Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “conjugated polymers”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Energy Transfer Mechanisms in Large Low-Bandgap Polymers from Time-Resolved Experiments and Nonadiabatic Molecular Dynamics Calculations

Conjugated polymers offer unprecedented chemical tunability for modulating energy transfer in a multitude of infrared light applications. In this work, we use a combination of time-resolved spectroscopic experiments and nonadiabatic molecular dynamics calculations to probe the photochemistry and nonradiative transitions in a recently synthesized narrow bandgap donor–acceptor conjugated polymer based on alternating cyclopentadithiophene and electronegative benzothiadiazole heterocycles. Using large-scale semi-empirical nonadiabatic molecular dynamics, which can treat a large 260-atom hexamer, we calculate an S 5 → S 1 lifetime of 34.75 fs, which is consistent with our time-resolved spectroscopic data. Our simulations suggest that vibronic motions of the central carbons in the cyclopentadithiophene functional groups are predominantly involved in the nonradiative transitions, and the excitation becomes more localized on a monomer fragment over time. The combined use of time-resolved experiments and nonadiabatic molecular dynamics calculations in this work provides mechanistic insight into chemical functionalities that can be tuned to enhance energy transfer in other prospective low-bandgap polymer materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Lyotropic Liquid Crystal Mediated Assembly of Donor Polymers Enhances Efficiency and Stability of Blade-Coated Organic Solar Cells

Conjugated polymers can undergo complex, concentration-dependent self-assembly during solution processing, yet little is known about its impact on film morphology and device performance of organic solar cells. Herein, lyotropic liquid crystal (LLC) mediated assembly across multiple conjugated polymers is reported, which generally gives rise to improved device performance of blade-coated non-fullerene bulk heterojunction solar cells. Using D18 as a model system, the formation mechanism of LLC is unveiled employing solution X-ray scattering and microscopic imaging tools: D18 first aggregates into semicrystalline nanofibers, then assemble into achiral nematic LLC which goes through symmetry breaking to yield a chiral twist-bent LLC. The assembly pathway is driven by increasing solution concentration – a common driving force during evaporative assembly relevant to scalable manufacturing. This assembly pathway can be largely modulated by coating regimes to give 1) lyotropic liquid crystalline assembly in the evaporation regime and 2) random fiber aggregation pathway in the Landau–Levich regime. The chiral liquid crystalline assembly pathway resulted in films with crystallinity 2.63 times that of films from the random fiber aggregation pathway, significantly enhancing the T80 lifetime by 50-fold. The generality of LLC-mediated assembly and enhanced device performance is further validated using polythiophene and quinoxaline-based donor polymers.

14 SOLAR ENERGY↗
DOE OSTI2024

Inter-Oligomer Interaction Influence on Photoluminescence in Cis-Polyacetylene Semiconductor Materials

Semiconducting conjugated polymers (CPs) are pivotal in advancing organic electronics, offering tunable properties for solar cells and field-effect transistors. Here, we carry out first-principle calculations to study individual cis-polyacetylene (cis-PA) oligomers and their ensembles. The ground electronic structures are obtained using density functional theory (DFT), and excited state dynamics are explored by computing nonadiabatic couplings (NACs) between electronic and nuclear degrees of freedom. We compute the nonradiative relaxation of charge carriers and photoluminescence (PL) using the Redfield theory. Our findings show that electrons relax faster than holes. The ensemble of oligomers shows faster relaxation compared to the single oligomer. The calculated PL spectra show features from both interband and intraband transitions. The ensemble shows broader line widths, redshift of transition energies, and lower intensities compared to the single oligomer. This comparative study suggests that the dispersion forces and orbital hybridizations between chains are the leading contributors to the variation in PL. It provides insights into the fundamental behaviors of CPs and the molecular-level understanding for the design of more efficient optoelectronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Radical Polymer-Based Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) are an emerging platform for bioelectronic applications. Significant effort has been placed in designing advanced polymers that simultaneously transport both charge and ions (i.e., macromolecules that are mixed conductors). Furthermore, the considerations for mixed organic conductors are often different from the established principles that are well-known in the solid-state organic electronics field; thus, the discovery of new OECT macromolecular systems is highly desired. Here, we demonstrate a new materials system by blending a radical polymer (i.e., a macromolecule with a nonconjugated backbone and with stable open-shell sites at its pendant group) with a frequently used conjugated polymer. Specifically, poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO) was blended with poly(3-hexylthiophene) (P 3 HT) to create thin films with distinct closed-shell and open-shell domains. Importantly, the sharp and unique oxidation–reduction (redox) potential associated with the radical moieties of the PTEO chain provided a distinct actuation feature to the blended films that modulated the ionic transport of the OECT devices. In turn, this led to controlled regulation of the doping of the P 3 HT phase in the composite film. By decoupling the ionic and electronic transport into two distinct phases and by using an ion transport phase with well-controlled redox activity, never-before-seen performance for a P3HT-based OECT was observed. That is, at loadings as low as 5% PTEO (by weight) OECTs achieved figure-of-merit (i.e., μC*) values >150 F V –1 cm –1 s –1 , which place the performance on the same order as state-of-the-art conjugated polymers despite the relatively common conjugated macromolecular moiety implemented. As such, this effort presents a design platform by which to readily create a tailored OECT response through strategic macromolecular selection and polymer processing.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Manipulation of intramolecular hydrogen bonds in conjugated pseudoladder polymer for semiconductivity and solution-processability

