Domain Structures of Poly(3-dodecylthiophene)-Based Block Copolymers Depend on Regioregularity

Kim, Jin-Seong,Han, Junghun,Kim, Youngkwon,Park, Hyeonjung,Coote, Jonathan P.,Stein, Gila E.,Kim, Bumjoon J. American Chemical Society 2018 Macromolecules Vol.51 No.11

<P>Microphase-separation behavior of conjugated-amorphous block copolymers (BCPs) is driven by a complex interplay between Flory-Huggins interaction (χ), liquid crystalline (LC) interaction, and crystallization. Herein, in order to elucidate the influence of LC interaction on the morphology of the BCPs, we report the effects of regioregularity (RR) on the microphase separation and molecular packing structures of poly(3-dodecylthiophene)-<I>block</I>-poly(2-vinylpyridine) (P3DDT-<I>b</I>-P2VP). To decouple the effect of LC interactions from crystallization kinetics, we investigate the morphological behavior of the P3DDT-<I>b</I>-P2VP at above the melting temperature of P3DDT (∼160 °C). Both electron microscopy and X-ray scattering show an abrupt reduction in the domain spacing of both lamellar and cylindrical phases as the RR of P3DDT block increases. Specifically, lower RR (i.e., 85, 79, and 70%) BCPs have larger domain spacings than high RR (94%) by 50% (lamellar) or 80% (cylindrical), even though the overall molecular weights and P2VP volume fractions were similar for each RR. We propose that the RR-driven transition in domain spacing is caused by a change in P3DDT conformations and interchain interactions. When RR is low, the system assembles into a typical bilayer structure like other semiflexible and flexible block copolymer systems. When RR is high, the less flexible P3DDT chains are extended, driving their assembly into an LC monolayer. Significantly, this study demonstrates that tunable RR provides a simple route to manipulate melt state self-assembly of conjugated-amorphous materials.</P> [FIG OMISSION]</BR>

Precise Control of Quantum Dot Location within the P3HT-<i>b</i>-P2VP/QD Nanowires Formed by Crystallization-Driven 1D Growth of Hybrid Dimeric Seeds

Kim, Yong-Jae,Cho, Chul-Hee,Paek, Kwanyeol,Jo, Mijung,Park, Mi-kyoung,Lee, Na-Eun,Kim, Youn-joong,Kim, Bumjoon J.,Lee, Eunji American Chemical Society 2014 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.136 No.7

<P>Herein, we report a simple fabrication of hybrid nanowires (NWs) composed of a p-type conjugated polymer (CP) and n-type inorganic quantum dots (QDs) by exploiting the crystallization-driven solution assembly of poly(3-hexylthiophene)-<I>b</I>-poly(2-vinylpyridine) (P3HT-<I>b</I>-P2VP) rod–coil amphiphiles. The visualization of the crystallization-driven growth evolution of hybrid NWs through systematic transmission electron microscopy experiments showed that discrete dimeric CdSe QDs bridged by P3HT-<I>b</I>-P2VP polymers were generated during the initial state of crystallization. These, in turn, assemble into elongated fibrils, forming the coaxial P3HT-<I>b</I>-P2VP/QDs hybrid NWs. In particular, the location of the QD arrays within the single strand of P3HT-<I>b</I>-P2VP can be controlled precisely by manipulating the regioregularity (RR) values of P3HT block and the relative lengths of P2VP block. The degree of coaxiality of the QD arrays was shown to depend on the coplanarity of the thiophene rings of P3HT block, which can be controlled by the RR value of P3HT block. In addition, the location of QDs could be regulated at the specific-local site of P3HT-<I>b</I>-P2VP NW according to the surface characteristics of QDs. As an example, the comparison of two different QDs coated with hydrophobic alkyl-terminated and hydroxyl-terminated molecules, respectively, is used to elucidate the effect of the surface properties of QDs on their nanolocation in the NW.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2014/jacsat.2014.136.issue-7/ja410165f/production/images/medium/ja-2013-10165f_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja410165f'>ACS Electronic Supporting Info</A></P>

Aqueous Soluble Fullerene Acceptors for Efficient Eco-Friendly Polymer Solar Cells Processed from Benign Ethanol/Water Mixtures

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>

Molecular Design of “Graft” Assembly for Ordered Microphase Separation of P3HT-Based Rod–Coil Copolymers

