Carrier transport in thin films of organic electroluminescent materials

Using the time of flight technique, the carrier mobilities of organic electroluminescent materials, N,N′-bis-(1-naphhyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), tris(8-hydroxyquinoline) aluminum (Alq), and Tb(AcA)3phen (AcA: acetylacetone, phen: phenanthroline) (Tb-complex), were measured. At room temperature and an electric field of 2.3×105 V/cm, the effective mobility of holes in NPB, electrons in Alq and Tb-complex were (8.8±2)×10−4, (6.7±2)×10−5 and (3±2)×10−4 cm2 V−1 S−1, respectively. The hole mobility of NPB shows an exponential root field dependence as commonly seen in some organic materials.