Electron Transport and Back Reaction in Electrochemically Self-Assembled Nanoporous ZnO/Dye Hybrid Films

T. Oekermann,†‡ T. Yoshida,*† H. Minoura,† K. G. U. Wijayantha,§ and L. M. Peter§
Gifu University, Graduate School of Engineering, Yanagido 1-1, Gifu 501-1193, Japan, University of Hannover, Institute of Physical Chemistry and Electrochemistry, Callinstrasse 3-3A, 30167 Hannover, Germany, and University of Bath, Department of Chemistry, Bath BA2 7AY, U.K.
J. Phys. Chem. B, 2004, 108 (24), pp 8364–8370
DOI: 10.1021/jp037831m
Publication Date (Web): May 20, 2004
Copyright © 2004 American Chemical Society
†

 Gifu University.

,
‡

 University of Hannover.

,
*

 Corresponding author. E-mail:  yoshida@apchem.gifu-u.ac.jp.

,
§

 University of Bath.

Abstract

Nanoporous ZnO/eosinY films prepared by electrochemical self-assembly have already shown promising characteristics for use in dye-sensitized solar cells, such as ease of preparation (no need for high-temperature sintering) and high dye loading. In this study, electron transport and back reaction in these films have been investigated by intensity modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). In contrast to sintered colloidal ZnO films, electrodeposited ZnO/eosinY films exhibit electron transit times (τD) that are much shorter than electron lifetimes (τn), leading to very efficient electron collection. The shorter transit times in the electrodeposited layers are due in part to the fact that the films are very thin, but in addition the electron diffusion coefficients are higher than in sintered colloidal ZnO films. Although the unusually high dye concentration in the electrochemically self-assembled film allows efficient light harvesting, it was found that not all dye molecules inject electrons. The low injection efficiency is probably due to the formation of dye aggregates.

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History

  • Published In Issue June 17, 2004
  • Received December 12, 2003
    Revised March 6, 2004

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