title: Mechanisms of electron transport and recombination in ZnO nanostructures for dye-sensitized solar cells.
abstract: ZnO 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.
authors.affiliation: Área de Química Física, Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, 41013 Sevilla (Spain); Departamento de Física Aplicada, CINVESTAV-IPN, Mérida, Yucatán, 97310 (México).
authors.forename: Alberto G
authors.initials: AG
authors.lastname: Vega-Poot
authors.forename: Manuel
authors.initials: M
authors.lastname: Macías-Montero
authors.forename: Jesus
authors.initials: J
authors.lastname: Idígoras
authors.forename: Ana
authors.initials: A
authors.lastname: Borrás
authors.forename: Angel
authors.initials: A
authors.lastname: Barranco
authors.forename: Agustín R
authors.initials: AR
authors.lastname: Gonzalez-Elipe
authors.forename: Francisco I
authors.initials: FI
authors.lastname: Lizama-Tzec
authors.forename: Gerko
authors.initials: G
authors.lastname: Oskam
authors.forename: Juan A
authors.initials: JA
authors.lastname: Anta
keywords: ZnO; dye-sensitized solar cells; electron transport; nanostructures; photoanodes