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

Abstract

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 N2,N2,N7,N7-tetrakis(4-(3,6-di-tert-butyl-9H- carbazol-9-yl)phenyl)-9,9-dimethyl-9H-fluoren-2,7-diamine (p-BCz-F) and N2,N2,N7, N7-tetrakis(4-(2,7-di-tert-butyl-9H-carbazol-9-yl)phenyl)-9,9-dimethyl-9H-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 (Tg) of 168 °C. Particularly, in terms of mobility, 1.42-fold higher could be also found for p-BCz-F (4.35 × 10−4 cm2V–1S−1) than m-BCz-F (3.05 × 10−4 cm2V–1S−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/m2, corresponding CE of 6.12 cd/A and L of 21055 cd/m2 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.