Comparison of Light Trapping in Diffractive and Random Pyramidal Structures

Abstract

Good light trapping is essential to make high efficiency silicon solar cells. As silicon wafers are being made increasingly thinner, light trapping becomes even more important. In this work we compare in simulations light trapping from conventional random pyramid textures, with structure sizes of several microns, to that of light trapping from diffractive structures with lattice periods comparable to the wavelength of light. More specifically we compare light trapping in front-side and double-sided random pyramidal textures to that of two different back-side bi-periodic structures applied to a 20 μm thick Si slab. We find that a photogenerated current density of 40.0 mA/cm is achieved for a double-sided pyramidal texture with a rear oxide layer and a silver reflector. This is slightly higher than the best diffractive structure with a planer front side and rear texture. The pyramidal textures show exceptional broad-band anti-reflection behavior, while the diffractive structures excel in the long-wavelength part of the solar spectrum.