Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P11: Polymers for Energy Storage and Conversion IIFocus
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Sponsoring Units: DPOLY Chair: Lisa Hall, Ohio State University Room: 270 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P11.00001: Controlling Crystal Microstructure to Minimize Loss in Polymer Dielectrics Daniel Miranda, Ciprian Iacob, Shihai Zhang, James Runt Polymer dielectric films are of great importance for high performance capacitors. For these films it is critical to reduce dielectric loss, as it diminishes efficiency and contributes to waste heat generation during device operation. Here, a model semi-crystalline polymer, poly(ethylene naphthalate) (PEN), was used to examine how morphological factors inhibit chain relaxations responsible for loss. This was achieved by manipulating the extent of crystallization and the crystalline microstructure through a combination of annealing and uniaxial drawing, and investigating their effects on dielectric performance. Varying crystallization conditions influenced the dynamic T$_{g}$ and extent of rigid amorphous fraction formation, but had a limited effect on loss magnitude. Film orientation however greatly reduced loss, through strain-induced crystallization and development of oriented amorphous mesophasic regions. Post-drawing annealing conditions were capable of further refining the crystal microstructure and, in turn, the dielectric properties. These findings demonstrate that semi-crystalline polymer morphology has a very strong influence on amorphous chain relaxations, and understanding how processing conditions affect morphology is critical to the rational design of polymer dielectrics. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P11.00002: Achieving dielectric enhancement in dipolar polymer blends: free volume increase while maintaining low loss Bing Zhang, Yash Thakur, Rui Dong, Wenchang Lu, Ciprian Iacob, James Runt, Qiming Zhang, Jerry Bernholc High dielectric constant and low loss are the key performance parameters for polymer dielectrics. We consider strongly dipolar polymers, such as PEEU and ArPTU, which have relatively high dielectric constants, high thermal stabilities and low loss. We show through both molecular dynamics simulations and experimental measurements that a nanostructured blend of these polymers results in a much enhanced dielectric constant while maintaining low loss. The blends have lower densities compared to the pure polymers, due to different chain periodicities and dipole mismatches, which lead to the formation of a glassy structure with slightly increased average interchain spacing. The increased free volume reduces barriers to dipole rearrangement along the applied electric field, thereby enhancing the dielectric response without increasing loss. [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P11.00003: Fabrication of laser induced periodic surface structures on P3HT/ PC$_{\mathrm{71}}$BM photovoltaic blends T.A. Ezquerra, J. Cui, A. Rodriguez-Rodriguez, M. Hernandez, M.C. Garcia-Gutierrez, A. Nogales, M. Castillejo, E. Rebollar Here we describe the conditions for fabrication of Laser Induced Periodic Surface Structures (LIPSS) over poly(3-hexylthiophene) (P3HT) spin-coated films. The structure and morphology of the LIPSS have been investigated by combining Atomic Force Microscopy(AFM), Conducting Atomic Force Microscopy (C-AFM) and Grazing Incidence X-ray Scattering at small angle (GISAXS) and wide angle (GIWAXS). Optimal LIPSS on P3HT are observed within a particular range of thicknesses and laser fluences. These conditions can be translated to the photovoltaic blend formed by the 1:1 mixture of P3HT and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) when deposited on an indium tin oxide (ITO) electrode coated with (poly(3,4 -- ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS). Solar cells formed by using either a bilayer of P3HT structured by LIPSS covered by PC71BM or a bulk heterojunction with a P3HT:PC71BM blend structured by LIPSS exhibit generation of electrical photocurrent under light illumination. These results suggest that LIPSS could be a compatible technology with organic photovoltaic devices. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:42PM |
