Construction of visible responsive broadband absorber utilizing strong coupling between plasmon and nanocavity modes and its application to light energy conversions

Nanoparticles colloidal solutions of metals such as gold (Au) and silver (Ag) show very intense color due to localized surface plasmon resonances (LSPRs). LSPRs which are collective oscillations of conduction electrons give rise to the enhancement of electromagnetic field in the vicinity of nanoparticles and are expected as a light harvesting optical antenna for light energy conversion devices based on their spectrum tunability. We have successfully developed the plasmon-induced energy conversions such as water splitting and ammonia synthesis systems as well as solid-state plasmonic solar cells based on the principle of plasmon-induced hot electron transfer from gold nanoparticles (Au-NPs) to the semiconductor electrode.^1-5 In these days, the plasmon-induced hot electron transfer has received considerable attention as a novel strategy for the solar energy conversion.^6,7 However, the insufficient absorption limited its solar energy conversion efficiency for the monolayer of Au-NPs only dispersed on the semiconductor electrode. In the present study, we apply the principle of modal strong coupling to visible responsive broadband absorber for plasmonic water splitting using Au-NPs/titanium dioxide (TiO2)/Au-film electrode.