Berlin 2005 – wissenschaftliches Programm
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SYOO: Organic Optoelectronics and Photonics
SYOO 6: Poster
SYOO 6.58: Poster
Montag, 7. März 2005, 18:00–20:00, Poster TU A
Experimental study of charge carrier trapping in PVK/TPD blends — •L. Kulikovsky1, F. Jaiser1, D. Neher1, S. Koeber2 und K. Meerholz2 — 1University of Potsdam, Am Neuen Palais 10, D-14469 Potsdam — 2University of Köln, Luxemburgerstr.116, D-50939, Köln
PVK is an important host material for molecular doped phosphorescent light-emitting diodes. However, little is known about the charge transport in this material. Here, we report on the experimental study of charge carrier trapping in PVK based materials doped with TPD. Blends with different low concentrations of TPD have been investigated. Using pulsed irradiation, regimes in which the photocurrent dynamic is dominated either by photogeneration, recombination or trapping can be distinguished. The measurements are interpreted by use of an adopted Schildkraut model (1). It is shown that on a short time scale the current dynamics is determined by photogeneration and trapping in shallow PVK traps and TPD traps. The current decrease at the pulse end is limited by recombination and later by detrapping. Surprisingly, trapping by the TPD traps is significant already in the very early stage of the transient carrier dynamics, indicating the absence of an energetic barrier for the capture of charges by the TPD molecules. By varying the illumination conditions, we have determined all trapping parameters for PVK and TPD.
(1) L. Kulikovsky et.al, Photocurrent dynamics in a poly(phenylene vinylene)-based photorefractive composite, PRB 69 (2004) 125216-1-11