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In situ detection of free and trapped electrons in dye-sensitized solar cells by photo-induced microwave reflectance measurements


Reference:

Dunn, H.K., Peter, L.M., Bingham, S.J., Maluta, E. and Walker, A.B., 2012. In situ detection of free and trapped electrons in dye-sensitized solar cells by photo-induced microwave reflectance measurements. Journal of Physical Chemistry C, 116 (41), pp. 22063-22072.

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    Official URL:

    http://dx.doi.org/10.1021/jp3072074

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    Abstract

    In order to study the behavior of photoinjected electrons in dye-sensitized solar cells (DSC), steady-state microwave reflectance measurements (33 GHz, Ka band) have been carried out on a working cell filled with electrolyte. The experimental arrangement allowed simultaneous measurement of the light-induced changes in microwave reflectance and open circuit voltage as a function of illumination intensity. In addition, frequency-resolved intensity-modulated microwave reflectance measurements were used to characterize the relaxation of the electron concentration at open circuit by interfacial transfer to tri-iodide ions in the electrolyte. The dependence of the free and trapped electron concentrations on open circuit voltage were derived, respectively, from conductivity data (obtained by impedance spectroscopy) and from light-induced near IR transmittance changes. These electron concentrations were used in the fitting of the microwave reflectivity response, with electron mobility as the main variable. Changes in the complex permittivity of the mesoporous films were calculated using Drude-Zener theory for free electrons and a simple harmonic oscillator model for trapped electrons. Comparison of the calculated microwave reflectance changes with the experimental data showed that the experimental response arises primarily from the perturbation of the real component of the complex permittivity by the high concentration of trapped electrons present in the DSC under illumination. The results suggest that caution is needed when interpreting the results of microwave reflectance measurements on materials with high concentrations of electron (or hole) traps, since an a priori assumption that the microwave response is solely determined by changes in conductivity (i.e., by free electrons) may be incorrect. The intensity-modulated microwave reflectance measurements showed that relaxation of the free and trapped electron concentrations occurs on a similar time scale, confirming that the free and trapped electron populations remain in quasi-equilibrium during the decay of the electron concentration.

    Details

    Item Type Articles
    CreatorsDunn, H.K., Peter, L.M., Bingham, S.J., Maluta, E. and Walker, A.B.
    DOI10.1021/jp3072074
    Related URLs
    URLURL Type
    http://www.scopus.com/inward/record.url?scp=84867540133&partnerID=8YFLogxKUNSPECIFIED
    DepartmentsFaculty of Science > Chemistry
    Faculty of Science > Physics
    Research CentresCentre for Sustainable Chemical Technologies
    Publisher StatementDunn_et_al.pdf: This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society and the Division of Chemical Education, Inc., after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp3072074
    RefereedYes
    StatusPublished
    ID Code33448

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