Charge carriers and triplets in OLED devices studied by electrically detected electron paramagnetic resonance

Organic light-emitting diodes (OLEDs) were investigated by an electron paramagnetic resonance (EPR) technique that uses the effective device conductance as the detection channel. This technique enables us to identify and study charge carriers and triplet excitons with high sensitivity. By using a series of model devices, it was demonstrated that this type of spectroscopy provides information regarding triplet energy transfer and the location of the recombination zone. The fundamental understanding about the extent of the recombination zone in various OLED architectures helps in the design of devices with improved performance.