Efficient Deep Blue Organic Light-Emitting Diodes Based on Wide Band Gap 4-Hydroxy-8-Methyl- 1.5-Naphthyridine Aluminum Chelate as Emitting and Electron Transporting Layer

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.