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Postpressing dependence of the effective electron diffusion coefficient in electrophoretically prepared nanoporous ZnO and TiO2 films

Published online by Cambridge University Press:  31 January 2011

S. Dor ,
Th. Dittrich ,
A. Ofir ,
L. Grinis  and
A. Zaban
S. Dor
Affiliation:
Department of Chemistry, Nano-Energy Research Center, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
Th. Dittrich
Affiliation:
Hahn-Meitner-Institute, 14109 Berlin, Germany
A. Ofir
Affiliation:
Department of Chemistry, Nano-Energy Research Center, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
L. Grinis
Affiliation:
Department of Chemistry, Nano-Energy Research Center, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
A. Zaban*
Affiliation:
Department of Chemistry, Nano-Energy Research Center, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
*
a)Address all correspondence to this author: e-mail: zabana@mail.biu.ac.il
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Abstract

The porosity of electrophoretically prepared nanoporous ZnO and TiO2 films was systematically decreased by postpressing at different pressures. The nanoporous structure of the films was fixed by sintering after the postpressing procedure. The postpressing-induced change of the internal surface area of the nanoporous films was monitored using the dye-removal technique. The effective electron diffusion coefficient (Deff) of the unpressed nanoporous films depended on the thickness according to Fick’s second law. When pressed, the diffusion coefficient of the films increases significantly. In nanoporous TiO2, the increase of Deff follows the percolation theory where transport rate depends on the particle-coordination number. In contrast to the TiO2 films, the value of Deff of pressed nanoporous ZnO films changed with the porosity much stronger than one would expect from the percolation theory with hard spheres. This property has been attributed to the strong increase of necking between ZnO nanoparticles with increasing pressure as indicated by a strong decrease of the internal surface area.

Keywords

Electronic materialDiffusionPhotovoltaic
Type
Articles
Information
Journal of Materials Research , Volume 23 , Issue 4 , April 2008 , pp. 975 - 980
Copyright
Copyright © Materials Research Society 2008

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