US Patent 8034465 Phosphorescent oled having double exciton-blocking layers

An organic light-emitting device comprising an anode; a cathode; a hole-transporting layer disposed between the anode and the cathode; a phosphorescent light-emitting layer disposed between the hole-transporting layer and the cathode, wherein the phosphorescent light-emitting layer includes at least one host and at least one phosphorescent dopant; a first exciton-blocking layer disposed between the hole-transporting layer and the phosphorescent light-emitting layer; wherein the first exciton-blocking layer has a triplet energy greater than the triplet energy of the host in the phosphorescent light-emitting layer; and a second exciton-blocking layer disposed between the first exciton-blocking layer and the phosphorescent light-emitting layer, wherein the second exciton-blocking layer is in contact with the phosphorescent light-emitting layer, and wherein the second exciton-blocking layer has a triplet energy less than the triplet energy of the first exciton-blocking layer.