Electron density and dye adsorption dependence of electron transport in dye-sensitized TiO_2 solar cells

摘要

In dye-sensitized solar cells, electron transport in nano-porous thin TiO_2 film electrodes plays an important role in energy conversion efficiency. Previous studies have revealed that the electron transport property is largely influenced by electron density in the electrodes and the preparation methods of the TiO_2 electrodes. In this paper, we study the electron diffusion in nano-porous TiO_2 electrodes with and without dye adsorption. The electron diffusion coefficient is derived from pulsed laser induced current transients in the presence and absence of bias light. Measurements are repeated with various light intensities to examine electron density dependence. The experiments are performed for the electrodes prepared from two different TiO_2 particles and for two different electrolytes. For all cases, dye adsorption is found to increase electron diffusion coefficients under the same electron density in the electrodes. The increase of diffusion coefficients is confirmed by open-circuit voltage transient measurements. The charge trap on the electrode surface is studied from the relationship between open-circuit voltage and charge density in the dyed TiO_2electrodes. The reduction of surface charge trap density due to the dye adsorption is discussed.