P11.00004: Simultaneously Ion- and Electron-Conducting Block Copolymer Binders for Battery Electrodes Invited Speaker: Rafael Verduzco Lithium-ion batteries provide a portable, on-demand source of electrical energy and are comprised of multiple components for storing and releasing ions, transporting charges, and maintaining mechanical integrity. Polymeric binders, although representing only a fraction of the battery, are an important component for maintaining adhesion between different parts. Polymers that are simultaneously ion- and electron-conducting and redox-active are potentially ideal materials for use in electrodes, and here we show that such polymers can improve both mechanical and electrochemical properties of electrodes. First, flexible, carbon-free hybrid battery cathodes are prepared using poly(3-hexylthiophene)-\textit{block}-poly(ethyleneoxide) (P3HT-$b$-PEO) as a binder. Only 5\textunderscore wt {\%} polymer was required to triple the flexibility of V$_{\mathrm{2}}$O$_{\mathrm{5}}$, and electrodes comprised of 10\textunderscore wt {\%} polymer had unusually high toughness (293\textunderscore kJ/m$^{\mathrm{3}})$ and specific energy (530\textunderscore Wh/kg), both higher than reduced graphene oxide paper electrodes. Next, we present work on self-doped conjugated polymeric binders, which provide stable conductivities and are fully water-processable. These materials are incorporated into V$_{\mathrm{2}}$O$_{\mathrm{5}}$ cathodes and suppress the crystallization of V2O5, even at thermal annealing temperatures above 400 $^{\circ}$ C, maintaining the more favorable aerogel structure. Finally, we discuss the design and development of conjugated and redox-active polymers in Silicon anodes. These results highlight the importance of tradeoffs between mechanical and electrochemical performance in the design of conjugated polymeric binders. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P11.00005: Optoelectronic Properties of Conjugated Block Copolymer with Flexible Linking Group Zhiqi Hu, Rafael Verduzco State-of-the-art organic photovoltaics (OPVs) are prepared by depositing a disordered, co-continuous donor and acceptor blend. While optimization of material processing has produced significant improvements in performance, a fundamental understanding of charge separation and recombination at the donor/acceptor interface is lacking. Block copolymers with donor and acceptor polymer blocks provide an opportunity for controlling the donor-accepter interfacial structure and understanding its relationship to charge separation and photovoltaic performance. Here, we report the synthesis and characterization of donor-\textit{linker}-acceptor block copolymers for use in OPVs. A series of poly(3-hexylthiophene)-block- poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2',2"-diyl) (P3HT-\textit{linker}PFTBT) are synthesized with flexible oligo-ethylene glycol (PEG) linkers. Photoluminescence measurements demonstrate that the insertion of a non-conjugated linker has a significant impact on energy transfer between the two blocks, and the block copolymers are used as additives for bulk heterojunction OPVs. This work provides insight into the charge separation process and demonstrates a technique for tailoring the donor-accepter interface in OPVs. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P11.00006: Morphological Effect on Performance of Organic Photovoltaics---In Terms of Entropy and Helmholtz Energy Eisuke Kawashima, Mikiya Fujii, Koichi Yamashita Organic photovoltaics (OPVs) are promising alternatives to conventional silicon solar cells, but the current major challenge is their low performance. Morphology---phase separation and crystallinity of organic semiconductors---is a key factor to improve performance, and depends not only on materials but also on manufacturing processes, {\it e.g.}, thermal annealing. At present, however, optimization scheme of morphologies is not established. In our previous study, we examined temperature dependence of morphologies and effects of morphology on performance by device-scale simulations. Bulk heterojunction morphologies were generated by reptation, and current density--voltage characteristics and transient absorption spectroscopy were simulated by Dynamic Monte Carlo (DMC); we elucidated the existence of the optimal annealing temperature for efficiency.\footnote{E. Kawashima, {\it et al.}, {\it Phys. Chem. Chem. Phys.}, \textbf{2016}, 18, 26456--26465} In this presentation, we show Helmholtz energy $F$ and entropy $S$ of charge separation evaluated by graph theory and DMC simulations. We revealed that (i) $S$ drastically decreases $F$, (ii) $F$ attains a maximum at e--h distance of {\it ca.} 6 nm, and (iii) charge separation efficiency is determined by barrier height of $F$. