Carbon nanostructure counter electrodes for low cost and stable dye-sensitized solar cells

Dye sensitized solar cells (DSCs) provide a low cost alternative to silicon solar cells due to their low material and fabrication cost. Usually DSCs utilize platinum to catalyze the iodine redox couple and complete the electric circuit. Since platinum is rare and expensive metal, nanostructured carbonaceous materials have been widely investigated as a promising alternative to replace it. Carbon nanostructures have shown significant properties such as high electrochemical activity, high corrosion resistance, and low cost which make them ideal for replacing platinum in the counter electrodes of DSCs. Here we reviewed the development in carbon based counter electrodes which utilize the advantages of high surface area and high electrocatalytic ability due to their nanostructured morphology. First, various carbon nanostructures including graphene, carbon nanotubes, carbon nanofibers, carbon nanoparticles, conductive carbon, carbon dye and composite carbon nanostructures are introduced. Second, carbon nanostructured counter electrode morphologies and their effects on DSC performance are discussed. Third, surface defects and their effects on cell performance are described. Finally, equivalent circuit models at the counter electrode-electrolyte interface are presented. This work will provide deep insights and guidance for researchers to design, develop and/or select carbon nanostructures for cost effective Pt-free or less-Pt loaded DSCs.