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- 저자 : Bumjoon Kim (검색결과 189 건)
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Kim, Wansun,Choi, Joonhyeong,Kim, Jae-Han,Kim, Taesu,Lee, Changyeon,Lee, Seungjin,Kim, Mingoo,Kim, Bumjoon J.,Kim, Taek-Soo American Chemical Society 2018 Chemistry of materials Vol.30 No.6
<P>High fracture resistance of polymer solar cells (PSCs) is of great importance to ensure long-term mechanical reliability, especially considering their potential in roll-to-roll printing processes and flexible devices. In this paper, we compare mechanical properties, such as the cohesive fracture energy, elastic modulus, and crack-onset strain, of all-polymer solar cells (all-PSCs) and fullerene-based solar cells (PCBM-PSCs) based on the same, representative low-bandgap polymer donor (PTB7-Th) as a function of acceptor content. The all-PSCs exhibit higher fracture energy (2.45 J m<SUP>-2</SUP>) than PCBM-PSCs (0.29 J m<SUP>-2</SUP>) at optimized device conditions. Additionally, a 15-fold higher crack-onset strain is observed in all-PSCs than in PCBM-PSCs. Dramatically different mechanical compliances observed for all-PSCs and PCBM-PSCs are investigated in detail by analysis of the blend morphologies as a function of acceptor content (either P(NDI2HD-T) or PCBM acceptors). The superior fracture resistance of all-PSCs is attributed to the more ductile characteristics of the polymer acceptor and the large degree of plastic deformation during crack growth, in contrast to the brittle nature of PCBM and the weak interaction between the polymer-rich phase and highly aggregated PCBM-rich domains. Therefore, this work demonstrates that replacing a small-molecule acceptor (i.e., PCBM) with polymeric materials can be an effective strategy toward mechanically robust PSCs.</P> [FIG OMISSION]</BR>
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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>
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Kim, Jin-Seong,Kim, Jae-Han,Lee, Wonho,Yu, Hojeong,Kim, Hyeong Jun,Song, Inho,Shin, Minkwan,Oh, Joon Hak,Jeong, Unyong,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2015 Macromolecules Vol.48 No.13
<P>While the regioregularity (RR) of conjugated polymers is known to have a strong influence on their inherent properties, systematic study of the RR effect has been limited due to the lack of a synthetic methodology. Herein, we successfully produced a series of poly(3-hexylthiophene)s (P3HTs) having a wide range of RR from 64 to 98%. Incorporation of controlled amounts of head-to-head (H-H) coupled dimer in modified Grignard metathesis polymerization allows a facile tuning of the RR of the P3HTs with comparable molecular weight and low polydispersity. Then, we investigated the effect of RR on structural, electrical, and mechanical properties of P3HTs in which a higher content of H-H regio-defects, namely lower RR, systematically lowered the degree of crystallinity. Although high RR P3HT (98%) had higher charge carrier mobility (1.81 x 10(-1) cm(2) V-1 s(-1)), its strong crystallinity induced high brittleness and stiffness, resulting in device failure under a very small strain, as shown in tensile and bending tests. The tensile modulus was reduced significantly from 287 MPa (RR 98%) to 13 MPa (RR 64%), and also the RR 64% P3HT film had much better mechanical resilience with an order of magnitude higher elongation at break than that of the RR 98% polymer. Our findings suggest that the mechanical and electrical properties of conjugated polymers can be systematically tuned by controlling the RR to meet the purposes of various organic electronic applications, i.e., flexible portable devices vs high-performance panels.</P>
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Kim, Youngkwon,Choi, Joonhyeong,Lee, Changyeon,Kim, Youngwoong,Kim, Changkyun,Nguyen, Thanh Luan,Gautam, Bhoj,Gundogdu, Kenan,Woo, Han Young,Kim, Bumjoon J. American Chemical Society 2018 Chemistry of materials Vol.30 No.16
