High-efficiency organic light-emitting diodes with tunable light emission by using aromatic diamine/5,6,11,12-tetraphenylnaphthacene multiple quantum wells

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Abstract
Organic light-emitting diodes (OLEDs) with multiple-quantum-well (MQW) structures, which consist of N, N ′ -bis-(1-naphthyl)-N, N ′ -diphenyl-1, 1 ′ biphenyl 4, 4 ′ -diamine and 5,6,11,12-tetraphenylnaphthacene (rubrene), and tris(8-hydroxyquinoline) aluminum ( Alq 3 ) as the electron transporting material, have been fabricated. The results demonstrate that the MQW structure can sharply increase the performance of OLEDs. The diode with a MQW number of 4 exhibits efficiency up to 8.1 cd/A, which is four times that of the conventional diodes without the MQW structure. It is also interesting to find that the light emission from Alq 3 and rubrene can be obtained together and the electroluminescent spectrum, which is independent of the driving voltage, varies with the well number. For the device with a well number of 6, pure rubrene light emission is obtained. Our work demonstrates that the organic MQW structure not only can efficiently control the carrier transporting, thus conducive to achieve an electron–hole balance, but also help to adjust the emitting zone in the devices, then providing an option to obtain different emission colors.