Conductivity Of Organic Materials Research Articles

Insoluble low-impedance organic battery cathode enabled by graphite grafting towards potassium storage.

Organic electrode materials are extensively applied for potassium storage as their sustainability and low cost. However, the organic electrodes' (i) solubility (such as naphthalene-1,4,5,8-tetracarboxylic dianhydride, NTCDA; 2,6-diaminoanthanthraquinone, DAQ, which are easily soluble in organic solvents) and (ii) intrinsic poor conductivity often result in high impedance and inferior electrochemical performance. Herein, the monomers of NTCDA and DAQ were polymerized (PND) to obtain an insoluble organic cathode, and a 5 wt% graphite (G) was also used to graft the PND sheet and increase its conductivity. Consequently, the as-prepared organic cathode (PND-G) achieved a long-life cycling performance of over 1500 cycles at 100 mA g-1. This work may provide guidelines for designing and developing insoluble and high conductive organic electrode materials.

Correlating Young's Modulus with High Thermal Conductivity in Organic Conjugated Small Molecules.

Attaining elevated thermal conductivity in organic materials stands as a coveted objective, particularly within electronic packaging, thermal interface materials, and organic matrix heat exchangers. These applications have reignited interest in researching thermally conductive organic materials. The understanding of thermal transport mechanisms in these organic materials is currently constrained. This study concentrates on N, N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8), an organic conjugated crystal. A correlation between elevated thermal conductivity and augmented Young's modulus is substantiated through meticulous experimentation. Achievement via employing the physical vapor transport method, capitalizing on the robust C═C covalent linkages running through the organic matrix chain, bolstered by π-π stacking and noncovalent affiliations that intertwine the chains. The coexistence of these dynamic interactions, alongside the perpendicular alignment of PTCDI-C8 molecules, is confirmed through structural analysis. PTCDI-C8 thin film exhibits an out-of-plane thermal conductivity of 3.1±0.1Wm-1K-1, as determined by time-domain thermoreflectance. This outpaces conventional organic materials by an order of magnitude. Nanoindentation tests and molecular dynamics simulations elucidate how molecular orientation and intermolecular forces within PTCDI-C8 molecules drive the film's high Young's modulus, contributing to its elevated thermal conductivity. This study's progress offers theoretical guidance for designing high thermal conductivity organic materials, expanding their applications and performance potential.

From neuromorphic to neurohybrid: transition from the emulation to the integration of neuronal networks

The computation of the brain relies on the highly efficient communication among billions of neurons. Such efficiency derives from the brain’s plastic and reconfigurable nature, enabling complex computations and maintenance of vital functions with a remarkably low power consumption of only ∼20 W. First efforts to leverage brain-inspired computational principles have led to the introduction of artificial neural networks that revolutionized information processing and daily life. The relentless pursuit of the definitive computing platform is now pushing researchers towards investigation of novel solutions to emulate specific brain features (such as synaptic plasticity) to allow local and energy efficient computations. The development of such devices may also be pivotal in addressing major challenges of a continuously aging world, including the treatment of neurodegenerative diseases. To date, the neuroelectronics field has been instrumental in deepening the understanding of how neurons communicate, owing to the rapid development of silicon-based platforms for neural recordings and stimulation. However, this approach still does not allow for in loco processing of biological signals. In fact, despite the success of silicon-based devices in electronic applications, they are ill-suited for directly interfacing with biological tissue. A cornucopia of solutions has therefore been proposed in the last years to obtain neuromorphic materials to create effective biointerfaces and enable reliable bidirectional communication with neurons. Organic conductive materials in particular are not only highly biocompatible and able to electrochemically transduce biological signals, but also promise to include neuromorphic features, such as neuro-transmitter mediated plasticity and learning capabilities. Furthermore, organic electronics, relying on mixed electronic/ionic conduction mechanism, can be efficiently coupled with biological neural networks, while still successfully communicating with silicon-based electronics. Here, we envision neurohybrid systems that integrate silicon-based and organic electronics-based neuromorphic technologies to create active artificial interfaces with biological tissues. We believe that this approach may pave the way towards the development of a functional bidirectional communication between biological and artificial ‘brains’, offering new potential therapeutic applications and allowing for novel approaches in prosthetics.

