Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A41: Focus Session: Organic Electronics and Photonics - Thermoelectric, Ferroelectric, and Piezoelectric Materials |
Hide Abstracts |
Sponsoring Units: DPOLY DMP Chair: Jennifer Schaefer, National Institute of Standards and Technology Room: 214A |
Monday, March 2, 2015 8:00AM - 8:12AM |
A41.00001: n-type doping through tethered functionality: a new paradigm for molecular design of solution-processed organic thermoelectrics Boris Russ, Maxwell J. Robb, Bhooshan C. Popere, Erin E. Perry, Jeffrey J. Urban, Michael L. Chabinyc, Craig J. Hawker, Rachel A. Segalman A scarcity of stable n-type doping mechanisms compatible with facile processing has been a major impediment to the advancement of n-type (electron transporting) organic thermoelectric materials. We recently demonstrated that trimethylammonium functionalization with hydroxide counterions, tethered to a perylene diimide core by alkyl spacers, facilitated solution-processing and resulted in extremely high carrier concentrations (10$^{\mathrm{20}}$carriers/cm$^{\mathrm{3}})$ and best-in-class thermoelectric performance in thin films. In this presentation, we report our recent findings on the underlying mechanism enabling charge carrier generation in these self-doping materials and its influence on material thermoelectric behavior. To draw these conclusions, we complement thermoelectric characterization with insights into chemical, electronic, and structural properties from XPS, optical spectroscopy, EPR, and GIWAXS experiments. Furthermore, we show that doping through tethered functionality can be extended to other n-type small molecule systems of interest, including naphthalene diimides and diketopyrrolopyrroles. Our findings help shape promising molecular design strategies for future enhancements in n-type thermoelectric performance. [Preview Abstract] |
Monday, March 2, 2015 8:12AM - 8:24AM |
A41.00002: Silver Nafion for Thermogalvanic Applications William Chang, Bhooshan Popere, Chris Evans, Boris Russ, Rachel Segalman Thermogalvanics convert a temperature gradient, typically from waste heat, into electrical power using a reversible electrochemical reaction. The conversion efficiency in thermogalvanics, like with thermoelectrics, are governed by the Seebeck coefficient, the carrier conductivity and the thermal conductivity of the material. We demonstrate that the material systems silver Nafion and silver poly-styrenesulfonate are air-stable, water processable materials that demonstrate extremely high Seebeck coefficients and moderate carrier conductivities. These power factors, when coupled with the low thermal conductivities inherent in polymers, results in materials with excellent thermogalvanic figure of merits. We show the dependence of these three material properties to material composition and processing. In this talk, we show how the Seebeck coefficient in silver Nafion and silver polystyrene-sulfonate are opposite in sign, allowing construction of a thermogalvanic device. With these ion conductors, we hope to open up a flexible pathway to waste heat recovery using materials typically studied for electrochemical applications. [Preview Abstract] |
Monday, March 2, 2015 8:24AM - 8:36AM |
A41.00003: Thermoelectric properties of hole- and electron-doped ambipolar polymers Anne Glaudell, Erin Perry, Ruth Schlitz, Michael Chabinyc The library of possible materials, both p- and n-type, for organic thermoelectric devices has been steadily growing with the continuous improvement in electrical properties and stability. Maximizing the thermoelectric power factor in these materials requires the simultaneous optimization of both electrical conductivity and thermopower. The challenge remains that charge transport is not well understood in organic materials due to energetic disorder from crystalline and non-crystalline domains. We have performed temperature-dependent measurements of both thermopower and electrical conductivity to uncover the relationship between microstructure and thermoelectric performance. These measurements were complemented by techniques such as electronic paramagnetic resonance (EPR) that help provide the carrier concentration to give a more complete picture of the competing charge transport mechanisms and structure-property relationships. We will present results on p- and n-type doping of ambipolar polymers that reveal the difference in thermopower for electrons and holes in the same material. An ideal thermoelectric device has n- and p-type legs with similar mechanical and thermoelectric properties, a balance more easily realized using the same polymer for each leg. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 9:12AM |
