Improved efficiency of polymer light-emitting diodes by inserting a hole transport layer formed without thermal treatment above glass transition temperature |
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Authors: | Masato Shakutsui Hiromi Matsuura Katsuhiko Fujita |
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Affiliation: | 1. Department of Applied Science for Electronics and Materials, Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga Koen, Kasuga, Fukuoka 816-8580, Japan;2. Department of Energy Science and Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan;3. Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga Koen, Kasuga, Fukuoka 816-8580, Japan |
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Abstract: | We have demonstrated a significant improvement in the performance of polymer light-emitting diodes (PLEDs) by inserting the fluorene-triatylamine copolymer as hole transport layer (HTL) without a thermal treatment above the glass transition temperature (Tg). A thin HTL insolubilized by a thermal treatment above Tg is often inserted as an interlayer between an anode buffer layer and a light-emitting polymer (LEP) in PLEDs fabricated by using a conventional solution process. The evaporative spray deposition using ultradiluted solution (ESDUS) method has enabled fabricating polymer bilayer structure without an insolublizing procedure. The bilayer PLEDs fabricated by ESDUS without the thermal treatment showed significantly higher and more stable external quantum efficiency than PLEDs having the conventional interlayer. Thermal treatment above Tg of the copolymer would induce degradation of its hole injection property. Furthermore, ESDUS bilayer devices showed much higher power efficiency than interlayer devices when calcium was used for cathode. The improvements would be caused by the enhancement of hole injection and the effective electron blocking at the copolymer/LEP interface in the ESDUS bilayer devices. |
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