Spin dependent transport and recombination in organic light-emitting diodes

Electrically detected magnetic resonance (EDMR) was used to study a series of multilayer organic devices based on aluminum (III) 8-hydroxyquinoline (Alq3). These devices were designed to identify the microscopic origin of different spin dependent process, i.e., hopping and exciton formation. For electroluminescent diode the EDMR signal can be decomposed in at least two Gaussian components with peak-to-peak linewidth (ΔHPP) of 1.6 mT and another with 2.0 mT to 3.4 mT. These components are dependent on the applied bias or current used during EDMR measurements. The narrower line was attributed to the exciton precursor cations, while the broad one to the anions. These attributions are supported by the investigation of unipolar diodes, where hopping process related to dication and dianion formation were observed. In this work it is found that the probability of singlet exciton formation during electrolumincscency is smaller than 25%