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HL: Fachverband Halbleiterphysik
HL 56: Organic Electronics and Photovoltaics: Electronic Properties II (jointly with DS, CPP, O)
HL 56.4: Vortrag
Mittwoch, 28. März 2012, 12:15–12:30, H 2032
Design rules for charge-transport efficient host materials for OLEDs — •Falk May1, Björn Baumeier1, Denis Andrienko1, and Christian Lennartz2 — 1Max Planck Institute for Polymer Research, Mainz, Germany — 2BASF SE, GVC/E - B009, Ludwigshafen, Germany
The use of blue phosphorescent emitters in organic light emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a pi-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous bis(triphenylsilyl)dibenzofuran, a typical deep-blue OLED host material, and show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings without inducing significant variations of local dipole moments, which otherwise would lead to additional energetic disorder, site energy correlations, and undesirable current filaments. By linking electronic structure, molecular packing, and mobility we provide a pathway to the rational design of hosts with high charge mobilities.