Effects of different nanostructural ZnS films on the characteristics of organic/inorganic heterostructure devices

Abstract

Organic/inorganic heterostructure ITO/poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV)/ ZnS/Al devices were fabricated. The effects of different nanostructural ZnS thin films on the characteristics of the devices were studied in detail. Different nanostructural ZnS thin films were prepared by glancing angle deposition (GLAD) technology. ZnS films were deposited on pieces of indium tin oxide (ITO) substrates coated with MEH-PPV in an electron beam evaporation system when the oblique angle was set to 0° and 80° respectively. During the deposition process, the base pressure of vacuum chamber was 3×10^-4 Pa, the deposition rate was fixed at 0.2 nm/s and the rotation rate of the substrate was 0.05 rev/s. Scanning electron microscope (SEM) images show that ZnS nanocrystalline films were formed on the substrates at different oblique angles, but the nanocolumnar structure was only formed at the situation of α=80°, and a continuous and uniform ZnS thin film was obtained at 0°. The electroluminescence (EL) intensities of the organic/inorganic heterostructure devices were enhanced compared with the single-layer devices, and the device with the nanocolumnar ZnS layer showed higher emission intensity compared with the one composed by the continuous ZnS film deposited at normal incidence under the same driving voltage. The different nanostructural ZnS films were found to have direct effects on the electrical and luminance characteristics of the organic/inorganic heterostructure devices.