<P>We present a new series of fullerene derivatives that exhibit solubility in ethanol/water solvent mixtures and implement these materials to fabricate polymer solar cells (PSCs) using environmentally benign solvents. In order to simultaneously optimize the processability of the fullerenes in ethanol/water solvent mixtures and device performance, different fullerene mono-adducts were designed by introducing oligoethylene glycol side chains with different lengths and number of branches. As a result, we achieved power conversion efficiencies up to 1.4% for PSCs processed from benign ethanol/water mixtures in air. Significantly, the new alcohol/water-soluble fullerene derivatives displayed electron mobilities up to 1.30 × 10<SUP>-4</SUP> cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, 150 times higher than those of a previously reported alcohol-soluble fullerene bis-adduct, owing to efficient packing of the fullerenes. Femtosecond transient absorption spectroscopy revealed the acceptor side chain to markedly impact geminate and/or nongeminate charge recombination in the PSCs. In addition, side chain optimization of these fullerenes produced well-intermixed morphologies with high domain purity when blended with p-type polymer to provide hole and electron transport pathways. Our results provide important guidelines for the design of electroactive materials for safe and environmentally benign fabrication of PSCs and other organic electronic devices.</P> [FIG OMISSION]</BR>
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Kim, Hyeong Jun,Kim, Jin-Seong,Kim, Youngkwon,Jung, Yeon Sik,Kim, Bumjoon J.,Kim, YongJoo Elsevier 2019 Polymer Vol.178 No.-
<P><B>Abstract</B></P> <P>In this study, we developed a simple coarse-grained simulation model framework to investigate the effect of regioregularity (RR) on the crystallization behavior of poly(3-hexylthiophene) (P3HT). To describe the regio-chemistry of P3HT, two different coarse-grained beads were designed to contain either regio-regularly substituted head-to-tail (HT) orientations or regio-irregularly substituted non-HT orientations, and two beads were randomly incorporated in a single polymer where the total RR was tuned from regio-random (RR = 50%) to regio-regular (RR = 100%). Based on our modeling, the crystallization behaviors in both bulk and solution states were investigated. As the number of irregularly substituted non-HT orientations increased, crystallization temperature in the bulk shifted to a lower temperature. When the RR of P3HT was lower than a critical RR value, which was 72.2% in our study, the crystallization of the P3HT chains was eventually suppressed. In the solution state, most of high RR P3HT chains stacked in parallel to produce nanowire (NW) structure to maximize the number of π-stackings in the system, whereas the P3HTs formed a globule structure when the RR value decreased below critical RR. To experimentally validate our simulation results, we synthesized a series of P3HTs having precisely controlled RRs from 66% to 95% with comparable molecular weights to the simulation. Well-matched experimental results suggested that our simplified model provides efficient computational guidance to describe the RR effect on crystalline feature of P3HTs for the various possible applications in organic optoelectronics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Simple coarse-grained model is developed to describe the effect of regioregularity (RR) on crystallization of P3HT. </LI> <LI> Experimental validation with a series of P3HTs having a wide range of RR from 66% to 95% is followed. </LI> <LI> Our model predicts critical RR value for crystallization of P3HT in bulk and solution. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Regioregularity-Driven Morphological Transition of Poly(3-hexylthiophene)-Based Block Copolymers
Kim, Jin-Seong,Kim, Yongjoo,Kim, Hyun-Jeong,Kim, Hyeong Jun,Yang, Hyunseung,Jung, Yeon Sik,Stein, Gila E.,Kim, Bumjoon J. American Chemical Society 2017 Macromolecules Vol.50 No.5
<P>Conjugated polymer-based block copolymers (BCPs) offer great potential to provide beneficial nanostructures for efficient organic optoelectronics. However, their complicated self-assembly behavior, which is attributed to the strong crystallization of conjugated blocks, is still not well understood due to the lack of a model BCP system. Herein, we develop a series of novel conjugated polymer-based BCPs, poly(3-hexylthiophene)-block-poly(2-vinylpyridine) (P3HT-b-P2VP), in which the regioregularity (RR) of the P3HT block was varied from 95 to 73%. The tunable RR content allows for precise regulation of P3HT crystallization with minimal influence on the microphase-separation force between the P3HT and P2VP blocks. When RR is high (i.e., 95 or 8S%), structure formation is controlled