Peripheral cyanohexyl substituent in wide bandgap polymer: increase the electron injection property for blue phosphorescence light emitting device

Novel blue phosphor host, PCNCzSi, using 3,6-linked carbazole with δ-π tetraphenylsilane segment as the main chain modified by peripheral cyanohexyl group was designed. The Si-carbazole backbone entitles the polymer with wide bandgap, high E(T) and good hole transporting ability. The introduction of peripheral CN group with high electron affinity enhances the electron injecting property of the polymer revealed by electron-only device and UPS measurement. Highly efficient spin-coated phosphorescent polymer light-emitting device, using PCNCzSi as the host for blue iridium complex, FIrpic, was realized. The maximum luminous efficiency and maximum external quantum efficiency of the device were 15 cd/A and 6.7%, respectively, which are very high values for blue phosphorescent device using polymers as hosts as known.