Si heterojunction solar cells employing graphene transparent conductive electrodes co-doped with gold chlorides and silver nanowires

Graphene/Si Schottky junction is highly attractive for its application in solar cells due to the excellence of graphene as a transparent conducting electrode. However, the high sheet resistance of the chemical vapor deposition-grown graphene films, mostly used for the solar cells, is still one of the principal factors limiting the power conversion efficiency of graphene/Si solar cells. Here, we report an approach of co-doping with gold (III) chloride (AuCl₃) and silver nanowires (Ag NWs) to reduce the sheet resistance (R_s) of graphene as well as to control its work function (W_G) for well-matched graphene/Si wafer junction. The molar concentration (n_D) of AuCl₃ is varied from 1 to 10 mM while the fraction (n_A) of Ag NWs is fixed at 0.1 wt% for the fabrication of the solar cells, based on n_A-dependent behaviors of R_s and W_G. The co-doped graphene/n-Si Schottky solar cells show a maximum power-conversion efficiency of 7.01% at n_D = 7.5 mM, resulting from the increased barrier height at the graphene/Si junction and the reduced sheet resistance/transmittance of graphene by the co-doping, as proved from the n_D-dependent behaviors of open-circuit voltage, DC conductivity/optical conductivity ratio, series resistance, and external quantum efficiency.