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P11.00007: The Influence of Backbone Correlation Length and Dopant Strength on the Thermoelectric Power Factor of Semiconducting Polymers Shrayesh Patel, Anne Glaudell, Eunhee Lim, Michael Chabinyc The performance of doped semiconducting polymers is strongly governed by processing methods and underlying thin-film microstructure. We report on the influence of different doping methods (solution vs vapor) on the thermoelectric power factor (PF) of PBTTT molecularly doped with F$_{n}$TCNQ ($n=$ 2 or 4). The vapor doped films have over two-orders of magnitude higher electronic conductivity ($\sigma )$ relative to solution-doped films. On the basis of resonant soft x-ray scattering, vapor-doped samples are shown to have a large orientational correlation length (OCL) ($e.g. $length-scale of aligned backbones) that correlate to a high apparent charge carrier mobility ($\mu )$. Interestingly, the Seebeck coefficient ($\alpha )$ is largely independent of OCL. This reveals that, unlike \quad electronic conductivity, leveraging strategies to improve $\mu $ does not have a dramatic impact on $\alpha $. Overall, our work introduces important general processing guidelines for the continued development of doped semiconducting polymers for thermoelectrics. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P11.00008: A theoretical study on charge transfer type excitons at donor/acceptor interfaces of organic solar cells. Azusa Muraoka, Reina Tachibana, Mikiya Fujii, Kenji Mishima, Koichi Yamashita The conversion of excitons into charges within organic solar cells is complicated by bound electron-hole pairs, or charge transfer states at donor/acceptor interfaces. It is necessary that charge transfer is further separated into free charge carriers to be transported to electrodes. It was experimentally verified that the “hot” process is more dominant than the energy-gradient-driven intermolecular hopping for charge separation of an electron and a hole after the exciton generation in efficient photoconversion systems. We analyze the conversion efficiency of bulk-heterojunction organic solar cells in several polymer (donor):fullerene (acceptor) blends, such as, PCPDTBT, PTB2, PTB7 and PTBF2 with PC70BM using density functional theory and time-dependent density functional theory, and compare the numerical results with the experimental data. We discuss on the followings: (i) the “charge transfer distance” may be a good “descriptor” to design donor materials of high charge carrier separation, (ii) to examine whether the direct optical generation of CT states takes place in the charge separation process of the D/A complex, and (iii) the CS process takes place by the “hot” or “cool” process by examining an electron coupling of the D/A complex. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P11.00009: Thermoelectric Transport in Organic Semiconductors Using Polymerized Ionic Liquid Gate Dielectrics Elayne Thomas, Bhooshan Popere, Haiyu Fang, Michael Chabinyc, Rachel Segalman Thermoelectric materials are able to convert a temperature gradient into usable electricity via the Seebeck effect. This phenomenon is directly related to the material's Seebeck coefficient, electrical conductivity, and electron (or hole) mobility, all of which depend on carrier concentration. Carrier concentration is difficult to determine in many organic materials, which prevents a fundamental understanding of their thermoelectric charge transport mechanisms. In this work, we have utilized a field effect transistor (FET) geometry to directly modulate the carrier concentration of a p-type semiconducting polymer via gating. To allow for controlled doping at high carrier concentrations, we employed a high-capacitance (1$\mu $F/cm$^{\mathrm{2}})$ polymerized ionic liquid (PIL) as the gate dielectric. PILs contain one ion covalently bonded to the polymer backbone and one mobile ion. We see that doping through the field effect yields power factors similar to more traditional chemical doping methods with the advantage of stable and well-controlled carrier concentration modulation. Our studies demonstrate that gating with PILs offers a platform to investigate thermoelectric transport in organic semiconductors to guide further development in these complex systems. