Photovoltaic properties of Au–merocyanine–TiO2 sandwich cells. I. Dark electrical properties and transient effects

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Abstract
The electrical properties of thin films (200–3000 Å) of merocyanine photosensitizing dye sandwiched between a TiO2 single crystal doped n type and a thin (200 Å) Au metal layer has been studied. Dark current voltage measurements revealed that the current is space‐charge limited at high current densities with an electron trapping density of ∼1017 cm−3. This was determined by using TiO2 as an electron injecting contact. Interpretation of the kinetics of rise and decay of the photocurrent suggests that the mobility of holes, the majority carriers in merocyanine, is dependent on traps, the dominant trapping level having a depth of 0.11 eV. The decay of the photocurrent is monomolecular at short times and dominated by bimolecular recombination kinetics for long times of the order of seconds. The high series resistance in the merocyanine prevents any band bending in the TiO2, as the entire built‐in voltage in the junction falls across the merocyanine film. This is supported by capacitance voltage data showing a complete absence of mobile charge carriers in the junction region.