Effects of Electric Field on the Performance of Graphene-Based Counter Electrodes for Dye-Sensitized Solar Cells: A Theoretical Study

We have investigated the influence of an external electric field on the performance of graphene-based counter electrode (CE) materials such as pristine, boron-doped graphene (BC5), and nitrogen-doped graphene (NC5) for dye-sensitized solar cells (DSSCs) using density functional theory calculations. The stable I2 adsorption geometries, electronic properties, and charge transfer between I2 and different graphene nanosheets in the presence and absence of an external electric field are calculated. We find that the NC5 graphene sheet exhibits high affinity for the I2 molecule and greater sensitivity to the external electric field. Our calculations indicate that the I2 dissociation on the NC5 graphene sheet is thermodynamically and kinetically favorable even in the absence of an external electric field; however, the I* atomic desorption energy is relatively large (0.70 eV), and it is the rate-determining step in the I3– reduction reaction. We demonstrate that a negative external electric field decreases the interaction between the I* atom and the NC5 graphene sheet and eases the I* desorption. The excellent catalytic property of the NC5 graphene sheet toward I2 dissociation and I* atom desorption makes it as an alternative nonmetallic CE for DSSCs.