Recent advances in white organic light-emitting diodes employing a single-emissive material

Abstract

Abstract. Recent progress in the development of materials and devices for single-doped white devices is presented with a particular focus on the development of platinum complexes exhibiting excimer emission. White organic light emitting diodes (WOLEDs) are strong candidates for the next generation of solid-state lighting, yet many of the best devices generate white light using multiple emitters embedded in a comparably complex device structure, raising the difficulty of consistently manufacturing these devices at a low cost and leading to challenges in color stability. These problems can be overcome by fabricating excimer-based WOLEDs, which construct a broad spectrum from a single emitter using blue monomer emission and red excimer emission. Through rational emitter design, the color quality and device efficiencies have steadily improved with recent achievements of external quantum efficiencies over 20% and a color rendering index greater than 80. Furthermore, recent applications of tetradentate platinum complexes for single-doped WOLEDs have yielded devices with a performance superior to many state-of-the-art multilayer WOLEDs as well as promising device operational stability. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Single‐Molecular White‐Light Emitters and Their Potential WOLED Applications

“…White emission from a single molecule, in fact, gives a perfect color reproducibility and stability. Based on these single‐molecule emitters, WOLEDs with high efficiencies have been successfully fabricated, which demonstrated the potential of using single light‐emitting molecules to simplify the device configuration of WOLEDs with good white color stability …”

“…By comparing with single fluorescent white‐light‐emitting materials, phosphorescent white emitters, especially for Pt(II) complexes, have the advantages of harvesting both 25% singlet and 75% triplet excitons in WOLEDs, thus raising the efficiency of device dramatically . The most common and acceptable mechanism for the excimer formation in Pt(II) complexes has been investigated by the research groups of Forrest and Cocchi, who proposed the involvement of the emissions of mono‐molecular (M‐M) excitons and bi‐molecular (B‐M) excimers.…”

Phosphorescent Pt(II) and Pd(II) Complexes for Efficient, High‐Color‐Quality, and Stable OLEDs

“…Nevertheless a number of problems remain with bidentate and tridentate ligands in general. Firstly, most tridentate Pt complexes exhibit significant excimer formation at elevated dopant concentrations, reducing the color quality of blue OLEDs and in some cases lowering the emission efficiency . Furthermore, the potential electrochemical instability of the halogen‐containing Pt complexes poses a significant challenge in the realization of long device operational stability.…”

“…With judiciously designed emitters, it is possible to generate blue emission from individual molecules alongside broad yellow to red emission from excimers, resulting in a white‐light generation based on a single emissive material. White OLEDs are designed where the relative excimer and monomer contributions can be tuned through the control of the dopant concentration, appropriate selection of host materials, and deposition conditions . Nevertheless, the achievement of broad white emission covering the visible spectrum poses several significant challenges, including: achieving sufficient blue emission, tuning the excimer emission energy (where the relationship between molecular structure and excimer emission is still poorly understood), and the simultaneous optimization of both emission spectra to span a wide range of the visible spectrum.…”

The role of photonics in energy

“…Since the development of phosphorescent OLEDs, these devices have been seriously considered for solid-state lighting applications. 308,309 Today, white OLEDs with efficiencies up to 100 lm∕W and color rendering indices close to 90% have been demonstrated by companies such as LG Chemical and Konica Minolta, and OLED lighting products have been introduced in the market place in the last couple years. 310,311 White OLEDs are typically devices with multiple emitters in a device stack.…”