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Article

Effect of Annealing Temperature on Back Electron Transfer and Distribution of Deep Trap Sites in Dye-Sensitized TiO₂, Studied by Time-Resolved Infrared Spectroscopy

Kan Takeshita* and Yutaka Sasaki

Center for Analytical Chemistry and Science, Inc., 1000 Kamoshida-cho, Aoba, Yokohama 227-0033, Japan

Masahiro Kobashi, Yuki Tanaka, and Shuichi Maeda

Science and Technology Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida-cho, Aoba, Yokohama 227-8502, Japan

Akira Yamakata, Taka-aki Ishibashi, and Hiroshi Onishi

Surface Chemistry Laboratory, Kanagawa Academy of Science and Technology (KAST), KSP East 404, 3-2-1 Sakado, Takatsu, Kawasaki 213-0012, Japan

J. Phys. Chem. B, 2004, 108 (9), pp 2963–2969

DOI: 10.1021/jp035416o

Publication Date (Web): February 7, 2004

To whom correspondence should be addressed. E-mail: 5503103@ cc.m-kagaku.co.jp. Phone: +81-45-963-3155. Fax: +81-45-963-4261.

Abstract

The effect of annealing temperature on electron dynamics in Ru complex-sensitized TiO₂ films was studied by highly sensitive measurement of transient IR absorption. The amount of electron injection and the back electron transfer rate were not influenced to a large extent by annealing temperature, but the distribution of deep trap sites was considerably influenced. The difference in solar cell efficiency due to annealing temperature was mainly attributed to the difference in the nature of deep trap sites. By extending the probe light window from the mid-IR (1000−4000 cm^-1) to the near-IR (−10000 cm^-1) region, we investigated deep trap sites directly and found that electrons in deep trap sites have absorption in the near-IR region whose peak locates around 7500 cm^-1. As a whole, the electron dynamics in the films annealed at higher than 400 °C were considerably different compared with those in the films annealed at lower than 400 °C.

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