Carbazolylene-Ethynylene Macrocycle based Conductive Covalent Organic Frameworks.

Two covalent organic frameworks consisting of carbazolylene-ethynylene shape-persistent macrocycles with azine (MC-COF-1) or imine (MC-COF-2) linkages were synthesized via imine condensation. The obtained 2D frameworks are fully conjugated which imparts semiconducting properties. In addition, the frameworks showed high porosity with aligned accessible porous channels along the z axis, serving as an ideal platform for post-synthetic incorporation of I2 into the channels to enable electrical conductivity. The resulting MC-COF-1 showed an electrical conductivity up to 7.8 × 10-4 S/cm at room temperature upon I2 doping with the activation energy as low as 0.09 eV. Furthermore, we demonstrated that the electrical properties of both MC-COFs are switchable between electron-conducting and insulating states by simply implementing doping-regenerating cycles. The knowledge gained in this study opens new possibilities for the future development of tunable conductive 2D organic materials.

Carbazolylene‐Ethynylene Macrocycle based Conductive Covalent Organic Frameworks

AbstractTwo covalent organic frameworks consisting of carbazolylene‐ethynylene shape‐persistent macrocycles with azine (MC‐COF‐1) or imine (MC‐COF‐2) linkages were synthesized via imine condensation. The obtained 2D frameworks are fully conjugated which imparts semiconducting properties. In addition, the frameworks showed high porosity with aligned accessible porous channels along the z axis, serving as an ideal platform for post‐synthetic incorporation of I2 into the channels to enable electrical conductivity. The resulting MC‐COF‐1 showed an electrical conductivity up to 7.8×10−4 S cm−1 at room temperature upon I2 doping with the activation energy as low as 0.09 eV. Furthermore, we demonstrated that the electrical properties of both MC‐COFs are switchable between electron‐conducting and insulating states by simply implementing doping‐regenerating cycles. The knowledge gained in this study opens new possibilities for the future development of tunable conductive 2D organic materials.

Injectable and tissue-conformable conductive hydrogel for MRI-compatible brain-interfacing electrodes

The development of flexible and stretchable materials has led to advances in implantable bio-integrated electronic devices that can sense physiological signals or deliver electrical stimulation to various organs in the human body. Such devices are particularly useful for neural interfacing systems that monitor neurodegenerative diseases such as Parkinson’s disease or epilepsy in real time. However, coupling current brain-interfacing devices with magnetic resonance imaging (MRI) remains a practical challenge due to resonance frequency variations from inorganic metal-based devices. Thus, organic conductive materials, such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), have recently been considered as promising candidates. Nonetheless, their conformability on curvilinear tissues remains questionable. In this study, we developed an injectable conductive hydrogel (ICH) composed of tyramine-conjugated hyaluronic acid (HATYR) and PEDOT:PSS for MRI-compatible brain-interfacing electrodes. Our ICH produced low impedance around 5 kΩ even under 10 Hz, demonstrating high confidence volumetric capacitance. Due to HATYR’s biocompatibility, histological and cytotoxicity assays showed almost no inflammation and toxicity, respectively; in addition, ICH was able to degrade into 40% of its original volume within four weeks in vivo. An electrocorticogram (ECoG) array was also patternable by syringe injections of ICH on a stretchable and flexible elastomeric substrate layer that conformed to curvy brain tissues and successfully recorded ECoG signals under light stimulation. Furthermore, MRI imaging of implanted devices did not show any artifacts, indicating the potential of the MRI-compatible hydrogel electrodes for advanced ECoG arrays. This study provides a promising solution for MRI-compatible neural electrodes, enabling the advancement of chronic neural interfacing systems for monitoring neurodegenerative diseases.

