Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q16: Organic Electronics III: Nanoscale Phenomena in Optoelectronically Active PolymersRecordings Available
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Sponsoring Units: DPOLY Chair: Rafael Verduco, Rice University Room: McCormick Place W-184A |
Wednesday, March 16, 2022 3:00PM - 3:12PM |
Q16.00001: Enhancing the dielectric breakdown strength and energy density of solid-state polymeric capacitors by chain end manipulations Mei Dong, David Tran, Nihar R Pradhan, Dharmaraj Raghavan, Jack F Douglas, Karen Wooley, Alamgir Karim The maximum energy density of a polymeric dielectric capacitor is limited by the breakdown of the dielectric material at high electric fields. Theoretically, it has been shown that chain ends contribute adversely to the electrical breakdown of polymer dielectrics. In this work, we experimentally demonstrate the role of chain ends indirectly and directly in the dielectric breakdown by using block copolymers (BCP) and cyclic polymer films respectively. The BCPs show an enhanced breakdown strength due to chain end segregation, resulting in energy densities of 5 J/cm3. For direct observation of the role of chain ends in the breakdown, we synthesized the cyclic polymers with high purity. The cyclic polymer films demonstrate ~50% enhancement in dielectric breakdown strength and as a result, the energy density in the cyclic polymer films increases by ~80% as compared to their linear counterparts. Interestingly, the cyclic polymer films show a higher refractive index and packing density as compared to their linear counterparts, which might be attributed to the elimination of chain end-based free volume. These insights into the structure-property relationship will help design next-generation polymeric energy storage materials and devices. |
Wednesday, March 16, 2022 3:12PM - 3:24PM |
Q16.00002: Tuning Performance of Organic Field-Effect Transistors through Modification of Polymer Dielectrics John T Barron, Jaewon Lee, Suchismita Guha For field-effect transistors (FETs) which utilize organic semiconductors, modifying the dielectric layer will largely influence device performance. Ferroelectric polymers are one such material which has been of interest for producing OFETs with low operating voltages owing to their high dielectric constant. Another method of enhancing the dielectric constant has been the incorporation of semiconducting and insulating nanoparticles. Cobalt-ferrite (CoFe2O4 or CFO) magnetic nanocrystals have been synthesized using a thermal decomposition method and coated with polymers such as poly(vinyl alcohol) (PVA). The insulating property make them attractive for dispersing in polymer dielectrics. After incorporating CFO nanoparticles into the polymer dielectrics, a decrease in the threshold voltage and subthreshold swing are observed for OFET devices. The application of an external magnetic field to such devices appears to further alter device behavior, acting as another tunable parameter. Pentacene and TIPS-Pentacene are used as the active semiconductor layers, and we will further discuss the use of donor-acceptor polymers based on diketopyrrolopyrrole (DPP) and isoindigo in OFET devices. |
Wednesday, March 16, 2022 3:24PM - 3:36PM |
Q16.00003: Recycling conjugated polymers from organic thin film transistors Louis Y Kirkley, James G Sutjianto, Enrique D Gomez Organic thin film transistors (OTFTs) fabricated from conjugated polymers have been a technological area of interest for their unique properties, such as solution processability, light weight, and flexibility; nevertheless, environmental sustainability hinders potential for industrial scale-up. Here, we demonstrate OTFT recycling by redissolving the semiconducting polymer active layer from OTFTs and recasting onto new bottom-gate, bottom-contact substrates. The redissolution process selectively strips the polymer from the substrate, allowing for facile use that lowers contamination risks. Device performance of reprocessed OTFTs have comparable mobilities to fresh OTFTs and even have lower hysteresis and off currents, suggesting a removal of ionic impurities by recycling. Showing the recyclability of these polymers from electronic devices increases their viability for sustainable production. |
Wednesday, March 16, 2022 3:36PM - 3:48PM |
Q16.00004: Polarized resonant soft X-ray scattering measurements in semicrystalline polymers and nanocomposites Dean M DeLongchamp Orientation and conformation in nanoscale amorphous regions often dominate the properties of soft materials. Robust correlations between structure in these amorphous regions and important properties are not well developed due to a lack of measurements with high spatial resolution and a sensitivity to molecular orientation. I will describe our approach to solving this issue using polarized resonant soft X-ray scattering (P-RSoXS), which combines principles of soft X-ray spectroscopy, small-angle scattering, and data fusion with real-space imaging to produce a molecular scale structure measurement for soft materials. |
Wednesday, March 16, 2022 3:48PM - 4:00PM |
