Studies on organic light-emitting diodes based on rubrene-doped zinc quinolate

We report on the fabrication and performance of organic light-emitting diodes (OLEDs) employing rubrene-doped metal chelate namely, zinc quinolate (Znq2) as emissive layer. Different OLED architectures were carried out to improve the device performance by doping varying concentrations (by wt%) of rubrene dye into Znq2 host. Enhanced electroluminescence (EL) intensity was achieved using oxygen-plasma-treated indium tin oxide as anode, N,N′-di-1-naphthyl-N,N′-diphenyl-1,1′-biphenyl-4,4′diamine (α-NPD) as hole-transport layer, 10 weight percent rubrene-doped Znq2 as emission layer, Znq2 as electron-transport layer, LiF as electron-injection layer and aluminum as cathode. It has been demonstrated that by using Znq2 as electron-transport layer and host for dopant (rubrene) is the most suitable device structure for achieving low drive voltage and high efficiency. Electroluminescence spectra of rubrene-doped OLED devices were also studied. The EL spectral peak was found to be shifted to 565 nm and spectral full-width at half maximum (FWHM) of rubrene-doped device was found to be 58 nm, while it was 95 nm in the case of a pure Znq2-based OLED device. No further significant changes in EL spectra, such as, spectral broadening, narrowing or peak shifting were observed on changing the concentration of the rubrene dye