Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 113: Organic Electronics and Photovoltaics: Devices (jointly with CPP, HL)

TT 113.5: Talk

Friday, March 20, 2015, 11:00–11:15, C 130

Combined electrical and optical analysis of the efficiency roll-off in phosphorescent organic light-emitting diodes — Sebastian Wehrmeister¹, •Tobias D. Schmidt¹, Lars Jäger¹, Thomas Wehlus², Andreas F. Rausch², Thilo C. G. Reusch², and Wolfgang Brütting¹ — ¹Institute of Physics, University of Augsburg, 86153 Augsburg — ²OSRAM OLED GmbH, 93049 Regensburg

We present a method for a comprehensive analysis of the efficiency roll-off with current density in phosphorescent organic light-emitting diodes (OLEDs). By combining electrical and optical excitation in time-resolved spectroscopic experiments we are able to measure the excited states lifetime for different driving conditions. It is thus possible to correlate changes of the triplet lifetime with a decrease of the radiative quantum efficiency of the emitting system due to exciton quenching processes. As compared to the conventional analysis of the measured external quantum efficiency (EQE) in dependence of the applied current density, the lifetime analysis is not affected by changes of the charge carrier balance with current, which can have a significant impact on the interpretation of the results. With this method we show that triplet-polaron quenching is the dominating quenching mechanism for the red phosphorescent emitter Ir(MDQ)₂(acac) doped into an α-NPD matrix up to current densities of 100 mA/cm².