Blue light-emitting devices from new conjugated poly(N-substituted-2,7-carbazole) derivatives

Light-emitting diodes derived from a new class of conjugated polymers, well-defined poly(N-substituted-2,7-carbazole) derivatives, are reported. Excimer-free electroluminescence in the blue range (424–432 nm) was observed. Good luminance (372 cd/m2 at 10 V) was reached in a device containing poly[N-(2-ethylhexyl)-2,7-carbazole] as the emitting material with indium tin oxide and Al as the electrodes. This high luminance value was achieved by adding ultrathin LiF layers next to the electrodes, and by using hole and electron transport molecules such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine and 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole.