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 d_z² 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 π–π 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.