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 TiO 2 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.

Dye-sensitized solar cells with different front contact materials to the nanoporous TiO 2 layer are used to investigate the influence of the front contact barrier on the photovoltaic performance. The study uses devices that have SnO 2 :F, ZnO:Al, Al, or Au contacts underneath an amorphous TiO 2 blocking layer and the nanocrystalline TiO 2 . These devices are illuminated via the semitransparent platinum back contact. Variations of the front contact have no significant influence on the open circuit voltage of the devices. In contrast, the fill factors of the solar cells exhibit systematic differences. The experimental current/voltage curves are fitted to a simple model that uses two diodes, one corresponding to the front contact/TiO 2 interface and a second one for the TiO 2 /electrolyte interface.

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