Red phosphorescent organic light-emitting diodes with indium tin oxide/single organic layer/Al simple device structure

A simple red phosphorescent organic light-emitting diode with a device structure of indium tin oxide (ITO)/single organic layer/Al was developed using a mixed host emitting layer of 2,7-bis(diphenylphosphoryl)spiro[fluorene-7,11′-benzofluorene] (SPPO21) and N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (NPB). Holes were directly injected from the ITO to the emitting layer through the NPB, while electrons were injected from the Al to the emitting layer through the SPPO21. The quantum efficiency of the simple device was comparable to that of the common red device.