We have demonstrated high-efficiency greenish-blue phosphorescent organic light-emitting diodes (PHOLEDs) based on a dimesitylboryl-functionalized C boolean AND N chelate Pt(II) phosphor, Pt(m-Bptrz) (t-Bu-pytrz-Me). Using a high triplet energy platform and optimized double emissive zone device architecture results in greenish-blue PHOLEDs that exhibit an external quantum efficiency of 24.0% and a power efficiency of 55.8 lm/W. This record high performance is comparable with that of the state-of-the-art Ir-based sky-blue organic light-emitting diodes. (C) 2014 AIP Publishing LLC.