An organic light-emitting device including a first electrode; a second electrode; and an organic layer disposed between the first electrode and the second electrode, wherein the organic layer comprises an emission layer, and wherein the organic layer comprises a first compound represented by Formula 1 and a second compound having the lowest excited triplet energy level greater than 2.73 electron volts: wherein in Formula 1, R11 to R33 are the same as described in the specification.