Novel host material for highly efficient blue phosphorescent OLEDs

We report the synthesis and characterization of a novel silane - fluorene hybrid, triphenyl-(4-(9-phenyl- 9H-fluoren-9-yl) phenyl) silane (TPSi-F), used as the host material for blue phosphorescent devices. TPSi-F is constructed by linking p-substituted tetraphenylsilane to the fluorene framework through a non-conjugated, sp(3)-hybridized carbon atom (C- 9) to enhance thermal and morphological stabilities, while maintaining the much needed higher singlet and triplet energy gap. Highly efficient sky-blue phosphorescent OLEDs were obtained when employing TPSi-F as the host and iridium(III) bis[(4,6-difluorophenyl) pyridinato-N,C-2'] (FIrpic) as the guest. The maximum external quantum efficiency (max. E. Q. E.) of this device reached as high as 15% (30.6 cd A(-1)). Furthermore, upon switching the guest from FIrpic to a new blue phosphor FIrfpy, better blue-emitting OLEDs were produced with a max. E. Q. E. of 9.4% (15.1 cd A(-1)). These TPSi-F based blue phosphorescent devices show a 2-fold enhancement in device efficiency compared with reference devices based on the conventional host material 1,3-bis(9-carbazolyl) benzene (mCP).