Improving the efficiency and stability of organic light-emitting devices using mixed emitting layers

Zoran D. Popovic; Hany Aziz; Carl P. Tripp; Nan-Xing Hu; Ah-Mee Hor; Gu Xu

doi:10.1117/12.332630

16 December 1998 Improving the efficiency and stability of organic light-emitting devices using mixed emitting layers

Zoran D. Popovic, Hany Aziz, Carl P. Tripp, Nan-Xing Hu, Ah-Mee Hor, Gu Xu

Proceedings Volume 3476, Organic Light-Emitting Materials and Devices II; (1998) https://doi.org/10.1117/12.332630
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1998, San Diego, CA, United States

Abstract

We studied an organic light emitting device (OLED) involving electroluminescence from a mixed layer consisting of a hole transport material (HTM) and an emitting electron transport material (ETM) and including thin electron and hole injection contacts. A naphthyl-substituted benzidine derivative (NPB) and tris (8-hydroxyquinoline) aluminum (ALQ₃) are used as the HTM and the emitting ETM, respectively. Following a control-experiment approach, the efficiency and the operational lifetime of OLEDs adopting the new structure are compared to those of conventional bilayer devices made of the same materials and fabricated under the same conditions. Efficiency is calculated from the luminance-current density-voltage characteristics. Lifetime tests are carried at constant current density in dry air. Photoluminescence is used to detect changes in the quantum efficiency of the ALQ₃ on mixing with the HTL. Compared to a conventional bilayer device, the new device structure leads to approximately 50 percent higher efficiency and an order of magnitude increase in the operational lifetime. The higher efficiency is attributed to (i) reduced leakage of charge carrier to the electrodes, (ii) exciton confinement away from the metal cathode, and (iii) higher quantum efficiency of the emitting electron transport material due to mixing with the hole transport material. Possible reasons for the higher stability are also discussed.

Citation Download Citation

Zoran D. Popovic, Hany Aziz, Carl P. Tripp, Nan-Xing Hu, Ah-Mee Hor, and Gu Xu "Improving the efficiency and stability of organic light-emitting devices using mixed emitting layers", Proc. SPIE 3476, Organic Light-Emitting Materials and Devices II, (16 December 1998); https://doi.org/10.1117/12.332630

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