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The doping effect on exciton behaviours in amorphous tris (8‐hydroxyquinolinato) aluminum (Alq3) were studied for the first time by transient photoluminescence (PL) measurements at room temperature. The dopants 4‐(diacynomethylene)‐2‐methyl‐6‐(p‐dimethylaminostyryl)‐4H‐pyan (DCM) and 5,6,11,12‐tetraphenylnaphthacene (rubrene) were used into Alq3 films at various concentration from 0.5 to 24 wt.% for this study. The exciton recombination rate was found sharply increased with doping concentration in Alq3 films. The exciton lifetime in pure Alq3 was found as ∼ 20 ns and it was reduced up to ∼8 ns with doping concentration. The exciton diffusion coefficient and diffusion length in doped films was found as 0.5 – 1.4 × 10–6 cm2 s–1 and 18–35 Å, respectively (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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