Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S15: Organic Electronics: Controlling Morphology and Charge TransportFocus
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Sponsoring Units: DPOLY Chair: Rafael Verduzco, Rice University Room: Room 207 |
Thursday, March 9, 2023 8:00AM - 8:36AM |
S15.00001: Tackling stability of polymer solar cells with thermocleavable side chains: materials and devices Invited Speaker: Wei You Record high efficiency for polymer solar cells (PSCs) has now approached 20%; however, there are a few roadblocks that significantly hamper its commercialization, in particular, stability. Increasing the glass transition temperature (Tg) of the materials used in PSCs can largely mitigate the thermal instability, yet most conjugated polymers used in high-efficiency PSCs only show low Tg values, mainly due the long and bulky side chains needed for solution processing of such polymers. Thermally removing cleavable side chains is an effective approach to re-gain the high Tg of CPs after the film formation, thereby achieving higher stability. This talk will focus on our recent efforts in applying thermocleavable side chains to achieve high stability of polymer solar cells, from archetypical polythiophenes to state-of-the-art donor-acceptor type copolymers. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S15.00002: Elucidating the hydrogen bonding location effect on morphology, mechanical and electrical properties of conjugated polymer/elastomer composites Yunfei Wang, Angela Awada, Kai-Lin Chen, Nathaniel L Prine, Yu-Cheng Chiu, Simon Rondeau-Gagné, Xiaodan Gu Developing stretchable semiconducting polymers plays an essential role with the growing demand for electronic skins, wearable, and implanted devices, sensors, etc. Hydrogen bond, a dynamic bond (HB), was reported able to effectively improve the stretchability of semiconductors when introduced either in pure conjugated polymers (CPs) or elastomer matrix of CP/elastomer composites. In this work, we combined these two methods that we introduced amide groups into both DPPTVT CP (DPPTVT-A) and elastomer matrix (amide-polyisobutylene, PIB-A) to fabricate dual hydrogen bond-crosslinked DPPTVT-A/PIB-A composites, and carefully studied the non-covalent hydrogen bonding location effect on morphology, electrical and mechanical properties. Their non-hydrogen bonding counterparts, DPPTVT and PIB, were selected as comparative reference fabricating uni-HB-crosslinked composites DPPTVT-A/PIB, DPPTVT/PIB-A and non-HB-crosslinked DPPTVT/PIB composites. Dual hydrogen bond-crosslinked composite DPPTVT-A/PIB-A showed micro-phase separation on the order of ~30 nm due to a combination of inter- and intramolecular HB interactions. In contrast, others show two-size phase separation, including macro-phase separation and fibril-like CP aggregation, characterized by the AFM-IR technique. However, the micro-phase separation morphology wasn’t beneficial to electrical properties. DPPTVT-A/PIB-A showed the lowest charge carrier mobility (0.03 cm2/V s), whereas DPPTVT/PIB-A, with the most fibril aggregation, showed the highest mobility (0.08 cm2/V s). The composite with PIB-A as elastomer matrix showed higher modulus due to the crosslink of elastomer. All composites showed high stretchability (crack onset strain >200%) originating from elastomers' high stretchability. This work provides a complete understanding of HB-crosslink effect on morphology and further influence on mechanical and electrical properties of CP/elastomer composite, which will guide the design of future stretchable semiconductors. |
Thursday, March 9, 2023 8:48AM - 9:00AM Author not Attending |
S15.00003: Emergent morphologies due to phase separation during meniscus-guided coating René d Bruijn, Jasper Michels, Paul Van der Schoot
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Thursday, March 9, 2023 9:00AM - 9:12AM |
S15.00004: Effect of solvent quality on chain conformation and optoelectronic properties of conjugated polymers by light scattering Guorong Ma, Zhiqiang Cao, Yunfei Wang, Xiaodan Gu Conjugated polymers (CPs) are suitable for next-generation organics electronics due to its advantages like tunable constitution and solution processibility. However, as for now there are limited knowledge about the solvent quality between the conjugated polymers and various solvents. Characterizations are mostly based on visual inspection of disappearance of large piece of the polymer chain. Even for those chain are visually dispersed, there is a lack of in-depth knowledge about if the polymers are actually dissolved to form individual chain or simply “dispersion” of small insoluble aggregates in solution. In this work, we report a static light scattering approach to quantify the solvent quality for poly(3-alkylthiophene-2,5-diyl) (P3ATs) and a donor-acceptor polymer PffBT4T-C9C13 with different length of sidechains in several