Berlin 2015 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 14: Organic photovoltaics and electronics - mostly cell design (with DS)
HL 14.4: Vortrag
Montag, 16. März 2015, 15:45–16:00, EW 202
Understanding thickness dependent onset voltage shifts in OLED IV-characteristics I: Internal electric field distributions — •Maybritt Kühn1,2, Eric Mankel1,2, Christof Pflumm3, Thomas Mayer1,2, and Wolfram Jaegermann1,2 — 1Technische Universität Darmstadt, Institute of Materials Science — 2InnovationLab GmbH, Heidelberg — 3Merck KGaA, Darmstadt
Steady-state IV measurements are used as important characterization method for organic light-emitting diodes (OLEDs). Surprisingly, in some OLED devices the current onset voltage increases significantly depending on the emission layer (EML) thickness by approximately 2.7 V/100nm. For experimental investigations of this phenomenon we focus on a three layer device architecture, using two different isomers synthesized by Merck as transport material in the EML - one showing changes in onset voltage (EML-A) the other (EML-B) not. To investigate the onset voltage shift the mean electric fields in the respective layers are determined in dependence of the current density. Therefore, systematic layer thickness variations of the injection layers and both EML materials were performed and the respective IV characteristics were evaluated. In contrast to EML-B a large field enhancement in EML-A can be identified induced by discontinuities of the electric field at the EML-A contacts. Using a simple drift model both EML field distributions and the discontinuities can be described quantitatively. Furthermore they can be allocated to a lack of bulk charge carriers, probably induced by an energetic interface barrier or trapped interface charges. A further consideration of the topic will be done in part 2.