An organic light-emitting device comprising: a first electrode; a second electrode facing the first electrode; and an organic layer disposed between the first electrode and the second electrode, wherein the organic layer comprises an emission layer, the emission layer comprises a first host and a dopant, the dopant is an organometallic compound including platinum, the organic light-emitting device satisfies a condition of: HOMO(D)−HOMO(Host 1)≥0.2 electron volts, HOMO(D) is a highest occupied molecular orbital (HOMO) energy level of the dopant in electron volts, HOMO(Host 1) is a HOMO) energy level of the first host in electron volts, and HOMO(D) and HOMO(Host 1) are each measured using a photoelectron spectrometer in an ambient atmosphere.