Organic Conductors Research Articles

Effects of Carrier Doping on the Transport in the Dirac Electron System α-(BEDT-TTF)2I3 under High Pressure

A zero-gap state with a Dirac cone type energy dispersion was discovered in an organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. Moreover, the Dirac cones are highly tilted in a k-space. This system, thus, provides a testing ground for the investigation of physical phenomena in the multilayered, massless Dirac electron system with anisotropic Fermi velocity. Recently, the carrier injection into this system has been succeeded. Thus, the investigations in this system have expanded. The recent developments are remarkable. This effect exhibits peculiar (quantum) transport phenomena characteristic of electrons on the Dirac cone type energy structure.

Pure Organic Conductors Based on Protonic-Defect Induction: From Semiconductors to Organic Metals

Abstract Protonic defects function as “lost positive point charges”, and their inclusion in molecules has great potential to control the total charge of a system. In other words, they have the ability to work as a dopant for hole injection. Carrier generation occurs when we confine and stabilize the protonic defects in hydrogen-bonding networks co-existing with a tetrathiafulvalene (TTF) skeleton, affording pure organic conductors without an addition of external dopant or electrochemical oxidation. Their conductivity varies in the range of six orders of magnitude from 10−4 to 102 S/cm, corresponding to molecular design. Moreover, anomalous isotope effects are observed in some electronic properties such as conductivity and thermopower, etc. In this account, the concept, molecular design, carrier generation and electronic properties of a series of the protonic-defect induced pure organic conductors are comprehensively reviewed from semiconductors to organic metals.

Effect of Long-Range Coulomb Interaction on NMR Shift in Massless Dirac Electrons of Organic Conductor

The nuclear magnetic resonance (NMR) with the site-dependent shift, at low temperatures is examined for a massless Dirac electrons in the organic conductor, alpha-(BEDT-TTF)_2I_3, where the sites of the four molecules in the unit cell are given by A (= A'), B, and C. The Dirac cone exists within an energy of 0.01 eV between the conduction and valence bands. The magnetic response function is calculated by taking account of the long-range Coulomb interaction and electron doping. Calculating the interaction within the first order in the perturbation, the chemical potential is determined self-consistently, and the self-energy and vertex corrections are taken to satisfy the Ward identity. The site-dependent shift is calculated at low temperatures of 0.0002 < T < 0.002 (T is temperature in the unit of eV) by correctly treating the wave function of the Dirac cone. At lower (higher) temperatures the self-energy (vertex) correction of the shift at all sites except for B is dominant and the sign is negative (positive), while the sign of the correction at the B site is always negative. For moderate doping, the shift as a function of T takes a minimum. The relevance of the shift to the experiment is discussed.

Specific Structural Disorder in an Anion Layer and Its Influence on Conducting Properties of New Crystals of the (BEDT-TTF)4A+[M3+(ox)3]G Family, Where G Is 2-Halopyridine; M Is Cr, Ga; A+ Is [K0.8(H3O)0.2

New crystals (1–4) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A+[M3+(ox)3]3−G}2−, where M is Cr, Ga; G is 2-chloropyridine, 2-bromopyridine; and A+ is [K0.8(H3O)0.2]+ have been prepared and their crystal structure and transport properties were studied. All crystals belong to the monoclinic group of the (BEDT-TTF)4A+[M3+(ox)3]G family with β″-packing type of conducting BEDT-TTF layers. In contrast to the known superconducting crystals with M3+ = Fe3+ and G = 2-chloro- or 2-bromopyridine (Tc = 4.0–4.3 K), crystals with Cr3+ and Ga3+ ions exhibit metallic properties down to 0.5 K without superconducting transition. Upon cooling these crystals, the incommensurate superstructure appears, which has never been observed before in the numerous β″-salts of the family. In addition, orthorhombic (sp. group Pbca) semiconducting crystals α″-(BEDT-TTF)5[Ga(ox)3]·3.4·H2O·0.6 EtOH (5) were obtained. It is a new compound in the family of BEDT-TTF crystals with tris(oxalato)metallate anions.

Organic conductor θ-(BEDT-TTF)Cd1.38I3 with layered perovskite-like structure

The organic conductor θ-(BEDT-TTF)Cd1.38I3 (1) (BEDT-TTF is bis(ethylenedithio)- tetrathiafulvalene) with layered perovskite-like structure was synthesized. In the crystal structure of 1, θ-type organic conducting layers, which are built up from BEDT-TTF stacks, alternate with inorganic insulating layers. The latter are composed of CdI6 octahedra and CdI4 tetrahedra linked together to form a two-dimensional anionic network. Measurements of the temperature dependence of the electrical resistance demonstrated that compound 1 is a semiconductor.

