Large-scale and sustainable development of copper indium gallium diselenide (CIGS) thin film photovoltaics requires material savings by thickness reduction. We propose to compensate for the low absorption in ultrathin CIGS layers by introducing a novel light trapping strategy based on a nanostructured back mirror. We show numerically that short circuit current densities above 35 mA/cm~2 can be reached for CIGS absorbers as thin as 200 nm. We have developed a fabrication process based on the transfer of the solar cell on a host glass substrate, and nanoimprint lithography on the back side. We present the first experimental results of CIGS solar cells with nanostructured gold mirror, and demonstrate EQE enhancement due to light trapping effects. We show our latest experimental results and discuss the perspectives of CIGS solar cells with thicknesses in the 200-300nm range with efficiencies above 15%.
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