Brick-like N-doped graphene/carbon nanotube structure forming three-dimensional films as high performance metal-free counter electrodes in dye-sensitized solar cells

The brick-like N-doped graphene-carbon nanotube (NGC) composites are designed by mechanically grinding the filtration films, which are fabricated to form a three-dimensional structure film as a counter electrode (CE). The N-doped graphene/carbon nanotube films with a three-dimensional brick-like structure can provide numerous vertical active edge sites. The excellent electrochemical catalytic activities of CE can be obtained by adjusting the different ratio of graphene to CNTs to control the size and N-doping content of breaking particles. NGC17 CE based dye-sensitized solar cells (DSSC) have reached a high efficiency (6.74%) close to platinum-based cells (6.89%). The excellent efficiency may be attributed to the following factors: a) the Delta E-p of NGC17 (304 mV) is lower than that of the Pt electrode (389 mV); b) the charge transfer resistance (R-ct) at the NGC17-CE/electrolyte interface was 1.78 Omega cm(-2), which is lower than that of a Pt-CE/electrolyte interface (8.97 Omega cm(-2)). (C) 2014 Elsevier B.V. All rights reserved.