Bipolar Hosts Based on a Rigid 9,10‐Dihydroanthracene Scaffold for Full‐Color Electrophosphorescent Devices

Abstract

Two bipolar hosts, CzDPO and CzDOxa, comprising a hole‐transporting carbazole and an electron‐transporting diphenyl phosphine oxide or oxadiazole with a saturated linker (9,10‐dihydroanthracene) have been synthesized and characterized. The saturated linker limited the effective extension of π conjugation, leading to high triplet energies (ET=2.97–2.98 eV). The diastereomers with a rigid configuration provided an amorphous thin film with high thermal (Td=415–444 °C) and morphological stability (Tg=188–224 °C). The high triplet energies and bipolar carrier transport characteristics (ambipolariy) of CzDPO and CzDOxa can facilitate exothermic energy transfer to the dopants and balance carrier injection/transport in the emission layers. As a result, they were utilized as universal hosts for various phosphorescent OLEDs (from blue to red), showing average external quantum efficiencies (ηext=8.2–13.1 %) and low efficiency roll‐off. In addition, we also fabricated dual‐emitter white organic light‐emitting diodes with a co‐doped single emissive layer. WOLED hosted by CzDOxa exhibited satisfactory device efficiencies (14.4 %, 25.7 cd A−1, 27 lm W−1) with highly stable chromaticity (CIEx=0.26–0.28 and CIEy=0.38) at brightnesses from 560 to 15200 cd m−2.

Exciplex forming a Phenyl-Spaced Phenoxazine D–A Cohost for a Highly Efficient Red-Phosphorescent Organic Light-Emitting Diode

“…To achieve bipolar hosts with high triplet energy, strategies, such as impeding electronic communication between electron-donating and electron-withdrawing moieties, have been developed. These include introducing a saturated bridging center or a highly twisted linker to minimize effective π conjugation. , Recent research has shown promising results in achieving a high external quantum efficiency for blue, green, and red PhOLEDs.…”

Combined experimental and density functional theory studies on novel 9‐(4/3/2‐cyanophenyl)‐9H‐carbazole‐3‐carbonitrile compounds for organic electronics

“…The bipolar materials with donor-acceptor (D-A) system comprising π or σ bridge have engaged with great significance because of their distinctive properties like well-defined structural system, balance hole and electron transport, ease of purification along with authentic reproducibility, high luminescence quantum yield, [16][17][18] and easy fabrication of large area devices. [19][20][21][22][23][24][25][26][27] Over a wide range of tailored D-A moieties along with unique architecture system with wise selection and proper linking of donor and acceptor motifs allows to tune the photophysical, thermal, and electrochemical properties. [28] Indeed, a host material for PhO-LEDs device should possess some inherent features: (I) higher triplet energy (E T ) than the phosphorescent guest, which prevent reverse energy transfer, (II) suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for effective charge injections into the emitting layer from the adjacent charge transporting layers, (III) large HOMO-LUMO energy gap (E g ) than the phosphorescent guest, and (IV) high glass transition temperature (T g ) to provide good film morphology and avoid morphological changes at device operating voltage and so on.…”