Size effects on supercooling phenomena in strongly correlated electron systems: IrTe2 and θ−(BEDT−TTF)2RbZn(SCN)4

We report that the sample miniaturization of first-order-phase-transition bulk systems causes a greater degree of supercooling. From a theoretical perspective, the size effects can be rationalized by considering two mechanisms: (i) the nucleation is a rare and stochastic event, and thus, its rate is correlated with the volume and/or surface area of a given sample; (ii) when the sample size decreases, the dominant heterogeneous nucleation sites that play a primary role for relatively large samples are annealed out. We experimentally verified the size effects on the supercooling phenomena for two different types of strongly correlated electron systems: the transition-metal dichalcogenide IrTe$_2$ and the organic conductor $\theta$-(BEDT-TTF)$_2$RbZn(SCN)$_4$. The origin of the size effects considered in this study does not depend on microscopic details of the material; therefore, they may often be involved in the first-order-transition behavior of small-volume specimens.

Hydrogels: Promising Energy Storage Materials

AbstractEnergy is essential for the economic growth of any country. There is a strong demand for the development of materials that can show potential towards higher power density and energy density. In this article, a promising class of polymeric materials, hydrogels have been discussed as an energy storage material. The hydrogels are advantageous as they possess in them the unique combination of organic conductors and conventional polymers. The article covers the synthetic approach of hydrogels which includes both the conventional synthesis and the new routes adopted followed by the application of hydrogels as energy storage materials. Finally, the future opportunities and prospects in the development of hydrogels as advanced energy storage materials are highlighted.

Antiferromagnetic Ordering in Organic Conductor λ-(BEDT-TTF)2GaCl4 Probed by 13C NMR

The ground state of $\lambda$-(BEDT-TTF)$_2$GaCl$_4$, which has the same structure as the organic superconductor $\lambda$-(BETS)$_2$GaCl$_4$, was investigated by magnetic susceptibility and $^{13}$C NMR measurements. The temperature dependence of the magnetic susceptibility revealed an antiferromagnetic (AF) correlation with $J/k_{\rm B} \simeq$ 98 K. NMR spectrum splitting and the divergence of $1/T_1$ were observed at approximately 13 K, which is associated with the AF transition. We found that the AF structure is commensurate according to discrete NMR peak splitting, suggesting that the ground state of $\lambda$-(BEDT-TTF)$_2$GaCl$_4$ is an AF dimer-Mott insulating state. Our results suggest that the superconducting phase of $\lambda$-type salts would be located near the AF insulating phase.

Effect of Interfacial Energetics on Charge Transfer from Lead Halide Perovskite to Organic Hole Conductors

The control and optimization of interfacial charge transfer processes is crucial to the design of efficient perovskite solar cells. Herein, we measure the yield and kinetics of hole transfer across the methylammonium lead triiodide perovskite|polymeric hole transport material heterojunction, as a function of the interfacial energy offset, ΔE, between the highest occupied molecular orbital of the hole transport material and the valence band edge of the perovskite. A combination of steady-state and time-resolved photoluminescence, along with transient absorption spectroscopy, revealed that only a small driving energy (ΔE ∼ 0.07 eV) is required to induce highly efficient hole transfer. The findings of this paper suggest that further improvements in the open-circuit voltage, and so the power conversion efficiency, of perovskite solar cells could be achieved by incorporating hole transport materials that provide an interfacial energy offset in the range 0 < ΔE < 0.18 eV.

Low toxicity environmentally friendly single component aqueous organic ionic conductors for high efficiency photoelectrochemical solar cells

Low-toxic, environment friendly single component organic ionic conductors are synthesized by facile methods and used as electrolytes in Dye Sensitized Solar Cells (DSSCs).

Microelectrode array and multichannel system for recording the electrical activity of neurons in vitro

Microelectrode array and multichannel system for recording the electrical activity of neurons in vitro

Cooperative loading of multisite receptors with lanthanide containers: an approach for organized luminescent metallopolymers.

