Metal Nanogrids for Broadband Absorption in Ultrathin GaAs Solar Cells: a Detailed Analysis of Photonic Resonance Mechanisms

29th European Photovoltaic Solar Energy Conference and Exhibition; 53-57
We propose to use metal nanogrids to enhance light absorption in ultrathin GaAs solar cells with 120 nm-thick and 220 nm-thick absorbers. Thanks to the transfer of the cells on a silver back mirror leading to Fabry Perot resonances in the semiconductor cavity, the short circuit current is increased by 40%. With an additional antireflection coating and a nanostructured back mirror, we obtain Jsc=17.4 mA/cm2 and 21.2 mA/cm2 for 120 nm and 220 nm-thick absorbers, respectively. It represents a two-fold enhancement of the Jsc compared to the non-transferred solar cells. We also show that is possible to realize really absorptive semiconductor devices within a few tens of nanometers. As a proof of concept, a super-absorber device consisting of a front nanogrid deposited on a 25 nm-thick GaAs layer absorbs more than 80% of the light over the 450-830 wavelength range.