Shape-stabilized phase change composites supported by biomass loofah sponge-derived microtubular carbon scaffold toward thermal energy storage and electric-to-thermal conversion

Integrating conductive carbon supports and organic phase change materials (PCMs) facilitates the development of thermal energy storage (TES) and conversion systems. Herein, we explore a novel phase change composite (PCC) based upon biomass-derived carbon scaffold incorporating polyethylene glycol (PEG) as a heat storage unit, which demonstrated a combination of good shape-stabilization, high thermal energy storage, and efficient electric-to-thermal conversion property. The carbon scaffold with a hollow microtubular structure was made from biomass loofah sponge (LS) through high-temperature carbonization in nitrogen. Compared with natural LS, the derived carbon scaffold exhibited favorable structural characteristics including a large specific surface area of 668.75 m2/g and a prominent micropore area of 303.37 m2/g, which could not only prevent PEG from leakage but also provide thermally and electrically conductive pathways in the PCM substance. The fabricated PCC displayed high thermal energy storage density (up to 137.6 J/g), outstanding electric-to-thermal conversion, enhanced thermal resistance, and robust temperature regulation properties. It provides an insightful strategy for fabrication and utilization of biomass-derived carbon scaffold based shape-stabilized PCCs in solar thermal energy storage, thermal management and thermoregulated textiles, and infrared stealth of important military targets, etc.

Characterization of Organic Conductive Materials as an Ecological Solution for RF Applications

The use of nonmetallic conductor materials in RF applications has recently become a highlighted issue when it comes to sustainability in the electronics industry, mainly because of the waste problems associated with heavy metals and the necessity of reducing and managing them. The replacement of metal in functional applications such as in electronics is therefore very important. Among these new materials, organic conductors are of great interest since they are, in general, biocompatible and biodegradable, allowing for the disposal of electronic devices, which reduces the negative environment impact caused by electronics waste. In this work, PEDOT:PSS and Carbon are investigated. Since these materials are available as conducting pastes or inks, the production of conducting patterns by printing techniques such as screen printing is possible, which can make the process less harmful to the environment, since it permits the use of organic substrates such as paper. In order to investigate the feasibility of these materials for RF signal transmission, screen printed PEDOT:PSS and Carbon transmission lines have been designed, fabricated and characterized. Results regarding conductivity, thickness, electric permittivity and S21 parameter are presented and will serve as a foundation for the development of further reaching applications utilizing organic materials.

Covalent‐Induced Heterostructure of Covalent‐Organic Frameworks and MXene as Advanced Electrodes with Motivated Pseudocapacitance Performance

AbstractHeterostructures based on covalent organic frameworks (COFs) and conductive materials have attracted more attentions to effectively apply COF‐related materials for supercapacitor. Here, the as‐prepared amino‐modified Ti3C2 MXene nanosheets are adopted to support the in‐situ growth of anthraquinone‐based COFs (AQ‐COF) to fabricate the heterostructures of COFs uniformly dispersed on surface of MXene, based on the covalent interaction between terminal C=O groups of COFs and amino units of MXene. Besides, the morphology and porous structures of COF@MXene heterostructures are optimized by controlling the amounts of MXene nanosheets. Combining the superiority from the two‐dimensional structure with high conductivity of MXene and porous structure with abundant redox‐active groups inherited from AQ‐COF, the COF@MXene‐15 heterostructure electrode delivers large surface area with optimal porous structures, leading to the maximally‐activated C=O units for charge‐storage and capacitance‐controlled electrochemical kinetics. Improved specific capacitance (290 F g−1 at 0.5 A g−1) and rate capability can be achieved for the COF@MXene‐15 heterostructure as the electrode for supercapacitor in Na2SO4 electrolyte. It is the first time to report the heterostructure of COFs and MXene as the electrode for supercapacitor, and this work would promote further application of COFs and related materials for other energy‐storage systems.

Graphene non-covalently functionalized with Gallic acid (Ga) as high performance electrode material for supercapacitors

Organic small molecules are a very promising kind of materials in energy storage devices because they are green, low-cost and renewable resources. However, the poor electrical conductivity of organic molecules limits their using as electrode materials. The combination of organic molecules and conductive carbon material is a useful method to enhance their electrical conductivity. Here, Gallic acid (Ga) functionalized graphene hydrogel (GH) composite (Ga/GH) was synthesized by a simple hydrothermal method. The Ga/GH composite exhibits outstanding electrochemical capacitance performance because of the incorporation of the Faradaic pseudocapacitance of Ga and the double-layer capacitance of graphene hydrogel. The specific capacitance can reach up to 483 F g −1 at 1 A g −1 . In addition, when the current density is increased to 100 A g −1 , the rate capability is up to 64.2%. Meanwhile, a Ga/GH//DQ-RGO and a Ga/GH//AC asymmetric capacitor were assembled by using Ga/GH as the positive electrode and 2,6-diaminoanthraquinon functionalized graphene composite (DQ-RGO) and activated carbon (AC) as the negative electrode, respectively. The Ga/GH//DQ-RGO ASC provides an energy density of 27 Wh kg −1 along with a power density of 0.908 kW kg −1 and two such devices in series successfully can illuminate 26 red light-emitting diodes (LEDs). And the Ga/GH//AC ASC provides an energy density of 19.11 Wh kg −1 . Two such devices in series can illuminate 20 red light-emitting diodes (LEDs).

