3.7 Dye absorption spectrum

A major problem, however, is the attachment of less dye, reducing the J. One approach to solve this problem is based on a plasmonic structure, such as silver (Ag NPs), gold (Au NPs), or gold nanorods [10]. Figure 15 displays the UV–Vis absorption spectra of one derivative of EY dye, which was dissolved in absolute ethanol. It is clear that the maximum absorption peak of EY is positioned at 526 nm; also, other small peak is located at 309 nm. EY exhibits a powerful absorption peak in the visible region, and its spectrum covers broader window than the others. The intensity of the observed absorption peaks in testing rang represents a part of energy losses in the transition in the UV region. In the DSSC application, it is much of interests to concentrate in the visible solar spectrum. In addition to that, the molar extinction coefficient of EY equals 112,000 (cmM)�<sup>1</sup> , corresponding to π ! π\* transitions of conjugated molecules [46, 47]. To investigate the effect on the light absorption enhancement of dye molecules of the DSSCs photoanode, the optical absorbance was measured of dye-sensitized plasmonic NP compositeembedded photoanode and compared them to that of the reference UZ photoanode. The results are shown in Figure 16. The relatively broad and strong enhancement is observed in the range of 250–550 nm with a maximum enhancement around 307 nm, which coincides with the absorption band position of decorated Ag NPs. These features suggest that dye molecules in the vicinity of Ag NPs can absorb more photons, presumably due to the intensified near-field effect of the surface plasmon and spectral overlap between the dye and plasmon, which may eventually lead to an increase in the number of charge carriers and Jsc values [14]. The plasmonic photoanode recorded higher absorbance than the pristine photoanode. This is a typical result in many reported works on plasmonic DSSCs [6]. The absorption in the visible region is shifted from 526 to 518.06 nm, as revealed in Figure 16. This can be explained by a change in the energy levels of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of EY compared to those in solution, due to the interaction between EY molecules and the ZnO film

Figure 15. UV–Vis absorption spectra of EY dyes dissolved in absolute ethanol.

Figure 16. UV–Vis adsorption spectra of EY dyes absorbed by UZ and DZ 1.0 Mol % Ag NPs.

[48, 49]. These results show a synergistic effect between the dye and plasmonic NPs, on the light absorption enhancement effect [6].
