Effect of imidazole derivatives in triphenylamine-based organic dyes for dye-sensitized solar cells

In order to study the influence of imidazole derivatives in triphenylamine-based organic dyes, two different imidazole derivatives are introduced into the phenyl ring of the triphenylamine core, coded as TPA-B5 and TPA-B6, respectively. The photophysical and electrochemical properties of the dyes are investigated by UV-vis spectroscopy and cyclic voltammetry. TPA-B5 increases the molar extinction coefficients and lambda(max) because of the extension of the pi-conjugation structure of the dye and non-planar structure of imidazole derivative. However, TPA-B6 does not increase the molar extinction coefficients and lambda(max) compared with a simple triphenylamine derived dye (TPA-1), which may be due to the planar structure of imidazole derivative and benzene ring. The structure of TPA-B6 is in favor of the formation of dye aggregates on the semiconductor surface and the recombination of conduction band electrons with triiodide in the electrolyte. Overall conversion efficiencies of 3.13% and 1.21% under full sunlight (AM 1.5G, 100 mW cm(-2)) irradiation are obtained for DSSCs based on the two new dyes, under the same conditions, the dye TPA-1 and ditetrabutylammonium cis-bis(isothiocyanato) bis(2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium(II) (N719) give overall conversion efficiencies of 2.23% and 5.38%, respectively. Although the overall conversion efficiencies of these dyes are not very high, the results will still afford significant value for future development of efficient D-pi-A sensitizers. (C) 2013 Elsevier B.V. All rights reserved.