Metal-Free Transparent Three-Dimensional Flexible Electronics by Selective Molecular Bridges.

Flexible and transparent electronics is a new generation of device enabling modern interactive designs, which facilitates the recent development of low-cost, lightweight, and flexible materials. Although conventional indium tin oxide material still dominates the major market, its brittleness and steadily increasing price drive scientists to search for other alternatives. To meet the high demand, numerous metallic or organic conductive materials have been developed, but their poor adhesion toward supporting substrates and the subsequent circuit patterning approach remains problematic. In this study, a robust metal-free flexible conductive film fabrication strategy is introduced. The flexible polyethylene terephthalate (PET) film is utilized as the base, where a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conductive layer is tightly linked onto this supporting substrate. An interface activation process, i.e., oxygen plasma treatment, generates PET surface active spots to react with the subsequently introduced poly(vinyl alcohol) (PVA) molecule functional groups. This spatially selective PVA molecular bridge therefore acts as a dual-function intermediate layer through covalent bonding toward PET and hydrogen bonding toward PEDOT:PSS to conjugate two distinct materials. This PEDOT:PSS/PVA/PET film delivers superior physical properties, such as a high conductivity of 38.2 Ω/sq and great optical transmittance of 84.1%, which are well tunable under conductive polymer thickness controls. The film is also durable and can maintain original electrical properties even under serious bending for hundreds of cycles. Relying on these outstanding performances, arbitrary conductive circuits are built on this flexible substrate and can function as normal electronics when integrated with multiple electronic parts, e.g., light-emitting diodes (LEDs). Superior electrical signal outputs are achieved when complicated stereo structures including folding, splicing, interlacing, and braiding are incorporated, enabling the use of these films for flexible three-dimensional electronics assembling. Space identifying smart key and lock pair, origami rabbit-carrot touch response, pressure-stimulated jumping frog, and moving dinosaur recognition designs realize these PEDOT:PSS/PVA/PET film-based human-machine interactive devices. This flexible, transparent, and conductive film generation approach by molecular bridge creation should facilitate future development of flexible or foldable devices with complex circuits.

Conductive Composite Fiber with Customizable Functionalities for Energy Harvesting and Electronic Textiles.

A fiber-based triboelectric nanogenerator (F-TENG) is an important technology for smart wearables, where conductive materials and triboelectric materials are two essential components for the F-TENG. However, the different physicochemical properties between conductive metal materials and organic triboelectric materials often lead to interfacial failure problems, which is a great challenge for fabricating high-performance and stable F-TENGs. Herein, we designed a new conductive composite fiber (CCF) with customizable functionalities based on a core-spun yarn coating approach, which was applicable for a fiber-based TENG (CCF-TENG). By combing a core-spun method and a coating approach, triboelectric materials could be better incorporated on the surface of conductive fibers with the staple fibers to form a new composite structure with enhanced interfacial properties. The applicability of the method has been studied using different conductive and staple fibers and coating materials as well as different CCF diameters. As a demonstration, the open-circuit voltage and power density of the CCF-TENG reached 117 V and 213 mW/m2, respectively. Moreover, a 2D fabric TENG was woven and used as a wearable sensor for motion detection. This work provided a new method for 1D composite fibers with customizable functionalities for the applications in smart wearables.

Polyacetylene Revisited: A Computational Study of the Molecular Engineering of N-type Polyacetylene.