The conformational coplanarity and local rigidity of π-conjugated backbones are critical for the semiconducting performance of organic electronic materials. The conformational coplanarity and local rigidity of π-conjugated backbones are critical for the semiconducting performance of organic electronic materials. While fusing the aromatic system into a ladder-type structure effectively enhances these properties, it also often results in poor solution processability and hence limits their transition to device application. To address this challenge, an intramolecularly hydrogen-bonded pseudoladder polymer (HPLP) system based on alternating hydrogen bond donating benzobisimidazole (BBI) and hydrogen bond accepting benzodifuran (BDF) units, is designed and synthesized. A Boc-protected precursor of HPLP allows for feasible solution processing of the polymer into thin films. Subsequently, in situ thermal Boc-deprotection generates the HPLP polymer, in which intramolecular hydrogen bonds form between each pair of neighboring repeating units, inducing coplanarity and rigidity throughout the entire backbone. This process is accompanied by a significant red-shift of the absorption spectrum, reduced bandgap, and enhanced rigidity, as confirmed by NMR, UV-Vis, and density functional theory analyses. HPLP films exhibit a three-order-of-magnitude enhancement in charge carrier mobility compared to the Boc-protected precursor and demonstrate excellent solvent resistance in organic thin-film transistors.

Miranda, Octavio↗
DOE OSTI2023

Polymer-Based Thermally Stable Chemiresistive Sensor for Real-Time Monitoring of NO 2 Gas Emission

Here, we present a thermally stable, mechanically compliant, and sensitive polymer-based NO 2 gas sensor design. Interconnected nanoscale morphology driven from spinodal decomposition between conjugated polymers tethered with polar side chains and thermally stable matrix polymers offers judicious design of NO 2 -sensitive and thermally tolerant thin films. The resulting chemiresitive sensors exhibit stable NO 2 sensing even at 170 °C over 6 h. Controlling the density of polar side chains along conjugated polymer backbone enables optimal design for coupling high NO 2 sensitivity, selectivity, and thermal stability of polymer sensors. Lastly, thermally stable films are used to implement chemiresistive sensors onto flexible and heat-resistant substrates and demonstrate a reliable gas sensing response even after 500 bending cycles at 170 °C. Such unprecedented sensor performance as well as environmental stability are promising for real-time monitoring of gas emission from vehicles and industrial chemical processes.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Green Electrode Processing Enabled by Fluoro-Free Multifunctional Binders for Lithium-Ion Batteries

The eco-friendly processing of conjugated polymer binder for lithium-ion batteries demands improved polymer solubility by introducing functional moieties, while this strategy will concurrently sacrifice polymer conductivity. Employing the polyfluorene-based binder poly(2,7-9,9 (di(oxy-2,5,8-trioxadecane))fluorene) (PFO), soluble in water-ethanol mixtures, a novel approach is presented to solve this trade-off, which features integration of aqueous solution processing with subsequent controlled thermal-induced cleavage of solubilizing side chains, to produce hierarchically ordered structures (HOS). The thermal processing can enhance the intermolecular π–π stacking of polyfluorene backbone for better electrochemical performance. Notably, HOS-PFO demonstrated a substantial 6–7 orders of magnitude enhancement in electronic conductivity, showcasing its potential as a functional binder for lithium-ion batteries. As an illustration, HOS-PFO protected SiOx anodes, utilizing in situ side chain decomposition of PFO surrounding SiOx particles after aqueous processing are fabricated. HOS-PFO contributed to the stable cycling and high-capacity retention of practical SiOx anodes (3.0 mAh cm -2 ), without the use of any conducting carbon additives or fluorinated electrolyte additives. It is proposed that this technique represents a universal approach for fabricating electrodes with conjugated polymer binders from aqueous solutions without compromising conductivity.

