We developed an ionic conductivity model of solid polymer electrolytes for dye-sensitized solar cells (DSSCs) based on the Nernst-Einstein equation in which the diffusion coefficient is derived from the molecular thermodynamic model. We introduced concentration-dependence of the diffusion coefficient into the model, and the diffusion coefficient was expressed by differentiating the chemical potential by concentration. The ionic conductivities of polymer electrolytes (PEO/LiI/I-2 system) were investigated at various temperatures and compositions. We prepared a set of PEO in which an EO : LiI mole ratio of 10 : 1 was kept constant for PEO.LiI.(I-2)(n) compositions with n = 0.02, 0.05, 0.1, 0.15, 0.2, and 0.3 (mole ratio of LiI : I-2). The ionic conductivities of the electrolytes were measured using a stainless steel/polymer-electrolyte/stainless steel sandwich-type electrode structure using alternating current impedance analysis. The values calculated using the proposed model agree well with experimental data. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3582-3587, 2010