Dye-sensitized solar cells equipped with graphene-based counter electrodes with different oxidation levels

This study examines the performance of dye-sensitized solar cells (DSCs) equipped with graphene nanosheet (GN) counter electrodes having different oxidation levels. A thermal deposition is adopted to adjust the O/C atomic ratio and surface oxygen functionalities on graphene sheets. By decreasing the O/C ratio, the GN electrode displays high catalytic activity toward the I-3(-)/I- redox reaction and lower charge-transfer resistance, as analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The DSC fabricated with the GN counter electrode also offers an improved incident photon-to-current efficiency and power conversion efficiency, in comparison with that equipped with graphene oxide electrodes. This improvement of cell performance could be attributed to the fact that the GN electrode, with a two-dimensional crystal of sp(2) carbon, serves as a semi-metal or a zero-bandgap semiconductor with remarkable high electron mobility. (C) 2012 Elsevier B.V. All rights reserved.