commonly used organic solvents (chlorobenzene, chloroform, tetrahydrofuran, and toluene). By comparing the second virial coefficient A2, the effect of sidechain length on conjugated polymer’s interaction with solvent was investigated on CPs solutions in various solvents and temperatures. We found that for non-polar solvent, solvent quality increases as alkyl sidechain length increases and temperature increases, as the A2 value increased from -5.89 to 1.35 ×10-3 cm-3mol/g2 as sidechain length changed from C6H13 to C12H25. However, PffBT4T-C9C13 are less soluble with a negative A2 on the order of 10^-6 cm-3mol/g2 in all the solvent and temperature range we tested, owing to the more rigid and polar backbone. Our work sheds light on the polymer solvent interaction and can provide useful knowledge to rationally guide the development of new conjugated polymers as well as selection of solvents to process semiconducting polymers. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S15.00005: Patterned self-assembly of twisted tetrathiafulvalene crystals through solvent vapor annealing St. John Whittaker Topographic patterning of materials on the sub-millimeter length scale has applications ranging from optical gratings to adhesive surfaces. Here, we explore the spontaneous reorganization of banded tetrathiafulvalene spherulites into regularly spaced ridges on the tens of microns length scale during solvent vapor annealing. Banded spherulites crystallize from the melt as fibrils grow radially outwards from a single nucleation center, twisting in concert with one another about the growth direction. While these spherulites are topographically flat, concentric rings of interference colors become apparent when viewed between crossed polarizers that arise from rhythmic oscillations in crystal orientations due to twisting. Once these films are exposed to methanol vapor, contrast between alternating bands appears even under linearly polarized light and increases over time. Scanning electron microscopy (SEM) revealed the appearance and darkening of specific bands to be associated with an orientation-dependent reorganization of TTF crystals in which crystalline outgrowths appear on alternating bands at the expense of the adjacent bands. After a period of 24 hours of exposure to methanol vapor, TTF films comprised isolated, concentric circles of crystal outgrowths whose crystal orientations are epitaxially determined by the underlying TTF surface. While the surface of these outgrowths appear smooth, cross-sectional SEM images revealed a porous inner structure, suggesting solvent-vapor induced reorganization to proceed through oriented attachment of TTF nanocrystals onto the surfaces of specific bands. X-ray diffraction patterns collected on these films revealed that TTF crystals maintained the metastable beta-polymorph, typically formed at elevated temperatures, throughout the solvent vapor annealing process. These studies point to the use of crystal twisting as a means of patterning by taking advantage of crystal orientation-dependent properties, such as solubility. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S15.00006: Crystal Twisting to Impart Chirality to Organic Semiconductor Crystals Stephanie S Lee, Sehee Jeong, Yongfan Yang, Alexander G Shtukenberg, Bart Kahr, St. John Whittaker Here we introduce crystal twisting about the fast growth direction as a general strategy to impart chirality to centrosymmetric organic semiconductor crystals. When crystallized from the melt, tetrathiafulvalene forms banded spherulites comprised of helicoidal crystalline fibrils that twist in concert as they grow radially outwards from the spherulite nucleation center. Similar behavior has been discovered for twenty-five different charge transfer complexes, triisopropylsilylethynyl anthradithiophene (TIPS ADT) and 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT). Compared to films of melt-processed straight crystals, films of twisted organic semiconductor crystals exhibit higher charge mobilities and photocurrent. Crystal twisting further introduces chirality to these films, with helicoidal fibrils adopting either a clockwise or counterclockwise twisting direction. As such, films of twisted organic semiconductor crystals exhibit strong circular dichroism and birefringence, opening new avenues for chiroptical applications. