Electron Dynamics in Dye-Sensitized Solar Cells Influenced by Dye-Electrolyte Complexation

Herein, we present the effect of ground-state complexation between organic photosensitizers and the utilized electrolyte in dye-sensitized solar cells. To do so, we selected a well-known standard organic dye, D149, and the traditional iodide/triiodide redox couple as a case study. First, we detected the ground-state interactions between the D149 dye and the electrolyte components in acetonitrile. These interactions in acetonitrile have been identified as well for the donor molecule of D149 and the ester form of D149. All of these ground-state complexes have relatively high binding constants in solution. In addition, a charge-transfer state has been detected for the [D149/I2] complex in acetonitrile, giving long-lived species with a lifetime of more than hundreds of nanoseconds. The presence of these adsorbed complexes on semiconductor surfaces such as ZrO2 and TiO2 have been confirmed via steady-state absorption and time-resolved emission. More importantly, these complexes adsorb on the semiconductor surfaces, showing different electron dynamics on the TiO2 in comparison to the adsorbed D149 itself, in which the electron injection and recombination processes have been greatly modulated. Such formed complexes on the semiconductor surfaces can certainly limit the efficiency of a working solar cell based on similar organic dyes. Thus, attention to the structural design of the photosensitizers to avoid such formed complexes should be highlighted, which opens a new pathway for improving the solar cell efficiencies based on organic dyes.