The electroluminescence (EL)-detected magnetic resonance (ELDMR) of abrupt junction and mixed layer N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB) / tris(quinolinolate) Al (Alq₃) OLEDs was measured at room temperature and at 20K, at current densities 0.83 ≤ J ≤ 83 mA/cm². The abrupt junction and mixed layer devices were indium tin oxide (ITO) / 5 nm copper phthalocyanine (CuPc) / 50 nm NPB / 40 nm Alq₃ / 1 nm CsF / Al, and ITO / 5 nm CuPc / 40 nm NPB / 20 nm 1:1 NPB:Alq₃ / 30 nm Alq3 / 1 nm CsF / Al, respectively. As expected, the devices exhibited a positive (EL-enhancing) spin 1/2 resonance at T = 20 K and a negative (ELquenching) spin 1/2 resonance at room temperature. It was found that the positive and negative resonance was stronger in the abrupt junction and in the mixed layer devices, respectively. The results are discussed in relation to the mechanisms responsible for these resonances, namely reduced quenching of singlet excitons by polarons and triplet excitons, and enhanced quenching by trions, respectively.

Date Published: 27 August 2009
PDF: 7 pages
Proc. SPIE 7415, Organic Light Emitting Materials and Devices XIII, 741522 (27 August 2009); doi: 10.1117/12.828559

Published in SPIE Proceedings Vol. 7415:
Organic Light Emitting Materials and Devices XIII
Franky So; Chihaya Adachi, Editor(s)