Influence of the Emission Site on the Running Durability of Organic Electroluminescent Devices

The influence of the emission site on the running durability of organic electroluminescent devices was examined. The fundamental device structure of MgIn/BeBq 2 /TPD/MTDATA/ITO ( BeBq 2 =bis(10-hydroxybenzo[h]quinolinato)beryllium, TPD=N,N ′ -diphenyl-N,N ′ -(3-methylphenyl)-1,1 ′ -biphenyl-4,4 ′ -diamine, MTDATA=4,4 ′ ,4 ′′ -tris(3-methylphenylphenylamino)triphenylamine) was employed. BeBq 2 has the electron transport property, and TPD and MTDATA have the hole transport property. The emitting material [rubrene] was doped in the TPD layer of device A and in the BeBq 2 layer of device B. Both devices A and B showed high luminance of more than 10000 cd/m 2 . However, the running lifetimes of devices A and B, in which the initial luminance of 500 cd/m 2 was reduced to one-half under a constant driving current, were 3554 h and 110 h, respectively. It was thus found that the emission site exerts an influence on the running durability.