Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light‐Emitting Diodes |
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| Authors: | Tae‐Woo Lee Mu‐Gyeom Kim Sang Hun Park Sang Yeol Kim Ohyun Kwon Taeyong Noh Jong‐Jin Park Tae‐Lim Choi Jong Hyeok Park Byung Doo Chin |
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| Affiliation: | 1. Samsung Advanced Institute of Technology Mt. 14‐1, Nongseo‐dong, Giheung‐gu Yongin‐si, Gyeonggi‐do 446‐712 (Korea);2. Pohang University of Science and Technology San 31 Hyoja‐dong, Nam‐gu Pohang, Gyeongbuk 790‐784 (Korea);3. Department of Chemistry Seoul National University Seoul 151‐742 (Korea);4. Department of Chemical Engineering Sungkyunkwan University Suwon 440‐746 (Korea);5. Department of Polymer Science and Engineering Dankook University Jukjeon‐dong, Suji‐gu, Yongin‐si, Gyeonggi‐do 448‐701 (Korea) |
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| Abstract: | The short device lifetime of blue polymer light‐emitting diodes (PLEDs) is still a bottleneck for commercialization of self‐emissive full‐color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three‐layer (BaF2/Ca/Al) cathode compared with conventional two‐layer cathodes (BaF2/Al and Ba/Al). Therefore, the roles of the BaF2 and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF2 layer should be deposited to the thickness of at least one monolayer (～3 nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF2 and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer. |
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| Keywords: | cathode materials electron transfer light‐emitting diodes polymeric |
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