A graphene-multi-walled carbon nanotube hybrid supported on oxide as a counter electrode of dye-sensitized solar cells

We report a solution-based method to prepare a hybrid material consisting of multi-walled carbon nanotubes and graphene. Raman spectroscopy shows that a decrease in the concentration of defects of hybrid, compared to graphene, which is confirmed by the D/G ratio, implying the repair of the conjugation system. Due to the increased surface areas of graphene and the increased spaces between graphene sheets, results of cyclic voltammetry and electrochemical impedance spectroscopy show that the electrocatalytic ability of the hybrid material affords a higher charge transfer rate, an improved exchange current density, and a lower internal resistance. Transmission and scanning electron microscopy images show that the hybrid counter electrode has a rough and porous structure, resulting in a lower resistance to diffusion, thereby increasing the total redox reaction rate at the counter electrode. Hybrid electrodes have a number of advantages over other electrodes made of graphene or platinum films, including a higher rate of charge transfer, a lower internal resistance, a lower resistance to diffusion, and a lower electron lifetime. The cell performance using a hybrid counter electrode (4.66%) reached 91.6% of that of cells prepared using a platinized fluorinated tin oxide electrode (5.09%). (C) 2012 Elsevier B.V. All rights reserved.