Light Trapping and Surface Passivation of Micron-Scaled Macroporous Blind Holes

Abstract

We fabricate a blind hole surface texture by anodic etching of macroporous Si. The blind holes, i.e., pores that do not penetrate the wafer completely, have an average diameter of 2.7 μm, a distance of 4 μm, and a depth of 9 μm. This texture is capable of reducing the AM1.5G photon flux-weighted front reflectance to 1.5% without depositing an antireflection coating. The μm-feature size makes it a less fragile alternative to common nm-sized black silicon structures. We passivate the blind holes by atomic layer deposited ${\rm AlO}_{x}$ . The blind hole texture allows for a carrier lifetime of (2.2 ± 0.25) ms corresponding to an effective surface recombination velocity of (8 ± 1.5) cm/s with respect to the macroscopic front surface. A direct comparison of the optical performance and the surface passivation quality with a standard ${\rm SiN}_{x}$ -coated random pyramid surface shows that blind holes allow for a relative efficiency gain of (3 ± 0.2)% when applied, e.g., in an otherwise perfect back-contacted solar cell.