Low turn-on voltage of doped organic light emitting diodes based on food dyes

Abstract

Three derivatives of food azo dye were investigated (Dyes 1, 2 and 4) by theoretical and experimental tools. Photophysical properties, based on theoretical estimations, experimental evaluations, electrochemical and photoelectrical properties were discussed. The compounds exhibited efficient emission of solid state with maximum fluorescence intensity at the range of 517–646 nm and PLQY (photoluminescence quantum yield) values at the range of 9–17% in non-doped solid state and 13–39% in doped solid state. In this study 90 wt percent of PBD (2-(4-tert-Butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole) have been used as the electron transporting host who derived balanced charge carrier transport for high internal and external efficiency of OLEDs (organic light emitting diodes). Ionization potential for compounds was found to be comparable (5.85 and 6.18 eV) by photoelectron emission spectrometry. According to the fabrication of devices for gaining charge mobility the layers of the dyes showed properties as a bipolar charge transporting with balanced hole and electron mobility and the values reaching to 1.27 × 10−4 cm2/Vs and 1.09 × 10−4 cm2/Vs respectively at high electric fields. Furthermore, OLEDs consist of azo dyes as an emitter layer fabricated by PVD (physical evaporation deposition) method and the maximum values of the best device showed, consist of, the low turn on voltage of 2.69 V and values of brightness, current efficiency, power efficiency, EQE (external quantum efficiency) 16432.40 cd/m2, 8.20 cd/A, 6.95 lm/w, 4.89% respectively.