Energy alignment and trap states in dye-doped tris-8-(hydroxyquinoline) aluminum light-emitting devices

Eric W. Forsythe; David C. Morton; Quoc Toan Le; Li Yan; F. Nuesch; Ching W. Tang; Yongli Gao

doi:10.1117/12.348397

18 May 1999 Energy alignment and trap states in dye-doped tris-8-(hydroxyquinoline) aluminum light-emitting devices

Eric W. Forsythe, David C. Morton, Quoc Toan Le, Li Yan, F. Nuesch, Ching W. Tang, Yongli Gao

Author Affiliations +

Proceedings Volume 3623, Organic Photonic Materials and Devices; (1999) https://doi.org/10.1117/12.348397
Event: Optoelectronics '99 - Integrated Optoelectronic Devices, 1999, San Jose, CA, United States

Abstract

Thermally stimulated luminescence has used to directly measure the trap states in intrinsic Alq₃ and Alq₃ doped with coumarin 6. For Alq₃ doped with coumarin 6, we observe an increase in the trap energy from 0.25eV for undoped Alq₃ to 0.32eV for doping concentrations as high as 2 percent. The origin of these trap states may be related to the relative energy level alignment between the Alq₃ host and coumarin dopant. Using UV photoemission spectroscopy, we have measured the solid state energy alignment of the highest occupied molecular orbitals between Alq₃ and coumarin 6. Finally, we report I-V curves for single layer devices as a function of doping with Al/LiF top and bottom contacts. The charge transport shows the trap states induced in the Alq₃ films due to the presence of the coumarin 6 molecules decrease the carrier mobility and increase the energetic disorder. These results can be directly observed from the measured I-V curves.

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Eric W. Forsythe, David C. Morton, Quoc Toan Le, Li Yan, F. Nuesch, Ching W. Tang, and Yongli Gao "Energy alignment and trap states in dye-doped tris-8-(hydroxyquinoline) aluminum light-emitting devices", Proc. SPIE 3623, Organic Photonic Materials and Devices, (18 May 1999); https://doi.org/10.1117/12.348397

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