Electron Diffusion Length in Nano-Porous TiO2 Electrode Directly Measured Using Partially Dye-Adsorbed Solar Cell and Effects of Electrolyte Solvent and Annealing Temperature

The electron diffusion length is directly evaluated from the dependence of photocurrent on the position of dyeadsorption front using the structure of selectively dye-adsorbed solar cell. By changing the thickness of the region without dye-adsorption, the thickness that the photocurrent starts to flow is defined as the electron diffusion length in nano-porous TiO2 layer. This method is applied to investigate the effects of the electrolyte solvent and the annealing temperature on the electron diffusion length in nano-porous TiO2 layer. It is suggested that viscosity and molecular size of solvent affects the diffusion of electron in TiO2 nano-porous layer from the results that the electron diffusion length is 1.6 times longer in aprotic acetonitrile solvent than in protic ethylene glycol solvent. At 600 degrees C annealing, the electron diffusion length shows the maximum of 27 +/- 1 1 m in LiI/I-2/acetonitlire at the incident photon flux of 2 : 2 +/- 10 15 cm(-2) s(-1) at 540 nm.