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

Abstract

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.