Narrowband emitting fluorophores exhibit immense potentials for organic light-emitting diodes (OLEDs) with high color purity. However, it's still hard to simultaneously realize short-wavelength ultraviolet (UV) or near ultraviolet emission (NUV) while maintaining a narrowed full width at half maximum (FWHM) value, and rare work focus on such challenging pursuit. Herein, an ingenious synthetic method was devised to achieve emitters with coplanar structure. 11-(4,6-diphenyl-1,3,5-triazin-2-yl)indolo[3,2,1-jk]carbazole (ICZ-TAZ) was designed to realize narrowed UV emission both in photoluminescence (PL) and electroluminescence (EL) which benefited from the suppression of vibronic coupling. UV/NUV OLEDs based on ICZ-TAZ achieve external quantum efficiency (EQE) maximums of 3.26 % peaks @ 388 nm and 4.02 % peaks @ 406 nm with small FWHM of 32 nm and 46 nm, respectively, corresponding with reduced efficiency rolloff at luminance of 100 cd m À 2 .
The “hot exciton” mechanism based on high‐lying reverse intersystem crossing process has great advantages in achieving high‐performance deep‐blue organic light‐emitting diodes (OLEDs). Nevertheless, how to solve the loss of high‐lying excitons to improve device performance further is a pressing and challenging issue. To break through this shackle, a novel deep‐blue emitter based on “exciton recovery” strategy is successfully design, namely CAT. By combining the transient absorption spectrum, theoretical calculation, magneto‐electroluminescence, and transient‐electroluminescence measurements, the multi‐channeled pathways of excitons utilization via hot exciton and triplet‐triplet annihilation processes is comprehensively demonstrated, and the proportion of singlet excitons by each channel. Finally, a high exciton utilization efficiency is successfully achieved, and the non‐doped OLED based on CAT exhibit an excellent external quantum efficiency of 10.39% with the CIE coordinates of (0.15, 0.087). Furthermore, the sensitized blue fluorescent OLED by CAT as host also achieves excellent performance. More importantly, the operational lifetime of the “multi‐channel” sensitized device is evaluated for the first time, performing the remarkable LT50 (lifetime to 50% of the initial luminance) of 320 h at 540 cd m−2. These results fully reveal the significance of the “exciton recovery” strategy and give new inspiration for exploring high‐performance blue OLEDs.
High efficiency and high color purity are two key factors for achieving non-doped deep-blue organic light-emitting diodes (OLEDs). Herein, a novel emitter 3,6-di-tert-butyl-9-(4'-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-[1,1'-biphenyl]-4-yl)-9H-carbazole (DTPCZTZ) with a weak donor-acceptor structure containing...
In this work, a near‐ultraviolet (NUV) emitter, 2MCz‐CNMCz, with hot‐exciton property is designed based on a “long‐short axis” strategy, which exhibits good thermal stability, bipolar carrier transport ability, and high T1 energy level. Its nondoped NUV organic light‐emitting diode (OLED) achieves a record maximum external quantum efficiency (ηext) of 7.76%, with a peak at 404 nm and CIE coordinates of (0.158, 0.039). The corresponding high exciton utilization efficiency (ηr) in the electroluminescence process reveals its potential as a functional sensitizing host. As expected, the TBPe‐based blue fluorescent OLED with 2MCz‐CNMCz as the host material shows better efficiency and lower efficiency roll‐off than that with traditional host material mCP. Meanwhile, the Ir complexes‐based green/yellow/red phosphorescent OLEDs with 2MCz‐CNMCz host are also fabricated, reaching high ηext values of 26.1%, 30.4%, and 20.4%, respectively, and displaying negligible efficiency roll‐offs at 1000 cd m−2, which are among the best OLED performances based on the same emitters. To the authors’ best knowledge, this is the first report on the design of high‐quality universal and functional host material, and may bring new inspiration to the preparation of high‐efficiency, low roll‐off, full‐color OLEDs.
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