Effect of layer number and metal-chloride dopant on multiple layers of graphene/porous Si solar cells

Porous silicon (PSi) is an attractive building block for Si-based solar cells due to its low reflectance. Here, PSi is prepared by metal-assisted chemical etching of a Si wafer on which Au nanoparticles are formed by sputtering for 5 s. The layer number (L_n) of graphene is varied to optimize multiple layers of graphene/PSi Schottky junction solar cells because the sheet resistance, work function, transmittance, and reflectance of graphene strongly depend on L_n. At L_n = 2, the best condition for the highest power conversion efficiency (PCE), various metal chlorides are employed as dopants for graphene. The PCE is maximally enhanced to 9.15% by doping the graphene with RhCl₃ and is reduced by only 20% of its original value (absolutely from 9.15% to 7.23%) during 10 days in air. These results are very meaningful in that even a single doping for graphene can be effective for achieving high PCE from graphene/PSi solar cells by controlling L_n.