Synthesis and Characterization of Thermally Crosslinkable Hole-Transporting Polymers for PLEDs

Two new thermally crosslinkable hole-transporting polymers, X-PTPA and X-PCz, were synthesized via Yamamoto coupling reactions. The number-averaged molecular weights (M-n) of X-PTPA and X-PCz were found to be 45,000 and 48,000, respectively, and therewith, polydispersity indices were of 1.8 and 1.7, respectively. Thermally crosslinked X-PTPA and X-PCz exhibit excellent solvent resistance and stable optoelectronic properties. The UV-visible maximum absorption peaks of X-PTPA and X-PCz in the thin film state are at 389 and 322 nm, respectively. The HOMO levels of X-PTPA and X-PCz are estimated to be -5.27 and -5.39 eV, respectively. Multilayered devices (ITO/crosslinked X-PTPA or X-PCz/SY-PPV/LiF/Al) were fabricated with SY (SuperYellow) as the emitting layer. The maximum efficiency of the multilayered device with a crosslinked X-PTPA layer is approximately three times higher than that of the device without a crosslinked X-PTPA layer and much higher than that of the crosslinked X-PCz device. This result can be explained by the observations that crosslinked X-PTPA produces increased electron accumulation within the emitter, SY, and also efficient exciton formation due to improved charge balance. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5111-5117