The Molecular Origin of Anisotropic Emission in an Organic Light-Emitting Diode

Abstract

Atomistic nonequilibrium molecular dynamics simulations have been used to model the induction of molecular orientation anisotropy within the emission layer of an organic light-emitting diode (OLED) formed by vapor deposition. Two emitter species were compared: racemic fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)) and trans-bis(2-phenylpyridine)(acetylacetonate)iridium(III) (Ir(ppy)(acac)). The simulations show that the molecular symmetry axes of both emitters preferentially align perpendicular to the surface during deposition. The molecular arrangement formed on deposition combined with consideration of the transition dipole moments provides insight into experimental reports that Ir(ppy) shows isotropic emission, while Ir(ppy)(acac) displays improved efficiency due to an apparent preferential alignment of the transition dipole vectors parallel to the substrate. The simulations indicate that this difference is not due to differences in the extent of emitter alignment, but rather differences in the direction of the transition dipoles within the two complexes.

New Mixed‐C^N Ligand Tris‐Cyclometalated IrIII Complexes for Highly‐Efficient Green Organic Light‐Emitting Diodes with Low Efficiency Roll‐Off

“…Speculative reasons for the enhanced PhOLED performance of complexes 3 and 4 compared to 2 and 5 are a favorable alignment of the transition dipoles of 3 and 4 , due to their mixed C ^ N ligand structure, and this could lead to enhanced outcoupling efficiencies compared to 2 and 5 which comprise three identical C ^ N ligands , . Also there may be favorable host‐guest supramolecular interactions in the emitting layers of D3 and D4 , again facilitated by the asymmetry of the complexes 3 and 4 …”

Systematic Control of the Orientation of Organic Phosphorescent Pt Complexes in Thin Films for Increased Optical Outcoupling

“…To date, studies on phosphorescent emitter orientation have largely focused on Ir complexes . While the common Ir(III) complexes used in organic light‐emitting diodes (OLEDs) have octahedral geometries, related Pt(II) complexes have square planar geometries.…”

Revealing the Interplay between Charge Transport, Luminescence Efficiency, and Morphology in Organic Light‐Emitting Diode Blends

“…In this manuscript, we use charge extraction experiments with a linearly increasing voltage based on a metal–insulator–semiconductor diode structure (MIS‐CELIV) to measure the hole mobility in blend films comprising Ir(ppy) 3 and TCTA across a range of Ir(ppy) 3 concentrations. The results of these experimental measurements are then related to atomic level morphologies generated using molecular dynamics simulations that mimic the evaporative formation of these blend films. The aim was to determine whether these transport measurements together with a range of other photophysical measurements were consistent with the simulated film morphologies.…”