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-(π-spacer)-acceptor organic dye. A major challenge for donor-(π-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 FTO becomes significant, and the recombination can be reduced by applying a c-TiO₂ layer.