Multi-resonant light trapping in ultrathin CIGS solar cells

We investigate ultrathin CIGS solar cells with a nanostructured back mirror. Numerical calculations are used to optimize the optical design based on multi-resonant absorption. The impact of the different materials (CdS/ZnS, metal of the back contact: Mo/Au/Ag) is studied, and short circuit current densities above 36 mA/cm2 are predicted for CIGS absorbers as thin as 200 nm. We have developed a fabrication process based on the transfer of the CIGS solar cells, and nanoimprint lithography for the nanostructured back mirror. Light-trapping effects and Jsc improvement are evidenced in our first experimental results.