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

Abstract The state of dye adsorption on TiO 2 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 TiO 2 electrodes by using micro-Raman spectroscopy. The Raman peak intensity ratio of adsorbed dye to TiO 2 , 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 TiO 2 electrodes immersed in a dye solution for different time scales. The statistical analysis of I d / I t distribution suggests that dyes adsorbed on TiO 2 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.