Effect of TiO2/reduced graphene oxide composite thin film as a blocking layer on the efficiency of dye-sensitized solar cells

Abstract

The objective of the present work was to study the change in efficiency of dye-sensitized solar cells due to introduction of a thin blocking composite layer of TiO2 and graphene. The reduced graphene oxide prepared by chemically exfoliation method was confirmed as few layer graphene through X-ray diffraction, Raman analysis and atomic force microscopy technique. X-ray photoelectron spectroscopy was used to study the oxygen functionalities in graphene oxide and in reduced graphene oxide. Graphene-doped TiO2 thin films were coated by sol-gel routed spin coating technique and characterized by ultraviolet-visible, photoluminescence analysis, Fourier transform infrared spectroscopy, X-ray diffraction studies, field emission scanning electron microscopy, and transmission electron microscopy. The effect of blocking layer on the efficiency of dye-sensitized solar cells was studied using the photocurrent-voltage characteristics and electrochemical impedance spectroscopy. The studies indicated that the titania-graphene composite thin film worked as both blocking layer and ohmic contact between porous TiO2 and fluorine-doped tin oxide glass improved the overall device performance by reducing the interfacial resistance which in turn depends on the doping concentration of graphene in TiO2. The device with blocking layer improved the photoconversion efficiency from 2.49 to 5.09 %.