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 stu...

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Bibliographic Details
Published in:Journal of applied physics 2015-06, Vol.117 (21)
Main Authors: Schmidt, Tobias D., Jäger, Lars, Noguchi, Yutaka, Ishii, Hisao, Brütting, Wolfgang
Format: Article
Language:English
Subjects:
Applied physics
Carrier injection
CHARGE CARRIERS
Charge injection
Charge transport
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
CORRELATIONS
Current carriers
Degradation
ELECTRIC POTENTIAL
Electrical measurement
Emitters
EXCITED STATES
Infrared radiation
LIFETIME
LIGHT EMITTING DIODES
OPERATION
Organic light emitting diodes
Phosphorescence
QUANTUM EFFICIENCY
QUENCHING
Radiative recombination
RECOMBINATION
TIME RESOLUTION
TRANSIENTS
Trapped charge
TRAPPING
TRAPS
TRIPLETS
VISIBLE RADIATION
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Summary: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)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.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4921829