In one embodiment of an
OLED device, a hole injection /
transport layer is added to the device structure in order to increase the number of holes injected into the emissive layer and reduce the number of electrons injected into the added hole injection /
transport layer. In a first configuration of the added hole injection /
transport layer, the added hole injection / transport layer is comprised of a non-doped hole transporting material that has an IP range between the highest IP value of the adjacent layer on the
anode-end and the lowest IP value of the adjacent layer on the “emissive layer”-end. Optionally, in addition, nearly all
electron affinities of the added hole injection / transport layer are less than the lowest
electron affinity of the adjacent layer on the “emissive layer”-end. In a second configuration of the added hole injection / transport layer, this layer is formed by
doping the hole transport material. The
dopant is able to abstract electrons from the hole transporting material. By
doping the hole transport material, the IP range of the hole transporting material is broadened. In addition or alternatively, the
doping produces more HOMO energy states thus allowing more holes to occupy these intermediate states at any one time.