High-efficiency graphene/Si nanoarray Schottky junction solar cells via surface modification and graphene doping

The current Si-based photovoltaic devices require high-quality raw materials and intricate processing techniques to construct complex device structures; further improvement in efficiency and a drastic decrease in cost are thus highly desired to promote their extensive applications. In this work, we conducted a comprehensive study on high-efficiency graphene/Si nanoarray Schottky junction solar cells. Besides the Si nanowire (SiNW) array, a Si nanohole (SiNH) array was first used for the device construction since it showed the advantages in terms of larger effective junction area while enhanced light absorption is retained. It was found that surface charge recombination as well as graphene conductivity and work function played important roles in determining the solar cell performance. By suppressing the surface recombination with appropriate surface passivation, together with the careful control of the graphene layer number and the doping level, we found that the device performance can be significantly improved. Eventually, by inserting a thin conducting polymer poly(3-hexylthiophene) (P3HT) as the electron blocking layer between Si nanoarrays and graphene films, maximum power conversion efficiencies (PCEs) of 8.71% and 10.30% were demonstrated for the devices based on SiNW and SiNH arrays, respectively, as a result of reduced carrier recombination in the anode. The PCEs demonstrated in this work are the highest values achieved thus far for the graphene/Si nanoarray solar cells. The present results suggest great potential of the graphene/Si nanoarrays as high-efficiency and low-cost photovoltaic devices. © 2013 The Royal Society of Chemistry.