Crosslinkable triphenylamine-based hole-transporting polymers for solution-processed polymer light-emitting diodes

Abstract We report the synthesis and characterization of a thermally crosslinkable hole-transporting poly(indenofluorene-co-triphenylamine) copolymer (X-IFTPA) containing a vinyl-functionalized triphenylamine moiety. This copolymer exhibited an exothermal peak at 125 °C in the first heating/cooling cycle of a differential scanning calorimetry study, indicating that crosslinking occurred. The highest occupied molecular orbital energy level of this copolymer was estimated to be −5.30 eV, as determined by cyclic voltammetry measurement. Flat and uniform films were formed by spin casting X-IFTPA from chlorobenzene solution. Crosslinking can be finished by thermally annealing the film at 150 °C for 24 min, which can be confirmed by reflectance Fourier transform infrared spectroscopy and UV–Vis absorption spectra. Multi-layer polymer light-emitting diodes (PLEDs) incorporating X-IFTPA as the hole transport layer and a green-light-emitting copolymer as the emissive layer exhibited enhanced luminous efficiency relative to that of a control device without a hole transport layer. Thus, the developed cross-linkable copolymer X-IFTPA is a promising material for the construction of efficient PLEDs.