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Modification of Exciton Lifetime by the Metal Cathode in Phosphorescent OLEDs, and Implications on Device Efficiency and Efficiency Roll-off Behavior

Authors

  • Dandan Song,

    1. Department of Electrical and Computer Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada
    2. Key Laboratory of Luminescence and Optical Information, (Beijing Jiaotong University), Ministry of Education, Institute of Optoelectronics Technology, Beijing Jiaotong University, Beijing, 100044, China
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  • Suling Zhao,

    1. Key Laboratory of Luminescence and Optical Information, (Beijing Jiaotong University), Ministry of Education, Institute of Optoelectronics Technology, Beijing Jiaotong University, Beijing, 100044, China
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  • Hany Aziz

    Corresponding author
    1. Department of Electrical and Computer Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada
    • Department of Electrical and Computer Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada.
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Abstract

Time resolved photoluminescence and electroluminescence measurements are used to study changes in the emission characteristics of materials typically used in phosphorescent organic light emitting devices (PhOLEDs). Studies on archetypical PhOLEDs with phosphorescent material, fac-tris(2-phenylpyridine) iridium (Ir(ppy)3), show that the lifetime of triplet exciton is modified when in close proximity to a metal layer. Interactions with a metal layer ∼30–100 nm away, as is typically the case in PhOLEDs, result in an increase in the spontaneous emission decay rate of triplet excitons, and causes the exciton lifetime to become shorter as the distance between the phosphorescent material and the metal becomes smaller. The phenomenon, possibly the result of the confined radiation field by the metal, affects device efficiency and efficiency roll-off behavior. The results shed the light on phenomena affecting the efficiency behavior of PhOLEDs, and provide new insights for device design that can help enhance efficiency performance.

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