Provided is an organic light emitting device that includes at least one organic layer between a first electrode and an emissive layer wherein the organic layer includes at least two organic materials and at least one of the organic materials consequently has a concentration gradient in the direction from the first electrode to a second electrode through a single solution process by self organization. Since the organic layer has a work function having a gradient in the direction from the first electrode to the second electrode, holes can be injected from the first electrode to the emissive layer, and thereby an organic light emitting device having high efficiency and a long lifetime can be obtained.