Tetraphenylsilane group containing carbazoles as high triplet energy host materials for solution-processable PhOLEDs

A series of solution processable, wide band-gap host materials composed of carbazole and tetraphenylsilane groups were designed and synthesized. Their thermal, electrochemical, and photophysical properties were fully investigated. The introduction of bulky tetraphenylsilane and \textit{tert}-butyl groups around the carbazole led to high glass transition temperatures (T$_{g})$ between 120 and 204 $^{\circ}$C. The triplet energies (E$_{T})$ of the synthesized materials were examined by low temperature (77 K) photoluminescence studies and determined as E$_{T}>$ 2.6 for all compounds. Phosphorescent organic light-emitting devices with the ITO/PEDOT:PSS/EML/TPBi/Cs$_{2}$CO$_{3}$/Al device structure were fabricated by using synthesized materials as the host and two kinds of phosphorescent emitters, FIrpic and Ir(ppy)$_{3}$, as the guests. The highest luminous and power efficiency values obtained by using FIrpic were 3.6 cd A$^{-1}$ and 1.48 lm W$^{-1}$, respectively, with commission International de I'Eclairage (CIE) coordinates of (0.17, 0.36), whereas these values were 7.8 cd A$^{-1}$ and 2.9 lm W$^{-1}$ for the device structure when Ir(ppy)$_{3}$ was used as the guest [CIE (0.28, 0.62)].