Organic Conductors Research Articles

Donor-Acceptor Copolymer with a Linear Backbone Induced Ordered and Robust Doping Morphology for Efficient and Stable Organic Electrochemical Devices.

Donor (D)-acceptor (A) copolymer-based organic mixed ionic-electronic conductors (OMIECs) exhibit intrinsic environmental stability for they have tailored energy levels. However, their figure-of-merit (μC*) is still falling behind the D-D polymers because of morphology deterioration during the electrochemical doping process. Herein, we developed two D-A copolymers with precisely regulated backbone curvature, namely PTBT-P and PTTBT-P. Compared to the curved PTBT-P and previously reported copolymers, PTTBT-P better keeps its backbone linear, leading to a long-range ordered doping morphology, which is revealed by the in operando X-ray technique. This optimized doping morphology enables a significantly improved operando charge mobility (μ) of 2.44 cm2 V-1 s-1 and a μC* value of 342 F cm-1 V-1 s-1, one of the highest values in D-A copolymer based on OECTs. Besides, we fabricated PTTBT-P-based electrochemical random-access memories and achieved ideal and robust conductance modulation. This study highlights the critical role of backbone curvature control in the optimization of doping morphology for efficient and robust organic electrochemical devices.

A simple pure organic single-component molecular conductor, [HEDT-TTF-dc], based on protonic-defected dicarboxylic acid

Based on protonic-defected dicarboxylic acid, a simple pure organic single-component molecular conductor, [HEDT-TTF-dc] has been successfully synthesized. The neutral HEDT-TTF-dc molecules form two-dimensional conducting layers, which are connected by hydrogen bond interaction. The electrical resistivity measurement exhibits a semiconducting behavior with a low activation energy of 0.1 eV. The magnetic susceptibility can be fit by the singlet-triplet model, which provides with the small energy gap corresponding to the activation energy.

Polycationic Open‐Shell Cyclophanes: Synthesis of Electron‐Rich Chiral Macrocycles, and Redox‐Dependent Electronic States

Abstractπ‐Conjugated chiral nanorings with intriguing electronic structures and chiroptical properties have attracted considerable interests in synthetic chemistry and materials science. We present the design principles to access new chiral macrocycles (1 and 2) that are essentially built on the key components of main‐group electron‐donating carbazolyl moieties or the π‐expanded aza[7]helicenes. Both macrocycles show the unique molecular conformations with a (quasi) figure‐of‐eight topology as a result of the conjugation patterns of 2,2’,7,7’‐spirobifluorenyl in 1 and triarylamine‐coupled aza[7]helicene‐based building blocks in 2. This electronic nature of redox‐active, carbazole‐rich backbones enabled these macrocycles to be readily oxidized chemically and electrochemically, leading to the sequential production of a series of positively charged polycationic open‐shell cyclophanes. Their redox‐dependent electronic states of the resulting multispin polyradicals have been characterized by VT‐ESR, UV/Vis‐NIR absorption and spectroelectrochemical measurements. The singlet (ΔES‐T=−1.29 kcal mol−1) and a nearly degenerate singlet‐triplet ground state (ΔES−T(calcd)=−0.15 kcal mol−1 and ΔES−T(exp)=0.01 kcal mol−1) were proved for diradical dications 12+2⋅ and 22+2⋅, respectively. Our work provides an experimental proof for the construction of electron‐donating new chiral nanorings, and more importantly for highly charged polyradicals with potential applications in chirospintronics and organic conductors.

Polycationic Open-Shell Cyclophanes: Synthesis of Electron-Rich Chiral Macrocycles, and Redox-Dependent Electronic States.

π-Conjugated chiral nanorings with intriguing electronic structures and chiroptical properties have attracted considerable interests in synthetic chemistry and materials science. We present the design principles to access new chiral macrocycles (1 and 2) that are essentially built on the key components of main-group electron-donating carbazolyl moieties or the π-expanded aza[7]helicenes. Both macrocycles show the unique molecular conformations with a (quasi) figure-of-eight topology as a result of the conjugation patterns of 2,2',7,7'-spirobifluorenyl in 1 and triarylamine-coupled aza[7]helicene-based building blocks in 2. This electronic nature of redox-active, carbazole-rich backbones enabled these macrocycles to be readily oxidized chemically and electrochemically, leading to the sequential production of a series of positively charged polycationic open-shell cyclophanes. Their redox-dependent electronic states of the resulting multispin polyradicals have been characterized by VT-ESR, UV/Vis-NIR absorption and spectroelectrochemical measurements. The singlet (ΔES-T=-1.29 kcal mol-1) and a nearly degenerate singlet-triplet ground state (ΔES-T(calcd)=-0.15 kcal mol-1 and ΔES-T(exp)=0.01 kcal mol-1) were proved for diradical dications 12+2⋅ and 22+2⋅, respectively. Our work provides an experimental proof for the construction of electron-donating new chiral nanorings, and more importantly for highly charged polyradicals with potential applications in chirospintronics and organic conductors.

