Organic light-emitting device

An organic light-emitting device, comprising:

• a light-transmitting substrate having a predetermined refraction index;
• a light-transmitting anode electrode having a refraction index that is different from the refraction index of the substrate, the anode electrode being spaced apart from the substrate;
• a composite film layer sandwiched between the substrate and the anode electrode so as to have an interface with the substrate and an interface with the anode electrode, the composite film layer having a refraction index that varies, in a direction perpendicular to the substrate, from a first value adjacent the interface with the substrate to a second value adjacent the interface with the anode electrode, the first value being substantially the same as the refraction index of the substrate and the second value being substantially the same as the refraction index of the anode electrode;
• an organic light-emitting layer on the anode electrode;
• and
• a cathode electrode on the light-emitting layer,
• wherein the composite film layer is a multi layer structure composed of a plurality of films made of at least two materials with different refraction indices, and the refraction index of the composite film layer varies as a function of the thickness of each film and the composition ratio of the at least two materials therein.