A morphologically stable host material for efficient phosphorescent green and red organic light emitting devices

A carbazole-based host material, 4,4′-N,N′-[di(3, 6-di(t-butyl)carbazole]biphenyl (ttbCBP), with four t-butyl steric spacers on peripheral carbazole moieties was effectively synthesized through Friedel–Crafts Alkylation. Owing to the presence of sterically hindered t-butyl groups, ttbCBP exhibits a high glass transition temperature (175 °C) and is morphologically stable. This host material also preserves the characteristics of wide band-gap of 3.2 eV and high triplet energy of 2.64 eV. In addition, ttbCBP has been shown to be effective hosts for green and red phosphorescent emitters in organic electrophosphorescent devices.