LIGHT TRAPPING IN SUNPOWER’S A-300 SOLAR CELLS

Light trapping in SunPower’s A-300 solar cells was experimentally investigated by measuring the escape reflectance and the quantum efficiency. It is concluded that the cells have a rear-internal reflection of 75–80% and a pathlength enhancement of Z ~ 6, indicating relatively good light trapping. Several means to increase Z are explored—white paint, rear texture, and tilted front texture—but it is found that the subsequent increase in cell efficiency does not warrant the increase in process complexity. The primary reason for this is that, with random pyramids at the front surface and a planar rear surface, few photons intersect the rear surface within the escape angle an Si–SiO2 interface; thus, a thick SiO2 on the rear is sufficient to provide high internal reflection.