Berlin 2005 – wissenschaftliches Programm
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SYOO: Organic Optoelectronics and Photonics
SYOO 6: Poster
SYOO 6.15: Poster
Montag, 7. März 2005, 18:00–20:00, Poster TU A
Spin selective electroluminescence from conjugated polymers in strong magnetic fields: implications for singlet-triplet ratios — •M. Reufer1, M. Walter1, J. M. Lupton1, J. Feldmann1, A. B. Hummel2, J. Kolb2, H. Roskos2, and U. Scherf3 — 1Photonics and Optoelectronics Group, Department of Physics and CeNS, Ludwig-Maximilians-Universität München — 2Physikalisches Institut, Johann Wolfgang Goethe Universität Frankfurt am Main — 3Fachbereich Chemie, Universität Wuppertal, Gauss-Str. 20, 42097 Wuppertal
Electroluminescence in conjugated polymers has attracted wide interest for applications in display devices. The efficiency of these materials is strongly affected by the spin statistics governing charge carrier recombination. We recently developed a technique to allow triplet excitons to be visualised directly by enabling strong, spatially localised spin-orbit coupling, which permits room temperature phosphorescence. Using this phosphorescence signature, we can directly probe the singlet to triplet ratio in organic light emitting diodes under strong magnetic fields. We observe a substantial negative magnetoresistance of up to 20 % at 8 T, while the singlet to triplet ratio of the emission is only weakly affected by the magnetic field and saturates above 1 T. This demonstrates that the magnetic field is not able to hybridise the two spin states or lead to spin alignment in the recombinant state, thus implying a substantial exchange splitting within the exciton precursor. In the absence of a strong spin mixing channel, device efficiencies above the spin statistical limit of 25 % appear improbable.