Cation-Dependence in Electrochemical Dedoping of Heterogeneous Organic Mixed Ionic-Electronic Conductors

Organic electrochemical transistors (OECTs) are emerging as next-generation bioelectronic devices and neuromorphic systems. In OECTs, permeation of mobile ions from an electrolyte leads to changes in bulk conductivity of the channel. The channel materials are typically organic mixed ionic-electronic conductors (OMIECs), which exhibit high performance in both electronic and ionic transport. Among these OMIECs, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is the most widely used. However, there have been ambiguities regarding the electrochemical doping process of PEDOT:PSS. This study aims to elucidate these ambiguities by investigating the ion dependence of the electrochemical doping process.

Polymer Bioelectronics: A Solution for Both Stimulating and Recording Electrodes.

The advent of closed-loop bionics has created a demand for electrode materials that are ideal for both stimulating and recording applications. The growing complexity and diminishing size of implantable devices for neural interfaces have moved beyond what can be achieved with conventional metallic electrode materials. Polymeric electrode materials are a recent development based on polymer composites of organic conductors such as conductive polymers. These materials present exciting new opportunities in the design and fabrication of next-generation electrode arrays which can overcome the electrochemical and mechanical limitations of conventional electrode materials. This review will examine the recent developments in polymeric electrode materials, their application as stimulating and recording electrodes in bionic devices, and their impact on the development of soft, conformal, and high-density neural interfaces.

Over 60h of Stable Water-Operation for N-Type Organic Electrochemical Transistors with Fast Response and Ambipolarity.

Organic electrochemical transistors (OECTs) are of great interest in low-power bioelectronics and neuromorphic computing, as they utilize organic mixed ionic-electronic conductors (OMIECs) to transduce ionic signals into electrical signals. However, the poor environmental stability of OMIEC materials significantly restricts the practical application of OECTs. Therefore, the non-fused planar naphthalenediimide (NDI)-dialkoxybithiazole (2Tz) copolymers are fine-tuned through varying ethylene glycol (EG) side chain lengths from tri(ethylene glycol) to hexa(ethylene glycol) (namely P-XO, X=3-6) to achieve OECTs with high-stability and low threshold voltage. As a result, the NDI-2Tz copolymers exhibit ambipolarity, rapid response (<10ms), and ultra-high n-type stability. Notably, the P-6O copolymers display a threshold voltage as low as 0.27V. They can operate in n-type mode in an aqueous solution for over 60h, maintaining an on-off ratio of over 105. This work sheds light on the design of exceptional n-type/ambipolar materials for OECTs. It demonstrates the potential of incorporating these ambipolar polymers into water-operational integrated circuits for long-term biosensing systems and energy-efficient brain-inspired computing.

Multi-Functional PEDOT:PSS as the Efficient Perovskite Solar Cells.

Poly(3,4-ethylenedioxythiophene) (PEDOT), particularly in its complex form with poly(styrene sulfonate) (PEDOT:PSS), stands out as a prominent example of an organic conductor. Renowned for its exceptional conductivity, substantial light transmissibility, water processability, and remarkable flexibility, PEDOT:PSS has earned its reputation as a leading conductive polymer. This study explores the unique effects of two additives, Bisphenol A diglycidyl ether (DGEBA) and Dimethyl sulfoxide (DMSO), on the PSS component of PEDOT:PSS films are shown. Both additives induce grain size growth, while DGEBA makes the PEDOT:PSS layer hydrophobic, which acts as a passivation to protect the perovskite layer, which is vulnerable to moisture. The other additive, DMSO, separates the PSS groups, resulting in increased conductivity through the free movement of holes. With these multi-modified p-type PEDOT:PSS, theITO/M-PEDOT:PSS/Perovskite/PCBM/Ag structured reverse structure solar cell has improved the power conversion efficiency (PCE) from 15.28% to 17.80% compared to the control cell with conventional PEDOT:PSS. It also maintains 90% for 500h at 60°C and 300h at 1 sun illuminating conditions.

