Substitution Effects of Phenothiazine and Porphyrin Dyes in Dye-sensitized Solar Cells Page: 26
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Phenothiazine
3
2
1
4
- Ferrocene
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Potential vs. Ag/AgCI (V)
Figure 2.3. Differential pulse voltammograms of the investigated compound in acetonitrile, 0.1
M (TBA)C104.
The energetics for electron injection were estimated from electrochemical and emission data.
The singlet excited state energy, Eoo for the phenothiazine dyes were calculated from the optical
absorption and emission data and were found to be 2.43-2.50 eV for Type-1 dyes and 2.97 eV for
Type-2 dye. By converting the oxidation potential to SHE (1.26 V for Type-1 and 1.11 eV for
Type-2 dyes) the excited state potential corresponding to the LUMO level (= Ex - Eo.o) were
estimated. These values were found to range between -1.17- -1.24 V for Type-1 and -1.85 V for
Type-2 dyes. The sufficiently negative LUMO levels of these dyes compared to the conduction
band energy of TiO2 being -0.5 V vs. SHE implies possibility of electron injection from the
excited dye into the conduction band of TiO2. Additionally, the HOMO levels of the
investigated dyes are sufficiently more positive than the iodine/iodide redox couple value being
0.40 V. This indicates the oxidized dyes formed after electron injection into the conduction
bands of TiO2 could thermodynamically accept electron from the iodide ions.26
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Hart, Aaron S. Substitution Effects of Phenothiazine and Porphyrin Dyes in Dye-sensitized Solar Cells, thesis, December 2013; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc407837/m1/32/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .