Synthesis and characterization of fluorene-derived PU as a thermo cross-linked hole-transporting layer for PLED

Novel hole-transporting polyurethane, denoted as P1, resulting from the condensation of 9, 9-bis(4-hydroxyphenyl)fluorene and isophorone diisocyanate (denoted as IPDI) has been developed. When P1 is thermally consolidated in the presence of 2-(phosphonooxy)ethyl methacrylate (P2M), it forms a distinguished hole-transport layer that leads to an extremely good performance of the phosphorescent PLED. In the study, the device of ITO/PEDOT: PSS/P1-P2M/Ir(ppy)3-t-PBD-PVK/Mg/Ag shows a high current efficiency of 27.6 cd/A and a low turn-on voltage of 6 V. In particular, the stable output efficiency of 17–22 cd/A within the range of 420–4400 cd/m2 at 12–20 V makes P1 a promising hole-transport material for phosphorescent PLED applications.