Organic Mixed Ionic-Electronic Conductors Based on Tunable and Functional Poly(3,4-ethylenedioxythiophene) Copolymers.

Organic mixed ionic-electronic conductors (OMIECs) are being explored in applications such as bioelectronics, biosensors, energy conversion and storage, and optoelectronics. OMIECs are largely composed of conjugated polymers that couple ionic and electronic transport in their structure as well as synthetic flexibility. Despite extensive research, previous studies have mainly focused on either enhancing ion conduction or enabling synthetic modification. This limited the number of OMIECs that excel in both domains. Here, a series of OMIECs based on functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) copolymers that combine efficient ion/electron transport with the versatility of post-functionalization were developed. EDOT monomers bearing sulfonic (EDOTS) and carboxylic acid (EDOTCOOH) groups were electrochemically copolymerized in different ratios on oxygen plasma-treated conductive substrates. The plasma treatment enabled the synthesis of copolymers containing high ratios of EDOTS (up to 68%), otherwise not possible with untreated substrates. This flexibility in synthesis resulted in the fabrication of copolymers with tunable properties in terms of conductivity (2-0.0019 S/cm) and ion/electron transport, for example, as revealed by their volumetric capacitances (122-11 F/cm3). The importance of the organic nature of the OMIECs that are amenable to synthetic modification was also demonstrated. EDOTCOOH was successfully post-functionalized without influencing the ionic and electronic transport of the copolymers. This opens a new way to tailor the properties of the OMIECs to specific applications, especially in the field of bioelectronics.

Photoluminescence Probes Ion Insertion into Amorphous and Crystalline Regions of Organic Mixed Conductors

AbstractOrganic mixed ionic‐electronic conductors (OMIECs) have emerged as promising materials for a wide range of next‐generation technologies, including bioelectronics and neuromorphic computing. The performance of these materials depends on the transport of ions through the polycrystalline polymer matrix as well as how the distribution of ions and polarons in crystalline and amorphous regions impacts electronic transport. However, it is often challenging to distinguish whether ions enter crystalline or amorphous regions. In this work, steady‐state and time‐resolved photoluminescence (PL) spectroelectrochemistry is used to probe initial ion insertion in crystalline and amorphous regions of the OMIEC material poly(3‐[2‐[2‐(2‐methoxyethoxy)ethoxy]ethyl]thiophene ‐2,5‐diyl) (P3MEEET) as a function of applied voltage. It is found that PL spectroelectrochemistry reports on the initial stages of electrochemical doping through the quenching of PL emission. By distinguishing between amorphous and crystalline contributions to the PL spectrum, ion insertion in crystalline and amorphous regions as a function of voltage is tracked. It is found that PL spectroelectrochemistry is much more sensitive to the initial injection of ions than complementary methods, highlighting its potential as a sensitive tool for interrogating ion injection in OMIECs.

In Situ Surface-Enhanced Raman Spectroscopy on Organic Mixed Ionic-Electronic Conductors: Tracking Dynamic Doping in Light-Emitting Electrochemical Cells.

In the domain of organic mixed ionic-electronic conductors (OMIECs), simultaneous transport and coupling of ionic and electronic charges are crucial for the function of electrochemical devices in organic electronics. Understanding conduction mechanisms and chemical reactions in operational devices is pivotal for performance enhancement and is necessary for the informed and systematic development of more promising materials. Surface-enhanced Raman spectroscopy (SERS) is a potent tool for monitoring electrochemical evolution and dynamic doping in operational devices, offering enhanced sensitivity to subtle spectral changes. We demonstrate the utility of SERS for in situ tracking of doping in OMIECs in an organic light-emitting electrochemical cell (LEC) containing a conjugated polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]; MEH-PPV), a molecular anion (lithium triflate), and an electrolyte network (poly(ethylene oxide); PEO). SERS enhancement is achieved via an interleaved layer of gold particles formed by spontaneous breakup of a deposited thin gold film. The results successfully highlight the ability of SERS to unveil time-resolved MEH-PPV doping and polaron formation, elucidating the effects of triflate ion transfer in the operating device and validating the electrochemical doping model in LECs.