Kim, Hyeong Jun,Paek, Kwanyeol,Yang, Hyunseung,Cho, Chul-Hee,Kim, Jin-Seong,Lee, Wonbo,Kim, Bumjoon J. American Chemical Society 2013 Macromolecules Vol.46 No.21

<P>Ordered structures of self-assembled block copolymers (BCPs) would be the ideal active-layer candidates for high-performance organic electronics. However, fabrication of such structures from BCPs of conjugated polymers has been very limited due to the strong rod–rod interactions between the conjugated blocks, which inhibit the formation of ordered structures. Here, we developed a novel molecular design of conjugated polymer-based graft copolymers to control the rigidity of the copolymers and to produce a variety of ordered nanostructures. A series of well-defined poly(3-hexylthiophene)-<I>graft</I>-poly(2-vinylpyridine) (P3HT-<I>g</I>-P2VP) copolymers were prepared via controlled polymerization, followed by microwave-assisted click reaction. We observed that controlling the molecular weights (<I>M</I><SUB>n</SUB>) of the grafted P2VP chains allowed us to regulate the rod–rod interaction of the copolymers systematically, as evidenced by differential scanning calorimetry and X-ray scattering measurements. As the <I>M</I><SUB>n</SUB> of the grafted P2VP chains increased, the crystallinity of the P3HT block in the copolymers gradually decreased so that the enthalpic interaction between P3HT and P2VP chains became more dominant than the rod–rod interaction of the P3HT moiety. Therefore, we produced thermally annealed, well-ordered nonfibril nanostructures of P3HT-based copolymers, including lamellae, hexagonally packed cylinders, and spheres.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2013/mamobx.2013.46.issue-21/ma401530q/production/images/medium/ma-2013-01530q_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma401530q'>ACS Electronic Supporting Info</A></P>

Polymer brushes on nanoparticles

Bumjoon Kim,G. H. Fredrickson,J. Bang,C. J. Hawker,E. J. Kramer 한국고분자학회 2007 한국고분자학회 학술대회 연구논문 초록집 Vol.2007 No.4

Facile Synthesis of <i>o</i>-Xylenyl Fullerene Multiadducts for High Open Circuit Voltage and Efficient Polymer Solar Cells

Kim, Ki-Hyun,Kang, Hyunbum,Nam, So Yeon,Jung, Jaewook,Kim, Pan Seok,Cho, Chul-Hee,Lee, Changjin,Yoon, Sung Cheol,Kim, Bumjoon J. American Chemical Society 2011 Chemistry of materials Vol.23 No.22

<P>The ability to control the lowest unoccupied molecular orbital (LUMO) level of an electron-accepting material is a critical parameter for producing highly efficient polymer solar cells (PSCs). Soluble bis-adducts of C<SUB>60</SUB> have great potential for improving the <I>V</I><SUB>OC</SUB> in PSCs because of their high LUMO level. In this work, we have developed a novel <I>o</I>-xylenyl C<SUB>60</SUB> bis-adduct (OXCBA) via a [4 + 2] cycloaddition between C<SUB>60</SUB> and an irreversible diene intermediate from α,α′-dibromo-<I>o</I>-xylene. OXCBA was successfully applied as the electron acceptor with poly(3-hexylthiophene) (P3HT) in a PSC, showing a high efficiency of 5.31% with <I>V</I><SUB>OC</SUB> of 0.83 V. This composite showed a nearly 50% enhancement in efficiency compared to the P3HT:PCBM control device (3.68% with <I>V</I><SUB>OC</SUB> of 0.59 V). Furthermore, tuning the molar ratio between C<SUB>60</SUB> and the α,α′-dibromo-<I>o</I>-xylene group from 1:1 to 1:3 in the reaction scheme enables facile control over the number of <I>o</I>-xylenyl solubilizing groups ultimately tethered to the fullerene, thus producing <I>o</I>-xylenyl C<SUB>60</SUB> mono-, bis-, and tris-adducts (OXCMA, OXCBA, and OXCTA) with different LUMO levels. As the number of solubilizing groups increased, <I>V</I><SUB>OC</SUB> values of the P3HT-based BHJ solar cells increased from 0.63 V (OXCMA) to 0.83 V (OXCBA) to 0.98 V (OXCTA). This series of <I>o</I>-xylenyl C<SUB>60</SUB> multiadducts provides a model system for investigating the molecular structure-device function relationship, especially with respect to changes in the number of solubilizing groups on the electron acceptor.</P><P>Tuning the molar ratio between C<SUB>60</SUB> and the α,α'-dibromo-<I>o</I>-xylene group from 1:1 to 1:3 enables facile control over the number of <I>o</I>-xylenyl solubilizing groups ultimately tethered to the fullerene, thus producing the novel <I>o</I>-xylenyl C<SUB>60</SUB> multi-adducts (mono-, bis-, and tris-adducts) for electron acceptors with different LUMO levels.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2011/cmatex.2011.23.issue-22/cm202885s/production/images/medium/cm-2011-02885s_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm202885s'>ACS Electronic Supporting Info</A></P>

