Localized surface plasmon resonance with broadband ultralow reflectivity from metal nanoparticles on glass and silicon subwavelength structures.

Metal nanoparticles (NPs) are well known to increase the efficiency of photovoltaic devices by reducing reflection and increasing light trapping within device. However, metal NPs on top flat surface suffer from high reflectivity losses due to the backscattering of the NPs itself. In this paper, we experimentally demonstrate a novel structure that exhibits localized surface plasmon resonance (LSPR) along with broadband ultralow reflectivity over a wide range of wavelength. Experimental results show that by depositing Ag NPs and Au NPs onto glass subwavelength structures (SWS) the backscattering effect of NPs can be suppressed, and the reflections can be considerably reduced by up to 87.5% and 66.7% respectively, compared to NPs fabricated on a flat glass substrate. Broadband ultralow reflection (< 2%) is also observed in the case of Ag NPs and Au NPs fabricated on cone shaped SWS silicon substrate over a wavelength range from 200 nm to 800 nm. This broadband ultralow reflectivity of Ag NPs and Au NPs on silicon SWS structure leads to a substantial enhancement of average absorption by 66.53% and 66.94%, respectively, over a broad wavelength range (200-2000 nm). This allows light absorption by NPs on SWS silicon structure close to 100% over a wavelength range from 300 nm to 1000 nm. The mechanism responsible for the increased light absorption is also explained.