The development of stable and highly conductive polymers, particularly n-type materials, remains an outstanding challenge in organic electronics. N-doped polyacetylene has long been studied as a highly conductive organic n-type material but suffers from extremely poor stability. Herein, we use DFT to model a series of n-doped polyacetylene derivatives, which have been functionalized with a range of electron-withdrawing substituents, with the goal of identifying attractive candidates for synthesis. We analyze the predicted molecular orbital energies, polymer planarity, and delocalization of charge carriers along the polymer backbone. In so doing, we develop key insights about the ideal substituents for both stable and highly conductive polyacetylene derivatives. This work will inform the modern synthesis and development of new polyacetylene derivatives. Beyond this, the work identifies a variety of new materials that have not yet been synthesized and should be good candidates for emerging optoelectronic applications including soft thermoelectrics, bioelectronics, and flexible device technologies.

High‐Performance Graphene/GaInP Solar Cell Prepared by Interfacial Chemical Modification with Poly(3,4‐Ethylenedioxythiophene):Poly(styrenesulfonate)

Graphene/semiconductor heterojunction based solar cell is realized as a promising candidate for high‐efficiency solar cells. However, the interface between graphene and the semiconductor should be further explored to enhance the performance of the solar cell. As graphene is impermeable to water and gases, encapsulating hole conducting organic material poly(3,4‐ethylene‐dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) at the interface is possible and can improve the surface passivation, p‐dope graphene, increase the barrier height, and speed up the transfer of carriers. Herein, a novel graphene/PEDOT:PSS/GaInP organic/inorganic Schottky heterojunction solar cell is designed and assembled via interfacial chemical modification. The cell exhibits an open‐circuit voltage (Voc) of 0.90 V under AM1.5 illumination, while the counterpart solar cell without PEDOT:PSS interlayer only gives a Voc of 0.49 V. In comparison with the PEDOT:PSS interlayer, indium tin oxide (ITO) film shows little effect on the improvement of Voc. The Voc of graphene/ITO/GaInP and ITO/PEDOT:PSS/GaInP solar cells is 0.11 and 0.37 V, respectively. As a result, the power conversion efficiency (PCE) of the Schottky junction solar cell with an interlayer reaches up to 4.55%, more than seven times that obtained without interlayer. The work has proven that integrating graphene/semiconductor heterostructure solar cells with organic conductive materials in the interface can achieve high PCE.

Permittivity acquisition of plasmonic materials at epsilon near zero wavelengths

Due to their unique optical properties, plasmonic materials are widely used in nonlinear optics, nanophotonics, optoelectronics, photocatalysis, biosensing, information storage, etc. Researchers usually need to know the detailed permittivity behavior at the vicinity of surface plasmons’ excitation wavelengths, which in turn are located near the zero points of the real part of the permittivity called epsilon-near-zero (ENZ). We hereby introduce a spectral fitting method to quickly obtain the materials' permittivity at the ENZ region and summarize the experiences of selecting dispersion models and optimizing model parameters. Specifically, we have made a detailed description of the optical constant fitting process for a series of plasmonic materials such as heavily doped semiconductors, transparent conductive oxides, organic conductive materials, two-dimensional materials, and sandwiched composites. Hopefully, to provide specific data and theoretical support for researchers in the field of photoelectric properties of plasmonic materials.

Flexible conductive blend of natural rubber latex with PEDOT:PSS

Natural Rubber Latex (NRL) obtained from Hevea brasiliensis is a biocompatible electrically insulating material with exceptional mechanical properties. Poly(3,4-ethylene dioxythiophene) poly(styrene sulfonate), PEDOT:PSS, on the other hand, is a biocompatible highly conductive organic material with poor flexibility. We hereby introduce a blend of NRL/PEDOT:PSS (N/P). This study involved different N/P volume ratios and temperatures of curing aiming at an optimal combination of good flexibility and conductivity. Low-temperature annealing, at 60 °C, dries and cures the blend in a few minutes and improves its tensile strength and conductivity. The blend can stretch more than 700% of its initial length and presents a good gauge factor and small resistance variation (R/R0) for ΔL/L0 of up to 100%. Among the different N/P concentrations, the membranes of an N/P ratio of 1/4 and those thermally cured have the most promising conductive flexible properties for bioelectronic applications.

