title: Multi-3,3'-Bicarbazole-Substituted Arylsilane Host Materials with Balanced Charge Transport for Highly Efficient Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes.
abstract: A series of 3,3'-bicarbazole (mCP)-functionalized tetraphenylsilane derivatives (SimCPx), including bis(3,5-di(9H-carbazol-9-yl)phenyl)diphenylsilane (SimCP2), tris(3,5-di(9H-carbazol-9-yl)phenyl)methylsilane (SimCP3-CH3), tris(3,5-di(9H-carbazol-9-yl)phenyl)phenylsilane (SimCP3-Ph), and tetrakis(3,5-di(9H-carbazol-9-yl)phenyl)silane (SimCP4), serving as bipolar blue hosts for bis[2-(4,6-difluorophenyl)pyridyl-N,C2']iridium(III) (FIrpic), have been synthesized by incorporating different ratios of mCP subunits into a central silicon atom. All of the SimCPx derivatives have wide bandgaps and high triplet energies because of the indirect linkage by silicon between each mCP subunit. The good solubility and high thermal and morphological stability of SimCPx are beneficial for forming amorphous and homogeneous films through solution processing. Density functional theory simulations manifest the better bipolar characteristics for SimCPx using three and four mCP units rather than the represented bipolar host SimCP2. As a result, SimCP4 presents the best electron-transporting ability for charge balance. Consequently, the lowest driving voltage of 4.8 eV, and the favorable maximum efficiencies of 14.2% for external quantum efficiency (28.4 cd A(-1), 13.5 lm W(-1)), are achieved by solution-processed, SimCP4-based blue phosphorescent organic light-emitting diodes as the highest performance among SimCPx, in which 32% improved device efficiencies compared to that of SimCP2 are obtained. It is inspiring to develop efficient bipolar hosts for blue phosphors by just incorporating monopolar carbazole into arylsilanes in two steps.
authors.affiliation: †State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
authors.forename: Dianming
authors.initials: D
authors.lastname: Sun
authors.affiliation: ‡State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
authors.forename: Xiaokang
authors.initials: X
authors.lastname: Zhou
authors.affiliation: †State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
authors.forename: Huihui
authors.initials: H
authors.lastname: Li
authors.affiliation: †State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Sun
authors.affiliation: †State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
authors.forename: Zhongjie
authors.initials: Z
authors.lastname: Ren
authors.affiliation: ‡State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
authors.forename: Dongge
authors.initials: D
authors.lastname: Ma
authors.affiliation: †State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
authors.forename: Shouke
authors.initials: S
authors.lastname: Yan
keywords: bipolar host; blue phosphorescent OLEDs; carbazole; small molecule host materials; tetraphenylsilane