Optimization of Porous Silicon Reflectance for Solar Cell Applications

Abstract

The potential use of porous silicon as an antireflective coating on solar cells has recently been recognized. This study investigates the effect of current density, anodization time, and surface conditions on the reflectance of porous silicon which was fabricated by anodizing (100) float zone single crystal Si wafers. The wafers were coated on one side with Al prior to anodization, and a HF-based solution was used as the electrolyte. Current densities of 5~100 mA/cm² were used to anodize both polished and unpolished wafers over time intervals ranging from 2sec–30 minutes. Reflectance properties were tested over the 400 - 1100 nm range, and minimum reflectances of 3–5% were achieved. The reflectance of the best porous Si sample normalized with respect to the sun’s spectrum compares favorably with the reflectance of a double layer ZnS/ MgF₂ with prior texturing.