Strategy for the Realization of Highly Efficient Solution-Processed All-Fluorescence White OLEDs—Encapsulated Thermally Activated Delayed Fluorescent Yellow Emitters

Abstract

Fabrication of highly efficient all thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs) through solution-process still remains a big challenge. Here, two encapsulated TADF molecules with a small singlet–triplet energy gap (ΔE ST) and high photoluminescence quantum yield (PLQY) were designed and synthesized as yellow emitters for solution-processed WOLEDs. The high current, power, and external quantum efficiencies of 41.6 cd A–1, 30.4 lm W–1, and 17.3% were achieved for the solution-processed all-fluorescence WOLEDs with a single-emission layer. In contrast, even with the same ΔE ST and PLQY, the corresponding unencapsulated parent emitters will account for nearly 50% loss of the potential device efficiency. This is for the first time that the small molecular TADF blue host and TADF yellow guest are used to construct solution-processed all-fluorescence WOLEDs, which exhibit high efficiency comparable with most of the vacuum-deposited all-fluorescence white devices. These results not only demonstrate the great potential of TADF emitters in achieving highly efficient solution-processed WOLEDs, but also testify the key role of molecular encapsulation in reducing polar-exciton quenching and enhancing electroluminescence performance.

Impedance Spectroscopy: A Versatile Technique to Understand Solution‐Processed Optoelectronic Devices

“…The fundamental challenges associated with the fabrication of electroluminescent devices are structure optimization and material characterization leading to higher luminance, low turn‐on voltage, high stability, high current efficiency, and external quantum efficiency. Recently, OLEDs have achieved commercialization in displays and solid‐state lightings . Due to the complex evaporation deposition procedures for multilayer devices, it is of great importance to understand the interfacial behaviors in the OLEDs.…”

High‐Efficiency White Organic Light‐Emitting Diodes Based on All Nondoped Thermally Activated Delayed Fluorescence Emitters

“…As summarized in Table , the device W10 exhibits the best performances, achieving a maximum EQE of 24.2%, CE of 51.7 cd A −1 , and PE of 46.4 lm W −1 , respectively. As compared in Table S1 (Supporting Information), the device performances in this work are among the highest values of the reported all‐fluorescence WOLEDs based on TADF emitters . More importantly, it is the first time to fabricate all‐TADF WOLEDs using an ultrathin emitting layer instead of doping technique, which not only simplify the device structure for reducing the fabrication complexity but also achieve high efficiencies.…”

White light emitting diode based on purely organic fluorescent to modern thermally activated delayed fluorescence (TADF) and perovskite materials

“…Ban et al explored an effective method for the first time by embedding a classical small TADF molecular structure for low cost solution processed WOLEDs [48]. To make a feasible solution processed device, two yellow TADF materials, Cz-4CzPN and Cz-4CzTPN were carefully developed.…”

“…17 a Molecular structures of the emitters, b energy transfer mechanism and molecular stacking depiction(Reproduced with permission from Ref. [48] Copyright © 2018, American Chemical Society)…”