck hierarchical photoanodes using a motheye template via the successive deposition of Au, SnO₂, and BiVO₄. The fabricated motheye structures exhibit a gradual change in their refractive index, which is excellent for reducing the reflection of high refractive index materials. In addition, the synergy between the light trapping effects of the nanocone array and gap-plasmon structure (reflector/spacer/antenna) maximizes the absorption of incident solar light. Due to this enhancement, a current density of 1.48 mA/cm² was obtained using a thin layer of BiVO₄ (200 nm) at 1.23 V vs. RHE under a simulated solar light (AM 1.5G). Our results can be applied toward many promising candidate materials used for photoanode and optoelectronic devices, where poor electronic properties and high reflectivity limit the absorption and power generation efficiencies.