Effect of thin gold interlayer on the electrical and dielectrical behaviors of ITO/MEH-PPV/Al structures

Abstract

The effects of inserting a thin gold (Au) layer between the indium tin oxide (ITO) electrode and the poly [2-methoxy-5-(2-ethylhexyl-oxy)-p-phenylenevinylene] (MEH-PPV) organic material on the electrical and interface state properties of a ITO/MEH-PPV/Al device are investigated through current–voltage I(V), and capacitance–voltage characteristics C(V). The modified anode was characterized by atomic force microscope (AFM), and UV–vis transmittance spectra. The atomic force microscopy (AFM) surface roughness analysis indicates that a uniform and smoother surface is formed when the ITO is covered by the Au interlayer. A decrease in the transmittance and the optical band gap is observed in ITO/Au anode. The ITO/Au/MEH-PPV/Al device shows improved current density–voltage characteristics as compared with the ITO/MEH-PPV/Al. Diode parameters such as ideality factor, barrier height, series resistance and Shunt resistance are calculated using Schottky model corrected from the series and Shunt resistances. In the presence of the Au interlayer, the junction resistance across the ITO/MEH-PPV interface is significantly reduced, leading to an improvement in hole injection.The interface state density (Nss) values and the time constant of the interface states (τ) are obtained by the development of a new approach by the fit of the capacitance with three capacitances in series, according to Nicollian and Goetzberger formula. A decrease in the interface state density is observed when the Au interlayer is introduced at the ITO/organic layer interface. The main factors contributing to such improvements induced by the thin gold buffer layer are discussed.