Extremely low reflectivity nanoporous black silicon surface by copper catalyzed etching for efficient solar cells

In this work, we report on a process based on copper (Cu) catalyzed etching of silicon (Si) to obtain extremely low reflectivity nanoporous `black silicon' (bSi) surface. We explore both one-step and two-step etching process, and find that one-step etching results in a uniformly etched surface reproducibly, compared with the two-step process. Adding ascorbic acid (C
₆
H
₈
O
₆
) in the one-step process recipe results in inverted pyramid shaped pores that enhance light trapping and lowers the bSi surface reflectivity. We observe that the optimum concentration of hydrogen peroxide (H
₂
O
₂
) in the etching solution depends on the sample size. The lowest spectrum-weighted-average reflectivity (R
_avg
) obtained from the optimized one-step etching process is 3.36%.