Organic Mixed Ionic Electronic Conductor Nanochannels for Vertical Electrochemical and Ionic Transistors

AbstractThin films of organic mixed ionic electronic conductors (OMIECs) constitute the functional layer in organic electrochemical transistors (OECTs), organic bioelectronic transducers and other ionic‐electronic devices. The thin‐film configuration constrains devices to be fabricated on impermeable substrates in the form of 2D microstructures with lateral electrodes to drive an electronic current through the thin film. In order to alleviate such constraints, novel OMIEC deposition methods are needed that produce alternatives to thin‐film devices and that are compatible with permeable substrates and electronic transport in the vertical direction. Here OMIECs filled nanoporous membranes are introduced as functional layer in devices with mixed ionic electronic transport. Electropolymerization of ethylenedioxythiophene (EDOT) monomers is used to fabricate OMIEC filled nanochannels. Electronic and ionic transport through such nanochannels are investigated and modulation of electronic as well as ionic carrier density by action of a third gate electrode is demonstrated. The novel OMIEC nanochannels enable the fabrication of vertical OECTs with high transconductance and organic ionic transistors using only additive fabrication methods.

Seebeck Effect of Dirac Electrons in Organic Conductors under Hydrostatic Pressure Using a Tight-Binding Model Derived from First Principles

Seebeck Effect of Dirac Electrons in Organic Conductors under Hydrostatic Pressure Using a Tight-Binding Model Derived from First Principles

Facile and rapid synthesis method of dielectric nanocomposite for simultaneous enhancement of electromagnetic wave absorbing/shielding characteristics

The present study involves the fabrication of poly[4-(2-thiophene)aniline] (PTA) nanocomposite for absorption-dependent shielding applications, demonstrating enhanced absorption and small reflection properties. The Microwave absorption characteristics of the fabricated polymer were studied at different loading ratios, resulting in a minimum reflection loss (RLmini) of − 44 dB for the 8 wt % loading ratio. The macromolecular architecture of the PTA material offers higher dielectric loss resulting from higher conduction and interfacial loss. Additionally, the shielding performance is also evaluated, and the sample containing 8 wt % filler demonstrates an impressive − 36.5 dB shielding efficacy. The performance of polymers is significantly impacted by their unit periodic order arrangement. Conducting polymers with linear structure and special π-orbitals angles possess unique characteristics in comparison to their branched and the random copolymer, making them highly sought after as efficient organic conductors, magnetic substances, electrochromic materials, and high dielectric agents. Monomer units contained two periodical cyclic structures and the creation of the inductive effects of heteroatoms elongates the conjugation and reduces the energy bandgap difference between the HOMO and LUMO levels, enabling smoother electron flow and enhancing absorption capacity. The findings indicate that PTA nanocomposite is a promising radar-absorbing coating material due to its superior absorption ability and outstanding shielding performance.

PH‐responsivity and photoconductivity for the organic mixed ionic electronic conductor of PANI/PSS composite films

AbstractThe influence of ionic‐electronic coupling on the electrical conductivity and the photoconductivity of organic mixed ionic electronic conductor (OMIECs) of polyaniline/poly (4‐styrene sulfonic acid) (PANI/PSS) composite films. PANI/PSS composite films are connected by blending the carbon atoms within the aromatic ring in PANI with sulfonate groups in PSS. The electrical conductivity of PANI/PSS composite film increases from to as the pH value increases from 3 to 9. The electrical conductivity of PANI/PSS composite films for all pH values increases continuously as the temperature increases. Additionally, the PANI/PSS composite films exhibit photo responses at UV light since the band structure can absorb the light in this region. The photoconductivity curves of PANI/PSS composite films for different pH values exhibit good consistency and repeatability. Modeling raising photoconductivity and decaying conductivity after light off leads us to understand the underlying physics of the ionic‐electronic coupling and other parameters on the photoconductivity of OMIECs, consequently building OMIEC devices for different photoconductivity applications.

Direct quantification of ion composition and mobility in organic mixed ionic-electronic conductors.

