Vertically Aligned Carbon Nanotubes/Graphene Hybrid Electrode as a TCO- and Pt-Free Flexible Cathode for Application in Solar Cells

Dye-sensitized solar cells (DSSCs) are an emerging photovoltaic technology with both low costs and good efficiency. However, the cathode used in most DSSCs is fluorine-doped tin oxide glass coated with a Pt film, which is both expensive and brittle and therefore limits the flexibility and large-scale implementation of this promising technology. We report here work which showed that flexible, seamlessly covalently bonded, three-dimensional vertically aligned few-walled carbon nanotubes (VAFWCNTs)/graphene on metal foil can act as a novel cathode free from transparent conducting oxide and Pt for application in DSSCs. This cathode has a lower charge transfer resistance and lower contact resistance between the catalyst and the substrate than the conventional combination in a brittle Pt/fluorine-doped tin oxide cathode. The covalently bonded graphene and VAFWCNTs ensure excellent electron transport through the electrode and the large surface area of the hybrid carbon materials rivals the catalytic capability of the Pt analogue. DSSCs utilizing this flexible VAFWCNTs/graphene hybrid cathode outperformed the Pt-based cells in both rigid (8.2% vs. 6.4%) and flexible (3.9% vs. 3.4%) assemblies. The VAFWCNTs/graphene on metal foil combination is a novel, inexpensive, high-performance, flexible cathode for application in solar cells.