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We have developed a high efficiency and deep blue organic light-emitting diodes (OLEDs) incorporating a 4-hydroxy-8-methyl-1,5-naphthyridine aluminum chelate (AlmND3) as the emitter and electron transporting layer (ETL). The blue AlmND3 emitter, with an electron withdrawing group added to the well-known green fluorophore tris(8-hydroxyquinolinato)aluminum (Alq3) , exhibited ambipolar charge transport as well as high electron and hole mobilities on the order of 10-5 cm2/V·s, as deduced time-of-flight measurements. The magnitude of the electron mobility was 10 times greater than that of the widely used Alq3 ETL, resulting in efficient charge balance in the AlmND3 device. Based on a simple configuration of double heterojunction device, a blue device with the maximum external quantum efficiency of 1.58% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.16, 0.08) was achieved at a brightness of 200 cd/m2 . This study has revealed the fundamental nature of charge transport in hydroxynaphthyridine metal chelate and shed a new light on the design of high performance blue OLEDs.
Date of Publication: Aug. 2011