Molecular‐Structure and Device‐Configuration Optimizations toward Highly Efficient Green Electroluminescence with Narrowband Emission and High Color Purity

Abstract

Thermally activated delayed fluorescence (TADF) materials that are able to realize electroluminescence showing simultaneously narrow emission band, high color purity, and high efficiency are highly demanded for display applications. Up to now, a few blue emissive TADF materials with such characteristics have been reported, while green TADF materials with such features are extremely scarce. Herein, two TADF compounds with highly efficient narrowband bluish green/green emission (full‐width at half‐maximum (FWHM): 22 and 21 nm in toluene) induced by multiple resonance effect are reported. An optimized organic light‐emitting diode based on the green emissive compound shows a fairly narrow electroluminescent spectrum (FWHM: 33 nm), as well as an excellent color purity with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.20, 0.65), which is a close resemblance to the standard green‐light CIE coordinates of (0.21, 0.71) defined by the National Television System Committee. Meanwhile, the maximum external quantum efficiency (EQE) up to 25.5% is achieved and a high EQE of 20.1% is maintained at a practical high luminance of 1000 cd m−2. The outstanding device performance of the compound makes it attractive for potential practical applications.

Molecular design of thermally activated delayed fluorescent emitters for narrowband orange–red OLEDs boosted by a cyano-functionalization strategy

“…9c,9f Notably, although the integration of ICT-induced emission in twisted D−A structure and MR-induced emission is considered as a promising way to finely tune the emission colors of MR-TADF materials, it would inevitably lead to emission broadening owing to the increased structure relaxation Please do not adjust margins Please do not adjust margins associated with the twisted D−A structure. For example, BCz-BN with purely MR-induced emission characteristic displays a blue emission (481 nm) with a small FWHM of 22 nm, 11 while m-Cz-BNCz that features an auxiliary carbazole group on HOMO distribution exhibits a green emission (519 nm) with an increased FWHM of 38 nm. 9c Therefore, the realization of redshifted emission for MR-TADF materials without sacrificing color purity remains an appealing yet challenging task.…”

Three‐ and Four‐Coordinate, Boron‐Based, Thermally Activated Delayed Fluorescent Emitters

“…Similarly, Wang and co-workers recently reported highly efficient, stable, narrowband, and pure green emitters (DtBuPhCzB) with an EQE of 25.5%, an FWHM of 33 nm, and CIE coordinates of (0.20, 0.65). [101] Pure green emission and stability of DtBuPhCzB were mainly attributed to the rigidified π-conjugated core skeleton and introduction of four extra t-butylphenyl groups on the carbazole moieties. The OLED device performances were studied at 1%, 2%, and 3% doping concentrations, and the best results were obtained at a 2% doping concentration.…”

Heavy-Atom Effect Promotes Multi-Resonance Thermally Activated Delayed Fluorescence

“…6 Nonetheless, documented MR-TADF examples featuring promising electroluminescence remain sparse, and tactics to improve their efficiency are of great importance. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Reverse intersystem crossing (RISC) process is a critical pathway for emitters to achieve TADF. [23][24][25][26][27] A fast rate constant of RISC (kRISC) of TADF emitter can efficient converted its T1 excitons to S1 state, promising high internal quantum efficiency (IQE), while inefficient RISC would conversely increase the concentration of triplet excitons to induce triplet-triplet annihilation (TTA) or other degradation events.…”