The structure–property correlations of a set of heteroleptic red- and green-emitting Ir(III) complexes with different temperature sensitivities and charge trapping capabilities are described, revealing superb performance in multi-layer phosphorescent organic light-emitting diodes (PhOLEDs) expressed by very high maximum luminous efficiencies up to 36.8 cd A⁻¹. Using 2-phenylpyridine and with 2-(naphthalen-1-yl)pyridine as the C⁁N ligand, the resulting red emitting complex featured a maximum luminous efficiency of 10.8 cd A⁻¹; one of the most excellent device performances within this class of red Ir(III) emitters.