Electronic Transport in Dye-Sensitized Nanoporous TiO2 Solar CellsComparison of Electrolyte and Solid-State Devices

This article compares the electronic transport properties of dye-sensitized solar cells using a liquid electrolyte with those of one using an organic hole conductor. Both types of solar cells differ by the reference energies for recombination and, in particular, by their recombination probabilities of photoinjected electrons from the titanium dioxide into the respective contact medium. For voltages below 0.8 V, the junction impedance of the electrolyte cell is dominated by diffusion and recombination of electrons from the TiO2 into the electrolyte. The impedance of the solid state exhibits a negative reactance, that is, an inductive behavior, which we attribute to conductivity modulation of the hole conductor by injected electrons.