We fabricated the organic light-emitting diodes (OLEDs) with sensitizer by solution process. The addition of sensitizer into the emission layer improved the device efficiency. 4,4'-N,N'-dicarbazole-biphenyl (CBP), bis(2-phenylquinoline) iridium(III) (acetylacetonate) [Ir(pq)(2)(acac)], tris(2-phenylpyridine) iridium [Ir(ppy)(3)] were used as host, red emitting dopant, and sensitizer, respectively. The sensitizer leads to the cascade energy transfer from the host into the red emitting dopant. The doping concentration of sensitizer was varied as 0 similar to 20 wt% and optimized. As a result, the device with 5% Ir(ppy)(3) shows the luminous efficiency, power efficiency, and quantum efficiency of 5.1 cd/A, 4.0 lm/W, and 3.0%, respectively. These efficiencies are about 3 times as high as that of device without sensitizer.