Enhancing the contrast and power efficiency of organic light-emitting diodes using CuPc/TiOPc as an anti-reflection layer

High contrast ratio and high power efficiency organic light-emitting diodes (OLEDs) using a dual electron transporting layer of copper phthalocyanine (CuPc)/ titanium oxide phthalocyanine (TiOPc) as an anti-reflection layer have been investigated. The OLED configuration comprises indium tin oxide (ITO)/4,4',4''-tris{N,-(3-methylphenyl)-N-phenylamino}- triphenylamine) (m-MTDATA)/N, N'-diphenyl-N,N'-bis(l-naphthyl-phenyl)-(l,l'-biphenyl)-4, 4'-diamine (NPB)/tris(8-hydroxyquinolino)-aluminium (Alq 3 )/CuPc/TiOPc/LiF/Al. The contrast ratio of the device with a CuPc/TiOPc anti-reflection layer is about double and the power efficiency higher than that of a conventional device without the anti-reflection layer. The improvement in the power efficiency and the contrast ratio of the device that is obtained using a CuPc/TiOPc anti-reflection layer is attributable to the stepwise electron transporting barrier and the reduced optical reflection from the cathode. The contrast ratio suffices for outdoor display applications.