Efficient plasmonic nanostructures for solar radiation absorption

Metal nanoparticles and nanorods allow surface plasmon (SP) propagation and localization, since noble metals exhibit in the visible and IR regimes a negative value of dielectric permittivity. The sensitivity of those structures lies in the sizing of single particles and in the engineering of the mutual interaction among them. The improvement of the efficiency of thin film solar cells can be accomplished using SP waves. One main strategy to achieve this goal relies on the principle that SPs, excited by a patterned backside electrode, are able to improve the absorptance of a closer active region (typical for polymer PV cells), or using metal nanoparticles to increase the absorption and energy conversion. In this paper, we investigate the variation of the field localization in a silica substrate, when gold or silver nanorods and bricks, placed on the top of the bulk material, are excited by a TM polarized plane wave impinging on the structure. The aim of our work is to evaluate the light localization and trapping in the silica substrate, in order to increase the scattering cross section. We consider two kind of structures in this context. The first comprises coupled nanorods where the field concentration is achieved by enhanced transmission phenomenon; the second consider an array of metal bricks placed at fixed distances behaving like pure scattering objects. The analysis has been performed considering actual 3D structures and using the simulation tool CST Studio Suite 2008, where the dispersion model of both silver and gold nanorods and bricks has been taken into account by Drude model.