Regensburg 2016 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: Focus: Triplet States in Organic Optoelectronics I

CPP 32.8: Talk

Wednesday, March 9, 2016, 12:00–12:15, H37

Using deposition technique to control phosphorescent emitter orientation in doped organic films — •Thomas Lampe, Tobias D. Schmidt, and Wolfgang Brütting — Institute of Physics, University of Augsburg, 86135 Augsburg, Germany

Introducing an overall horizontal orientation of transition dipole moments of heteroleptic Ir-complexes is a promising concept to improve efficiencies of organic light-emitting diodes. To investigate the impact of deposition technique on molecular orientation, we prepared doped films of four different phosphorescent iridium complexes in various organic host materials both by thermal evaporation and by solution processing and compared the observed emitter orientation. All heteroleptic Ir-complexes show comparable horizontal alignment if fabricated from the gas phase, while isotropic orientation or even a slightly vertical trend is observed in the solution processed samples. These findings can be explained by the creation of an interface between vacuum and the aromatic host material during evaporation and the lack of this feature when processed from solution. The underlying mechanism of molecular orientation can then be explained by the interaction of aliphatic and aromatic parts of the Ir-complexes with this interface during deposition from the gas phase. The absence of horizontal orientation of the phosphors in layers deposited from liquid preparation techniques has important implications for solution processed OLEDs.