Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light-Emitting Diodes
✍ Scribed by 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
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 472 KB
- Volume
- 19
- Category
- Article
- ISSN
- 1616-301X
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✦ Synopsis
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 (BaF~2~/Ca/Al) cathode compared with conventional two‐layer cathodes (BaF~2~/Al and Ba/Al). Therefore, the roles of the BaF~2~ and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF~2~ 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 BaF~2~ and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer.