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Charge transport in disordered organic semiconducting dendrimers studied by space-charge-limited transient currents

Marek Zdzislaw Szymanski 1, 2
1 LEMOH - Laboratoire d'Electronique Moléculaire Organique et Hybride
SYMMES - SYstèmes Moléculaires et nanoMatériaux pour l’Energie et la Santé : DRF/INAC/SYMMES
Abstract : The thesis concerns space-charge-limited transient current measurements in thin (le500 nm) organic films. Such films find important applications in organic electronics, where they are referred to as organic semiconductor layers. Electrical transport in such films depends on bulk charge carrier transport and trapping, as well efficiency of charge carrier injection from electrodes. These, are all in turn depend on disorder inherent to organic materials. The transient measurement approach is very attractive, as it can, in principle, deliver information on all these aspects in one single measurement. In the thesis, three main contributions are presented. 1) A transimpedance amplifier based setup for space-charge-limited current transient measurement is validated. This type of setup is superior to the widely used bridge circuit, notably because of better current sensitivity, bandwidth, no need for bridge symmetry and no need for per sample adjustment. It is demonstrated that initial displacement current spike, which saturates the amplifier at the beginning of measurement, does not introduce error in the measurement of mobility. 2) A dendrimer molecule has been investigated. Experimental current responses are shown to be in agreement with the drift-diffusion model. However, obtaining agreement requires well defined initial conditions in experiment as well as in simulation, and also complete theoretical model of the sample. In the case of dendrimer, this model had to take into account both contact barrier and trapping effects. Furthermore, better agreement was obtained when taking disorder effects into account. 3) The impossibility of obtaining any agreement without complete physical model of the sample indicates that trapping, contact barrier and mobility parameters could be fitted without ambiguity. Therefore, complete electrical characterization consistent with simulation can be obtained using the transient technique. The results obtained further increase well known usefulness of transient space-charge-limited current characterization of thin organic films.
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Marek Zdzislaw Szymanski. Charge transport in disordered organic semiconducting dendrimers studied by space-charge-limited transient currents. Condensed Matter [cond-mat]. Université de Grenoble, 2012. English. ⟨NNT : 2012GRENY065⟩. ⟨tel-01429670⟩

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