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

TLDR

Light‑trapping structures in thin‑film crystalline silicon solar cells enhance absorption and reduce material usage. An inverted nanopyramid light‑trapping scheme fabricated at wafer scale via low‑cost wet etching boosts broadband absorptance of thin‑film c‑Si to near the Yablonovitch limit with minimal angle dependence, enabling sub‑10 µm films to match the absorptance of 300 µm planar wafers, reducing material use by over 30‑fold, limiting surface‑area growth to 1.7×, and thereby cutting material and processing costs while preserving high efficiency for future thin‑film c‑Si solar cells. Opt.

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.