An electrical model of the dye-sensitized solar cell

Abstract

An electrical model of the dye-sensitized solar cell (DSC) is presented, which relates material parameters to cell performance. Based on these parameters, the model permits the calculation of steady-state properties as e.g. internal currents or particle densities and the complete I– V characteristic of a DSC. The cell is modelled as a pseudo-homogeneous effective medium, consisting of the nanoporous TiO 2 semiconductor, the light-absorbing dye and the redox electrolyte, which are intermixed. Continuity and transport equations are applied to all the charge carriers involved: the electrons in the TiO 2 conduction band, and the iodide, triiodide and cations of the electrolyte. The macroscopic electric field, resulting from the unbalanced charge-carrier distribution under illumination, is calculated using Poisson's equation. The front and back cell boundaries are modelled as an ohmic metal–semiconductor contact and as a redox electrode via a current-overpotential equation, respectively. One of the main simplifications of this model is the consideration of only one-electron loss mechanism: the relaxation from the TiO 2 conduction band to the redox electrolyte. This allows a direct coupling of photon absorption with electron injection. The model is described in detail, and exemplary numerical results are presented, which demonstrate the feasibility of the model. The influence of the most important material parameters, such as electron mean lifetimes and mobilities, on the cell performance are illustrated.