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The new host materials are reported to boost the multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) based pure deep‐blue organic light emitting diodes (OLEDs) toward further shortening the emission full width at the half maximum (FWHM). Based on an unusual asymmetric design concept, two new host compounds Bz2cb and Bz2cbz are synthesized. Despite possessing a compact and rigid molecular packing in crystal, Bz2cbz shows pure amorphous morphology via vapor deposition, as confirmed by the grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) analysis. Via incorporating a promising MR‐TADF emitter, ν‐DABNA‐O‐Me, into Bz2cb and Bz2cbz films, highly pure deep‐blue OLEDs are successfully demonstrated. Remarkably, the Bz2cbz device exhibits a 464 nm electroluminescence (EL) with narrow FWHM of 22 nm, accompanied by the reduction of the 0–1 vibronic sideband, and a maximum external quantum efficiency (EQEmax) of 28.2%, which, overall, reaches the true‐blue Commission Internationale de l'Eclairage coordinates (CIE) of (0.13, 0.07) and the high blue index of 253. The amorphous film formation turns out to be an important factor that is previously unrecognized to externally fine‐tune the MR‐TADF OLEDs toward even higher color purity. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) is a promising approach to harvest triplet excitons and achieve high-performance organic light-emitting diodes (OLEDs) for displays. In this study, we synthesized two new TADF emitters, 4Ac25CzPy and 4Ac35CzPy, featuring acridan–pyrimidine–carbazole moieties. Remarkably, a slight modification in the carbazole group position enables precise control of luminous color, resulting in emissions at 483 nm and 494 nm for 4Ac25CzPy and 4Ac35CzPy, respectively, in the electroluminescent device. Both compounds exhibit small energy difference between their singlet and triplet states (ΔEST) of 0.14 eV and 0.15 eV, confirming their TADF characteristics. Notably, OLEDs utilizing 4Ac35CzPy achieve outstanding performance with the maximum external quantum efficiency (ηEQE) of 21.2% and a photoluminescence quantum yield of 65.1%. This high efficiency is attributed to efficient energy transfer from the host to the emitter. Moreover, the 4Ac35CzPy device exhibits a high light outcoupling efficiency of 0.3, further enhancing its remarkable performance. [ABSTRACT FROM AUTHOR]

Based on the classic 1,1′:4′,1″‐terphenyl fluorophore, a novel near‐ultraviolet (NUV) fluorescent BB4Ph (4,4″′‐bis(2,3,4,5‐tetraphenylphen‐1‐yl)(1,1′:4′,1″‐terphenyl) is designed, synthesized, and characterized. BB4Ph exhibits a NUV fluorescence with a λmax of 373 and 380 nm in solution and as a thin film, respectively. The grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals BB4Ph having a high value of order parameter (SGIWAXS) of 0.59 for a molecular layer array normal to the substrate; the angle‐dependent photoluminescence (ADPL) measurement shows Θ (horizontal–dipole ratios) as high as 95% with the neat film. The non‐doped BB4Ph organic light‐emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with 1931 Commission Internationale de l' Eclairage coordinates (CIEx,y) of (0.16, 0.04), a NUV electroluminescence. With 4P‐Cz (9,9′‐(1,1′:4′,1″:4″,1′″‐quaterphenyl‐4,4′″‐diyl)dicarbazole) as a dopant emitter, doped BB4Ph OLEDs show the highest EQE of 6.99% and a NUV 1931 CIEx,y (0.16, 0.04). The photoluminescence quantum yield is measured for the thin film of BB4Ph and 4P‐Cz:BB4Ph as 68% and 96%, respectively. Hence, the low limits of light outcoupling efficiency (ηout) of the two individual OLEDs are estimated as 31% and 29%, respectively. [ABSTRACT FROM AUTHOR]

In this study, a steady state and time‐dependent exciton diffusion model including singlet and triplet excitons coupled with a modified Poisson and drift‐diffusion solver to explain the mechanism of hyper triplet–triplet fusion (TTF) organic light‐emitting diodes (OLEDs) is developed. Using this modified simulator, various characteristics of OLEDs, including the current‐voltage curve, internal quantum efficiency, transient spectrum, and electric profile are demonstrated. This solver can also be used to explain the mechanism of hyper‐TTF‐OLEDs and analyze the loss from different exciton mechanisms. Furthermore, we perform additional optimization of hyper‐TTF‐OLEDs that increases the internal quantum efficiency by ≈33% (from 29% to 40%). [ABSTRACT FROM AUTHOR]

Four bipolar molecules, named 1-, 2-, 3-, and 4-3cbzBIZ, composed of tricarbazole (3cbz) substituted benzimidazole, were synthesized and characterized. They not only exhibit good thermal stability with remarkably high glass transition temperatures and decomposition temperatures, especially 4-3CbzBIZ (Tg > 193 °C, Td > 453 °C), but also show superior thermal photoluminescence stability at elevated temperatures. Their morphological stabilities have also been affirmed using atomic force microscopy pictures after 30 min during 80 °C annealing. The FIrpic doped 4-3cbzBIZ organic light-emitting diode (OLED) shows sky-blue electroluminescence from FIrpic with a high external quantum efficiency (ηEQE) of 28.6% with an amazingly small efficiency roll-off (ηEQE = 27.3% at a luminance of 1000 cd m−2). Furthermore, the green OLED with Ir(ppy)3 doped in 4-3cbzBIZ exhibits excellent device thermal stability and a longer operational lifetime than the OLED with CBP as the host. In particular, a significant lifetime improvement by 11.6 times was obtained at an elevated temperature of 80 °C. The high efficiency and high-temperature stability of the OLED were ascribed to the balanced bipolar carrier-transporting properties, high Tg and rigidity of 4-3cbzBIZ. The present work of developing orthogonally linked donor–acceptor hosts provides a strategy of material design to develop high thermal stability OLEDs. [ABSTRACT FROM AUTHOR]