Enhanced carrier collection observed in mechanically structured silicon with small diffusion length

Abstract

The diffusion length of minority charge carriers in the silicon bulk Ldiff is an important characteristic of optoelectronic devices fabricated from low cost silicon wafers. In this study computer simulations have been carried out to calculate the beneficial effects of a macroscopic surface texturization on the charge carriergeneration and the collection probability. Textured solar cells should be able to collect charge carriers more effectively resulting in an increased current due to the special emitter geometry resulting from the texture, decreased reflection losses, and the inclined penetration of the light. In order to prove this expected behavior, deeply V-textured solar cells have been processed and characterized on low cost silicon reaching an Ldiff of about 25 μm. Spatially resolved high resolution measurements of the internal quantum efficiency exhibit a strongly increased signal in the texture tips which is the first experimental proof of the increased charge carrier collection probability of deeply textured solar cells. This effect can further be seen in cross sectional electron beam induced current measurements and the mechanical texture results in an overall gain in short circuit current density of about 11% and in efficiency of about 8% relatively.