Patent ID: 7579089

Claim:
A light emitting device comprising: a first electrode; a hole transporting region comprising a hole transporting material adjacent to the first electrode; a light emitting region comprising a first layer over the hole transporting region, a second layer over the first layer, and a light emitting layer sandwiched between the first layer and the second layer, an electron transporting region over the second layer, the electron transporting region comprising an electron transporting material; and a second electrode over the electron transporting region, wherein the first layer, the second layer, and the light emitting layer comprise the hole transporting material and the electron transporting material, wherein the light emitting layer further comprises a dopant, wherein the second layer further comprises a blocking material, and wherein an energy difference between a highest occupied molecular orbit and a lowest unoccupied molecular orbit of the blocking material is larger than an energy difference between a highest occupied molecular orbit and a lowest unoccupied molecular orbit of the hole transporting material and the electron transporting material.