This study demonstrates high-efficiency organic electrophosphorescent devices (OLEDs) using the green electrophosphorescent molecule, fac-tris(2-phenylpyridine)iridium (Ir(ppy)3), doped into various electron-transport layer (ETL) hosts. Using 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole as the host, a maximum external quantum efficiency (ηext) of 15.4 ± 0.2% and a luminous power efficiency of 40 ± 2 Im/W were achieved. The internal quantum efficiency (ηint) approached 100%, indicating efficient radiative recombination of both singlet and triplet excitons. The performance was attributed to the favorable energy level alignment between the host and the dopant, promoting efficient energy transfer. The study also explored the role of single and double heterostructures, suggesting that exciton formation in Ir(ppy)3 occurs near the hole-transport layer/ETL interface. Further improvements in efficiency are expected through enhanced light out-coupling techniques.This study demonstrates high-efficiency organic electrophosphorescent devices (OLEDs) using the green electrophosphorescent molecule, fac-tris(2-phenylpyridine)iridium (Ir(ppy)3), doped into various electron-transport layer (ETL) hosts. Using 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole as the host, a maximum external quantum efficiency (ηext) of 15.4 ± 0.2% and a luminous power efficiency of 40 ± 2 Im/W were achieved. The internal quantum efficiency (ηint) approached 100%, indicating efficient radiative recombination of both singlet and triplet excitons. The performance was attributed to the favorable energy level alignment between the host and the dopant, promoting efficient energy transfer. The study also explored the role of single and double heterostructures, suggesting that exciton formation in Ir(ppy)3 occurs near the hole-transport layer/ETL interface. Further improvements in efficiency are expected through enhanced light out-coupling techniques.