Photocurrents in the ZnO and TiO2 Photoelectrochemical Cells Sensitized by Xanthene Dyes and Tetraphenylporphines. Effect of Substitution on the Electron Injection Processes

Abstract

The photocurrents in zinc oxide and titanium dioxide electrodes sensitized by anionic xanthene dyes (Eosine Y, Phloxine B, Erythrosine, and Rose Bengal) and metal tetraphenylporphines were studied in aqueous solutions. The quantum efficiencies of the photocurrents sensitized by anionic xanthene dyes were unaffected by substitution of the dye with various halogen atoms, while those sensitized by the tetraphenylporphines were affected by changing the central metal. It is concluded from these results that the electron injection from the excited xanthene dyes to the semiconductor electrodes is a process so rapid (<<0.1 ns) that no internal quenching processes can compete with it, while that from the tetraphynelporphines is relatively slow competing with the internal deactivation processes. It is also concluded that the electron back transfer from the semiconductor conduction band to the oxdized dye decreases the sensitization efficiency.

Porphyrin dyes for TiO2 sensitization

“…In past years, a number of organic dyes, such as phthalocyanines, [6][7][8][9] perylene bis-amides, [10][11][12] xanthenes, [13][14][15] hemicyanines [16][17][18] and porphyrins [19][20][21][22][23] have been tested as sensitizers, but the light-to-electricity conversion efficiency is rather modest compared to that shown by metal polypyridine complexes. 4,5,7,24,25 At present, it is still unclear why these dyes have limited performance and the reported photocurrent efficiencies for classes of homologous species differ widely in value.…”

Photosensitization of Nanocrystalline ZnO Films by Bis(2,2‘-bipyridine)(2,2‘-bipyridine-4,4‘-dicarboxylic acid)ruthenium(II)

“…A lot of work on the dye sensitization of TiO 2 , − ZnO, − and SnO 2 , − with various dyes, for example, rhodamine, rose bengal, methylene blue, cresyl violet, ruthenium complexes, etc., has been reported in the past from various labs around the world. In these studies, the semiconductors employed had been largely in the single or polycrystalline form.…”

Femtosecond Electron-Transfer Dynamics at a Sensitizing Dye−Semiconductor (TiO2) Interface

“…Photoinduced electron transfer between dyes and colloidal semiconductors plays a vital role in silver halide photography, electrophotography, and more recently in solar energy cells. Sensitizing semiconducting oxides such as TiO 2 , , SnO 2 , and ZnO 2 has proven an effective way to achieve electron injection for solar cells . The photostability of TiO 2 , combined with its ability to effectively and quickly separate charge, makes it a potentially attractive material for solar energy cells.…”