Triarylboron‐Based Fluorescent Organic Light‐Emitting Diodes with External Quantum Efficiencies Exceeding 20 %

Triarylboron compounds have attracted much attention, and found wide use as functional materials because of their electron‐accepting properties arising from the vacant p orbitals on the boron atoms. In this study, we design and synthesize new donor–acceptor triarylboron emitters that show thermally activated delayed fluorescence. These emitters display sky‐blue to green emission and high photoluminescence quantum yields of 87–100 % in host matrices. Organic light‐emitting diodes using these emitting molecules as dopants exhibit high external quantum efficiencies of 14.0–22.8 %, which originate from efficient up‐conversion from triplet to singlet states and subsequent efficient radiative decay from singlet to ground states.     

Nondoped Deep‐Blue Organic Light‐Emitting Diodes with Color Stability and Very Low Efficiency Roll‐Off: Solution‐Processable Small‐Molecule Fluorophores by Phosphine Oxide Linkage

A series of solution‐processable small molecules PO1 – PO4 were designed and synthesized by linking N‐phenylnaphthalen‐1‐amine groups to a phenyl phosphine oxide core through a π‐conjugated bridge, and their thermal, photophysical, and electrochemical properties were investigated. The phosphine oxide linkage can disrupt the conjugation and allows the molecular system to be extended to enable solution processability and high glass transition temperatures (159–181 °C) while preserving the deep‐blue emission. The noncoplanar molecular structures resulting from the trigonal‐pyramidal configuration of the phosphine oxide can suppress intermolecular interactions, and thus these compounds exhibit strong deep‐blue emission both in solution and the solid state with high photoluminescent quantum yield (PLQY) of 0.88–0.99 in dilute toluene solution. Solution‐processed nondoped organic light‐emitting diodes featuring PO4 as emitter achieve a maximum current efficiency of 2.36 cd A^?1 with CIE coordinates of (0.15, 0.11) that are very close to the NTSC blue standard. Noticeably, all devices based on these small‐molecular fluorescent emitters show striking deep‐blue electroluminescent color stability and extremely low efficiency roll‐off.     

Effective Host Materials for Blue/White Organic Light‐Emitting Diodes by Utilizing the Twisted Conjugation Structure in 10‐Phenyl‐9,10‐Dihydroacridine Block

Two new 10‐phenyl‐9,10‐dihydroacridine derivatives attached by dibenzothiophene (DBT) and dibenzofuran (DBF) were synthesized. The influence of the substituents of these materials was studied by theoretical calculations (DFT calculation) and experimental measurements. Owing to the twisted N‐phenyl ring, both molecules possess sufficiently high triplet energies and are suitable as hosts for phosphorescent organic light‐emitting diodes. To evaluate the electroluminescent (EL) performance of these materials, FIrpic‐based blue PHOLEDs and two‐color white PHOLEDs (FIrpic and PO‐01 as the dopants) were fabricated using the common device structures. High external quantum efficiencies (EQE) of 21.1 % and 20.9 % for FIrpic‐based blue PHOLEDs were achieved by FPhAc and TPhAc, respectively. The white device based on the host FPhAc achieved a higher performance, with a maximum EQE of 24.7 % than the device with TPhAc as host material.     

Highly Efficient Near‐Infrared Delayed Fluorescence Organic Light Emitting Diodes Using a Phenanthrene‐Based Charge‐Transfer Compound

Significant efforts have been made to develop high‐efficiency organic light‐emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) emitters with blue, green, yellow, and orange–red colors. However, efficient TADF materials with colors ranging from red, to deep‐red, to near‐infrared (NIR) have been rarely reported owing to the difficulty in molecular design. Herein, we report the first NIR TADF molecule TPA‐DCPP (TPA=triphenylamine; DCPP=2,3‐dicyanopyrazino phenanthrene) which has a small singlet–triplet splitting (ΔE_ST) of 0.13 eV. Its nondoped OLED device exhibits a maximum external quantum efficiency (EQE) of 2.1 % with a Commission International de L′Éclairage (CIE) coordinate of (0.70, 0.29). Moreover, an extremely high EQE of nearly 10 % with an emission band at λ=668 nm has been achieved in the doped device, which is comparable to the most‐efficient deep‐red/NIR phosphorescent OLEDs with similar electroluminescent spectra.