# Absorption Enhancement for Ultra-Thin Solar Fuel Devices with Plasmonic Gratings

## TL;DR

This paper demonstrates that nanostructured plasmonic gratings can significantly enhance light absorption in ultra-thin solar fuel devices, potentially improving their efficiency and performance.

## Contribution

The study introduces a novel nanostructured back contact design that boosts absorption by 47% in ultra-thin CuBi₂O₄ solar fuel devices through plasmonic resonances.

## Key findings

- Absorption increased by 47% due to plasmonic modes.
- Resonances linked to metal-insulator-metal plasmons and surface plasmon polaritons.
- Device maintains high absorption enhancement at incident angles up to 75°.

## Abstract

We present a concept for an ultra-thin solar fuel device with a nanostructured back contact. Using rigorous simulations we show that the nanostructuring significantly increases the absorption in the semiconductor, CuBi$_2$O$_4$ in this case, by 47\% (5.2~mAcm$^{-2}$) through the excitation of plasmonic modes. We are able to attribute the resonances in the device to metal-insulator-metal plasmons coupled to either localised surface plasmon resonances or surface plasmon polaritons. Rounding applied to the metallic corners leads to a blueshift in the resonance wavelength while maintaining absorption enhancement, thus supporting the possibility for a successful realization of the device. For a 2D array, the tolerance of the polarization-dependent absorption enhancement is investigated and compared to a planar structure. The device maintains an absorption enhancement up to incident angles of 75$^{\circ}$. The study highlights the high potential for plasmonics in ultra-thin opto-electronic devices such as in solar fuel generation.