Browsing by Author "Lin, Yen-Hao"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    All-Conjugated Block Copolymers for Organic Photovoltaics
    (2015-04-20) Lin, Yen-Hao; Verduzco, Rafael; Wong, Michael S; Barron, Andrew R
    Organic photovoltaics (OPVs) are a promising source of alternative energy due to cost effectiveness and process simplicity. However, the performance of OPVs must be improved to produce viable devices. This can be achieved by optimizing the optoelectronic properties of constituent materials, tuning the nanostructures of materials within active layer of OPVs and defining a well-defined interface between electron-donor materials and electron-acceptor materials. The above opportunities can potentially be addressed with using all-conjugated block copolymers in that self-assembly of block copolymers can lead to well-defined nanostructures driven by thermodynamics. The focus of this thesis is on the synthesis and development of all-conjugated block copolymers in which one block is an electron-donor polymer and the other is an electron-acceptor polymer. We focus primarily on poly(3-hexylthiophene) (P3HT)-based block copolymers in which the electron-donor P3HT is made from Grignard metathesis polymerization (GRIM) and the other block is synthesized by Suzuki-Miyaura polycondensation reaction for wide variety of electron-acceptor polymers. Subsequently, the nanostructures of polymers were studied on a model series of all-conjugated block copolymer: poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene) (P3HT–b–PF) under different processing conditions with using differential scanning calorimetry (DSC) and grazing-incidence X-ray scattering (GIXS). This reveals strong process-structure-property relationships of all-conjugated block copolymers. Furthermore, using our two-step synthetic route, we prepared an all-conjugated block copolymer poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′,-benzothiadiazole)] (P3HT–b–PFTBT) that exhibits over 3% PCEs as the active layer in a solution processed OPV due to the formation of lamellae of the block copolymers and preferential π-π stacking direction of the P3HT perpendicular to the substrate. In addition to covalently linked block copolymers, we applied a quadruple hydrogen group, 2-ureido-4[1H]-pyrimidinone (UPy), as polymeric end functionalities to reduce macro-phase separation in polymer blends. In the polymer blends OPVs comprised of P3HT and PFTBT, the UPy hydrogen bonding group reduces macro-phase separation in polymer blends and leads to improved power conversion efficiency of OPVs from 0.43% to 0.77% under 155 oC annealing condition. This thesis demonstrates that both the covalently linked and hydrogen bonding linked all-conjugated block copolymers are potential to enhance performance of OPVs. Furthermore, with the advancement in synthetic techniques and better understandings on structure-processing-property relationships of all-conjugated block copolymers, we are able to apply those into more emerging conjugated polymers and engineer molecules for efficient energy generation in OPVs.
  • Thumbnail Image
    Item
    Highly Flexible Self-Assembled V2O5 Cathodes Enabled by Conducting Diblock Copolymers
    (Macmillan Publishers Limited, 2015) An, Hyosung; Mike, Jared; Smith, Kendall A.; Swank, Lisa; Lin, Yen-Hao; Pesek, Stacy L.; Verduzco, Rafael; Lutkenhaus, Jodie L.
    Mechanically robust battery electrodes are desired for applications in wearable devices, flexible displays, and structural energy and power. In this regard, the challenge is to balance mechanical and electrochemical properties in materials that are inherently brittle. Here, we demonstrate a unique water-based self-assembly approach that incorporates a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-block-poly(ethyleneoxide) (P3HT-b-PEO), with V2O5 to form a flexible, tough, carbon-free hybrid battery cathode. V2O5 is a promising lithium intercalation material, but it remains limited by its poor conductivity and mechanical properties. Our approach leads to a unique electrode structure consisting of interlocking V2O5 layers glued together with micellar aggregates of P3HT-b-PEO, which results in robust mechanical properties, far exceeding the those obtained from conventional fluoropolymer binders. Only 5 wt % polymer is required to triple the flexibility of V2O5, and electrodes comprised of 10 wt % polymer have unusually high toughness (293 kJ/m(3)) and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes. Furthermore, addition of P3HT-b-PEO enhances lithium-ion diffusion, eliminates cracking during cycling, and boosts cyclability relative to V2O5 alone. These results highlight the importance of tradeoffs between mechanical and electrochemical performance, where polymer content can be used to tune both aspects.
