Two new highly efficient homoleptic green-emitting meridional iridium(III) complexes, namely, mer-tris[5-hexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one]iridium(III) (mer-Ir1) and mer-tris[5-ethylhexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one]iridium(III) (mer-Ir2), were designed and synthesized at high temperature. These new Ir(III) complexes consist of an amide bridged trifluoromethyl substituted phenylpyridine skeleton with a longer alkyl chain. Interestingly, both Ir(III) complexes, mer-Ir1 and mer-Ir2, show bright green emission (λ_max = 528 nm) with high photoluminescence quantum yields of 42 and 51% in solution at room temperature, respectively. Their thermal, photophysical, electrochemical, and electroluminescence (EL) properties were fully investigated. Both complexes were used as dopants for solution-processed green phosphorescent organic light-emitting diodes (PHOLEDs). Notably, the device using mer-Ir2 as a new green dopant exhibited excellent EL performance with a maximum external quantum efficiency of 20.03% and maximum current efficiency of 67.81 cd A⁻¹. To the best of our knowledge, this is the first time that particularly Ir(C^N)₃-based mer-Ir(III) isomers showing excellent EL performance with high luminous efficiency in the green region via solution-processed PHOLEDs have been reported.