A41.00004: Conductance and Thermopower in Thiophene and Oxidized Thiophene Single-Molecule Junctions Invited Speaker: Latha Venkataraman Organic electronic materials have impacted the development of semiconducting, photovoltaic and thermoelectric devices. The precise control afforded over molecular design by organic synthesis allows for device properties to be readily tailored facilitating varied functionality. Measuring charge transfer characteristics and thermoelectric properties in organic devices and across metal-organic interfaces is of critical importance for understanding structure-function relations and single molecule measurements offer an ideal test bed for such measurements. In this talk, I will review the scanning tunneling microscope break-junction technique used to measure conductance in single-molecule devices focusing on molecular systems that have strong potential for application in organic and photovoltaic devices. Specifically, I will discuss measurements of thiophene and oxidized thiophene oligomers and illustrate how structure and conformations impact both the electronic characteristics and the dominant charge carrier in these systems. I will end this talk discussing results with a new class of thiophene derivatives where the charge carriers are changed from holes to electrons as the length of the oligomer is increased. With these measurements, we illustrate a new means to tune p- and n-type transport in organic materials. [Preview Abstract] |
(Author Not Attending)
|
A41.00005: Thermoelectricity in Disordered Organic Semiconductors under the Premise of the Gaussian Disorder Model and its Variants Dan Mendels, Nir Tessler Charge transport in disordered organic systems has been in recent decades mainly discerned from the perspective of a variety of phenomenological models prominent of which those stemming from the Gaussian Disorder Model. But while the use of these models has been prevalent, uncertainty regarding the extent of their validity remains due to the large number of free parameters they consist and their frequent deficiency to consistently account for large sets of experiments while keeping model input parameters and distributions unchanged. In the presented study, we have investigated using Monte Carlo simulations the thermoelectric properties of disordered organic semiconductors under the premise of the Gaussian Disorder Model and its variants. Doing so enabled the provision of additional dimensions for comparison between the aforementioned theoretical frameworks and real systems, beyond those based on extensively studied charge transport properties, and the provision of a frame-of-reference for rising interest in these systems for thermoelectric applications. To illustrate the potential existing in the implementation of combined transport and thermoelectric investigation, strategies will be discussed to experimentally deduce the DOS shape, infer whether a system's activation energy originates from its energetic disorder or a polaron activation energy (while deducing the given polaron activation energy), and discerning whether a system's energetic disorder is spatially correlated or accompanied by off-diagonal disorder. [Preview Abstract] |
Monday, March 2, 2015 9:24AM - 9:36AM |
A41.00006: Morphology of PEDOT:PSS/SWCNT Composites: Insight into Carbon Nanotube Based Organic Thermoelectric Matrices Thusitha Etampawala, Mehran Tehrani, Mark Dadmun Carbon nanotube (CNT) loaded poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) nanocomposites are promising materials as the active layer in organic thermoelectric devices. Improvements in the thermoelectric performance of these nanocomposites have been hampered by the lack of an understanding of the correlation between thermo-electrical performance and morphology. In this study, the morphology of highly conducting single walled CNT/PEDOT:PSS nanocomposites were probed by small and ultra-small angle neutron scattering (SANS and USANS respectively) as a function of CNT loading (10wt{\%}, 30wt{\%} and 50wt{\%},), sonication duration to control the CNT dispersion, and presence and absence of ethylene glycol (EG) in the deposition solution of PEDOT:PSS. The morphology of these composites is currently being correlated to their thermo-electric performance. The SANS and USANS profiles were analyzed with the hierarchical Beaucage model. Further, the USANS data were fit to a two ellipsoidal form factor, which is consistent with the analysis of the USANS data by the Beaucage model and SEM results. These results reveal that the sonication duration and presence of EG effectively de-bundle the CNTs and disperse them in the PEDOT:PSS matrix. [Preview Abstract] |
