Multi-resonance induced thermally activated delayed uorescent (MR-TADF) materials have shown great potential in high-e ciency and narrowband organic light-emitting diodes (OLEDs). However, obvious e ciency roll-off attributed to slow reverse intersystem crossing (RISC) process hinders MR-TADF materials from practical applications. Here, we report a heavy-atom incorporating emitter, namely BNSeSe, based on selenium-integrated boron-nitrogen skeleton, showing 100% photoluminescence quantum yield and the highest rate of RISC (k RISC ) of 2.0 × 10 6 s -1 among MR-TADF molecules. The corresponding OLEDs exhibit excellent external quantum e ciency (EQE) up to 36.8% and ultra-low roll-off character at high brightness (with very small roll-off values of 2.8% and 14.9% at 1000 cd m -2 and 10000 cd m -2 , respectively). Furthermore, the outstanding capability to harvest triplet excitons also enables BNSeSe to be a superior sensitizer for hyper uorescence (HF) device, which shows state-of-the-art performance with record high EQE of 40.5%, power e ciency (PE) beyond 200 lm W -1 and luminance close to 200000 cd m -2 .
Full TextOrganic light-emitting diodes (OLEDs) with simultaneously high e ciency and narrowband emission become increasingly important for the demands on energy-saving and high-quality of displays. Thanks to the pioneer work by Hatakeyama et al., multi-resonance (MR) thermally activated delayed uorescent (TADF) emitters have emerged with the astonishing narrowband emission that could ful ll the requirements. 1,2 A high external quantum e ciency (EQE) up to 34% and electroluminescence (EL) with full width at half maximum (FWHM) of 18 nm demonstrated their great potential towards practical applications. 3 However, MR-TADF emitters usually possess long delay lifetime of several tens of microsecond, which usually leads to large e ciency roll-off at high brightness and thus impede their commercialization. [4][5][6][7][8][9][10]
High‐color‐purity blue and green organic light‐emitting diodes (OLEDs) have been resolved thanks to the development of B/N‐based polycyclic multiple resonance (MR) emitters. However, due to the derivatization limit of B/N polycyclic structures, the design of red MR emitters remains challenging. Herein, a series of novel red MR emitters is reported by para‐positioning N–π–N, O–π–O, B–π–B pairs onto a benzene ring to construct an MR central core. These emitters can be facilely and modularly synthesized, allowing for easy fine‐tuning of emission spectra by peripheral groups. Moreover, these red MR emitters display excellent photophysical properties such as near‐unity photoluminescence quantum yield (PLQY), fast radiative decay rate (kr) up to 7.4 × 107 s−1, and most importantly, narrowband emission with full‐width at half‐maximum (FWHM) of 32 nm. Incorporating these MR emitters, pure red OLEDs sensitized by phosphor realize state‐of‐the‐art device performances with external quantum efficiency (EQE) exceeding 36%, ultralow efficiency roll‐off (EQE remains as high as 25.1% at the brightness of 50 000 cd m−2), ultrahigh brightness over 130 000 cd m−2, together with good device lifetime.
Bismuth nanodendrites with a high performance are designed and synthesized for ERC. The catalyst exhibits high selectivity and activity as well as excellent stability for ERC.
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