Phenomenological modeling of dye-sensitized solar cells under transient conditions

Abstract

A phenomenological model is proposed for a better understanding of the basic working mechanisms of dye-sensitized solar cells (DSCs). A steady-state approach allows the construction of the I– V characteristics, giving important informations about the main factors that influence DSCs’ performance. On the other hand, the transient approach model is an important tool to relate the phenomenological behavior with certain dynamic techniques, such as Electrochemical Impedance Spectroscopy (EIS). Bearing in mind the uncertainty arising from fitting the experimental Nyquist diagrams to general electrical analogues, this transient model contributes for a deeper understanding of the DSCs and for obtaining the relevant kinetic parameters with higher accuracy. The one-dimensional transient phenomenological model presented here assumes that the injected conduction-band electrons may recombine only with the electrolyte redox species. Due to the small dimension of the titania particles, no significant electrical potential gradient is considered, resulting only in a diffusive electron transport across the semiconductor. For modeling purposes, the mesoscopic porous structure, consisting of TiO 2 nanoparticles covered with light-absorbing dye molecules and interpenetrated by the I - / I 3 - redox mediator (electrolyte), is considered as a homogeneous nanocrystalline structure of thickness L. The continuity and transport governing equations are defined for the mobile species involved: electrons in the TiO 2 conduction band and I - / I 3 - ions in the electrolyte. The simulated results are in straight agreement with the experimental data.