In-Situ Fabrication of a Self-Aligned Selective Emitter Silicon Solar Cell Using the Gold Top Contacts To Facilitate the Synthesis of a Nanostructured Black Silicon Antireflective Layer Instead of an External Metal Nanoparticle Catalyst

Silicon solar cells with nanopore-type black silicon (b-Si) antireflection (AR) layers and self-aligned selective emitter (SE) are reported in which the b-Si structure is prepared without the traditional addition of a nanoparticle (NP) catalyst. The contact-assisted chemical etching (CACE) method is reported here for the first time, in which the metal top contacts on silicon solar cell surfaces function as the catalysts for b-Si fabrication and the whole etching process can be done in minutes at room temperature. The CACE method is based on the metal-assisted chemical etching (MACE) solution but without or metal precursor in the Si etchant (HF:H2O2:H2O), and the Au top contacts, or catalysts, are not removed from the solar cell surface after the etching. The effects of etching time, HF and H2O2 concentration, and the HF:H2O2 ratio on the b-Si morphology, surface reflectivity, and solar cell efficiency have been investigated. Higher [HF] and [H2O2] with longer etching time cause collapse of the b-Si nanoporous structure and penetration of the p-n junctions, which are detrimental to the solar cell efficiency. The b-Si solar cell fabricated with the HF:H2O2:H2O volume ratio of 3:3:20 and a 3 min etch time shows the highest efficiency 8.99% along with a decrease of reflectivity from 36.1% to 12.6% compared to that of the nonetched Si solar cell.