Cascade hole transport in efficient green phosphorescent light‐emitting devices achieved by layer‐by‐layer solution deposition using photocrosslinkable‐conjugated polymers containing oxetane side‐chain moieties |
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Authors: | Jicheol Shin Hyun Ah Um Min Ju Cho Tae Wan Lee Kyung Hwan Kim Jung‐Il Jin Seogshin Kang Taehan Park Sung Hoon Joo Joong Hwan Yang Dong Hoon Choi |
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Affiliation: | 1. Department of Chemistry, Research Institute for Natural Sciences, Korea University, 5 Anam‐dong, Sungbuk‐gu, Seoul 136‐701, Korea;2. LG Display R&D Center, 1007 Deogeun‐ri, Wollong‐myeon, Paju‐si, Gyeonggi‐do, 413‐811, Korea |
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Abstract: | A hole‐injection/transport bilayer structure on an indium tin oxide (ITO) layer was fabricated using two photocrosslinkable polymers with different molecular energy levels. Two photoreactive polymers were synthesized using 2,7‐(or 3,6‐)‐dibromo‐9‐(6‐((3‐methyloxetan‐3‐yl)methoxy)hexyl)‐9H‐carbazole) and 2,4‐dimethyl‐N,N‐bis(4‐ (4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)phenyl)aniline via a Suzuki coupling reaction. When the oxetane groups were photopolymerized in the presence of a cationic photoinitiator, the photocured film showed good solvent resistance and compatibility with a poly(N‐vinylcarbazole) (PVK)‐based emitting layer. Without the use of a conventional hole injection layer (HIL) of poly(3,4‐ethylenedioxythiophene)/(polystyrenesulfonate) (PEDOT:PSS), the resulting green light‐emitting device bearing PVK: 5‐4‐tert‐butylphenyl‐1,3,4‐oxadiazole (PBD):Ir(Cz‐ppy)3 exhibited a maximum external quantum efficiency of 9.69%; this corresponds to a luminous efficiency of 29.57 cd/A for the device K‐4 configuration ITO/POx‐I/POx‐II/PVK:PBD:Ir(Cz‐ppy)3/triazole/Alq3/LiF/Al. These values are much higher than those of PLEDs using conventional PEDOT:PSS as a single HIL. The significant improvement in device efficiency is the result of suppression of the hole injection/transport properties through double‐layered photocrosslinked‐conjugated polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 |
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Keywords: | conjugated polymers electrophosphorescence hole transport layer iridium(III) complex light‐emitting diodes (LED) luminescence oxetane photocrosslink photoluminescence photopolymerization solubility synthesis |
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