We report highly efficient blue electrophosphorescent organic light-emitting diodes (OLEDs) incorporating a bipolar host, 2,7-bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF), doped with iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C 2′ ]picolinate (FIrpic). PCF, which contains diphenylphosphine oxide groups appended onto a carbazole/fluorene hybrid, displays both electron- and hole-transporting characteristics, resulting in a low turn-on voltage (2.6 V) and greatly improved power efficiencies. In addition, the sterically hindered structure of PCF provides a compatible environment for the FIrpic dopant, alleviating concentration quenching of the phosphor at high doping levels. The device doped with 28 wt % FIrpic exhibited maximum EL efficiencies of 30.8 cd/A and 26.2 lm/W (at 121 cd/m2). Even at a high brightness of 1000 cd/m2, the efficiencies remained high (26.9 cd/A and 19.6 lm/W).

A highly efficient blue‐light emitter, 2‐tert‐butyl‐9,10‐bis[4′‐(diphenyl‐phosphoryl)phenyl]anthracene (POAn) is synthesized, and comprises electron‐deficient triphenylphosphine oxide side groups appended to the 9‐ and 10‐positions of a 2‐tert‐butylanthracene core. This sophisticated anthracene compound possesses a non‐coplanar configuration that results in a decreased tendency to crystallize and weaker intermolecular interactions in the solid state, leading to its pronounced morphological stability and high quantum efficiency. In addition to serving as an electron‐transporting blue‐light‐emitting material, POAn also facilitates electron injection from the Al cathode to itself. Consequently, simple double‐layer devices incorporating POAn as the emitting, electron‐transporting, and ‐injecting material produce bright deep‐blue lights having Commission Internationale de L'Eclairage coordinates of (0.15,0.07). The peak electroluminescence performance was 4.3% (2.9 cd A−1). For a device lacking an electron‐transport layer or alkali fluoride, this device displays the best performance of any such the deep‐blue organic light‐emitting diodes reported to date.

Highly efficient blue electrophosphorescent organic light‐emitting diodes incorporating a bipolar host, 2,7‐bis(diphenylphosphoryl)‐9‐[4‐(N,N‐diphenylamino)phenyl]‐9‐phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6‐difluoro‐phenyl)pyridinato‐N,C2´]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron‐donating (p‐type) triphenylamine group and an electron‐accepting (n‐type) 2,7‐bis(diphenyl‐phosphoryl)fluorene segment linked through the sp3‐hybridized C9 position of the fluorene unit. The lack of conjugation between these p‐ and n‐type groups endows POAPF with a triplet energy gap (ET) of 2.75 eV, which is sufficiently high to confine the triplet excitons on the blue‐emitting guest. In addition, the built‐in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF‐based device doped with 7 wt% FIrpic exhibits a very low turn‐on voltage (2.5 V) and high electroluminescence efficiencies (20.6% and 36.7 lm W−1). Even at the practical brightnesses of 100 and 1000 cd m−2, the efficiencies remain high (20.2%/33.8 lm W−1 and 18.8%/24.3 lm W−1, respectively), making POAPF a promising material for use in low‐power‐consumption devices for next‐generation flat‐panel displays and light sources.

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