Architectural Engineering of Rod–Coil Compatibilizers for Producing Mechanically and Thermally Stable Polymer Solar Cells

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>

Impact of Terminal End-Group of Acceptor-Donor-Acceptor-type Small Molecules on Molecular Packing and Photovoltaic Properties

Kim, Sang Woo,Lee, Yu Jeong,Lee, Young Woong,Koh, Chang Woo,Lee, Yeran,Kim, Min Je,Liao, Kin,Cho, Jeong Ho,Kim, Bumjoon J.,Woo, Han Young American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.46

<P>In this study, we synthesized two acceptor-donor-acceptor (A-D-A)-type small molecules (SMs) (P3T4-VCN and P3T4-INCN) with different terminal end-groups (dicyanovinyl (VCN) and 2-methylene-3-(1,1-dicyanomethylene)indanone (INCN)) based on the 1,4-bis(thiophenylphenylthiophene)-2,5-difluorophenylene (P3T4) core that possesses high coplanarity because of intrachain noncovalent Coulombic interactions. We investigated the influence of terminal end-groups on intermolecular packing and the resulting electrical and photovoltaic characteristics. A small change in the end-group structure of the SMs induces a significant variation in the torsional structures, molecular packing, and pristine/blend film morphology. It is noteworthy that the less crystalline P3T4-INCN with tilted conformation is highly sensitive to post-treatments (i.e., additives and annealing) such that it permits facile morphological modulation. However, the highly planar and crystalline P3T4-VCN exhibits a strong tolerance toward processing treatments. After morphology optimization, the fullerene-based bulk-heterojunction solar cell of tilted P3T4-INCN exhibits a power conversion efficiency (PCE) of 5.68%, which is significantly superior to that of P3T4-VCN:PC<SUB>71</SUB>BM (PCE = 1.29%). Our results demonstrate the importance of the terminal end-group for the design of A-D-A-type SMs and their sensitivity toward the postprocessing treatments in optimizing their performance.</P> [FIG OMISSION]</BR>

Surface Intaglio Nanostructures on Microspheres of Gold-Cored Block Copolymer Spheres

Kim, Minsoo P.,Ku, Kang Hee,Kim, Hyeong Jun,Jang, Se Gyu,Yi, Gi-Ra,Kim, Bumjoon J. American Chemical Society 2013 Chemistry of materials Vol.25 No.21

<P>The confined self-assembly of block copolymers (BCPs) can be used to generate hierarchically structured composite microspheres. In this study, microspheres of gold-cored BCP (Au-BCP) spheres were first produced from an evaporative toluene-in-water-emulsion in which polystyrene-<I>b</I>-poly(4-vinylpyridine) (PS-<I>b</I>-P4VP) BCPs incorporated with Au precursors (AuCl<SUB>4</SUB><SUP>–</SUP>) were dissolved in toluene. Interestingly, the addition of cetyltrimethylammonium bromide (CTAB) into the microspheres resulted in the selective extraction of Au precursors within the Au-BCP spheres near the surface of the microsphere because of the strong electrostatic attraction between the CTAB and Au precursors. Therefore, regular-patterned porous nanostructures on the surface of Au-BCP microspheres were formed, of which the size could be varied by controlling the molecular weight of the PS-<I>b</I>-P4VP polymers. In addition, the depth of the pores could be modulated independently by tuning the amounts of Au precursors that were incorporated into the Au-BCP spheres (λ). This method was then generalized using other additives (i.e., thiol-terminated molecules) that had a favorable interaction with the Au precursors, producing both controlled inner and surface morphologies of the microspheres. Pores at surface could be used to successfully load various metal nanoparticles, potentially making them useful in optical, catalytic, and drug-delivery or therapeutic applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2013/cmatex.2013.25.issue-21/cm402868q/production/images/medium/cm-2013-02868q_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm402868q'>ACS Electronic Supporting Info</A></P>

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>