Molecularly engineered host materials for high performance inkjet-printed thermally activated delayed fluorescence organic light-emitting diodes

Due to the low cost and high performance of thermally activated delayed fluorescence (TADF) materials, TADF based organic light-emitting diodes (OLEDs) are highly attractive for future display panels. To improve the material usage and direct pixelation, inkjet printing (IJP) is deemed as one of the most potential technologies for fabricating large-area and flexible OLEDs, which requires the materials to be solution processable and inkjet printable. However, there are only a few host materials with appropriate thermal stability and solution processability to meet the requirements for IJP fabrication of OLEDs. Herein, three new host materials for solution-processed OLEDs have been designed and synthesized with different molecular symmetries by molecularly engineering the widely used 4,4 ' -bis(9-carbazolyl)-2,2 ' -biphenyl (CBP), named AC1, AC2, and AC3. Among them, AC2 and AC3 showed comparatively high thermal stability. Spin-coating processed TADF-OLEDs (4CzIPN as the emitter) based on the three hosts have been fabricated, and the AC2-based TADF-OLED exhibited the highest maximum external quantum efficiency (EQE) of 16.4%. Its IJP fabricated device also achieved a maximum EQE of 11.0%, which is the highest among reported TADF-OLEDs by IJP fabrication.