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Park, Hyeonjung,Ma, Boo Soo,Kim, Jin-Seong,Kim, Youngkwon,Kim, Hyeong Jun,Kim, Donguk,Yun, Hongseok,Han, Junghun,Kim, Felix Sunjoo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2019 Macromolecules Vol.52 No.20
<P>In this work, we develop mechanically robust and high-performance organic thin-film transistors (OTFTs) based on poly(3-hexylthiophene) (P3HT) regioblock copolymers (<I>block</I>-P3HTs). These <I>block</I>-P3HTs consist of regioregular (<I>rre</I>) and regiorandom (<I>rra</I>) P3HTs, where the highly crystalline <I>rre</I> block allows efficient charge transport while the amorphous <I>rra</I> block provides mechanical robustness and interdomain connection. To examine the effects of the molecular architecture on the OTFT performance and stretchability, we prepare a series of <I>block</I>-P3HTs having different number-average molecular weight (<I>M</I><SUB>n</SUB>) values of <I>rra</I> blocks (from 0 to 32 kg mol<SUP>-1</SUP>) and a fixed <I>M</I><SUB>n</SUB> of <I>rre</I> blocks (11 kg mol<SUP>-1</SUP>). Thin films of all of the <I>block</I>-P3HTs exhibit a high charge-carrier mobility due to the formation of well-developed edge-on crystallites from the <I>rre</I> blocks confined within the <I>rra</I> domains, leading to a hole mobility of 1.5 × 10<SUP>-1</SUP> cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, which is superior to that of the <I>rre</I> P3HT homopolymer. In addition, the mechanical toughness of <I>block</I>-P3HT thin films is remarkably enhanced by the <I>rra</I> block. While the <I>rre</I> P3HT homopolymer thin film shows a brittle behavior with an elongation at break of only 0.3%, the elongation at break of the <I>block</I>-P3HT thin films increases by a factor of 100, yielding 30.2% with increasing <I>M</I><SUB>n</SUB> of the <I>rra</I> block, without sacrificing the electrical properties. In particular, a noticeable enhancement of both elongation at break and toughness is observed between <I>M</I><SUB>n</SUB> values of the <I>rra</I> block of 8 and 20 kg mol<SUP>-1</SUP>, indicating that the critical molecular weight of <I>rra</I> P3HT plays an important role in determining the mechanical response of the <I>block</I>-P3HT thin films. This study provides guidelines and strategies to improve the mechanical properties of organic electroactive materials without the disruption of optoelectrical properties, which is critical to fabricate high-performance soft electronics.</P> [FIG OMISSION]</BR>
Choi, Joonhyeong,Kim, Wansun,Kim, Donguk,Kim, Seonha,Chae, Junsu,Choi, Siyoung Q.,Kim, Felix Sunjoo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2019 Chemistry of materials Vol.31 No.9
<P>Mechanical properties of conducting polymers are an essential consideration in the design of flexible and stretchable electronics, but the guidelines for the material design having both high mechanical and electrical properties remain limited. Here we provide an important guideline for the design of mechanically robust, electroactive polymer thin films in terms of the molecular weight of the polymers. These studies based on a highly efficient, representative n-type conjugated polymer (P(NDI2OD-T2)) revealed a marked enhancement in mechanical properties across a narrow molecular weight range, highlighting the existence of a critical molecular weight that can be exploited to engineer films that balance processability and mechanical and electronic properties. We found the thin films formed from high molecular weight polymers (i.e., number-average molecular weight (<I>M</I><SUB>n</SUB>) ∼ 163 kg mol<SUP>-1</SUP>) to exhibit superior mechanical compliance and robustness, with a 114-fold enhanced strain at fracture and a 2820-fold enhanced toughness, as compared to those of low molecular weight polymer films (<I>M</I><SUB>n</SUB> = 15 kg mol<SUP>-1</SUP>). In particular, we observed a jump in the mechanical properties between the <I>M</I><SUB>n</SUB> = 48 and 103 kg mol<SUP><B>-</B>1</SUP>, yielding a 26-fold enhanced strain at fracture and a 160-fold enhanced toughness. The significant improvement of tensile properties indicates the presence of a critical molecular weight at which entangled polymer networks start to form, as supported by the analysis of the thermal and crystalline properties, specific viscosity, and microstructure. Our work provides useful guidelines for the design of conjugated polymers with recommendations for the best combinations of mechanical robustness and electrical performance for flexible and stretchable electronics.</P> [FIG OMISSION]</BR>
전도성 고분자의 전기전도도 향상 연구 및 이를 이용한 투명전극 응용
임소은 ( Soeun Im ),김소연 ( Soyeon Kim ),김세열 ( Seyul Kim ),김선주 ( Felix Sunjoo Kim ),김중현 ( Jung Hyun Kim ) 한국공업화학회 2015 공업화학 Vol.26 No.6
투명 전극의 응용분야가 확대되고 시장의 규모가 커짐에 따라 기존 투명 전극 재료인 ITO (Indium Tin Oxide)를 대체할 차세대 투명전극의 개발에 관심이 집중되고 있다. 다양한 후보군 중에서도 대표적인 전도성 고분자인 PEDOT : PSS [poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate)]는 기계적 유연성을 갖고 있으면서도 소재와 공정 상의가격 경쟁력이 크기 때문에 미래 소자 구현을 위한 투명전극 재료로 주목을 받고 있으며, 현재 PEDOT : PSS의 전기전도도 수준을 ITO나 금속의 수준으로 향상시키기 위해 다양한 화학적/물리적 처리를 통한 기능성 향상에 많은 연구가진행 중이다. 본 총설에서는 전도성 고분자의 전기 전도도를 향상시키기 위한 다양한 공정 기술에 대한 연구 현황을짚어보고자 한다. 대표적으로 유기용매, 이온성 액체, 계면활성제 등과 같은 첨가제와 박막에 대한 산 처리 공정, 물리적 인장을 통한 전기전도도 향상 연구를 들 수 있다. 또한 이러한 공정을 적용하여 전도성 고분자 투명 전극을 전자및 에너지 소자에 응용한 사례도 간략히 소개하고자 한다. As the need for next-generation flexible electronics grows, novel materials and technologies that can replace conventional indium tin oxide (ITO) for transparent electrodes have been of great interest. Among them, a conducting polymer, especially poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS) is one of the most promising candidates because it is mechanically flexible, inexpensive, and capable of being processed in solution. Currently, there are a lot of research efforts on enhancing its electrical conductivity to the level of ITO or metal electrodes through chemical and/or physical processing. In this review article, we present various additives and pre-/post-deposition processing methods for improving the electrical conductivity of PEDOT : PSS. Some of representative reports are also introduced, which demonstrated the use of conductivity-enhanced PEDOT : PSS as transparent electrodes in electronics and energy conversion.
