Carbazole or carbazole-3-carbonitrile /pyridine host materials for efficient solution-processable blue phosphorescent and green TADF OLEDs

Two carbazole or carbazole-3-carbonitrile/pyridine-based bipolar materials were designed and synthesized as the hosts for solution-processed sky-blue PhOLEDs and green TADF-OLEDs. The solution-processed blue PhOLEDs based on 2,6-CzPy and CN-2,6-CzPy were fabricated exhibiting CE max of 27.4, 14.0 cd A −1 and PE max of 11.1, 5.6 lm W −1. Remarkably, the turn-on voltage ( V on ) of device A and B based on 2,6-CzPy drops slightly, as the doping concentration increasing from 10% to 15%. The green TADF-OLED based on 2,6-CzPy shows CE max of 10.6 cd A −1, EQE of 3.0%. Although the rational introduction of cyano substituents can significantly upgrade the thermal stability of the hosts. T g and T d of CN-2,6-CzPy improved by 53 °C and 83 °C than 2,6-CzPy. Nevertheless, the introduction of cyano substituents leads to CN-2,6-CzPy exhibiting deeper HOMO and generating a large hole injection barrier is not conducive to improve device performance.