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Title: Analyzing degradation effects of organic light-emitting diodes via transient optical and electrical measurements

Although the long-term stability of organic light-emitting diodes (OLEDs) under electrical operation made significant progress in recent years, the fundamental underlying mechanisms of the efficiency decrease during operation are not well understood. Hence, we present a comprehensive degradation study of an OLED structure comprising the well-known green phosphorescent emitter Ir(ppy){sub 3}. We use transient methods to analyze both electrical and optical changes during an accelerated aging protocol. Combining the results of displacement current measurements with time-resolved investigation of the excited states lifetimes of the emitter allows for a correlation of electrical (e.g., increase of the driving voltage due to trap formation) and optical (e.g., decrease of light-output) changes induced by degradation. Therewith, it is possible to identify two mechanisms resulting in the drop of the luminance: a decrease of the radiative quantum efficiency of the emitting system due to triplet-polaron-quenching at trapped charge carriers and a modified charge carrier injection and transport, as well as trap-assisted non-radiative recombination resulting in a deterioration of the charge carrier balance of the device.
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Institute of Physics, University of Augsburg, Augsburg (Germany)
  2. Department of Electronics and Bioinformatics, School of Science and Technology, Meiji University, Kawasaki (Japan)
  3. (Japan)
  4. Center of Frontier Science, Chiba University, Chiba (Japan)
Publication Date:
OSTI Identifier:
22412897
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 21; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CHARGE CARRIERS; CORRELATIONS; ELECTRIC POTENTIAL; EXCITED STATES; LIFETIME; LIGHT EMITTING DIODES; OPERATION; QUANTUM EFFICIENCY; QUENCHING; RECOMBINATION; TIME RESOLUTION; TRANSIENTS; TRAPPING; TRAPS; TRIPLETS; VISIBLE RADIATION