Diffuse reflectance and absorption characterization of a plasmonic back reflector for application in thin film si solar cells

A plasmonic back reflector has been fabricated for light-trapping application in thin film Si photovoltaic devices. The back reflector comprises of a 2D array of self-organized Ag NPs separated from a planar Ag mirror by a ZnO layer deposited by atomic-layer deposition. The diffuse reflectance and parasitic absorption losses can be modulated by varying the ZnO thickness. A maximum diffuse reflectance peak value of 30% at 950 nm, with a bandwidth of 400nm, is observed for ∼100 nm diameter NPs at a distance of 50 nm from the Ag mirror. Finite-difference time-domain simulations of a 100nm Ag sphere near a mirror were used to understand the experimentally observed trends in diffuse reflectance and parasitic absorption, with distance from the mirror. Particles very close to the mirror can couple to delocalized surface plasmons or exhibit Fano resonance effects, thereby increasing parasitic absorption. Particles situated away from the mirror are influenced by driving-field effects due to the interaction of incident and reflected photons, which modulate the scattering cross-section.