Novel carbazole host materials for solution processed TADF Organic Light Emitting Diodes

Several functional and internal layers have been used to improve the performance of solution-processed Organic Light Emitting Diodes (OLED) devices. In the case of thermally activated delayed fluorescence (TADF) OLEDs, a large number of emitter materials have already been reported, but the design and development of potential host materials are overlooked. Efficient solution processable host materials for TADF OLEDs can reduce the complexity in the device architecture and production cost. In this work, we utilized a series of carbazole-based solution-processable host materials (ME4, ME5, ME9, ME10, and ME13) to fabricate the 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) based green TADF OLEDs. Among them, the ME9 composing device showed the best performance. The resultant device exhibited a maximum power efficacy of 40.0 lm/W, current efficacy of 44.7 cd/A, and external quantum efficiency of 14.1% with a maximum luminance of 16,220 cd/m2. The excellent performance may attribute to the low singlet-triplet energy gap (ΔEST), high photoluminescence quantum yield (PLQY), high thermal stability, and unique porous morphology of the ME9.