Polarization-diverse broadband absorption enhancement in thin-film photovoltaic devices using long-pitch metallic gratings

We numerically investigated the impact of long-pitch (>800 nm) metallic gratings on the absorption enhancement in thin-film photovoltaic devices. We found that gratings with such a long pitch can simultaneously enhance the absorption of TM- and TE-polarized sunlight by inducing lateral Fabry-Perot resonances of surface plasmon-polaritons and guided modes at the same time. The grating duty cycle turned out to be the most important factor in realizing the two enhancement effects in the same spectral regime. Especially for the TM light, the combined effect of long grating pitch and duty-cycle adjustment led to the formation of three plasmonic resonances that simultaneously cover the ridge and groove surfaces. All of these produced a polarization-diverse absorption enhancement corresponding to a factor of 1.17-1.18 increase in the photocurrent over a wide range of the grating pitch. (C) 2011 Optical Society of America