An organic light-emitting device includes a substrate, an anode disposed over the substrate, at least one organic light-emitting layer disposed over the anode, a buffer layer disposed over the organic light emitting layer, and a cathode disposed over the buffer layer. The cathode layer includes a first cathode layer, a second cathode layer, and a third cathode layer. The first cathode layer includes conductive material. The second cathode layer includes electron transport material. The third cathode layer includes conductive material.