An organic light-emitting diode includes a first electrode, an intermediate layer on the first electrode, and a second electrode on the intermediate layer. The intermediate layer includes an emission layer including an organic material, and a functional layer between the second electrode and the emission layer and including at least one of a metal compound and a semiconductor compound including at least one of an oxygen atom and a sulfur atom. An oxygen concentration in the functional layer increases toward the second electrode, and a sulfur concentration in the functional layer increases toward the emission layer.