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Proceedings Paper

Charge separation and charge transport in nanostructured TiO2 film electrodes
Author(s): Henrik Lindstrom; Anders Hagfeldt; Hakan Rensmo; Anita Solbrand; Sven Sodergren; Sten-Eric Lindquist
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Paper Abstract

Photoelectrochemical measurements have been performed on film electrodes consisting of linked nano-sized TiO2 colloids. The film thickness ranged from 1 - 40 micrometers. The film network was attached to a thin transparent conducting layer of SnO2 allowing for photogenerated electrons to be collected in an outer electrical circuit. By illuminating electrodes of different thicknesses with monochromatic light from either side, it was possible to induce charge separation in different regions of the film network. In this way, it was proved that electrons have different probabilities of reaching the back contact depending on the location in the film where they are created. The results also illustrate the importance of the redox species in the cavities of these porous electrodes. By adding acceptors to the electrolyte it was possible to alter the conditions for charge transfer in the nanocrystalline film. It was shown that electron acceptors such as oxygen or iodine in the solution strongly affects the rate of charge transfer at the particle-electrolyte interface and the transport of electrons throughout the TiO2 film-network. Modification of the semiconductor-electrolyte interface with surface adsorbed pyridine induced major changes in the charge transfer events at the interface. The photocurrent yields were greatly improved by this surface treatment. The effect of pH in solution was also investigated. The rate of charge transfer at the particle-electrolyte interface was changed at high surface density of OH--ions. This was explained due to the change of the surface energy causing different driving forces for redox reactions, but also due to the more negatively electrostatic surface potential of the particles preventing the encounter of negatively charged redox species with the colloid surface. Phototransient measurements indicated a depletion of redox species in the pores of the film. Thereby it was pointed out that the dynamics of the redox species in the confined cavities of the film are a limiting factor for the charge separation efficiency in nanocrystalline film. The photovoltage in anaerobic solutions sustained for very long periods, indicating that the linked particles may work as reservoirs for photoexcited electrons if the access to electron acceptors in the solution is choked. It was concluded that surface processes are favored at the small semiconductor particles used in this study.

Paper Details

Date Published: 23 August 1995
PDF: 9 pages
Proc. SPIE 2531, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIV, (23 August 1995); doi: 10.1117/12.217355
Show Author Affiliations
Henrik Lindstrom, Uppsala Univ. (Sweden)
Anders Hagfeldt, Uppsala Univ. (Sweden)
Hakan Rensmo, Uppsala Univ. (Sweden)
Anita Solbrand, Uppsala Univ. (Sweden)
Sven Sodergren, Uppsala Univ. (Sweden)
Sten-Eric Lindquist, Uppsala Univ. (Sweden)

Published in SPIE Proceedings Vol. 2531:
Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIV
Carl M. Lampert; Satyen K. Deb; Claes-Goeran Granqvist, Editor(s)

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