Relaxation and Excitation Rate Modifications by Metal Nanostructures for Solar Energy Conversion Applications

Abstract

Metal nanostructures supporting plasmonic resonances offer pronounced modifications of an electromagnetic environment for efficient light harvesting in solar energy conversion applications. Since these modifications may give rise to competing effects, boosting overall conversion efficiency needs optimization of structural and spectral parameters of emitter-metal nanostructure hybrid systems. Here, we employ finite-difference time-domain simulations to investigate modifications in relaxation and excitation rates of a dipole emitter in proximity to three representative gold nanostructures, namely nanospheres, nanorods, and slot antennas. We present detailed investigations of parameter space in terms of nanostructure type, emitter position, and spectral range to identify regions of optimum performance for solar energy conversion applications. Our results suggest that for selected parameter sets, hybrid systems yield substantial enhancement in the excitation rate as well as suppression of luminescence, which are primary considerations in photovoltaic and photocatalysis applications, whereas regions of enhanced luminescence are more favorable for luminescent solar concentrators. Nanostructures with a higher aspect ratio are found to be more efficient. Particularly, the gap modes of slot antennas exhibit pronounced suppression of luminescence yield and light confinement over a broad spectral range from 550 nm up to 2200 nm, besides offering a larger usable volume compared to singular nanoparticles investigated here.