by crystallization of P3HT, and the ultimate structure is characterized by nanoscale P3HT fibrils in an amorphous matrix. In contrast, as RR decreases to 78 and 73%, P3HT crystallization is suppressed. The self-assembly is controlled by the enthalpic interaction between P3HT and P2VP blocks, much like typical BCPs having two flexible blocks, and thermal annealing drives the formation of well-ordered lamellar or cylindrical phases. This morphological behavior is consistent with a Monte Carlo simulation based on a newly developed coarse-grained model. Significantly, this novel class of RR-controlled P3HT-based BCPs provides a simple method to tune bulk and thin film morphology for a variety of applications in nanostructured organic electronics.</P>
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Kim, Hyeong Jun,Kim, Jae-Han,Ryu, Ji-Ho,Kim, Youngkwon,Kang, Hyunbum,Lee, Won Bo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2014 ACS NANO Vol.8 No.10
<P>While most high-efficiency polymer solar cells (PSCs) are made of bulk heterojunction (BHJ) blends of conjugated polymers and fullerene derivatives, they have a significant morphological instability issue against mechanical and thermal stress. Herein, we developed an architecturally engineered compatibilizer, poly(3-hexylthiophene)-<I>graft</I>-poly(2-vinylpyridine) (P3HT-<I>g</I>-P2VP), that effectively modifies the sharp interface of a BHJ layer composed of a P3HT donor and various fullerene acceptors, resulting in a dramatic enhancement of mechanical and thermal stabilities. We directly measured the mechanical properties of active layer thin films without a supporting substrate by floating a thin film on water, and the enhancement of mechanical stability without loss of the electronic functions of PSCs was successfully demonstrated. Supramolecular interactions between the P2VP of the P3HT-<I>g</I>-P2VP polymers and the fullerenes generated their universal use as compatibilizers regardless of the type of fullerene acceptors, including mono- and bis-adduct fullerenes, while maintaining their high device efficiency. Most importantly, the P3HT-<I>g</I>-P2VP copolymer had better compatibilizing efficiency than linear type P3HT-<I>b</I>-P2VP with much enhanced mechanical and thermal stabilities. The graft architecture promotes preferential segregation at the interface, resulting in broader interfacial width and lower interfacial tension as supported by molecular dynamics simulations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-10/nn503823z/production/images/medium/nn-2014-03823z_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn503823z'>ACS Electronic Supporting Info</A></P>
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Kim, Ji-Hoon,Song, Chang Eun,Shin, Nara,Kang, Hyunbum,Wood, Sebastian,Kang, In-Nam,Kim, Bumjoon J.,Kim, BongSoo,Kim, Ji-Seon,Shin, Won Suk,Hwang, Do-Hoon American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.24
<P>Two semiconducting conjugated polymers were synthesized via Stille polymerization. The structures combined unsubstituted or (triisopropylsilyl)ethynyl (TIPS)-substituted 2,6-bis(trimethylstannyl)benzo[1,2-<I>b</I>:4.5-<I>b</I>′]dithiophene (BDT) as a donor unit and benzotriazole with a symmetrically branched alkyl side chain (DTBTz) as an acceptor unit. We investigated the effects of the different BDT moieties on the optical, electrochemical, and photovoltaic properties of the polymers and the film crystallinities and carrier mobilities. The optical-band-gap energies were measured to be 1.97 and 1.95 eV for PBDT-DTBTz and PTIPSBDT-DTBTz, respectively. Bulk heterojunction photovoltaic devices were fabricated and power conversion efficiencies of 5.5% and 2.9% were found for the PTIPSBDT-DTBTz- and PBDT-DTBTz-based devices, respectively. This difference was explained by the more optimal morphology and higher carrier mobility in the PTIPSBDT-DTBTz-based devices. This work demonstrates that, under the appropriate processing conditions, TIPS groups can change the molecular ordering and lower the highest occupied molecular orbital level, providing the potential for improved solar cell performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-24/am401926h/production/images/medium/am-2013-01926h_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am401926h'>ACS Electronic Supporting Info</A></P>
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