Transport and recombination in organic light-emitting diodes studied by electrically detected magnetic resonance

We have used electrically detected magnetic resonance (EDMR) to study a series of multilayer organic devices based on aluminum (III) 8-hydroxyquinoline (Alq<sub>3</sub>). These devices were designed to identify the microscopic origin of different spin-dependent processes, i.e. hopping and exciton formation. The EDMR signal in organic light-emitting diodes (OLEDs) based on Alq<sub>3</sub> is only observed when the device is electroluminescent, and is assigned to spin-dependent exciton formation. It can be decomposed in at least two Gaussians: one with peak-to-peak line (&Delta;H<sub>pp</sub>) of 1.6 mT and another with &Delta;H<sub>pp</sub> of 2.0 to 3.4 mT, depending on bias and temperature. The g-factors of the two components are barely distinguishable and close to 2.003. The broad line is attributed to the resonance in Alq<sub>3</sub> anions. while the other line is attributed to cationic states. These attributions are supported by line shape and its electrical-field dependence of unipolar Alq<sub>3</sub>-based diodes, where hopping process related to dication and dianion formation is observed. In these unipolar devices, it is shown that the signal coming from spin-dependent hopping occurs close to organic semiconductor/metal interfaces. The sign of the magnetic-resonance-induced conductivity change is dominated by charge injection rather than charge mobility. Our results indicate that the probability of singlet exciton formation in our OLEDs is smaller than 25%

Published in:
European Physical Journal E, 18, 1, 21
EDP Sciences; Springer-Verlag
Departamento de Fisica e Matematica, FFCLRP-USP, Ribeirao Preto, Brazil
Copyright 2006, IEE
organic light-emitting diodes
electrically detected magnetic resonance
multilayer organic devices
aluminum 8-hydroxyquinoline
electroluminescent device
spin-dependent exciton formation
cationic states
dication formation
dianion formation
spin-dependent hopping
organic semiconductor-metal interfaces
charge injection
charge mobility
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 Record created 2007-04-03, last modified 2018-01-27

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