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 H-1 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)(2)acac to obtain a device with moderate performance (5300 cd/m(2) 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. (C) 2010 Elsevier Ltd. All rights reserved.