Effects of Surface Modification on Dye-Sensitized Solar Cell Based on an Organic Dye with Naphtho[2,1-b:3,4-b′]dithiophene as the Conjugated Linker

We have investigated the effects of surface modification on the dye-sensitized solar cell (DSSC) based on a donor-(pi-spacer)-acceptor. organic dye. A major challenge for donor-(pi-spacer)-acceptor molecules as sensitizers in DSSCs is the fast recombination reactions that occur at both the photoanode (e.g., TiO2) surface and the fluorine-doped tin oxide (FTO) electrode, which presents unfavorable effects on the DSSC performance. The two interfaces of TiO2/electrolyte and FTO/electrolyte are passivated selectively in a DSSC using an organic dye with Naphtho[2,1-b:3,4-b']dithiophene as the conjugated linker and the I-/I-3(-) electrolyte. The current density-voltage characteristics, the dark current analysis, the open circuit voltage-light intensity dependence, and the transient photovoltage/photocurrent results indicate that the recombination processes are affected strongly by surface passivation under variable light intensity. At high light intensity, the recombination reaction at the TiO2 surface is dominant. In this case, silane passivation of the TiO2 surface can suppress recombination significantly, while the c-TiO2 layer makes little contribution to the reduction of the recombination. At low illumination intensity, the recombination at TiO2 becomes significant, and the recombination can be reduced by applying a c-TiO2 layer.