The present invention is directed to simplified OLED structures comprising an
anode layer, a hole injecting layer (HIL) in direct contact with the anode layer,
an emissive organic electron transporting layer (ETL) in direct contact with the
hole injecting layer, and a cathode layer in direct contact with the emissive organic
electron transporting layer. The hole injecting material used in the hole injecting
layer is characterized, in particular, as being an organic material having an ionization
potential that is not more than about 0.7 eV greater than the ionization potential
of the material used for the anode layer. The emissive organic electron transporting
layer comprises an organic electron transporting material and an organic hole-trapping
emissive material, for example, an organic phosphorescent material that produces
emission from a triplet excited state of an organic molecule.
