(Invited) Surface Modification of Wide Band-Gaped Anode of Dye-Sensitized Solar Cells by Ionic Liquid Molecules

Dye-sensitized solar cells have attracted worldwide attention due to its unique properties such as cost effective, temperature insensitive, and with high quantum efficiency under low illuminations. Among all studies, the topic of replacement of commonly used liquid electrolyte solution to reduce solution leakage becomes one of the emerging research focuses. The replacement of solvent of electrolyte solution by ionic liquid is one of the approaches. The reduced leakage by these approaches is expected to realize yet at the expense of reduced solar cell efficiency, due to lowered charge transfer rates in the electrolyte solutions. However, we found that the partial replacement of commonly used electrolyte solution by imidazolium salt solution enhances the solar cell efficiency instead.

In this study, we report that the surface treatment of the wide band-gaped anode of titanium oxide by ionic liquid molecules accounts for at least part of the solar cell efficiency enhancement. We found that the imidazole-derived molecules act as barrier for electron-hole premature recombination between photoelectrons transported on the conduction band of anode and the holes in the electrolyte on the anode/electrolyte interface. The significant efficiency enhancement is not necessarily due to increased dye adsorption on anodes, because we can manage a reduced dye adsorption condition while the solar cell still provides enhanced efficiency.

The ligand of imidazolium salts plays a very crucial role on the effectiveness of imidazole-derived molecules on the enhancement of solar cell efficiency. The presence of sulfite ligand secures the molecule adhesion on titanium oxide through the sulfite ligand itself.

We would like to present the parameters of treatment of such sequence of imidazole and dye adsorption, the use of solvent, dip duration time, and solution concentration. From the interrogation of the experiment results, we can confirm the exact role of imidazole-derived molecules on the enhancement of the solar cell efficiency.