Enhanced performance of organic light emitting device by insertion of conducting/insulating WO3 anodic buffer layer

Tungsten oxide (WO3) ultrathin film with high optical transparency is deposited on indium-tin oxide glass as hole injection layer of organic light emitting device (OLED). As-deposited WO3 film is amorphous and insulating, wherein the buffer thickness of 0.5 nm shows enhancement of hole injection in OLED. The device performance is further enhanced after the as-deposited WO3 film is thermally treated, which is ascribed to lowering of the effective energy barrier height for hole injection. The annealed buffer layer is identified to be a semiconductor with crystalline structure. Although the thickness of the annealed WO3 buffer layer is up to 1.5 nm, the device performance is still better than that of unmodified OLED. The difference in anodic buffer thickness dependent device performance for both types of WO3 films is determined by the electrical property.