Initial rise of transient electroluminescence in doped Alq₃ films

Abstract

The doping effect on initial rise of transient electroluminescence (EL) in organic light emitting diodes (OLEDs) is investigated. The dopants red light emitter 5,6,11,12‐tetraphenylnaphthacene (Rb) and 4‐(diacynomethylene)‐2‐methyl‐6‐(p‐dimethylaminostyryl)‐4H‐pyan (DCM), and yellow light emitter 3‐(2′‐benzothiazolyl)‐7‐diethylaminocoumarin (C‐6) were used in green light emitter tris‐(8‐hydroxyquinoline) aluminum (Alq3) film with various concentrations from 0.5 to 24 wt%. The increase of EL delay time and the slower rise of EL saturation were observed with doping concentrations. The values of EL delay time was found from 0.78 to 1.86 µs in doped OLED compared to 0.74 µs in pure Alq3 device. The EL saturation time was found from 1.2 to 2.8 µs for different doping concentration. We have also estimated the carrier mobility from the transient EL measurements. The charge‐carrier mobility was found as 0.5–1.2 × 10−5 cm2 V−1 s−1 in doped Alq3 films.

Emission properties of dopants rubrene and coumarin 6 in Alq3 films

“…The lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of Alq 3 is at $ 3.0 and $ 5.7 eV, respectively, with respect to the vacuum level. The LUMO and HOMO of rubrene (Rb) is at 3.15 and 5.36 eV and that of coumarin 6 (C-6) is at 2.7 and 5.4 eV, respectively [10].…”