High performance organic light emitting diodes using substoichiometric tungsten oxide as efficient hole injection layer

► Hydrogen reduced tungsten oxides with controlled stoichiometry. ► Beneficial optical properties, surface morphology and increased conductivity. ► Unique hole injection properties of substoichiometric tungsten suboxide oxide WO2.5. ► Elucidation of the hole injection mechanism via gap states. ► Dramatic device performance improvement due to ohmic contact formation.