An organic light-emitting device, comprising: a first electrode; a second electrode; and an organic layer located between the first electrode and the second electrode, wherein the organic layer comprises an emission layer, wherein the emission layer comprises a host, a sensitizer, and an emitter, wherein the host, the sensitizer, and the emitter are different from each other, and wherein the sensitizer is represented by Formula 1: M1(L1)(L2)  Formula 1 wherein, in Formula 1, M1 is Au, Ag, or Cu, L1 is a ligand represented by Formula 2-1 or Formula 2-2, and L2 is a ligand represented by one of Formulae 3-1, 3-2, or 3-3: wherein A21, A31, A32, X31, R21 to R24, R31 to R35, b23, and b33 are as defined herein, and * indicates a binding site to M1 in Formula 1.