Application of wide-energy-gap material 3,4-di(9H-carbazol-9-yl) benzonitrile in organic light-emitting diodes

A material with a wide energy gap, 3,4-di(9H-carbazol-9-yl)benzonitrile (2CzBN), was synthesized and applied in organic light-emitting diodes (OLEDs). Pure blue electroluminescence with a peak wavelength of 436 nm and Commission Internationale de l'Èclairage (CIE) coordinate of (0.160, 0.084) were obtained for an OLED containing 2CzBN as an emitter, although its external emission efficiency was limited to around 1% because of the lack of thermally activated delayed fluorescence (TADF) activity. In contrast, a highly efficient TADF-based OLED was obtained when 2CzBN was used as a host instead of an emitter by taking advantage of the high triplet energy (2.92 eV) and unexpected electron transport capability of 2CzBN.