A 19.9%-efficient ultrathin solar cell based on a 205-nm-thick GaAs absorber and a silver nanostructured back mirror
Hung-Ling Chen, Andrea Cattoni, Romaric De Lépinau, Alexandre W. Walker, Oliver Höhn, David Lackner, Gerald Siefer, Marco Faustini, Nicolas Vandamme, Julie Goffard, Benoît Behaghel, Christophe Dupuis, Nathalie Bardou, Frank Dimroth & Stéphane Collin
Abstract
Conventional photovoltaic devices are currently made from relatively thick semiconductor layers, ~150 µm for silicon and 2–4 µm for Cu(In,Ga)(S,Se)2, CdTe or III–V direct bandgap semiconductors. Ultrathin solar cells using 10 times thinner absorbers could lead to considerable savings in material and processing time. 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 multi-resonant absorption in planar active layers, and we report a 205-nm-thick GaAs solar cell with a certified efficiency of 19.9%. 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 a pathway for further improvements and shows that 25% efficiency is a realistic short-term target.
Acknowledgements
The authors acknowledge discussions with J.-F. Guillemoles, electromagnetic simulation support from P. Lalanne, J.-P. Hugonin and C. Sauvan and financial support through French ANR project NANOCELL (grant no. ANR-15-CE05-0026) and the French Renatech network.
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Alexandre W. Walker
Present address: National Research Council of Canada, Ottawa, Ontario, Canada
Affiliations
Centre for Nanoscience and Nanotechnology (C2N), CNRS, University Paris-Sud/Paris-Saclay, Palaiseau, France
Hung-Ling Chen, Andrea Cattoni, Romaric De Lépinau, Nicolas Vandamme, Julie Goffard, Benoît Behaghel, Christophe Dupuis, Nathalie Bardou & Stéphane Collin
Institut Photovoltaïque d’Ile-de-France (IPVF), Palaiseau, France
Romaric De Lépinau, Julie Goffard & Stéphane Collin
Fraunhofer Institute for Solar Energy Systems (ISE), Freiburg, Germany
Alexandre W. Walker, Oliver Höhn, David Lackner, Gerald Siefer & Frank Dimroth
Laboratoire Chimie de la Matière Condensée de Paris, Sorbonne Université, CNRS, Collège de France, Paris, France
Marco Faustini
Contributions
H.-L.C. carried out most of the fabrication steps for the solar cell experiments at C2N and performed optical modelling and results analysis. A.W.W., O.H., D.L. and F.D. designed the optimized GaAs solar cell layer structure, D.L. wrote the recipe for epitaxy growth and G.S. evaluated the characterization results in the Fraunhofer ISE CalLab. H.-L.C., A.C., R.D.L., M.F., N.V., J.G., B.B., C.D. and N.B. developed and optimized the fabrication process. A.C. and M.F. specifically developed the nanoimprint process for TiO2 sol–gel films. N.V. contributed to the design and modelling of the devices. A.C. and S.C. developed the concept of ultrathin solar cells with a nanostructured back mirror and supervised the project. H.-L.C. and S.C. wrote the manuscript. All authors participated in the discussions and improvements of the manuscript.
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Correspondence to Stéphane Collin.
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The authors declare no competing interests.
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Supplementary Information
Supplementary Figs. 1–18, Supplementary Notes 1–5, Supplementary Table 1, Supplementary refs. 1–8.
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