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P11.00010: Achieving Novel Relaxor Ferroelectric Behavior in a Nylon Terpolymer Zhongbo Zhang, Lei Zhu, Morton Litt Novel ferroelectric polymers, featured by narrow electric displacement-electric (D-E) loops, are attractive for electric energy storage applications due to their high dielectric constant and low loss properties. Currently, only poly(vinylidene fluoride) (PVDF)-based copolymers (e-beamed) and terpolymers show this behavior due to the formation of nanodomains. It is desirable to achieve novel ferroelectricity in other polar polymers such as nylons by modifying the crystal structure. In this presentation, a terpolymer of nylon 11, nylon 12 and N-methylated nylon 11 are synthesized, which show narrow D-E loops. The purpose of copolymerizing nylon 11 and nylon 12 is to introduce chemical defects (i.e., dangling amide groups) in the mesomorphic phase and to achieve nanodomains. The bulky N-methylated nylon 11 comonomers serve for the physical pinning effect. With the help of copolymerization and the pinning effect, the nylon terpolymer exhibits narrow D-E loops at elevated temperatures. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P11.00011: Structure-Function Relationships of Ferroelectric Polymers. Eleni Pavlopoulou, Jon Maiz, Nicoletta Spampinato, Mario Maglione, Georges Hadziioannou Poly(vinylidene fluoride), PVDF, and its copolymers with trifluoroethylene, P(VDF-co-TrFE) have been long appreciated for their excellent ferroelectric properties. Although they have been mainly studied in the 80s and 90s, understanding their performance is still lacking. Yet the increasing use of P(VDF-co-TrFE) thin films in organic electronic devices during the last ten years revives the need for apprehending the function of these materials. In this work we investigate the structure of P(VDF-co-TrFE) films and correlate it to their ferroelectric properties. Our results show that ferroelectric performance is solely driven by the fraction of polymer that has been crystallized in the ferroelectric phases of PVDF. The relations between remnant polarization, coercive field and dipole switching rate of P(VDF-co-TrFE) with the ferroelectric crystallinity are demonstrated. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P11.00012: Ferroelectric Properties of Large Area Evaporated Vinylidene Fluoride Thin Films Keith Foreman, Shashi Poddar, Adam Workman, Sara Callori, Stephen Ducharme, Shireen Adenwalla Organic electronics provide advantages in price, processing, and functionality. Poly(vinylidene fluoride) (PVDF) is a popular organic ferroelectric used a in wide variety of applications. The VDF oligomer features a higher surface charge density than PVDF and its copolymers and oligomer thin films can be deposited in vacuum, allowing for deposition on a metallic thin film without breaking vacuum. Despite these advantages, there has been little work towards employing the VDF oligomer in devices. Here, we report on stable and tunable ferroelectric behavior of large area VDF oligomer thin films and the interface with Co thin films. Pyroelectric measurements are used to identify the operating temperature of VDF oligomer-based devices and probe the stability of the ferroelectric polarization states over long periods of time. Using capacitance-voltage, current-voltage, and x-ray diffraction measurements, the remanent polarization and crystalline phase are reported, and the effects of annealing are clarified. X-ray photoelectron spectroscopy is used to characterize the VDF/Co interface. Finally, piezoresponse force microscopy is used to demonstrate large area ferroelectric domain writing VDF oligomer thin films. This work sets the stage for VDF oligomer based organic electronics. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P11.00013: Stretching-Induced Novel Relaxor Ferroelectric Behavior In a Poly(vinylidene fluoride-\textit{co}-trifluoroethylene-\textit{co}-hexafluoropropylene) Random Terpolymer Lei Zhu, Yue Li, Thibaut Soulestin, Bruno Ameduri, Fabrice Domingues Dos Santos Poly(vinylidene fluoride-\textit{co}-trifluoroethylene) [P(VDF-TrFE)]-based random terpolymers can exhibit unique relaxor ferroelectric behavior due to the formation of ferroelectric nanodomains by inclusion of relative bulky third monomers in the isomorphic crystalline structure. When the third monomer is too large such as hexafluoropropylene (HFP), they tend to be excluded from the crystalline lattice under normal crystallization conditions. Nonetheless, uniaxial stretching is found to induce the relaxor ferroelectric behavior for the P(VDF-TrFE-HFP) terpolymer. On the basis of structural characterization using X-ray diffraction and infrared spectroscopy, the relaxor ferroelectric behavior is found to be induced by inclusion of the large HFP units in P(VDF-TrFE) crystals upon stretching. The included HFP units not only expand the lateral interchain spacing to facilitate easier dipole/domain switching, but also divide the original large ferroelectric domains into nanodomains. As a result, the relaxor ferroelectric behavior is successfully achieved for the stretched films. [Preview Abstract] |
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