Plasmonic near-field enhancement for planar ultra-thin photovoltaics

We propose a planar ultrathin absorber concept exploiting plasmonic resonance absorption enhancement. We calculate a maximum absorption of 89.8% for TM-polarized normally incident light in a 5-nm thin-film absorber with a single-pass absorption of only 1.7%, i.e., a 53 times increase in absorption. Broadband and wide-angle absorption is demonstrated. Averaging over isotropic incidence for TM polarization, the absorption is enhanced by a factor of 48. Despite low TE absorption, the average absorption enhancement over all angles and both polarizations is 28, well above the 2-D Lambertian light-trapping limit of π n.