Provided is an organic light-emitting device including a first electrode; a second electrode facing the first electrode; and an organic layer between the first electrode and the second electrode, the organic layer including an emission layer. The emission layer includes a first compound represented by Formula 1-1 or Formula 1-2 below, a second compound represented by Formula 2 below, and a third compound represented by Formula 3 below: where Ar1 to Ar8, R1 to R3, A, L1, L2, a1, a2, b1, b2, c1, c2, l1, and l2 are as defined in the specification.