Abstract: 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 and a fluorescent compound, wherein the fluorescent compound comprises a 3n-?*-to-1?-?* energy transition from a 3n-?* excited state to a 1?-?* excited state, an energy level in a 1n-?* excited state of the fluorescent compound is greater than an energy level in the 1?-?* excited state of the fluorescent compound, the fluorescent compound emits a fluorescent light by radiative energy transition of an exciton in the 1?-?* excited state to a ground state, and the energy level in the 1n-?* excited state, the energy level in the 1?-?* excited state, and the energy level in the 3n-?* excited state are each independently calculated by using a time dependent-Density Functional Theory method.