Raman spectroscopic study of dye adsorption on TiO2 electrodes of dye-sensitized solar cells

The state of dye adsorption on TiO2 electrodes in dye-sensitized solar-cell (DSSC) systems is important for its power-conversion efficiency (PCE). We propose a non-destructive and quantitative method to evaluate the amount of adsorbed dye on TiO2 electrodes by using micro-Raman spectroscopy. The Raman peak intensity ratio of adsorbed dye to TiO2, I-d/I-t, is defined as a dye adsorption parameter. Based on a comparison between I-d/I-t and the amount of dye evaluated from UV-vis absorption, the quantitativity and reproducibility of our method are verified. We investigated the change of I-d/I-t spatial distribution of TiO2 electrodes immersed in a dye solution for different time scales. The statistical analysis of I-d/I-t distribution suggests that dyes adsorbed on TiO2 electrodes with chemical coordination increase at first, and after their saturation, dye aggregations are formed over the chemisorption layer. We also describe the effect of the I-d/I-t distribution on PCE. From a comparison of PCE and I-d/I-t distribution obtained from various immersion processes, it was considered that the PCE of DSSCs can be optimized by minimizing the I-d/I-t dispersion. (C) 2014 Elsevier B.V. All rights reserved.