Aging induced traps in organic semiconductors

Trap states in organic single layer devices have been detected by the metho d of thermally stimulated currents (TSC). These devices have been exposed t o potentially harmful atmospheres of oxygen and humid nitrogen in order to investigate the influence of ambient atmosphere on the trap spectrum of mat erials used for organic light-emitting diodes. Discrete traps with activati on energies of 105 and 140 meV have been found in alpha -NPD (N,N ' -di(1-n aphthyl)-N,N ' -diphenylbenzidin). In 1-NaphDATA (4,4 ' ,4 " -Tris(N-2-naph thyl)-N-phenylaminotriphenylamin) discrete trap levels with activation ener gies of 100 and 235 meV are present. The exposure to humidity forms a deep hole trap of 0.5 eV in 1-NaphDATA, whereas in alpha -NPD no new trap was de tected. The influence of the so generated traps on the charge transport is demonstrated by I-V characteristics. (C) 2001 Elsevier Science B.V. All rig hts reserved.