A 19.9%-efficient ultrathin solar cell based on a 205-nm-thick GaAs absorber and a silver nanostructured back mirror
Résumé
Conventional photovoltaic devices are currently made of relatively thick semiconductor layers, about 150 µm for silicon, and 2-4 µm for CIGS, CdTe or III-V direct bandgap semiconductors. Ultrathin solar cells using 10 times thinner absorbers could lead to considerable material and processing time savings. Theoretical models suggest that light trapping can compensate for the reduced single-pass absorption, but optical and electrical losses have greatly limited the performances of previous attempts. Here, we propose a strategy based on multiresonant absorption in planar active layers, and we report a 205 nm-thick GaAs solar cell with a certified 19.9% efficiency. It uses a nanostructured silver back mirror fabricated by soft nanoimprint lithography. Broadband light trapping is achieved with multiple overlapping resonances induced by the grating and identified as Fabry-Perot and guided-mode resonances. A comprehensive optical and electrical analysis of the complete solar cell architecture provides the pathway for further improvements and shows that 25% efficiency is a realistic shortterm target.
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