Electroluminescence- and electrically-detected magnetic resonance studies of spin 1/2 polaron and singlet exciton dynamics in multilayer small molecular organic light-emitting devices

The electroluminescence (EL)- and electrically-detected magnetic resonance (ELDMR and EDMR, respectively) of tris-(S-hydroxyquinoline) Al (Alq(3))]/[buffer]/Al-based organic light-emitting devices (OLEDs) are described. Positive spin 1/2 ELDMR and EDMR observed at T < 60 K are similar to the typical photoluminescence-detected magnetic resonance of pi-conjugated polymers, and consequently attributed to enhanced polaron recombination and consequent reduction of singlet exciton quenching by trapped and free polarons. A negative spin 1/2 EL- and current-quenching (negative) resonance is observed at T greater than or equal to 60 K. Its amplitude increases with T, and it is much stronger in devices with an AlOx buffer layer than in those with a CsF buffer. Its behavior is consistent with magnetic resonance enhancement of the spin-dependent formation of dianions at the organic/cathode interface.