Charge transfer improvement of ZnO-based dye-sensitized solar cells modified with graphite nanosheets and bilayer photoelectrode structures

Abstract

In this work, dye-sensitized solar cells (DSSCs) were fabricated with different photoelectrode structures consisting of a ZnO-based photoelectrode, a ZnO/Au Schottky barrier-based photoelectrode, graphite nanosheets loaded on a ZnO (GZnO)-based photoelectrode, graphite nanosheets loaded on a ZnO nanoparticles (GZnO NPs)-based photoelectrode and graphite nanosheets loaded on a ZnO nanoparticles/ZnO (GZnO NPs/ZnO) as a bilayer-based photoelectrode. The photovoltaic characteristics of DSSCs were investigated based on: the power conversion efficiency (PCE), short-circuit current density (Jsc), open-circuit voltage and fill factor. The kinetics electron transport of DSSCs was carried out using electrochemical impedance spectroscopy (EIS). The semi-circle in the Nyquist plot was calculated to represent the charge transfer resistance (Rct). It was found that the GZnO NPs/ZnO bilayer-based photoelectrode exhibited the maximum Jsc (9.185 mA/cm2) and maximum PCE (2.37%), which resulted by the minimum Rct in the device. The result can be interpreted as showing that a graphite nanosheet structure improves the electron transport property which produces an excellent charge transfer mechanism in the photoelectrode. Accordingly, enhanced performance of ZnO-based dye-sensitized solar cells with graphite nanosheets loaded on a ZnO nanoparticles layer could be simply explained in terms of the charge transfer mechanism.