Q16.00005: Studying Stress and Conductivity Relaxations of CNT-Infused Rubber Materials Claire Onsager, Can C Aygen, Sahar Meir, Lev Rovinsky, Noa Lachman Senesh, Matthew Grayson Stress relaxation experiments are important to study polymer properties. We are focused on the parallel study of stress relaxation and conductivity relaxation in carbon nanotube (CNT) infused rubber composites. Observations of relaxations are essential for predicting future behavior, as the polymers retain memory in the form of elastic deformations with slow relaxation times. We constructed a specialized device for stress relaxation experiments. Our device applies calibrated strain in the form of stretching and measures conductivity and force responses over time. The setup is housed in an isothermal chamber whereby a proportional-integral controller maintains constant temperatures. Initial ambient temperature data shows clear force fluctuations corresponding to room temperature changes throughout a day. The several weeks of data needed to observe important relaxation features are thus only possible in the absence of temperature fluctuations. With this system, stress-relaxation data of various samples are obtained and compared with polymers of various CNT compositions. The setup design and relaxation data will be shown to demonstrate the measurement technique, the scales by which these relaxations occur, and how the force and conductivity relaxations of similar polymers compare. |
Wednesday, March 16, 2022 4:00PM - 4:12PM |
Q16.00006: Theory of a Ferroelectric Carbon Nanothread Bohan Xu Nanothreads are one-dimensional rigid sp3 carbon frameworks synthesized by pressure-induced polymerization of aromatic precursors such as benzene or furan. Here we predict that pyrrole-based nanothreads may exhibit ferroelectricity through reorientations of lone pairs within a 1D stack of –NH functional groups that are anchored in the rigid nanothread backbone. To help realize the stacking geometry needed for ferroelectricity, we describe a strategy of nanothread structural control based on steric crowding of bulky side groups. By this method we identify a family of pyrrole-based precursors such as 3-trifluoroumethyl-pyrrole that are energetically favored to form ferroelectric threads over non-ferroelectric isomers. |
Wednesday, March 16, 2022 4:12PM - 4:24PM |
Q16.00007: Ultra-Stretchable, Transparent Ionic Sensory Platforms for Next-Generation Wearable Artificial Skins Yong Min Kim The primary technology of next‐generation wearable electronics pursues the development of highly deformable and stable systems. Here, nonvolatile, highly transparent, and ultrastretchable ionic conductors based on polymeric gelators [poly(methyl methacrylate‐ran‐butyl acrylate), PMMA‐r‐PBA] and ionic liquids (IL) are proposed. A crucial strategy in the molecular design of polymer gelators is copolymerization of PMMA and IL‐insoluble low glass transition temperature (Tg) polymers that can be deformed and effectively dissipate applied strains. Highly stretchable (elongation limit ≈850%), mechanically robust (elastic modulus ≈3.1 × 105 Pa), and deformation durable gels are obtained by judiciously adjusting the molecular characteristics of polymer gelators and gel composition. An extremely simple “ionic” strain sensory platform is fabricated by directly connecting the stretchable gel and a digital multimeter, exhibiting high sensitivity, stable operation, and nonvolatility. Moreover, the skin‐type strain sensor, referred to as ionoskin, is demonstrated. The gels are attached to a part of the body and various human movements are successfully monitored. The ionoskin renders the opportunity to achieve wearable ubiquitous electronics such as healthcare devices and smart textile systems. |
Wednesday, March 16, 2022 4:24PM - 4:36PM |
Q16.00008: Routes Forward for Evaporated Small Molecule Organic Solar Cells Pascal Kaienburg, Andreas Lauritzen, Irfan Habib, Moritz Riede, Anna Jungbluth
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Wednesday, March 16, 2022 4:36PM - 4:48PM |
Q16.00009: Correlating Excited States Populations, Molecular Geometry, and Efficiency for Small Molecule OPVs Kristen Burson, Tyler Wiegand, Hudson Smith, Catherine N Ryczek, Adriana S Cruz, Christopher J Collison The efficiency of organic photovoltaics (OPVs) depends critically on the morphology of the active layer and the nature of the excited states. A framework for tailoring binary donor:acceptor blend ratios to optimize device efficiency can be established by correlating device efficiencies, morphology, and excited state populations. To assess excited state populations the extinction coefficient for each species must be determined. Here we present a study of Squaraine:PCBM OPVs using atomic force microscopy, spectroscopy, and device efficiency data. The intrinsic extinction coefficients of Squaraine and PCBM are established by collecting spectroscopy and thickness data. Thickness measurements additionally reveal mixing geometries characterized by incorporation into the interstices, depending on blend ratio. We connect optimal blend ratios with the population of excited state species. The approach can be extended to optimize other small molecule devices. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q16.00010: Tuning solvent quality to push performance of donor-acceptor films in OPVs Stephen H Wong, Guoyan Zhang, Enrique D Gomez Organic photovoltaics (OPVs) have the potential for high specific power, flexibility, and solution processability. Yet the factors governing performance of OPVs are complex due to the interplay between chemistry, processing, and morphology. Tuning the solvent quality prior to casting the active layer can further improve the power conversion efficiency (PCE). Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione)] (PM6) and 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2",3’':4’,5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6) were used to fabricate OPV’s in conjunction with a variety of solvent additives using chloroform as a host solvent. The addition of small amounts of acetone leads to a specific regime of solvent quality where Y6 is well solvated but PM6 has marginal solubility. This leads to perturbations to the active layer bulk heterojunction morphology and improved short circuit current, open circuit voltage, fill factor, and PCE in resulting devices. |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q16.00011: Excitonic properties of pi-conjugated acene ethynylene-bridged polymers from a trivial to a non-trivial insulating phase Davide Romanin, Alex Chin, Matteo Calandra In recent papers (Refs. [1]-[2]) it was shown that it is possible to observe a topological phase transition in 1D acene ethynylene-bridged polymers from a trivial to a non-trivial insulating phase as a function of the monomer acene size. Combining tight-binding, DFT and GW calculations they showed that such quantum phase transition was accompanied by a ethylenic-to-cummulenic transition in the molecular bridges between the acenes, and that the presence of a topological transition could provide a route to novel organic metals. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q16.00012: Understanding Intermolecular Charge Transport in Cucurbit[8]uril Encapsulated Pyridinium Dimers Jialing Li, Hao Yu, Songsong Li, Nicholas E Jackson, Jeffrey S Moore, Charles M Schroeder Device performance in organic electronics is intimately controlled by a balance between intramolecular and intermolecular charge transport. Despite recent progress in understanding intermolecular charge transport, it remains challenging to control the conformation and orientation of conjugated polymer backbones to maximize orbital overlap. In this talk, we introduce a new strategy for studying interchain charge transport at the single molecule level using pi-stacked junctions driven by host-guest complexation. Extensive chemical characterization demonstrates that homoternary complexes are formed between four types of pyridinium monomers and cucurbit[8]uril (CB[8]) in a head-to-tail structure with high affinity. Intermolecular charge transport through π-stacked dimers is directly studied using scanning tunneling microscope-break junction (STM-BJ) technique, revealing unexpectedly high conductance levels over long-distance transport pathways compared to isolated, single pyridinium junctions. Density functional theory simulations show planarized geometries and strong LUMO-LUMO coupling upon the formation of the supramolecular complex, thereby facilitating intermolecular charge transport. Overall, this work provides a new approach to understand and modulate intermolecular charge transport with well-defined pi-stacked pyridinium dimers encapsulated by a host cavity for functional molecular electronic devices. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q16.00013: Optical properties of Thienylfuran linear oligomers Vinicius A Bastos, Tales J da Silva, Marilia J Caldas Thiophene oligomers are promising for photovoltaics due to stability and strong absorption in the visible region. A recent proposal is co-polymerization with furan units, building linear thienylfuran oligomers[1]. We present a theoretical study of thiophene, furan and thienylfuran short chains, using different methodologies - from Hartree-Fock HF and Density Functional Theory DFT, to Moller-Plesset perturbation HF-MP2, many-body perturbation G0W0@DFT and Bethe-Salpeter Equation[2-4]. We investigate monomers T and F up to linear tetramers with different sequencing of units TT, TF or FF. For any TT sequencing we find a torsion angle of 150°, while all others result planar. Interestingly, we find that the first optical transitions start from ∼4 eV for dimers and reach a promising threshold of ∼3 eV for the tetramers, at this point with ionization potentials of ∼7 eV. Regarding the conduction band minimum of ∼4.2 eV for much used semiconducting oxides, this can lead to efficient photovoltaic charge-transfer in real applications. |
Wednesday, March 16, 2022 5:36PM - 5:48PM |
Q16.00014: Universal features of dynamics of localized electronic states Anatoly Obzhirov, Eric J Heller In a number of systems, electronic transport can be viewed as dynamics of localized electronic states. However, there is no universal theory that describes time evolution of localized states. In this work, we present universal features of such motion. They originate from the concept of adiabatic change of character near an avoided crossing. It is shown that localized electronic states move by interchanging positions with adjacent localized states that form an avoided crossing. Avoided crossings formed by two adjacent electronic states would be adiabatic, whereas avoided crossing formed by two distant electronic states would be diabatic. To illustrate this idea, we develop a numerical model based on Anderson localized states. Based on our observations, we discuss universal features of relaxation time. The presented perspective could give new insights on Metal-Insulator transitions and electron transport in nanostructures, superlattices, and disordered semiconductors. |
Wednesday, March 16, 2022 5:48PM - 6:00PM |
Q16.00015: Accurate Charge Mobility Simulation and Validation in Organic Semiconductors Daniel Vong, Adam Moule, Makena A Dettmann, Lucas Cavalcante The charge mobility, which is the figure of merit in organic molecular semiconductors, is modulated by the intermolecular dynamic disorder. Knowledge of the full phonon spectrum is essential for accurate calculations of mobility and high mobility molecular design rules. Although phonons can be computed accurately, it is not known which phonons specifically contribute to dynamic disorder. Recently, it was proposed that a single long-axis mode dominates mobility reducing dynamic disorder and that the displacement along the long-axis of the molecule is the only relevant design rule. However, most vibrational spectroscopy techniques under-measure the phonons, and thereby limit the accuracy of calculated phonons. |
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