Chemically doped hole transporting materials with low cross-linking temperature and high mobility for solution-processed green/red PHOLEDs

Abstract

Recently, developing insoluble cross-linkable functional layers plays a vital role for solution-processed organic light emitting diodes (OLEDs). Here, two vinyl-based cross-linkable hole transporting materials V-TPAVTPD and V-TPAVCBP are designed and synthesized. Additionally, cationic photoinitiator 4-octyloxydiphenyliodonium hexafluoroantimonate (OPPI) is first introduced to chemically induce vinyl-based photo cross-linking process, aiming at lowering cross-linking temperature and enhancing hole mobility. As a result, cross-linking can occur at expressly low temperature of 120 °C with >95% solvent resistance. Moreover, hole mobility is markedly enhanced with the value higher than 10−3 cm2 V−1 s−1. When applying hole transporting layers (HTLs) to solution-processed green and red phosphorescent OLEDs, devices exhibit excellent properties. Particularly, the maximum current efficiency of 54.0 cd A−1 (green), 9.8 cd A−1 (red) and external quantum efficiency of 15.5% (green), 15.0% (red) are obtained when OPPI doped V-TPAVCBP serves as HTL. This low temperature feasible cross-linking process to prepare HTLs with preferable hole mobility promotes the development of OLEDs.