  • Thumbnail Image
    Item
    Lamellar and liquid crystal ordering in solvent-annealed all-conjugated block copolymers
    (The Royal Society of Chemistry, 2014) Lin, Yen-Hao; Yager, Kevin G.; Stewart, Bridget; Verduzco, Rafael
    All-conjugated block copolymers are an emerging class of polymeric materials promising for organic electronic applications, but further progress requires a better understanding of their microstructure including crystallinity and self-assembly through micro-phase segregation. Here, we demonstrate remarkable changes in the thin film structure of a model series of all-conjugated block copolymers with varying processing conditions. Under thermal annealing, poly(3-hexylthiophene)-b-poly(90,90-dioctylfluorene) (P3HT-b-PF) all-conjugated block copolymers exhibit crystalline features of P3HT or PF, depending on the block ratio, and poor π- π stacking. Under chloroform solvent annealing, the block copolymers exhibit lamellar ordering, as evidenced by multiple reflections in grazing incidence wide and small-angle X-ray scattering (GIWAXS and GISAXS), including an in-plane reflection indicative of order along the π- π stacking direction for both P3HT and PF blocks. The lamellae have a characteristic domain size of 4.2 nm, and this domain size is found to be independent of block copolymer molecular weight and block ratio. This suggests that lamellar self-assembly arises due to a combination of polymer block segregation and π- π stacking of both P3HT and PF polymer blocks. Strategies for predicting the microstructure of all-conjugated block copolymers must take into account intermolecular π- π stacking and liquid crystalline interactions not typically found in flexible coil block copolymers.
  • Thumbnail Image
    Item
    Segregation of Amphiphilic Polymer-Coated Nanoparticles to Bicontinuous Oil/Water Microemulsion Phases
    (American Chemical Society, 2017) Qi, Luqing; ShamsiJazeyi, Hadi; Ruan, Gedeng; Mann, Jason A.; Lin, Yen-Hao; Song, Chen; Ma, Yichuan; Wang, Le; Tour, James M.; Hirasaki, George J.; Verduzco, Rafael
    Polymer-coated nanoparticles are interfacially active and have been shown to stabilize macroscopic emulsions of oil and water, also known as Pickering emulsions. However, prior work has not explored the phase behavior of amphiphilic nanoparticles in the presence of bicontinuous microemulsions. Here, we show that properly designed amphiphilic polymer-coated nanoparticles spontaneously and preferentially segregate to the bicontinuous microemulsion phases of oil, water, and surfactant. Mixtures of hydrophilic and hydrophobic chains are covalently grafted onto the surface of oxidized carbon black nanoparticles. By sulfating hydrophilic chains, the polymer-coated nanoparticles are stable in the aqueous phase at salinities up to 15 wt % NaCl. These amphiphilic, negatively charged polymer-coated nanoparticles segregate to the bicontinuous microemulsion phases. We analyzed the equilibrium phase behavior of the nanoparticles, measured the interfacial tension, and quantified the domain spacing in the presence of nanoparticles. This work shows a novel route to the design of polymer-coated nanoparticles which are stable at high salinities and preferentially segregate to bicontinuous microemulsion phases.
  • Thumbnail Image
    Item
    Supramolecular block copolymer photovoltaics through ureido-pyrimidinone hydrogen bonding interactions
    (Royal Society of Chemistry, 2016) Lin, Yen-Hao; Nie, Wanyi; Tsai, Hsinhan; Li, Xiaoyi; Gupta, Gautam; Mohite, Aditya D.; Verduzco, Rafael
    A challenge in the development of bulk heterojunction organic photovoltaics (BHJ OPVs) is achieving a desirable nanoscale morphology. This is particularly true for polymer blend OPVs in which large-scale phase separation occurs during processing. Here, we present a versatile approach to control the morphology in polymer blend OPVs through incorporation of self-associating 4 2-ureido-4[1H]-pyrimidinone (UPy) endgroups onto donor and acceptor conjugated polymers. These UPy functionalized polymers associate to form supramolecular block copolymers during solution blending and film casting. Atomic force microscopy measurements show that supramolecular associations can improve film uniformity. We find that the performance of supramolecular block copolymer OPVs improves from 0.45% to 0.77% relative to the non-associating conjugated polymer blends at the same 155 °C annealing conditions. Impedance measurements reveal that UPy endgroups both increase the resistance for charge recombination and for bulk charge transport. This work represents a versatile approach to reducing large-scale phase separation in polymer–polymer blends and directing the morphology through supramolecular interactions.