AN ORGANIC ELECTROLUMINESCENT DEVICE WITH A MOLECULARLY DOPED POLYMERHOLE TRANSPORT LAYER

Electroluminescent (EL) devices have been fabricated using four differ ent polymers with different glass transition temperatures (T-g) disper sed with ylphenyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (TPD) as a hole transport layer and tris(8-hydroxyquinoline) aluminum (Alq(3)) a s an emitting layer It was found that the higher the T of the polymer, the longer the lifetime of the device. From observations of TPD-doped polymer films with optical microscope and atomic force microscope, di spersing TPD in the polymers was found to suppress the crystallization that causes the roughness of the film surface. It was also observed t hat the higher the T of the host polymers, the more difficult TPD crys tallization was. The property of the EL device with polyethersulfone ( PES) dispersed with TPD was also investigated. The lifetime of EL devi ce with the TPD doped PES film was improved more than five times at a current density below 10 mA/cm(2) compared with the device with a conv entional TPD hole transport layer. (C) 1997 by John Wiley & Sans, Ltd.