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Tuning the pore size in electrodeposited ZnO films using surfactants as structure-directing additives
|Cathrin Boeckler 1, Armin Feldhoff 1, Michael Wark 1, Keigo Ichinose 2, Tsukasa Yoshida 2, Torsten Oekermann 1
1. Leibniz University Hannover, Institute of Physical Chemistry and Electrochemistry, Callinstrasse 3-3A, Hannover 30167, Germany
Dye-sensitized p-n solar cells are a concept to avoid the leakage of the liquid electrolyte used in conventional dye-sensitized solar cells by replacing it by a p-type semiconductor. CuSCN (p-type) electrodeposited into porous electrodeposited ZnO (n-type) is a promising combination due to the usually good charge carrier transport in electrodeposited semiconductors. Porous ZnO films can be obtained by co-deposition with large organic molecules, e.g. dye molecules with functional groups that interact with the growing ZnO film. However, a systematic tuning of the pore size, which will be important in order to find the optimum pore size for CuSCN deposition, has not been achieved yet with these additives. We have now explored the possibilites of surfactants, which are often used as additives in sol-gel methods, in the electrodeposition of ZnO. With anionic surfactants such as sodium docecyl sulfate lamellar ZnO structures are deposited if the surfactant concentration in electrodepostion bath is above half the critical micelle concentration (cmc), i.e. when surface micelles start to form on the growing ZnO film. The distance between the ZnO layers can be tuned by changing the chain length of the surfactant. However, an easily accessible porosity like that formed by micelles in sol-gel films could not be observed. Larger pores compared to those in ZnO films deposited with dye molecules or surfactants alone could be obtained by a combination of both kinds of additives. The anionic dye eosin Y and the cationic surfactant n-dodeclypyridinium chloride in concentrations above the cmc were found to form mixed aggregates. SEM images show pore diameters in the range of several tens of nanometers, compared to only 10 nm if only eosin Y is used. Preliminary results of CuSCN deposition in ZnO films with different pore sizes will also be reported.
Presentation: Oral at E-MRS Fall Meeting 2007, Symposium B, by Cathrin Boeckler
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-10 10:50 Revised: 2009-06-07 00:44