Efficient light-trapping nanostructures in thin silicon solar cells

We examine light-trapping in thin crystalline silicon periodic nanostructures for solar cell applications. Using group theory, we show that light-trapping can be improved over a broad band when structural mirror symmetry is broken. This finding allows us to obtain surface nanostructures with an absorptance exceeding the Lambertian limit over a broad band at normal incidence. Further, we demonstrate that the absorptance of nanorod arrays with symmetry breaking not only exceeds the Lambertian limit over a range of spectrum but also closely follows the limit over the entire spectrum of interest for isotropic incident radiation. These effects correspond to a reduction in silicon mass by two orders of magnitude, pointing to the promising future of thin crystalline silicon solar cells.National Science Foundation (U.S.) (UC Berkeley SINAM)National Science Foundation (U.S.) (TeraGrid resources provided by Purdue University under Grant Number TG-PHY100046

Efficient Light Trapping in Inverted Nanopyramid Thin Crystalline Silicon Membranes for Solar Cell Applications

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.United States. Dept. of Energy (Sunshot Project Award DEEE0005320)National Science Foundation (U.S.) (Nanoscale Science and Engineering Initiative Award CMMI-0751621)Massachusetts Institute of Technology. Laboratory for Energy and the Environmen

15.7% Efficient 10-μm-Thick Crystalline Silicon Solar Cells Using Periodic Nanostructures

Only ten micrometer thick crystalline silicon solar cells deliver a short-circuit current of 34.5 mA cm[superscript −2] and power conversion efficiency of 15.7%. The record performance for a crystalline silicon solar cell of such thinness is enabled by an advanced light-trapping design incorporating a 2D inverted pyramid photonic crystal and a rear dielectric/reflector stack.United States. Dept. of Energy (SunShot Initiative Award DE-EE0005320)National Science Foundation (U.S.) (Nanoscale Science and Engineering Initiative Award CMMI-0728069)Martin Family Society of Fellows for Sustainabilit