Thickness-dependent efficiency of directly grown graphene based solar cells

It is of immense interest to improve the power conversion efficiency of graphene/silicon Schottky junction solar cells. The ultrathin graphene has essential properties, such as tunable work function to increase Schottky barrier height and built-in potential for efficient charge transport in photovoltaic devices. Here, we use plasma-enhanced CVD to grow graphene directly on planar n-type silicon to fabricate solar cells compatible for industrial-level applications. A key component to our accomplishment is the optimization of directly grown, continuous layers of graphene to achieve superior performance. Thus, by controlling the graphene thickness, the work function is significantly improved, the open circuit voltage is increased, and the energy conversion efficiency is enhanced. While the transfer of CVD grown graphene has limitations due to cracks and impurities during the complex process, our direct growth method demonstrates an efficiency of 5.51% on bare planar silicon with a large device area. Furthermore, the efficiency is remarkably increased to 9.18% by adding and doping a polymer layer. Interestingly, with the addition of a doped polymer layer, the cell exhibits excellent stability for at least one month. Our result suggests a promising simple path to fabricate high efficiency solar cells at low temperature and low cost.