Monday, March 2, 2015 9:36AM - 9:48AM |
A41.00007: Exploiting the Different Polarity in Piezoresistive Characteristics of Conducting Polymers for Strain Gauge Applications Melda Sezen, Jeffrey T. Register, Yao Yao, Branko Glisic, Yueh-Lin Loo Piezoresistivity defines the change in resistance of a material in response to mechanical stress. We exploited the effects of structural modifications on the piezoresistive properties of conducting polymers, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) doped polyaniline, PANI-PAAMPSA, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, for strain gauge applications. Under tensile deformation, the resistances of as-cast PANI-PAAMPSA and PEDOT:PSS increase due to increased separation between the electrostatically stabilized conducting polymer particles. Upon solvent annealing in dichloroacetic acid, DCA, PANI-PAAMPSA's resistance decreases whereas PEDOT:PSS's resistance still increases with tension. While DCA treatment reduces the electrostatic interactions between PANI and PAAMPSA, it only removes the PSS overlayer in PEDOT:PSS. The change in the polarity of PANI-PAAMPSA's piezoresistivity is attributed to the unlocking of the globular structure of the as-synthesized conducting polymer complex with DCA-treatment, which then enables strain-induced crystallization on deformation. By tuning the piezoresistive characteristics of the polymers through structural modification, we can design strain gauge circuits for monitoring the conditions of civil structures. [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:00AM |
A41.00008: Temperature-dependent electrical transport in ferroelectric organic field-effect transistors Amrit Laudari, Suchismita Guha Ferroelectric dielectrics, permitting access to nearly an order of magnitude range of polarization with temperature as the tuning parameter, offer a great test-bed to monitor the changes in interfacial transport in organic field-effect transistors (OFETs) as the polarization strength is tuned. Temperature-dependent transport studies have been carried out from pentacene and other organic semiconductor-based OFETs using the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFe) as a gate insulating layer. By fits to an Arrhenius-type dependence of the charge carrier mobility as a function of temperature, the activation energy in the ferroelectric phase is found to increase as the thickness of the PVDF-TrFe layer increases. For thicknesses of the dielectric layer above 100 nm, the activation energy is found to be greater than 150 meV, which greatly reduces in the paraelectric phase of the dielectric. The weak temperature-dependence of the charge carrier mobility in the ferroelectric phase of PVDF-TrFe may be attributed to a polarization fluctuation driven transport. The threshold voltage decreases upon increasing temperatures with a large change above the ferroelectric to paraelectric phase transition temperature. [Preview Abstract] |
Monday, March 2, 2015 10:00AM - 10:12AM |
A41.00009: Ferroelectrically-driven photocurrent in P3HT-based diodes Eleni Pavlopoulou, Carine Lacroix, Antigoni Paspali, Guillaume Fleury, Cyril Brochon, Eric Cloutet, Fabrice Domingues Dos Santos, Mario Maglione, Georges Hadziioannou Blends of ferroelectric and semiconducting polymers are known to phase separate in thin film configuration, forming semiconducting columnar structures embedded in a ferroelectric matrix. These blends have been used in the past to fabricate non-volatile bistable diodes. In this work we demonstrate that the phase separated network of poly(3-hexylthiophene), P3HT, and poly(vinylidenefluoride-co-trifluoroethylene), P(VDF-co-TrFE), can be also used for the extraction of photocurrent under illumination. Furthermore, we provide experimental proofs on the ferroelectric origin of this photocurrent and we show that its magnitude depends on the polarization characteristics of the pre-polarized P(VDF-co-TrFE) matrix. The devices we propose herein can provide an alternative to the existing organic photovoltaic devices. [Preview Abstract] |