Kim, Kimyung,Park, Min Soo,Na, Yaena,Choi, Jongwan,Jenekhe, Samson A.,Kim, Felix Sunjoo Elsevier 2019 ORGANIC ELECTRONICS Vol.65 No.-
<P><B>Abstract</B></P> <P>Polystyrene-grafted alumina nanoparticles were synthesized by silane coupling between dimethylchlorosilane-terminated polystyrene (PS) and gamma-type alumina nanoparticles and characterized. The surface grafting density of the polystyrene chains on the nanoparticles was estimated to be 0.13 molecules per square nanometer. The Al<SUB>2</SUB>O<SUB>3</SUB>-PS nanoparticles are solution processable in organic solvents, including ethyl acetate, butyl acetate, and toluene, which enabled preparation of blends with polystyrene or poly (methyl methacrylate). The dielectric constant of the Al<SUB>2</SUB>O<SUB>3</SUB>-PS nanoparticle/polymer blend films is composition tunable from 2.59 to 7.79. The alumina-PS nanoparticles and their blends with polymers were found to form efficient surface passivation films on the oxide dielectric layer in organic field-effect transistors (OFETs).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polystyrene-grafted alumina core-shell nanoparticles were synthesized through simple silane coupling and the processability in various organic solvents was improved. </LI> <LI> Structure, electrical properties, composite film formation of alumina-PS nanoparticles were characterized. </LI> <LI> Alumina-PS nanoparticles were applied as a surface modification agent in organic field-effect transistors. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Choi, Jongwan,Kim, Felix Sunjoo 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
<P>We studied the influence of photoanode thickness on the photovoltaic characteristics and impedance responses of the dye-sensitized solar cells based on a ruthenium dye containing a hexyloxyl-substituted carbazole unit (Ru-HCz). As the thickness of photoanode increases from 4.2 mu m to 14.8 mu m, the dye-loading amount and the efficiency increase. The device with thicker photoanode shows a decrease in the efficiency due to the higher probability of recombination of electron-hole pairs before charge extraction. We also analyzed the electron-transfer and recombination characteristics as a function of photoanode thickness through detailed electrochemical impedance spectroscopy analysis.</P>
Choi, Jongwan,Kim, Nakjoong,Oh, Jin-Woo,Song, Heeseok,Choi, Moonhyun,Hong, Jinkee,Kim, Felix Sunjoo Korean Physical Society 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.11
<P>We studied a series of fullerene derivatives, which had been functionalized by an electron-donating group (triphenylamine) or an electron-accepting group (cyanobenzene), for use as photosensitizers in photoconducting polymer composites. The functionalized fullerenes were synthesized via the Prato reaction. The electronic energy levels of the fullerene derivatives and photo-charge-generation efficiencies of charge-transfer complex between the photoconducting polymer and the dopant were investigated by using density functional theory calculations, optical absorption spectroscopy, and xerographic discharge methods.</P>
Na, Yaena,Kim, Felix Sunjoo American Chemical Society 2019 Chemistry of materials Vol.31 No.13
<P>Organic electrolyte-gated transistors (OEGTs) utilizing high-capacitance ion gel dielectrics for low-voltage electronics often suffer from unintentional electrochemical doping processes (i.e., ion migration and charge transfer) and device degradation due to ion penetration into the semiconducting layer. Here, we report a simple and novel approach to fabricate a nanodroplet-embedded semiconducting polymer layer for reducing the undesired electrochemical doping processes of polymer-based OEGTs using poly(3-hexylthiophene) (P3HT) as a semiconducting layer and an insulating polymer/ionic liquid gel as a gate insulator. The semiconductor P3HT is cast from a stock solution blended with a small amount of ionic liquid (IL) as a nanodroplet component. Electrochemical devices employing the IL nanodroplet-embedded P3HT (P3HT/IL) film as an active layer exhibit ideal capacitive polarization and reliable transistor operation. Electrochemical impedance spectroscopy reveals that the P3HT/IL blends share a structural similarity with the gate dielectric ion gels. The IL nanodroplets dispersed in the active layer secure the local charge balance in the active layer and therefore reduce the slow electrochemical transport processes under applied biases. In OEGT characteristics, the current level of the nanodroplet-embedded devices becomes higher and more stable against operational bias stressing. Additionally, our devices show little hysteresis compared to that shown by the device of pristine P3HT without IL nanodroplets.</P> [FIG OMISSION]</BR>