Universal host materials based on carbazole-formate derivatives for blue, green and red phosphorescent organic light-emitting diodes

Abstract

The design of universal hosts suitable for different color dopants is still desired for efficient organic light-emitting diodes (OLEDs). In this work, two novel carbazole-formate based isomers (2CzMC and 4CzMC) with planar donor‒π‒acceptor (D‒π‒A) structures were designed and synthesized as the hosts for phosphorescent OLEDs (PhOLEDs). Due to the weak intramolecular charge transfer character and limited conjugation extensions, both 2CzMC and 4CzMC showed wide-bandgap emissions around 380 nm and high triplet energy levels (2.83 eV for 2CzMC, and 2.90 eV for 4CzMC). The photoluminescent spectra of 2CzMC and 4CzMC doped films with blue, green and red phosphors exhibited completely energy transfer from the hosts to the dopants. PhOLEDs devices with similar structures employing these doped film as emitter layers achieved excellent performance. Especially for 4CzMC-FIrpic based blue device, the external quantum efficiency (EQE) reached as high as 18.9%. This study showed a molecular design strategy to develop novel carbazole-based hosts for different color PhOLEDs.