Electrically detected magnetic resonance of organic and polymeric light emitting diodes

We have used electrically detected magnetic resonance (EDMR) to study the spin dependent processes on the operation of diodes based on poly(2-metoxy-5-(2'-etil-hexiloxy)-1,4-phenylene vinylene) (MEH-PPV) and on tris-8-hydroxyquinoline-aluminum (Alq3). In MEH-PPV based diodes, the EDMR signal is found to be composed of two lines, a Lorentzian with ΔHpp=5 G and a Gaussian with ΔHpp=24 G. The g-factor of both components is about 2.0022. The signal is quenching, typically 10-5 in amplitude, and is assigned to the spin-dependent fusion of two like-charged polarons to spinless bipolarons. The signal dependence on temperature and on injected current is investigated. For bipolar Alq3 diodes the EDMR signal can be decomposed in at least two Gaussians, depending on the bias and temperature of measurements. The two components are characterized by g-factors close to 2.004 and a peak-to-peak linewidth (ΔHpp) of 12 and 24 G, respectively. The broad line is attributed to the resonance in Alq anions, while the 12 G is attributed to cationic states