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Title

Mechanisms of electron transport and recombination in ZnO nanostructures for dye-sensitized solar cells

AuthorsVega-poot, A. G.; Macías-Montero, M. ; Idígoras, Jesús; Borrás, Ana ; Barranco, Ángel ; Lizama-Tzec, Francisco I.; Oskam, G.; Anta, Juan A.
AdvisorGonzález-Elipe, Agustín R.
KeywordsNanostructures
Photoanodes
ZnO
Electron transport
Dye-sensitized solar cells
Issue Date2014
PublisherJohn Wiley & Sons
CitationChemphyschem : a European journal of chemical physics and physical chemistry 15: 1088- 1097 (2014)
AbstractZnO is an attractive material for applications in dye-sensitized solar cells and related devices. This material has excellent electron-transport properties in the bulk but its electron diffusion coefficient is much smaller in mesoporous films. In this work the electron-transport properties of two different kinds of dye-sensitized ZnO nanostructures are investigated by small-perturbation electrochemical techniques. For nanoparticulate ZnO photoanodes prepared via a wet-chemistry technique, the diffusion coefficient is found to reproduce the typical behavior predicted by the multiple-trapping and the hopping models, with an exponential increase with respect to the applied bias. In contrast, in ZnO nanostructured thin films of controlled texture and crystallinity prepared via a plasma chemical vapor deposition method, the diffusion coefficient is found to be independent of the electrochemical bias. This observation suggests a different transport mechanism not controlled by trapping and electron accumulation. In spite of the quite different transport features, the recombination kinetics, the electron-collection efficiency and the photoconversion efficiency are very similar for both kinds of photoanodes, an observation that indicates that surface properties rather than electron transport is the main efficiency-determining factor in solar cells based on ZnO nanostructured photoanodes. Two very different behaviors of the electron-transport properties are found in nanostructured ZnO-based photoanodes. Texturized samples show a voltage-independent transport time, whereas films produced from nanocrystalline powders exhibit a voltage-dependent signal, consistent with trap-limited electron diffusion.
URIhttp://hdl.handle.net/10261/114768
DOI10.1002/cphc.201301068
Identifiersdoi: 10.1002/cphc.201301068
issn: 1439-7641
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