Monday, March 2, 2015 10:12AM - 10:24AM |
A41.00010: Ferroeletricity and Double Hysteresis Loop Behavior in Even-Numbered n-Nylons Zhongbo Zhang, Lei Zhu, Morton Litt Ferroelectric (FE) property in odd-numbered n-nylons has been known for a long time. In comparison, even-numbered n-nylons are claimed to be non-ferroelectric due to their non-polar crystalline structure, where the direction of hydrogen bonded dipoles alternates. Nevertheless, in this presentation, FE property is discovered in even n-nylons, and it is related to the mesomorphic crystalline structure formed via quenching and/or stretching. Although there was an earlier claim maintaining that FE behavior in melt-quenched nylon 6 was due to the amorphous phase, the conclusion is debatable and the understanding of the FE mechanism is still lacking. We find that poorly bonded amide dipoles, which result from the defective crystalline mesophase, play an important role in the FE behavior of nylon 12. In this mesophase, the chain conformation is smectic-like, twisted, and the hydrogen bonds are randomized. Therefore, this mesophase is abundant in defects and poorly bonded dipoles, which can easily flip under electric field. In addition, the hydrogen-bonded amides can serve as pinning points and induce double hysteresis loop behavior. This understanding illustrates that FE in even n-nylons originates from the defective crystalline phase rather than the amorphous region. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 10:36AM |
A41.00011: Relaxor Ferroelectric Behavior from Strong Physical Pinning in a Poly(vinylidene fluoride-\textit{co}-trifluoroethylene-\textit{co}-chlorotrifluoroethylene) Random Terpolymer Lei Zhu, Lianyun Yang, Brady Tyburski, Fabrice Domingues Dos Santos Although narrow single hysteresis loop (SHL) is observed for electron beam (e-beam) irradiated poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] random copolymers owing to strong chemical pinning in isomorphic (or defect-modified) crystals, it has not been achieved for P(VDF-TrFE)-based random terpolymers, such as P(VDF-TrFE-CFE) (CFE is 1,1-chlorofluoroethylene), which only exhibits double hysteresis loops (DHLs). This is attributed to the weak physical pinning of CFE units in isomorphic crystals. In this work, the comonomer CFE in the terpolymer was replaced by the larger chlorotrifluoroethylene (CTFE). Intriguingly, narrow SHLs were exclusively observed for the P(VDF-TrFE-CTFE) terpolymer above room temperature. This was attributed to the stronger physical pinning force of the larger CTFE, which has a smaller dipole moment (only 0.64 Debye). This result provides us further insight into the structure and behavior of relaxor ferroelectric polymers, which can help to design and develop new ferroelectric polymers with more desirable properties and enhanced performance. [Preview Abstract] |
Monday, March 2, 2015 10:36AM - 10:48AM |
A41.00012: ABSTRACT MOVED TO M6.00013 |
Monday, March 2, 2015 10:48AM - 11:00AM |
A41.00013: Enhanced Electrical Conductivity due to Morphological Changes in Polyanaline-Titania Core-Shell Nanocomposites Nelson Coates, Jianfeng Liu, Rachel Segalman, Jeffrey Urban Conducting polymer-inorganic nanoparticle composites are a valuable class of advanced materials with a wide range of applications due their extensive physical and chemical tunability. Although effective medium theories are often used to predict the behavior of these materials, the actual physical properties can be distinctly different from their constituents due to a variety of structural or electrical interfacial interactions that may manifest. Here, we present electrical conductivity data for TiO2 nanoparticles coated with polyanaline, along with structural characterization of the conducting polymer as a function of component volume fraction. For these composites, we find that the electrical conductivity cannot be explained by a 2-component effective medium theory, but rather is correlated to a structural change in the polymer. We hypothesize that the organic-inorganic interface induces a structural change in a region of polymer surrounding the nanoparticle which improves the electrical conductivity of the composite. These results emphasize the importance of controlling interfacial interactions in organic-inorganic composites, and demonstrate the potential for using such interactions as a way to tune electrical transport. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700