Dresden 2009 – scientific programme

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DS: Fachverband Dünne Schichten

DS 21: Organic Thin Films I

DS 21.4: Talk

Wednesday, March 25, 2009, 10:15–10:30, GER 38

Intermolecular bipolaronic nature of electroluminescence in Organic Light Emitting Field Effect Transistor
— •Eugenio Lunedei, Paolo Annibale, Fabio Biscarini, and Carlo Taliani — Institute for the Study of Nanostructured Materials ISMN-CNR, Bologna, Italy

Spectrally resolved light emission from an operating α-Sexithienyl (α-T6) thin film Field Effect Transistor (FET) was measured and its electroluminescence properties put in relation to the ns-time resolved fluorescence. Light emission, following charge carrier injection, matches closely the delayed (Δt>5ns) photoluminescence, but not the prompt one and exhibits a non-excitonic character. Injection of electrons in the FET channel takes place via high-electric field induced tunnelling through the drain electrode contact barrier. The spatial sites of radiative recombination inside FET channel are correlated to regions located at interfacial areas between layered domains where inter-molecular bipolarons (π-dimers) are effectively formed. The formation of such stacks of radical cations gives rise to new allowed optical transitions, with a spectroscopic fingerprint markedly different from that of the bulk crystalline states. Radiative emission from π-dimer states appears to be the fundamental mechanism involved in light emission from electro-optical organic devices based on well ordered layered thin films.