Highly efficient single emitter white phosphorescent organic light-emitting diodes based on Pt(ii) emitters

Abstract

In this study, we fabricate highly efficient white platinum(II) emitters with high color rendering indices for phosphorescent, organic light-emitting diodes (PhOLEDs) using new tetradentate ligands prepared with difluoropyrido-pyridyl and meta-xylyl amine linkers. We study the effects of the meta-xylyl amine linker and side chains on material characteristics. The perpendicular geometry of the bulky m-xylyl-amine based on the planar tetradentate core inhibits alignment of dimer platinum atoms during dz2 orbital interaction, permitting efficient blue emission via metal-ligand to ligand transition (3MLLCT) at low doping ratios. At high doping ratios, efficient white photoluminescence was observed because of the excimer emission around 550 nm originateing from the p-p ligand interaction. We used density functional theory (B3LYP/LACVP**) to investigate the photophysical properties of Pt(II) emitters. The ligand-dependent properties of Pt(II) emitters were explored using photoluminescence quantum yield. Fabricated single-emitter white PhOLEDs with optimized dopant concentrations and device thicknesses exhibited very efficient light-emitting performances: an external quantum efficiency of 16.93% and a current efficiency of 28.92 cd A(-1). Additionally, the color rendering index was high at 83.39, yielding attractively white PhOLEDs that exhibited only marginal electroluminescence spectral changes at various driving voltages. We show how to optimize single-emitter white PhOLEDs and describe the effects of the Pt ligand geometry on excimer formation.