Absorption Enhancement for Ultrathin Solar Fuel Devices with Plasmonic Gratings

We present a concept for an ultrathin solar fuel device with a nanostructured back-contact. Using rigorous simulations, we show that the nanostructuring significantly increases the absorption in the semiconductor, CuBi₂O₄ in this case, by 47% (5.2 mA cm^-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 localized surface plasmon resonances or surface plasmon polaritons. Rounding applied to the metallic corners leads to a blue shift 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°. The study highlights the high potential for plasmonics in ultrathin optoelectronic devices such as in solar fuel generation. © Copyright 2018 American Chemical Society.