Ion transport in organic mixed ionic-electronic conductors (OMIECs) is crucial due to its direct impact on device response time and operating mechanisms but is often assessed indirectly or necessitates extra assumptions. Operando x-ray fluorescence (XRF) is a powerful, direct probe for elemental characterization of bulk OMIECs and was used to directly quantify ion composition and mobility in a model OMIEC, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), during device operation. The first cycle revealed slow electrowetting and cation-proton exchange. Subsequent cycles showed rapid response with minor cation fluctuation (~5%). Comparison with optical-tracked electrochromic fronts revealed mesoscale structure-dependent proton transport. The calculated effective ion mobility demonstrated thickness-dependent behavior, emphasizing an interfacial ion transport pathway with a higher mobile ion density. The decoupling of interfacial effects on bulk ion mobility and the decoupling of cation and proton migration elucidate ion transport in conventional and emerging OMIEC-based devices and has broader implications for other ionic conductors writ large.

Time-resolved Spectroelectrochemical Investigation of Organic Mixed Conductors.

Organic mixed ionic and electronic conductors (OMIECs) are an emerging class of materials that have been applied for a wide range of electrochemical applications. Due to the complexity inherent to the ionic-electroniccoupling, understanding the underlying mechanisms involved in the OMIEC operation is an exciting and very lively research field. In this work, we highlight the use of time-resolved Vis-NIR spectroelectrochemistry tocharacterize these materials. We discuss an example, where we show that by combining this tool with spectraldecomposition, we are able to understand fundamental aspects of the doping in an OMIEC film. The methodswe present here can be generalized and used to characterize any electrochromic material.

Orbital hybridization of donor and acceptor to enhance the conductivity of mixed-stack complexes

Mixed-stack complexes which comprise columns of alternating donors and acceptors are organic conductors with typically poor electrical conductivity because they are either in a neutral or highly ionic state. This indicates that conductive carriers are insufficient or are mainly localized. In this study, mixed-stack complexes that uniquely exist at the neutral–ionic boundary were synthesized by combining donors (bis(3,4-ethylenedichalcogenothiophene)) and acceptors (fluorinated tetracyanoquinodimethanes) with similar energy levels and orbital symmetry between the highest occupied molecular orbital of the donor and the lowest unoccupied molecular orbital of the acceptor. Surprisingly, the orbitals were highly hybridized in the single-crystal complexes, enhancing the room-temperature conductivity (10−4–0.1 S cm−1) of mixed-stack complexes. Specifically, the maximum conductivity was the highest reported for single-crystal mixed-stack complexes under ambient pressures. The unique electronic structures at the neutral–ionic boundary exhibited structural perturbations between their electron-itinerant and localized states, causing abrupt temperature-dependent changes in their electrical, optical, dielectric, and magnetic properties.

The Role of Side Chains and Hydration on Mixed Charge Transport in n-Type Polymer Films.

Introducing ethylene glycol (EG) side chains to a conjugated polymer backbone is a well-established synthetic strategy for designing organic mixed ion-electron conductors (OMIECs). However, the impact that film swelling has on mixed conduction properties has yet to be scoped, particularly for electron-transporting (n-type) OMIECs. Here, the authors investigate the effect of the length of branched EG chains on mixed charge transport of n-type OMIECs based on a naphthalene-1,4,5,8-tetracarboxylic-diimide-bithiophene backbone. Atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and scanning tunneling microscopy (STM) are used to establish the similarities between the common-backbone films in dry conditions. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and in situ GIWAXS measurements reveal stark changes in film swelling properties and microstructure during electrochemical doping, depending on the side chain length. It is found that even in the loss of the crystallite content upon contact with the aqueous electrolyte, the films can effectively transport charges and that it is rather the high water content that harms the electronic interconnectivity within the OMIEC films. These results highlight the importance of controlling water uptake in the films to impede charge transport in n-type electrochemical devices.

An organic artificial soma for spatio-temporal pattern recognition via dendritic integration

A novel organic neuromorphic device performing pattern classification is presented and demonstrated. It features an artificial soma capable of dendritic integration from three pre-synaptic neurons. The time-response of the interface between electrolytic solutions and organic mixed ionic-electronic conductors is proposed as the sole computational feature for pattern recognition, and it is easily tuned in the organic dendritic integrator by simply controlling electrolyte ionic strength. The classifier is benchmarked in speech-recognition experiments, with a sample of 14 words, encoded either from audio tracks or from kinematic data, showing excellent discrimination performances in a planar, miniaturizable, fully passive device, designed to be promptly integrated in more complex architectures where on-board pattern classification is required.