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S15.00007: Deuteration Effects on Thermal, Crystallization, and Optoelectronic Properties of Donor-Acceptor Conjugated Polymers Kundu Thapa Deuteration is a popular method in spectroscopic and scattering techniques such as NMR and neutron scattering to control signal contrast. The abundant hydrogen of the polymers has significant differences in scattering cross section compared to deuterium, which alters scattering length density and promotes contrasts. As contrast fundamentally governs neutron scattering, the deuteration of parts of the polymer allows for understanding the structure and dynamics of a given polymer at a molecular level. However, despite the efforts in the past, there are few works on deuteration influences on electronically active conjugated polymers (CPs). Hence, this work investigated high-performing donor-acceptor (D-A) CPs with deuterated sidechains to study their influences on thermal, crystal ordering, and optoelectronic properties. The polymers, such as polyalkylthiophene (P3ATs) and diketopyrrolopyrrole (DPP) based polymers, were explored. Thermal measurements showed that P3AT had lower melting and crystallization after deuteration, whereas DPP polymers had the opposite trend. However, the morphology and optoelectronic properties had no changes upon deuteration, as confirmed by microscopic and scattering studies and thin-film transistor measurements. Hence, the deuteration studies popular in neutron scattering should be performed carefully, especially for dynamics studies. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S15.00008: Self-assembly of Periodic, Sub-micron Topography in Organic Semiconducting Thin Films Wan-Ju Hsu, John Bangsund, Russell J Holmes Certain glassy thin films based on conjugated small molecules are found to spontaneously form periodic patterns during crystallization via thermal annealing. These sinusoidal surface structures are formed perpendicular to the crystal growth direction and originate in the amorphous region within a micron of the crystal front. Previous work has shown that the periodicity of these self-assembled, well-aligned patterns can be tuned from 800 nm to 2,400 nm by varying film thickness and annealing temperature. This phenomenon likely reflects competition between crystal growth and free surface mass transport during the crystalline to amorphous conversion. In contrast to other methods that can induce patterns in organic thin films, this method is capable of producing aligned patterns, without additional anisotropic stress application or substrate patterning. This talk will examine the role of metal-oxide underlayers as a means to engineer the kinetics of film transformation and hence, pattern periodicity. We find that an MoOx underlayer results in lower crystal growth rate and longer pattern period, suggesting an important role for the film-substrate interaction. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S15.00009: Modeling conjugated polymers as ribbon-like chains Jian Qin, Wes Michaels, Andrew J Spakowitz The conformational statistics of conjugated polymers (CP) and ladder polymers are often described using the worm-like chain (WLC) statistics. The WLC model captures the bending stiffness but neglects the anisotropy of CP monomers. Here, we develop a ribbon-like chain (RLC) model that generalizes the WLC model by explicitly incorporating the anisotropic bending stiffness and the finite twist stiffness. The free-chain conformational statistics are fully solved, that predict the correlations of monomeric orientations along the CP backbone, the raidus of gyrations, the end-to-end distance etc. Three persistence lengths are introduced, accouting for the relaxation of the orientations along the two normal directions and the tangent direction, respectively. The regimes of the conformational statistics are discussed that include the 2D WLC and 3D WLC model as limiting cases. A simple method for parameterizing the model using molecular simulations is proposed and demonstrated for a few representative polymers. The framework may serve as a starting point for systematically building coarse-grained models of CPs. |
Thursday, March 9, 2023 10:12AM - 10:24AM Author not Attending |
S15.00010: Understanding Single-Molecule Charge Transport in Multi-state, Ladder-type Conjugated Molecules Jialing Li, Bo-Ji Peng, Shi Li, Daniel P Tabor, Lei Fang, Charles M Schroeder Development of stimuli-responsive materials is critical for new advances in molecular electronics. Our work focuses on the ability to precisely control the switching of electronic signals in single molecules using triggered changes in pH, mechanical force, optical or electric fields. Polyaniline (PANI) serves as a popular functional material due to its versatile chemical and electrochemical doping states arising from controlled changes in the conjugation and net charge change along the backbone. However, aniline cores suffer from chemical instabilities and a flexible backbone for facile bond rotation, which can lead to elusive electronic properties and hinder charge transport efficiency. To overcome these challenges, we synthesized and studied the charge transport properties of a new class of ladder-type redox-active molecules. In particular, pernigraniline molecules were modified with a ladder-type strategy to lock the molecular conformation, thereby restricting the free rotation of backbone bonds. We