Dresden 2014 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 85: Organic light emission
HL 85.3: Talk
Thursday, April 3, 2014, 10:00–10:15, POT 006
OLED - a light emitting thermistor? — •Axel Fischer1, Thomas Koprucki2, Klaus Gärtner2, Daniel Kasemann1, Björn Lüssem1, Karl Leo1, Annegret Glitzky2, and Reinhard Scholz1 — 1Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden — 2Weierstraß-Institut (WIAS), Mohrenstraße 39, 10117 Berlin
For lighting applications, OLEDs need much higher brightness than for displays, causing substantial self-heating. Recently, it has been shown that the temperature-activated transport in organic semiconductors favors thermal runaway and the occurrence of negative differential resistance (NDR) [1]. Here, we show by experiment and simulation that OLEDs produce such a strong electrothermal feedback that S-shaped NDR occurs similar to a thermistor device [2] but with the difference that the OLED comes along with a laterally extended crossbar architecture. Self-heating combined with the sheet resistance of the transparent electrode produces regions with declining voltage across the organic layers under rising voltage applied to the contacts. Interestingly, a part of these regions shows decreasing currents. Then, the current density becomes extremely inhomogeneous because regions with increasing and decreasing currents can occur at the same time, leading to strong local variations in luminance. [1] A. Fischer, P. Pahner, B. Lüssem, K. Leo, R. Scholz, T. Koprucki, K. Gärtner, and A. Glitzky, Phys. Rev. Lett. 110, 126601 (2013) [2] A. Fischer, T. Koprucki, K. Gärtner, M. L. Tietze, J. Brückner, B. Lüssem, K. Leo, A. Glitzky, and R. Scholz, subm. to Adv. Funct. Mater. (2013)