In Situ Observation of N719 on TiO2 in Dye-Sensitized Solar Cells by IR Absorption Spectroscopy

An in situ observation system of cis-di(thiocyanato)bis(2,2'-bipyridyl-4,4"-dicarboxylate)rutheniumu(II) (N719) dye adsorbed on TiO 2 electrodes in dye-sensitized solar cells (DSCs) was developed by using IR absorption spectroscopy with a multiple internal reflection geometry. By using the IR spectra obtained from the in situ system, we discuss the adsorption mechanism of N719 dye on the TiO 2 electrodes, how to promote the power generation and preserve the long-term stability in DSCs. The binding of N719 to the TiO 2 surface is strengthened by the iodine electrolyte. When N719 dye was adsorbed on TiO 2 electrodes by immersing them in the dye solution, followed by being dried in air, the dye molecule anchored on the surface with a bidentate coordination of COO by using one of four carboxylate moieties in N719. After the N719 dye was immersed in the iodine electrolyte, all the carboxylic moieties formed the bidentate coordination to connect to the TiO 2 surface. We discuss a possibility of enhancement in the power generation by rinsing the N719-adsorbed TiO 2 with the iodine electrolyte. During the power generation of the DSC under a light exposure, the adsorbed N719 remained stable although water as contamination appears in the electrolyte. The measure for suppressing the water contamination for the long-term stability is also discussed in this article.