We designed and synthesized a novel yellow-emitting iridium complex, bis[2-(9-ethyl-9H-carbazol-3-yl)-benzothiazole]iridium(III) acetoacetonate [(Btc)2Ir(acac)], for use in phosphorescent organic light-emitting diodes. The synthesized compound was characterized by 1H NMR and 13C NMR. Photophysical and electrochemical studies revealed photoluminescence emission at 555 nm (in solution) with a band gap energy of 2.37 eV. The phosphorescent organic light-emitting diodes based on ITO/PEDOT:PSS/α-NPD/TCTA/CBP:(Btc)2Ir(acac)(8%)/BCP/Alq3/LiF/Al exhibited a yellow emission at 562 nm with a high luminous efficiency of 35.4 cd/A, a maximum external quantum efficiency of 12.9% at 7.4 V, and a very outstanding luminance of 100,048 cd/m2. Because of its high electroluminescent performance, efficient white phosphorescent organic light-emitting devices using this new iridium complex in the structure of ITO/TAPC/DCzPPy(x%):FIrpic(14%):(Btc)2Ir(acac)(y%)/Bphen/LiF/Al were fabricated. The device, with a new iridium(III) complex doping concentration of 0.15%, exhibited a maximum luminous efficiency as high as 41.6 cd/A at 5 V, CIE coordinates of (0.34, 0.46), a maximum luminance of 25,010 cd/m2, and a maximum power efficiency of 28.9 lm/W, respectively.