Improvement of efficiency and stability utilizing a wide band gap material as the host for red organic light-emitting diodes

摘要

We present red organic light-emitting diodes (OLEDs) with high efficiency and stability based on a wide band gap host material 9,10-di (2-naphthyl) anthracene (ADN). In these diodes, N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4' diamine(NPB) and tris-(8-ydroxy-quinoline) aluminium (Alq) are used as hole and electron transport layers, respectively. 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl) quinolizino-[9,9a,1gh] coumarin (C545T) and 4-(dicyano-methylene)-2-t -butyl-6-(1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran (DCJTB) are co-doped into the ADN emitting layer. Utilizing the two-step energy transfer from ADN to C545T and then from C545T to DCJTB, we achieved pure red organic light-emitting devices, which showed improved optical and electrical characteristics. Compared with devices where the emitting layer is made of Alq and DCJTB, the emission efficiency and stability of the ADN-based devices are greatly improved and the turn-on voltage is also decreased. The co-doping technique provides a promising way of utilizing wide band gap materials as the host to make red OLEDs, which will be useful in improving the electroluminesent performance of devices and simplifying the process of fabricating full colour OLEDs.