Effect of doping on photovoltaic characteristics of graphene

Chemical doping of CVD grown graphene by introducing PTSA (n-type) and NBD (p-type) dopants is explored. This type of doping is key building block for photovoltaic and optoelectronic devices. Doped graphene samples display (1) high transmittance in the visible and near-infrared spectrum and (2) tunable graphene sheet resistance and work function. Large area and uniform graphene films were produced by chemical vapor deposition on copper foils and transferred onto quartz as transparent substrates. For n doping, a solution of p-toluenesulfonic acid (PTSA) was first dropped and spin-coated on the graphene/quartz and then annealed at 100°C for 10 min to make graphene uniformly n-type. Subsequently, a bare graphene was transferred on another quartz substrate, a solution of 4-nitrobenzenediazonium tetrafluoroborate (NBD) was dropped and spin-coated on the surface of graphene and similarly annealed. As a result, the graphene was p and n doped on the different quartz substrates. Doped graphene samples were characterized by different techniques. Experimental results suggested that doped graphene sheets with tunable electrical resistance and high optical transparency can be incorporated into photovoltaics and optoelectronics devices.