Hopping Transport of Electrons in Dye-Sensitized Solar Cells

Abstract

A calculation of the chemical diffusion coefficient of electrons, Dn, in dye-sensitized solar cells, is presented, in the framework of the hopping model, where electron transport occurs by direct transitions between localized states in an exponential distribution. The Fermi-level dependence of Dn in the transport energy approximation is exactly the same as that in the multiple trapping model, but there are differences concerning the meaning of the parameters governing electron transport and the values of relevant energy levels inferred from experiments. The hopping model appears to describe well the experimental data of Dn from high-efficiency dye solar cells at various temperatures. The subject of electron transport in nanostructured semicon-ductors surrounded by electrolytes has been amply studied, especially in relation to the characteristics of dye-sensitized solar cells (DSC).1 The physical quantity of central interest is the chemical diffusion coefficient of electrons, Dn,2 which is measured by the common techniques such as intensity modu-lated photocurrent spectroscopy (IMPS), transient photocurrent under a small perturbation of the illumination, or impedanc