title: Black film for improving the contrast ratio of organic light emitting diodes.
abstract: 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/m2 during ambient light of 33.5 cd/m2. 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 Al/CuPc/Al/CuPc/Al structure.
authors.affiliation: Institute of Microelectronics and Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan.
authors.forename: Jian-Ji
authors.initials: JJ
authors.lastname: Huang
authors.forename: Yi-Cheng
authors.initials: YC
authors.lastname: Lin
authors.forename: Yan-Kuin
authors.initials: YK
authors.lastname: Su
authors.forename: Yi-Lin
authors.initials: YL
authors.lastname: Wu
authors.forename: Fuh-Shyang
authors.initials: FS
authors.lastname: Juang