Carbazole‐Decorated Organoboron Emitters with Low‐Lying HOMO Levels for Solution‐Processed Narrowband Blue Hyperfluorescence OLED Devices

Abstract

The hyperfluorescence has drawn great attention in achieving efficient narrowband emitting devices based on multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters. However, achieving efficient solution‐processed pure blue hyperfluorescence devices is still a challenge, due to the unbalanced charge transport and serious exciton quenching caused by that the holes are easily trapped on the high‐lying HOMO (the highest occupied molecular orbital) level of traditional diphenylamine‐decorated emitters. Here, we developed two narrowband blue organoboron emitters with low‐lying HOMO levels by decorating the MR‐TADF core with weakly electron‐donating carbazoles, which could suppress the hole trapping effect by reducing the hole traps between host and MR‐TADF emitter from deep (0.40 eV) to shallow (0.14/0.20 eV) ones for facilitating hole transport and exciton formation, as well as avoiding exciton quenching. And the large dihedral angle between the carbazole and MR‐TADF core makes the carbazole act as a steric hindrance to inhibit molecular aggregation. Accordingly, the optimized solution‐processed pure blue hyperfluorescence devices simultaneously realize record external quantum efficiency of 29.2%, narrowband emission with a full‐width at half‐maximum of 16.6 nm, and pure blue color with CIE coordinates of (0.139, 0.189), which is the best result for the solution‐processed organic light‐emitting diodes based on MR‐TADF emitters.

Delocalizing Electron Distribution in Thermally Activated Delayed Fluorophors for High-efficiency, Long-lifetime Blue Electroluminescence

“…Due to the superior performances of 4CzBN-PhCN and 4tCzBN-PhCN, we further evaluated their effectiveness as sensitizers for a deep blue MR emitter t-BuCz-DABNA. 41 The devices are noted as TSF-DB and TSF-SB for those using 4CzBN-PhCN and 4tCzBN-PhCN as sensitizers, respectively. It is interesting to note that, though t-BuCz-DABNA possesses a blue-shifted emission peak compared with both sensitizers, large overlaps were observed between the sensitizers' emission and the emitter's absorption spectra as illustrated in Supplementary Fig.…”

Enhanced X-ray Imaging with Gd2O2S:Pr-Epoxy Composite Films: Synthesis, High-Resolution Performance, and Flexibility

“…Scintillation materials, which emit light when excited by high-energy particles, are available in various forms, including organic, − inorganic, − and organic–inorganic composite scintillators. , Organic scintillators offer quick response and flexibility but suffer from lower efficiency and radiation resistance. − In contrast, inorganic scintillators deliver higher efficiency and durability but at a higher cost and with fabrication limitations. − Organic–inorganic composite scintillators, combining organic substances with inorganic scintillation components, offer a promising solution by merging the benefits of both types, such as cost-effectiveness and tunable scintillation properties . These advantages of organic–inorganic composite scintillators make them suitable for practical applications in X-ray panel imaging.…”

Understanding and modulating the horizontal orientations and short‐range charge transfer excited states for high‐performance narrowband emitters

“…Recently, Hatakeyama et al. pioneered a novel design of organic light‐emitting materials christened as multiple resonance thermally activated delayed fluorescence (MR‐TADF), by constructing rigid boron‐ and nitrogen‐doped polycyclic aromatic hydrocarbons (B, N‐PAHs) to surmount the aforementioned shortcomings 2,11–40 . Unlike traditional D‐A configurations, these B,N‐PAHs are capable of ensuring precise delineations of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals at atomic scales, that is, the formation of unique short‐range charge‐transfer (SR‐CT) excitations 20,21 .…”

“…Consequently, theoretically, MR‐TADF with a diminished single triplet energy gap ( ΔE st s) is capable of harvesting S 1 and T 1 excitons through reverse intersystem crossing (RISC), while mitigating the vibrational coupling and relaxation (to attain a narrowband emission) through the formation of specified nonbonding orbitals. Indeed, since the inception of classical DABNA‐1, numerous high‐performance red (R), 22–24 green (G), 25–31 and blue (B) 2,32–37 MR‐TADF emitters have surfaced, yielding narrowband OLEDs external quantum efficiencies (EQEs) exceeding 30% or small FWHMs less than 30 nm. Despite the proliferation of various color tuning methodologies, 38–40 little has been elucidated regarding how to precisely control device performance without altering the materials' inherent MR‐TADF attributes (such as consistent emission wavelength, FWHM, and so on).…”