25 ENERGY STORAGE↗
DOE OSTI2021

Super-Resolution Photothermal Patterning in Conductive Polymers Enabled by Thermally Activated Solubility

Doping induced solubility control (DISC) patterning is a recently developed technique which uses the change in polymer solubility upon doping, along with an optical dedoping process, to achieve high resolution optical patterning. DISC patterning is remarkable because the process resolution exceeds the linear Abbe’s diffraction limit, however, no mechanism has been proposed to explain such high resolution. Here, we use diffraction to spatially modulate the light intensity and determine the dissolution rate, revealing a superlinear dependence on light intensity, which yields features that are sharper than the profile of the writing photomask. This rate law is independent of wavelength, indicating that patterning resolution is not dominated by an optical dedoping reaction, as was previously proposed. Instead we show here that the optical patterning mechanism is primarily controlled by the thermal profile generated by the laser. To quantify this effect, the thermal profile and dissolution rate are modeled using a finite-element model and compared against patterned line cross sections as a function of wavelength, laser intensity, and dwell time. Our model reveals that although the laser-generated thermal profile is broadened considerably beyond the lasers resolution, the highly temperature dependent dissolution rate results in selective dissolution near the peak of the thermal profile. Therefore, the key factor in achieving super-resolution patterning is a strongly temperature dependent dissolution rate|a common feature of many polymers. In addition to suggesting several routes to improved resolution, our model also demonstrates that doping is not required for optical patterning of conjugated polymers, as was previously believed. Instead, we demonstrate that superlinear resolution optical patterning is attainable in any conjugated polymer simply by tuning the solvent quality during patterning, thus extending the applicability of our method to a wide class of materials. Here, we demonstrate the generality of photothermal patterning by writing sub-400 nm features into undoped Pff-BT4T-2OD.

36 MATERIALS SCIENCE↗
DOE OSTI2020

3,4‐Dicyanothiophene—a Versatile Building Block for Efficient Nonfullerene Polymer Solar Cells

Abstract In this contribution, a versatile building block, 3,4‐dicyanothiophene (DCT), which possesses structural simplicity and synthetic accessibility for constructing high‐performance, low‐cost, wide‐bandgap conjugated polymers for use as donors in polymer solar cells (PSCs), is reported. A prototype polymer, PB3TCN‐C66, and its cyano‐free analogue polymer PB3T‐C66, are synthesized to evaluate the potential of using DCT in nonfullerene PSCs. A stronger aggregation property in solution, higher thermal transition temperatures with higher enthalpies, a larger dipole moment, higher relative dielectric constant, and more linear conformation are exhibited by PB3TCN‐C66. Solar cells employing IT‐4F as the electron acceptor offer power conversion efficiencies (PCEs) of 11.2% and 2.3% for PB3TCN‐C66 and PB3T‐C66, respectively. Morphological characterizations reveal that the PB3TCN‐C66:IT‐4F blend exhibits better π–π paracrystallinity, a contracted domain size, and higher phase purity, consistent with its higher molecular interaction parameter, derived from thermodynamic calculations. Moreover, PB3TCN‐C66 offers a higher open‐circuit voltage and reduced energy loss than most state‐of‐the‐art wide‐bandgap polymers, without the need of additional electron‐withdrawing substituents. Two additional polymers derived from DCT also demonstrate promising performance with a higher PCE of 13.4% being achieved. Thus, DCT represents a versatile and promising building block for constructing high‐performance, low‐cost, conjugated polymers for application in PSCs.

Zhang, Bo↗
DOE OSTI2023

Counterion Control and the Spectral Signatures of Polarons, Coupled Polarons, and Bipolarons in Doped P3HT Films

When an electron is removed from a conjugated polymer, such as poly(3-hexylthiophene-2,5-diyl) (P3HT), the remaining hole and associated change in the polymer backbone structure from aromatic to quinoidal are referred to as a polaron. Bipolarons are created by removing the unpaired electron from an already-oxidized polymer segment. In electrochemically-doped P3HT films, polarons, and bipolarons are readily observed, but in chemically-doped P3HT films, bipolarons rarely form. This is explained by studying the effects of counterion position on the formation of polarons, strongly coupled polarons, and bipolarons using both spectroscopic and X-ray diffraction experiments and time-dependent density functional theory calculations. The counterion positions control whether two polarons spin-pair to form a bipolaron or whether they strongly couple without spin-pairing are found. When two counterions lie close to the same polymer segment, bipolarons can form, with an absorption spectrum that is blueshifted from that of a single polaron. Otherwise, polarons at high concentrations do not spin-pair, but instead J-couple, leading to a redshifted absorption spectrum. The counterion location needed for bipolaron formation is accompanied by a loss of polymer crystallinity. Finally, these results explain the observed formation order of single polarons, coupled single polarons, and singlet bipolarons in electrochemically- and chemically-doped conjugated polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Organic Electrochemical Transistor Channel Materials: Copolymerization Versus Physical Mixing of Glycolated and Alkoxylated Polymers