Molecular conductors composed from Organic-Transistor Materials

Assistant Professor Tomofumi Kadoya is part of a team within the Graduate School of Material Science at the University of Hyogo in Japan. He is engaged with a range of different investigations related to conductive organic materials. One of the main focuses of Kadoya's research is organic transistors and organic charge-transfer (CT) complexes. CT complexes achieve conductivity by chemical doping but in organic transistors, conduction carriers are generated by field effect, where an electric field is used to control the flow of current. Among the many goals of the research, Kadoya and his team want to increase the methods and types of organic doping.

Electromagnetic interference shielding of polypyrrole nanostructures

Polypyrrole (PPy) is an electrically conductive organic material perspective for application in the field of electromagnetic interference shielding (EMI). The presented fundamental study focuses on the shielding efficiency of three various morphologies of PPy (globules, nanotubes and microbarrels). Powdered samples in both protonated and deprotonated form were embedded at various concentrations (1, 3 and 5 % w/w) in a composite system with a transparent silicone matrix cured at temperatures 25 and 150 °C. The ability of PPy to reflect or absorb electromagnetic radiation in the C-band region covering the range from 5.85 to 8.2 GHz was evaluated. The relationship between the morphology of PPy, its DC and AC electrical conductivity, permittivity and shielding efficiency was studied. The PPy nanotubes with the DC conductivity of 60.8 S cm–1 exhibited shielding efficiency S21 = –13.27 dB at 5% w/w concentration in the composite, which corresponds to transparency of 21.7 % only. It was found that the magnitude of electrical conductivity together with the aspect ratio of PPy morphology determines the shielding efficiency whereas the type of morphology is responsible for absorption or reflection mechanism of EMI shielding. Hence, the appropriate adjustment of both the electrical conductivity and the morphology should be used in the future lightweight and flexible EMI shields with tunable shielding efficiency and mechanism of shielding.

Measurement of Electrophysiological Signals In Vitro Using High‐Performance Organic Electrochemical Transistors

AbstractBiological environments use ions in charge transport for information transmission. The properties of mixed electronic and ionic conductivity in organic materials make them ideal candidates to transduce physiological information into electronically processable signals. A device proven to be highly successful in measuring such information is the organic electrochemical transistor (OECT). Previous electrophysiological measurements performed using OECTs show superior signal‐to‐noise ratios than electrodes at low frequencies. Subsequent development has significantly improved critical performance parameters such as transconductance and response time. Here, interdigitated‐electrode OECTs are fabricated on flexible substrates, with one such state‐of‐the‐art device achieving a peak transconductance of 139 mS with a 138 µs response time. The devices are implemented into an array with interconnects suitable for micro‐electrocorticographic application and eight architecture variations are compared. The two best‐performing arrays are subject to the full electrophysiological spectrum using prerecorded signals. With frequency filtering, kHz‐scale frequencies with 10 µV‐scale voltages are resolved. This is supported by a novel quantification of the noise, which compares the gate voltage input and drain current output. These results demonstrate that high‐performance OECTs can resolve the full electrophysiological spectrum and suggest that superior signal‐to‐noise ratios could be achieved in high frequency measurements of multiunit activity.

Air-Stability and Carrier Type in Conductive M3(Hexaaminobenzene)2, (M = Co, Ni, Cu).

Herein, we investigate the effects of changing the metal ions in the M-HAB system, with HAB = hexaaminobenzene ligands and M = Co, Ni, Cu. The phyiscal characteristics of this MOF family are insensitive to changes in the metal cation, which enables systematic evaluation of the effect of metal cation identity on electrical transport properties. We observe that the metal ion profoundly influences the electrical conductivity and dominant carrier type in the resulting MOF and the air-stability thereof. Cu-HAB and Co-HAB are determined to exhibit n-type conduction under both ambient and nitrogen conditions; Ni-HAB is found to be ambipolar, with its dominant carrier type dramatically affected by the environment. We examine these results through calculation of the band structure, the partial density of states, and charge transfer analysis. Unlike traditional conductive organic materials, we find that the air-stability is not well predicted by the LUMO level of these n-type MOFs but instead is additionally dependent on the occupancy and orientation of the metal ion's d-orbitals and the resulting interaction between the metal ion and ligand. This study provides fundamental insights for rational design of air-stable, electronically conductive MOFs.