further studied the single molecule charge transport properties of ladder-type pernigraniline molecules using the scanning tunneling microscope-break junction (STM-BJ) method. Our results show a 100-fold increase in molecular conductance for pernigraniline molecules upon full protonation and lithiation. Intermolecular charge transport is also observed via the formation of stacked dimers assisted by π-π interaction. Experimental results are complemented by DFT calculations, which reveals smaller energy gaps and extended molecular conformations for higher protonated and lithiated states. Overall, our work shows that ladder-type molecules with functional aniline moieties provide a promising class of materials with well-defined electronic properties at different prontonation and oxidation states. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S15.00011: Ion Transport in 2D Nanostructured π-Conjugated Thieno[3,2-b]thiophene-Based Liquid Crystal Zhongyang Wang, Chaoqiuyu Wang, Yangyang Sun, Joseph W Strzalka, Christopher K Ober, Fernando A Escobedo, Paul F Nealey, Shrayesh Patel Leveraging the self-assembling behavior of liquid crystals designed for controlling ion transport is of both fundamental and technological significance. Here, we have designed and prepared a new liquid crystal that contains (2,5-bis(5-(2,5,8,11-tetraoxatridecan-13-yl)thiophen-2-yl)thieno[3,2-b]thiophene (BTTT) as mesogenic core and conjugated segment and symmetric tetra(ethylene oxide) (PEO4) as polar side chains for ionic conducting regions. Driven by the crystallization of the BTTT cores, BTTT/PEO4 exhibits well-ordered smectic phases over the temperature range of 15.7 °C to 71.5 °C as confirmed by differential scanning calorimetry, polarized optical microscope, temperature dependent wide-angle X-ray scattering and grazing incidence wide-angle X-ray scattering (GIWAXS). We adopted a combination of experimental GIWAXS and molecular dynamics (MD) simulations to better understand the molecular packing of BTTT/PEO4 films, particularly when loaded with the ion conducting salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). It was found that forming a smectic layered structure with an irregular interface between the BTTT core and the PEO4 side chain enhances ion conduction in BTTT/PEO4. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S15.00012: Thermoelectric Transport Signatures of Carrier Interactions in Polymer Electrochemical Transistors Dionisius Hardjo Lukito Tjhe, Xinglong Ren, Ian Jacobs, Tarig Mustafa, Thomas Marsh, Yuxuan Huang, Lu Zhang, William Wood, Ahmed Mansour, Gabriele d'Avino, David Beljonne, Norbert Koch, Henning Sirringhaus Electronic phase transitions of polymers in the high carrier density regimes are still not well understood. Early works in the field have elegantly demonstrated that several polymers could be turned from a band-insulator to a metal upon chemical doping. However, little is known about carrier interaction effects that would be expected to arise, for instance, as the metallic state gets doped even more. The closest transport signature to that of a correlated system so far is the Efros-Skhlovskii variable-range hopping temperature dependence of electrical conductivity, reflecting the opening of a Coulomb gap around the Fermi level because of interactions between localised carriers in the insulating regime. |
Thursday, March 9, 2023 10:48AM - 11:00AM |
S15.00013: Vapor-to-glass preparation of biaxially aligned glassy liquid crystal Jianzhu Ju, Debaditya Chatterjee, Paul Voyles, Harald Bock, Mark D Ediger Physical vapor deposition (PVD) provides a unique tool for the additive manufacture of organic light-emitting diode (OLED) displays, where high surface molecular mobility and surface equilibration provide excellent control of molecular order. While existing work has demonstrated that out-of-plane uniaxial symmetry can be prepared by PVD below Tg, here in this work we introduce the additional dimension of in-plane alignment by combining conventional substrate alignment into PVD. With the collective effect of substrate templating and surface equilibration mechanism, biaxial bulk alignment is achieved up to 50 K below Tg with single-component disk-like (phenanthroperylene ester) and rod-like (itraconazole) mesogens. The structural anisotropy is characterized by GIWAXS and the optical anisotropy is measured with polarized optical microscopy, where 70% degree of polarization can be obtained in the 250 nm PVD film. Practically, this presented preparation of biaxially aligned mesogens points out the possibility to add an ordered and highly customizable individual layer into a device directly from vapor at low processing temperature without risking destroying the structure in the underlying layers, which may lead to the development for next-generation organic electronic devices. |
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