Impact of temperature on the efficiency of organic light emitting diodes

Organic light emitting devices (OLEDs) are known to heat up when driven at high brightness levels required for lighting and bright display applications. This so called Joule heating can in the extreme case lead to a catastrophic failure (breakdown) of the device. In this work, we compare the effect of Joule heated and externally heated OLEDs by their electrical and optical response. A reduction in resistance is observed at elevated temperatures, both, for Joule heating, and for externally heated samples driven at low current density. In both cases, we attribute the change in resistance to a higher mobility of charge carriers at the elevated temperatures. Additionally, we observe a quenching of the emission efficiency in heated single layers as well as in OLEDs, treated with an external heat source as well as on Joule heated samples.