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The use of mixed hosts has been demonstrated to be an effective way to improve the efficiency of phosphorescent organic light-emitting diodes (PhOLEDs). In this study, a macrospirocyclic oligomer (Cz-F)4 based on carbazole and fluorene is synthesized as a solution-processable matrix host material for blue PhOLEDs. The oligomer exhibits a high triplet level, good film-forming ability, solution processability, and doping compatibility. As a result, a blue solution-processed PhOLED based on a (Cz-F)4/TAPC [1,1-bis((di-4-tolylamino) phenyl) cyclohexane] mixed host achieves a maximum current efficiency of 18.8 cd/A with a turn-on voltage of 3.3 V. When a ternary mixed-host system composed of (Cz-F)4, TAPC, and OXD-7 [1,3-bis(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene] is employed, the device exhibits a low turn-on voltage of 2.8 V, and the driving voltages are only 3.8–4.6 V at the practical luminance of 100–1000 cd/m2. Even at 5000 and 10 000 cd/m2, the driving voltages are only 5.7 and 6.6 V, resp...

A bipolar macrospirocyclic trimer based on 4,5-diazafluorene and triphenylamine was prepared as a host for solution-processed blue phosphorescent organic light emitting diodes. The oligomer exhibits a high triplet energy of 2.88 eV, excellent thermal and morphological stability, good film-forming ability and solution processability. A solution-processed phosphorescent device based on FIrpic and the trimer achieved a maximum current efficiency of 10.0 cd A −1 with a low current efficiency roll-off at the practical luminance (9.6, 10.0, 9.4 cd A −1 at 102, 207, 1096 cd m −2 , respectively). The oligomer additionally showed excellent chemical compatibility with the common host for solution-processing technology. A blue phosphorescent device using mixed hosts of the trimer/4,4′-cyclohexylidenebis( N,N -bis(4-methyl -phenyl)benzenamine) achieved a low turn-on voltage of 3.0 V, a maximum luminance of 28,368 cd m −2 , and a maximum current efficiency of 17.7 cd A −1 (11.9 lm W −1 ), which is almost three times that of a single 4,4′-cyclohexylidenebis( N,N - bis(4-methylphenyl)benzenamine)-hosted device.

Two pyrene-functionalized oligofluorenes (TPA-PyF3 and CBP-PyF3) are prepared using the condensation reaction by the Friedel–Crafts procedure. In the produced oligomers, the triphenylamine or N,N′-dicarbazolyl-4,4′-biphenyl core serves as a spacer bearing spiro-linked fluorene moieties to form a multi-H shaped structure. This specific structure efficiently retards the crystallization tendency of the pyrene groups, and gives the materials completely amorphous morphological structure and film forming ability. Solution-processed OLEDs with the structure of ITO/PEDOT:PSS (25 nm)/TPA-PyF3 or CBP-PyF3 (40 nm)/TPBI (35 nm)/Ca (10 nm)/Ag (100 nm) show low turn-on voltages of 3.6 V, and the maximum external quantum efficiencies reach 1.78% and 2.07% for TPA-PyF3 and CBP-PyF3, respectively. Moreover, both devices exhibit stable deep-blue light emission with Commission International de I'Eclairage (CIE) coordinates of around (0.16, 0.09) at the brightness of 100–1000 cd m−2. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015

A novel triphenylamine-fluorene oligomer with macro-spirocyclic structure was designed and prepared as a host for exciplex based white phosphorescent organic light-emitting diodes (white PhOLEDs), in which only iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2)picolinate (FIrpic) was employed as the dopant. The device exhibited a comparatively high performance with a maximum luminance and current efficiency of 14 213 cd m−2 and 22.6 cd A−1, respectively.

Three bipolar hosts, namely TPA-DAF, TPA-DAF2, and TPA-DAF3, comprising an electron-donating triphenylamine (TPA) group and electron-accepting 4,5-diazafluorene (DAF) units are investigated for phosphorescent organic light-emitting diodes (PhOLEDs). Given the nonplanar structure of the sp(3)-hybridized C9 atom in DAF unit, these molecules have a highly nonplanar configuration, good film-forming property, and high triplet energy (ET) of 2.88-2.89 eV. Among them, TPA-DAF shows more balanced carrier injecting/transporting ability, suitable highest occupied molecular orbital (MO) energy level and higher current density, and therefore TPA-DAF-based devices exhibit the best performances, having an extremely slight efficiency roll-off with current efficiency of 20.0 cd/A at 973 cd/m(2), 19.5 cd/A at 5586 cd/m(2), and 17.6 cd/A at 9310 cd/m(2) for blue PhOLEDs; 23.5 cd/A at 1059 cd/m(2) and 15.3 cd/A at 8850 cd/m(2) for green PhOLEDs; and 12.2 cd/A at 1526 cd/m(2), 10.5 cd/A at 5995 cd/m(2), and 9.2 cd/A at 8882 cd/m(2) for red PhOLEDs, respectively. The results also provide a direct proof for the influence of charge balance on the device performance.

A novel bipolar oligomer (TPA-PO)3 was prepared as a host material for efficient blue phosphorescent organic light-emitting diodes (OLEDs). Through the C-9s of the fluorene units, three triphenylamine units attached to diphenylphosphine oxide are connected in series to form a macrocyclic structure. The solution-processed phosphorescent device based on FIrpic and (TPA-PO)3 achieved a maximum current efficiency of 19.4 cd A(-1) and a maximum luminance of 11,500 cd m(-2) with a relatively low efficiency roll-off.