Synthesis and optoelectronic properties of thermally cross-linkable hole-transporting poly(fluorene-co-triphenylamine)

This paper describes the synthesis of a new thermally cross-linkable hole-transporting poly(fluorene-co-triphenylamine) (PFTV) by Suzuki coupling reaction and its application in polymer light-emitting diodes (PLEDs). The characteristics of PFTV were analyzed by 1H NMR, differential scanning calorimetry, optical spectroscopy, cyclic voltammetry, and atomic force microscopy. Its HOMO level lies between those of PEDOT:PSS and poly(9,9-dioctylfluorene), forming a stepwise energy ladder to facilitate hole-injection. Multilayer device with thermally cross-linked PFTV as hole-transporting layer (ITO/PEDOT:PSS/HTL/PFO/LiF/Ca/Al) was readily fabricated by successive spin-coating processes, its maximum luminance efficiency (2.27 cd/A) was significantly higher than that without PFTV layer (0.50 cd/A). In addition, the PFTV was successfully applied as host for red-emitting Ir(piq)2acac to obtain a device with moderate performance (5300 cd/m2 and 2.64 cd/A). The PFTV is a promising hole-transporting material for the fabrication of multilayer PLEDs by wet processes as well as a potential host for phosphorescent PLEDs.