title: Characteristics of high efficiency dye-sensitized solar cells.
abstract: Impedance spectroscopy was applied to investigate the characteristics of dye-sensitized nanostructured TiO2 solar cells (DSC) with high efficiencies of light to electricity conversion of 11.1% and 10.2%. The different parameters, that is, chemical capacitance, steady-state transport resistance, transient diffusion coefficient, and charge-transfer (recombination) resistance, have been interpreted in a unified and consistent framework, in which an exponential distribution of the localized states in the TiO2 band gap plays a central role. The temperature variation of the chemical diffusion coefficient dependence on the Fermi-level position has been observed consistently with the standard multiple trapping model of electron transport in disordered semiconductors. A Tafel dependence of the recombination resistance dependence on bias potential has been rationalized in terms of the charge transfer from a distribution of surface states using the Marcus model of electron transfer. The current-potential curve of the solar cells has been independently constructed from the impedance parameters, allowing a separate analysis of the contribution of different resistive processes to the overall conversion efficiency.
authors.affiliation: Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: Qing
authors.initials: Q
authors.lastname: Wang
authors.forename: Seigo
authors.initials: S
authors.lastname: Ito
authors.forename: Michael
authors.initials: M
authors.lastname: Grätzel
authors.forename: Francisco
authors.initials: F
authors.lastname: Fabregat-Santiago
authors.forename: Iván
authors.initials: I
authors.lastname: Mora-Seró
authors.forename: Juan
authors.initials: J
authors.lastname: Bisquert
authors.forename: Takeru
authors.initials: T
authors.lastname: Bessho
authors.forename: Hachiro
authors.initials: H
authors.lastname: Imai