High efficiency has been achieved in polymer light-emitting diodes (PLEDs) exhibiting red emission by doping a fluorescence host material, poly(vinylcarbazole) (PVK), with an iridium(III) complex, bis[2-(2 ′-benzothienyl)-pyridinato-N,C3′] iridium(acetylacetonate) (BtpIr). The electroluminescence spectrum has a maximum wavelength of 614 nm. The highest external quantum efficiency is 3.3%. Due to its short triplet excited lifetime (∼5 μs), the quenching of the triplet exciton in BtpIr-doped PVK PLEDs has been shown to be suppressed compared to platinum(II)-2,8,12,17-tetraethyl- 3,7,13,18-tetramethylporphyrin-doped PVK PLEDs. 65% of the peak efficiency can be sustained at high-current density and at the very high brightness of 1350 cd/m2. We suggest that both triplet-triplet annihilation and polaron-triplet annihilation involves exciton quenching.