Highly stable organic light-emitting devices with a uniformly mixed hole transport layer

Highly stable organic light-emitting devices were made by using a uniformly mixed hole transport layer (UM-HTL) composed of a mixture of 2-methyl-9,10-di(2-naphthyl)anthracene (MADN) and N,N-bis(1-naphthyl)-N,N-'-diphenyl,1,1(')-biphenyl-4,4(')-diamine (NPB) in a 3:7 (MADN:NPB) ratio. The lifetime of 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]-pyrano[6,7,8-ij]quinolizin-11-one doped green device with UM-HTL can be greatly improved to 2.7 times longer than that of the conventional device (NPB based HTL) without impacting on its driving voltage and emissive color significantly. This improvement in stability can be attributed to the fact that the unstable [Alq(3)(+)] species formed by electro-oxidation have been effectively suppressed.