Changes in electronic structure of 8-hydroxyquinoline aluminum/Al interface by insertion of thin electron injection layers

Tomohiko Mori; Motofumi Suzuki; Shizuo Tokito; Yasunori Taga

doi:10.1117/12.372732

17 December 1999 Changes in electronic structure of 8-hydroxyquinoline aluminum/Al interface by insertion of thin electron injection layers

Tomohiko Mori, Motofumi Suzuki, Shizuo Tokito, Yasunori Taga

Author Affiliations +

Proceedings Volume 3797, Organic Light-Emitting Materials and Devices III; (1999) https://doi.org/10.1117/12.372732
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

Abstract

The electronic structures of 8-hydroxyquinoline aluminum (Alq₃)/electron injection layer/Al interfaces, used in organic electroluminescent devices, were measured by ultraviolet photoelectron spectroscopy (UPS). LiF and alkaline earth fluorides (CaF₂, SrF₂ and BaF₂) were used as an electron injection layer. Shifts of the highest occupied molecular orbital (HOMO) level and the vacuum level of Alq₃ layer due to the insertion of the fluorides were observed. These shifts indicate that the alkaline earth fluoride layers as well as the LiF layer at the Alq₃/Al interface reduce the barrier height for electron injection from the Al to Alq₃. The reduction of the barrier height is consistent with the driving voltage in the organic EL device in which these fluorides are used as the electron injection layers. We believe that lowering in the driving voltage in organic EL devices with the thin insulator layers, such as LiF and alkaline earth fluorides, is attributable to the reduction of the barrier height.

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Tomohiko Mori, Motofumi Suzuki, Shizuo Tokito, and Yasunori Taga "Changes in electronic structure of 8-hydroxyquinoline aluminum/Al interface by insertion of thin electron injection layers", Proc. SPIE 3797, Organic Light-Emitting Materials and Devices III, (17 December 1999); https://doi.org/10.1117/12.372732

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