Efficiency enhancement in dye-sensitized solar cells by interfacial modification of conducting glass/mesoporous TiO2 using a novel ZnO compact blocking film

A novel and thin ZnO compact blocking film is employed at the interface of fluorine-doped tin oxide (FTO) substrate and mesoporous TiO2, and its influence on dye-sensitized solar cells (DSSCs) is investigated. The ZnO film prepared by spin-coating method on FTO is characterized by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and UV-vis spectrophotometer. The ZnO film is firstly employed as an energy barrier between FTO and mesoporous TiO2 film in DSSCs, which improves open-circuit photovoltage (V-oc) and fill factor (FF) with compensation of J(sc) decrease, finally increasing energy conversion efficiency from 5.85% to 6.70%. Electrochemical impedance spectra (EIS) analysis and open-circuit voltage decay (OCVD) technique reveal that the existence of the energy barrier not only resulted in the effect of suppressing back electrons transfer from FTO to electrolyte but also blocking the electrons injection from the conductive band of TiO2 to FTO. The former effect effectively reduces the recombination which occurs in the region of FTO substrate, and the latter leads to remarkable increment of electron density in the TiO2, thus resulting in enhanced V-oc and FF. These results suggest that the methodology of introducing the semiconductor with a more negative conduction band edge than TiO2 as the compact blocking film in DSSCs may be feasible. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.