Journal
NANO LETTERS
Volume 12, Issue 6, Pages 2792-2796Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl2045777
Keywords
Light trapping; photovoltaics; optical absorption; inverted pyramids; thin-film solar cells
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Funding
- DOE [DEEE0005320]
- Nanoscale Science and Engineering Initiative of the National Science Foundation under NSF through the Center for Scalable and Integrated Nano-247 manufacturing at U. C. Berkeley [CMMI-0751621]
- MIT Laboratory for Energy and the Environment (LFEE)
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Thin-film crystalline silicon (c-Si) solar cells with light-trapping structures can enhance light absorption within the semiconductor absorber layer and reduce material usage. Here we demonstrate that an inverted nanopyramid light-trapping scheme for c-Si thin films, fabricated at wafer scale via a low-cost wet etching process, significantly enhances absorption within the c-Si layer. A broadband enhancement in absorptance that approaches the Yablo-novitch limit (Yablo-novitch, E. J. Opt. Soc. Am. 1987, 72, 899-907) is achieved with minimal angle dependence. We also show that c-Si films less than 10 pm in thickness can achieve absorptance values comparable to that of planar c-Si wafers thicker than 300 pm, amounting to an over 30-fold reduction in material usage. Furthermore the surface area increases by a factor of only 1.7, which limits surface recombination losses in comparison with other nanostructured light-trapping schemes. These structures will not only significantly curtail both the material and processing cost of solar cells but also allow the high efficiency required to enable viable c-Si thin-film solar cells in the future.
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