Activation Energy of Electron Transport in Dye-Sensitized TiO2 Solar Cells
Various characteristics of dye-sensitized nanostructured TiO2 solar cells, such as electron transport and electron lifetime, were studied in detail using monochromatic illumination conditions. The electron transport was found to be a thermally activated process with activation energies in the range of 0.10-0.15 eV for light intensities that varied 2 orders of magnitude. Electron lifetimes were detd. using a new method and found to be significantly larger (>1 s) than previously detd. An av. potential was detd. for electrons in the nanostructured TiO2 under illumination in short-circuit conditions. This potential is ∼0.2 V lower than the open-circuit potential at the same light intensity. The electron transport time varies exponentially with the internal potential at short-circuit conditions, indicating that the gradient in the electrochem. potential is the driving force for electron transport in the nanostructured TiO2 film. The applicability of the conventionally used trapping/detrapping model is critically analyzed. Although exptl. results can be fitted using a trapping/detrapping model with an exponential distribution of traps, the distribution parameters differ significantly between different types of expt. Furthermore, the exptl. activation energies for electron transport are smaller than those expected in a trapping/detrapping model.
Record created on 2015-07-06, modified on 2016-09-28