Warm White Device Research Articles

Undoped highly efficient green and white TADF-OLEDs developed by DMAC-BP: manufacturing available via interface engineering

We report on the development of green and white OLEDs with high efficiency based on Bis(4-(9,9-dimethylacridin-10(9H)-yl) phenyl)methanone (DMAC-BP) manufactured by a facile vacuum evaporation technique via device interfaces engineering. Single, double, and three organic layer undoped OLEDs based on DMAC-BP have been fabricated. Among the developed green devices, the performance of three-layer structured OLEDs is the optimum when mCP (1,3-Bis(carbazol-9-yl)benzene) works as the hole transport layer (HTL) and electron block layer (EBL). The measured maximum external quantum efficiency (EQE), current efficiency (CE), power efficiency (PE), and luminance are 8.1%, 25.9 cd/A, 20.3 lm/W, and 42,230 cd/m2, respectively. Importantly, the OLEDs retain the most of their performance at 1000 cd/m2, and the EQE, CE, and PE are 7.2%, 23.7 cd/A, and 19.1 lm/W, respectively. The achieved high efficiency is attributed to the bipolar transport characteristics of DMAC-BP and the matched bandgap between HTL and emission layer (EML). In addition, WOLEDs with DMAC-BP as green layer are all warm white devices. Among them, the structure of green-red-blue (device W3) demonstrates the best performance with a maximum EQE and brightness of 4.4% and 7525 cd/m2. Our findings will facilitate the great potential applications of undoped TADF emitters, and establish a good foundation for the preparation of high-efficiency and low-cost commercial OLEDs.

High performance organic light-emitting diodes with tunable color range from orange to warm white based on single thermally activated delayed fluorescence emitter

In this work, we reported the highly efficient organic light-emitting diodes based on orange-emitting thermally activated delayed fluorescence emitter 1,4-dicyano- 2,3,5,6-tetrakis(3,6-diphenyl-carbazol-9-yl)benzene (4CzTPN-Ph). By utilizing the bipolar material 2,6-bis(3-(9H-carbazol-9-yl)phenyl)-pyridine (26DCzPPy) and hole type material 4,4′,4″-Tri(9-carbazoyl)triphenylamine (TcTa) as host and ladder materials, respectively, the optimized single light-emitting layer (EML) orange device obtained the maximum brightness, external quantum efficiency, current efficiency and power efficiency up to 41791 cd/m2, 13.1%, 42.97 cd/A and 44.98 lm/W, respectively. Except for the 570 nm characteristic emission, interestingly, there is another emission peak at about 475 nm, which increases rapidly with decreasing doping concentration. Therefore, device color shifts gradually from orange to warm white with decreasing doping concentration due to the increasing relative intensity of exciplex emission. Finally, warm white device (Commission Internationale de L'Eclairage (CIE) Coordinates at (0.337, 0.476)) based on single TADF emitter with the maximum brightness, external quantum efficiency, current efficiency and power efficiency up to 23560 cd/m2, 10.2%, 32.33 cd/A and 32.75 lm/W, respectively, was also obtained.

Novel distorted donor-acceptor type deep blue fluorescent emitter for high efficiency in non-doped blue and cool white organic light-emitting diodes

Distorted donor-acceptor type blue fluorescent emitter, 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1,8-dimethyl-9H-carbazole (DmCzTrz), was developed for use as a high efficiency and non-doped deep blue fluorescent emitter and a deep blue emitter in hybrid white organic light-emitting diodes. The novel distorted donor-acceptor based non-doped DmCzTrz blue fluorescent organic light-emitting diodes achieved high quantum efficiency of 6.8% with a deep blue color coordinate of (0.15,0.10). The DmCzTrz blue emitter was doped with green and red triplet emitters to develop the hybrid white organic light-emitting diodes, and high quantum efficiency of 19.4% in cool white device and 20.8% in warm white device were demonstrated.

Controlling the Chromaticity of Small‐Molecule Light‐Emitting Electrochemical Cells Based on TIPS‐Pentacene

This work demonstrates a novel proof‐of‐concept to implement pentacene derivatives as emitters for the third generation of light‐emitting electrochemical cells based on small‐molecules (SM‐LECs). Here, a straightforward procedure is shown to control the chromaticity of pentacene‐based lighting devices by means of a photoinduced cycloaddition process of the 6,13‐bis(triisopropylsilylethynyl) (TIPS)‐pentacene that leads to the formation of anthracene‐core dimeric species featuring a high‐energy emission. Without using the procedure, SM‐LECs featuring deep‐red emission with Commission Internationale d'Eclairage (CIE) coordinates of x = 0.69/y = 0.31 and irradiance of 0.4 μW cm−2 are achieved. After a careful optimization of the cycloaddition process, warm white devices with CIE coordinates of x = 0.36/y = 0.38 and luminances of 10 cd m−2 are realized. Here, the mechanism of the device is explained as a host–guest system, in which the dimeric species acts as the high‐energy band gap host and the low‐energy bandgap TIPS‐pentacene is the guest. To the best of the knowledge, this work shows the first warm white SM‐LECs. Since this work is based on the archetypal TIPS‐pentacene and the photoinduced cycloaddition process is well‐knownfor any pentacenes, this proof‐of‐concept could open a new way to use these compounds for developing white lighting sources.

Rational Design of Dibenzothiophene-Based Host Materials for PHOLEDs

A series of systematical designed host materials based on dibenzothiophene (DBT) were synthesized. Their physical properties were comprehensively characterized and compared with classic carbazole analogues. The different electron donating abilities of DBT and carbazole play an important role in the structure–property correlations. In this report, we demonstrate that the charge transport balance of host materials can be manipulated by utilizing the less electron-donating nature of DBT with proper design. Both the experimental data and theoretical calculations indicated possible bipolar property in meta-linked materials based on DBT. Through single carrier devices, an atypical bipolar transporting property was found in m-TPDBT. The meta- and ortho-linked DBT based materials exhibit decent performance in FIrpic based PHOLEDs. The best performed m-TPDBT was used as host in white phosphorescent organic light emitting diodes (PHOLEDs). Promising results were achieved with both double and single emitting layer configurations. A maximum power efficiency of 41.0 lm W–1 was achieved for warm white devices.

61.2: Phosphorescent Stacked OLEDs for Warm White Lighting Applications

AbstractWe report record lifetime for an all‐phosphorescent stacked white OLED pixel with an extended lifetime to LT70=25,000 hours at L0=3,000 cd/m2 with 1.72x external outcoupling enhancement and a power efficacy of 60 lm/W. This warm white device meets En ergy Star criteria with CIE 1931 (x, y)=(0.452, 0.420), CCT=2,882K, CRI=83, and demonstrates exceptional color stability as a function of luminance and aging.

Developments in solution processable polymer light-emitting diodes

A device structure that enables the combination of phosphorescent green and fluorescent blue emitters in a solution processed polymer organic light-emitting diode device has been developed. Results demonstrate that it is possible to tune the color of emission by appropriate formulation of the polymers that are used. This enabled the development of a warm white device that had CIE coordinates of (0.462, 0.426), and an external quantum efficiency (EQE) of 13.1%. This EQE was limited by the efficiencies of the emitters used rather than through any internal quenching, and thus the device structure offers potential for further development.