Regulation of peripheral tert-butyl position: Approaching efficient blue OLEDs based on solution-processable hole-transporting materials

Abstract Solution-processable hole transporting materials (HTMs) play a vital role in organic light emitting diodes (OLEDs) with the purpose of reducing costs and improving productivity. Herein, two twisted HTMs N 2 , N 2 , N 7 , N 7 -tetrakis(4-(3,6-di- tert -butyl-9 H - carbazol-9-yl)phenyl)-9,9-dimethyl-9 H -fluoren-2,7-diamine ( p -BCz-F ) and N 2 , N 2 , N 7 , N 7 -tetrakis(4-(2,7-di- tert -butyl-9 H -carbazol-9-yl)phenyl)-9,9-dimethyl-9 H -fluoren-2,7-diamine ( m -BCz-F ), have been successfully synthesized. The two compounds are endowed with superior solubility in common organic solvents, facilitating solution-processed OLEDs. By simply changing position of peripheral tert -butyl moiety, the material performance could be regulated. The HTMs p -BCz-F exhibits superior glass transition temperature ( T g ) of 168 °C . Particularly, in terms of mobility, 1.42-fold higher could be also found for p -BCz-F (4.35 × 10 −4 cm 2 V – 1 S −1 ) than m -BCz-F (3.05 × 10 −4 cm 2 V – 1 S −1 ). Similarly, the p -BCz-F -based blue devices with BCzVBi as the emitter show better performance with maximum current efficiency (CE) of 7.05 cd/A and luminance (L) of 23365 cd/m 2 , corresponding CE of 6.12 cd/A and L of 21055 cd/m 2 for m -BCz-F -based devices. In short, the different position of peripheral tert -butyl on carbazolyl moiety will lead to different performance and it provided a simple strategy to design solution-processable HTMs for efficient OLEDs.