Investigations of electron-injection mechanisms and interfacial chemical reactions of Bphen doped with rubidium carbonate in OLEDs

Mei-Hsin Chen; Dong-Seok Leem; C. T. Lin; G. R. Lee; Tun-Wen Pi; Jang-Joo Kim; Chih-I Wu

doi:10.1117/12.794142

2 September 2008 Investigations of electron-injection mechanisms and interfacial chemical reactions of Bphen doped with rubidium carbonate in OLEDs

Mei-Hsin Chen, Dong-Seok Leem, C. T. Lin, G. R. Lee, Tun-Wen Pi, Jang-Joo Kim, Chih-I Wu

Author Affiliations +

Proceedings Volume 7051, Organic Light Emitting Materials and Devices XII; 70511C (2008) https://doi.org/10.1117/12.794142
Event: Photonic Devices + Applications, 2008, San Diego, California, United States

Abstract

The effectiveness of carrier injection in electron transport layers has been investigated for high efficiency organic light emitting devices. Via ultraviolet and x-ray photoemission spectroscopy (UPS and XPS), the carrier band structures, interfacial interactions and electron-injection mechanisms are discussed. Acting as a good hole blocking layer with higher mobility for electrons, 4,7-diphenyl-1, 10-phenanthroline (Bphen) was chosen to be the electron transport layer. The performance of device used Rb₂CO₃ doped into Bphen is obviously better than the device even used LiF with aluminum as cathode. According to the UPS spectra, the Fermi level of Bphen after doped with the ratio of 2% and 8% rubidium carbonate (Rb₂CO₃) shifts toward the lowest unoccupied molecular orbital as a result of charge transfer from rubidium atom to Bphen, showing that electron-injection ability would be improved based on strong n-type doping effect. Moreover, when aluminum is deposited as a thin layer on the surface of Bphen doped with Rb₂CO₃, the peak around 5 eV, which is attributed to the delocalized Pi-electrons decreases as gap states appear around 2.8 eV at the top of the highest occupied molecular orbital. There are changes in the binding energy of core levels of rubidium, nitrogen and aluminum, which indicates a negative charge transfer to Bphen at the interface that could have the reduction of electroninjection barrier height. Thus, the interfacial chemical reaction leads to the excellent electron injection ability could be demonstrated.

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Mei-Hsin Chen, Dong-Seok Leem, C. T. Lin, G. R. Lee, Tun-Wen Pi, Jang-Joo Kim, and Chih-I Wu "Investigations of electron-injection mechanisms and interfacial chemical reactions of Bphen doped with rubidium carbonate in OLEDs", Proc. SPIE 7051, Organic Light Emitting Materials and Devices XII, 70511C (2 September 2008); https://doi.org/10.1117/12.794142

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