title: Efficient light trapping in inverted nanopyramid thin crystalline silicon membranes for solar cell applications.
abstract: 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 Yablonovitch limit (Yablonovitch, 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 μm in thickness can achieve absorptance values comparable to that of planar c-Si wafers thicker than 300 μm, 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.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge Massachusetts 02139, United States.
authors.forename: Anastassios
authors.initials: A
authors.lastname: Mavrokefalos
authors.forename: Sang Eon
authors.initials: SE
authors.lastname: Han
authors.forename: Selcuk
authors.initials: S
authors.lastname: Yerci
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Branham
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
mesh_terms: D011211:Electric Power Supplies; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008027:Light; D008567:Membranes, Artificial; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D012031:Refractometry / Q000295:instrumentation*; D012542:Scattering, Radiation; D012825:Silicon / Q000737:chemistry*; D012993:Solar Energy
chemical_list: D008567:Membranes, Artificial; D012825:Silicon