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

Abstract

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/cm(2) 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. (C) 2020 Elsevier Inc. All rights reserved.