Organic electrochemical transistors (OECTs) feature a polymer channel capable of conducting both ions and electronic charges. The choice of the channel material is critical for OECT performance. Many efforts have focused on improving performance via the chemical tunability of conjugated polymers – through backbone, side chain, and molar mass engineering – leading to useful design principles for accumulation-mode OECT materials. However, tuning the chemical structure of conjugated polymers often requires time-consuming optimization of the synthesis route. Meanwhile, variations in molar mass, dispersity, structural defects, and metal content present challenges when attempting to analyze the detailed effects of structural modifications, as multiple performance-determining factors are often (unintentionally) changed at the same time. Therefore, this study explores blended channel materials obtained by physically mixing glycolated and alkoxylated polymers in different ratios, and compares their OECT performance with the corresponding statistical copolymers. It is shown that mixing two well-performing materials creates blends that enable rational tuning of the transistor properties without compromising on performance. Thus, channels based on blends of alkoxylated and glycolated polymers hold promise for OECT technology with tailored response, as only two materials are needed to achieve any desired side chain ratio, simplifying the optimization of OECT characteristics.

copolymerization↗
DOE OSTI2024

Solution-based electrical doping of organic photovoltaics with non-fullerene acceptors facilitated by solvent vapor pre-treatment

Solution-based electrical doping of organic semiconductors using 12-molybdophosphoric acid (PMA) hydrate has been shown to allow p-type doping of conjugated polymers over a limited depth from the surface, enabling the fabrication of organic solar cells with a simplified device architecture. However, the doping level of certain conjugated polymers using PMA was found to be limited by the polymer film volume. Here, we report a modified PMA doping technique based on film volume expansion that is applicable to device fabrication, leading to hole-collecting layer-free non-fullerene organic photovoltaic devices, which exhibit a comparable photovoltaic performance to those with a commonly evaporated MoO3 hole-collecting layer.

Materials Science↗
DOE OSTI2022

Real time quantification of mixed ion and electron transfer associated with the doping of poly(3-hexylthiophene)

Conjugated polymers have promising applications in electronics and energy storage due to the polymer's tunable conductivity and redox activity. For example, the conductivity of poly(3-hexylthiophene) (P3HT) is heavily dependent upon the doping level and the dopant type. This feature becomes especially important when considering P3HT or similar conjugated polymers for devices that require switching between electronic states (conductive vs. insulating). In this study, the mechanism of mixed ion-electron transfer studied using electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) is discussed. During cyclic voltammetry and galvanostatic charge–discharge experiments, the mass change of a P3HT film is monitored in real time. Distinct mass transfer regions are quantified as a function of doping level and potential, which are then correlated to changes with in situ conductance and spectroelectrochemical response. To identify the time scale at which the doping reaction transitions from kinetic to diffusion control, electrochemical impedance spectroscopy is coupled with EQCM-D. Finally, this work gives valuable insight into the nature of mixed ion–electron transfer, including its time scale, as it relates to the electronic properties of P3HT.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Tacky Elastomers to Enable Tear-Resistant and Autonomous Self-Healing Semiconductor Composites

Mechanical failure of π-conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear-resistant and room-temperature self-healable semiconducting composite is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both a record-low elastic modulus (<1 MPa) and ultrahigh deformability with fracture strain above 800%. More importantly, failure behavior is not sensitive to precut notches under deformation. Autonomous self-healing at room temperature, both mechanical and electronic, is demonstrated through the physical contact of two separate films. The composite film also shows device stability in the ambient environment over 5 months due to much-improved barrier property to both oxygen and water. Butyl rubber is broadly applicable to various p-type and n-type semiconducting polymers for fabricating self-healable electronics to provide new resilient electronics that mimic the tear resistance and healable property of human skin.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Semiconducting to Metallic Electronic Landscapes in Defects-Controlled 2D π-d Conjugated Coordination Polymer Thin Films

Two-dimensional coordination polymers (2DCPs) have been predicted to exhibit exotic properties such as superconductivity, topological insulating behavior, catalytic activity, and superior ion transport for energy applications; experimentally, these materials have fallen short of their expectation due to the lack of synthesis protocols that yield continuous, large crystallite domains, and highly ordered thin films with controllable physical and chemical properties. Herein, the fabrication of large-area, highly ordered 2DCP thin films with large crystallite domains using chemical vapor deposition (CVD) approaches is described. It is demonstrated that defects and the packing motifs of 2DCP thin films may be controlled by adjusting the vapor–vapor and vapor–solid interactions of the metal and organic linker precursors during the CVD fabrication process. Such control allows for the fabrication of defects-controlled 2DCP thin films that show either semiconducting or metallic behavior. The findings provide the first demonstration of tuning the electrical properties of sub 100 nm-thick continuous 2DCP thin films by controlling their electronic landscape through defect engineering. As such, it is determined that large-area, highly ordered 2DCP thin films may undergo a semiconducting to metallic transition that is correlated to changes in morphology, crystalline domain sizes, crystallite orientation, defect interactions, and electronic structure.

2D coordination polymers↗