High-brightness solution-processed phosphorescent OLEDs with pyrimidine-based iridium(III) complexes

Two heteroleptic cyclometalated iridium(III) complexes, Ir(ppm)2(pic) and Ir(ppm)2(taz), using 4,6-diphenyl pyrimidine (Hppm) as a cyclometalating ligand, were successfully synthesized and characterized. Strong emission at 555 and 532 nm with high photoluminescence quantum yields of 83% and 86% in PMMA at 298 k were obtained for Ir(ppm)2(pic) and Ir(ppm)2(taz), respectively. Solution-processed organic light-emitting diodes (OLEDs) based on Ir(ppm)2(pic) and Ir(ppm)2(taz) showed high-brightness of 112 233 and 125 072 cd m−2, peak current efficiencies of 30.6 and 40.4 cd A−1 and maximum external quantum efficiencies of 10.4 and 17.3%, respectively, accompanied by very low efficiency roll-off values. The ancillary ligand taz tuned the emission to saturated green, and more importantly, it can significantly increase the spectral stability and device efficiency.