Light-Trapping Properties of a Diffractive Honeycomb Structure in Silicon

Thinner solar cells will reduce material costs, but require light trapping for efficient optical absorption. We have already reported development of a method for fabrication of diffractive structures on solar cells. In this paper, we create these structures on wafers with a thickness between 21 and 115 μm, and present measurements on the light-trapping properties of these structures. These properties are compared with those of random pyramid textures, isotropic textures, and a polished sample. We divide optical loss contributions into front-surface reflectance, escape light, and parasitic absorption in the rear reflector. We find that the light-trapping performance of our diffractive structure lies between that of the planar and the random pyramid-textured reference samples. Our processing method, however, causes virtually no thinning of the wafer, is independent of crystal orientation, and does not require seeding from, e.g., saw damage, making it well suited for application to thin silicon wafers.