This paper presents a black film with double period metal-organic cathode structure for reducing the cathode reflection and enhancing the contrast ratio (CR) in organic light emitting diodes (OLEDs). The absorption and destructive interference effect caused by the copper-phthalocyanine (CuPc) and ultra thin aluminum (Al) periodic layers decrease the ambient light. The double-period black film structure (Al/CuPc/Al/CuPc/Al) has the lowest reflected luminance of 2.61 cd/m 2 during ambient light of 33.5 cd/m 2. The device CR without any black film is only 82.5. The device with single period black film (Al/CuPc/Al) obtains up to 267.1 and the highest CR of 958 can be achieved with a double period black film AI/CuPc/AI/CuPc/AI structure.
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