Determination of the effective diffusion constant of I/sub 3//sup -/ ions in nanoporous TiO/sub 2/ networks

A device structure similar to the dye sensitized solar cells is investigated by current/voltage measurements. Using a platinum front electrode directly in contact to the nanoporous TiO/sub 2/ layer, we find diffusion limitation due to triiodide I/sub 3//sup -/. From the value of the maximum current density we calculate the I/sub 3//sup -/ diffusion constant D/sub T/ in a nanoporous medium. In addition, we evaluate a quantitative model to describe the complete I/V-characteristic of the device. Fitting the model to the experimental data we deduce a diffusion constant for I/sub 3//sup -/ of D/sub T/ = 1.24 (/spl plusmn/ 0.02)/spl times/10/sup -5/ cm/sup 2/s/sup -1/ in the bulk of the electrolyte and an effective diffusion constant of D/sub T//sup eff/ = 0.44 (/spl plusmn/ 0.02)/spl times/10/sup -5/ cm/sup 2/s/sup -1/ within the pores of the TiO/sub 2/ network.