Metal-containing (bio)organic polymers are materials of continuously increasing importance for applications in energy storage and conversion, drug delivery, shape-memory items, supported catalysts, organic conductors and smart photonic devices. The embodiment of luminescent components provides a revolution in lighting and signaling with the ever-increasing development of polymeric light-emitting devices. Despite the unique properties expected from the introduction of optically and magnetically active lanthanides into organic polymers, the deficient control of the metal loading currently limits their design to empirical and poorly reproducible materials. We show here that the synthetic efforts required for producing soluble multi-site host systems Lk are largely overcome by the virtue of reversible thermodynamics for mastering the metal loading with the help of only two parameters: (1) the affinity of the luminescent lanthanide container for a single binding site and (2) the cooperative effect which modulates the successive fixation of metallic units to adjacent sites. When unsymmetrical perfluorobenzene-trifluoroacetylacetonate co-ligands (pbta-) are selected for balancing the charge of the trivalent lanthanide cations, Ln3+, in six-coordinate [Ln(pbta)3] containers, the explored anti-cooperative complexation processes induce nearest-neighbor intermetallic interactions twice as large as thermal energy at room temperature (RT = 2.5 kJ mol-1). These values have no precedent when using standard symmetrical containers and they pave the way for programming metal alternation in luminescent lanthanidopolymers.

Dual functional hetero-anthracene based single component organic ionic conductors as redox mediator cum light harvester for solid state photoelectrochemical cells

We have synthesized a novel solid organic ionic conductor (SOIC) that acts as a redox mediator and a light absorbing material at the same time.

Donor–anion interactions in quarter-filled low-dimensional organic conductors

In contrast to currently accepted ideas anions play an essential role in directing the structural and transport properties of many molecular conductors.

The thermoelectric power of band-filling controlled organic conductors, β′-(BEDT-TTF)3(CoCl4)2−x(GaCl4)x

The carrier-number dependence of the thermoelectric power is investigated in the band-filling controlled organic conductors, β′-(BEDT-TTF)3(CoCl4)2−x(GaCl4)x (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene).

Ultrasonic wave generation in two-band organic conductors due to thermoelectric effect

A linear thermoelectric generation of a longitudinal ultrasonic wave in organic conductors with two conducting channels, quasi-one dimensional (q1D) and quasi-two dimensional (q2D), is investigated theoretically. The magnetic field and temperature dependences of the amplitude of generated through Nernst effect wave in [Formula: see text]-(BEDT-TTF)2KHg(SCN)4 for two boundary conditions, isothermal and adiabatic are obtained. Findings show a preference of one type of a boundary over another in the wave generation and propagation depending on the magnetic field strength and temperature. At lower temperatures and above B[Formula: see text]=[Formula: see text]4 T, the wave amplitude for adiabatic boundary is smaller compared to the one for isothermal boundary although there is a heat flux through the conductor’s surface in the latter. Both the q1D and q2D charge carriers contribute to the observation of the effect but with different magnitude due to the different drift velocity along the direction of wave propagation.

水素結合プロトン—π電子連動系有機伝導体κ-H3(Cat-EDT-TTF)2の非線形伝導

水素結合プロトン—π電子連動系有機伝導体κ-H3(Cat-EDT-TTF)2の非線形伝導

Second harmonic wave generation from Joule heating in layered organic conductors

The amplitude of a second harmonic wave (SHW) generated from Joule heating as a heat source in organic conductor β-(BEDT-TTF)2IBr2 is analyzed as a function of the magnetic field strength and its orientation with respect to the plane of the layers. Angular oscillations of the SHW amplitude are correlated with the angular changes of in-plane conductivity that arise from the periodic dependence of charge carriers velocity on the field orientation. It was found that the nonlinear effect of wave generation leads to a shift between the position of the peaks of the wave amplitude and in-plane conductivity. This allows an important information on the parameter values of organic conductors as well as wave velocity to be obtained. Magnetic field dependence shows that the wave is not strongly attenuated with increasing field and might give insights on the interactions between the electromagnetic, temperature and acoustic oscillations. We found that these observations are completely different compared to those of linear acoustic wave generation. It has been shown that the necessary conditions for observing the nonlinear acoustic wave generation are fulfilled in a wide range of fields and angles that allow the acoustic properties of organic conductors to be studied in detail.

Benchmarking organic mixed conductors for transistors

Organic mixed conductors have garnered significant attention in applications from bioelectronics to energy storage/generation. Their implementation in organic transistors has led to enhanced biosensing, neuromorphic function, and specialized circuits. While a narrow class of conducting polymers continues to excel in these new applications, materials design efforts have accelerated as researchers target new functionality, processability, and improved performance/stability. Materials for organic electrochemical transistors (OECTs) require both efficient electronic transport and facile ion injection in order to sustain high capacity. In this work, we show that the product of the electronic mobility and volumetric charge storage capacity (µC*) is the materials/system figure of merit; we use this framework to benchmark and compare the steady-state OECT performance of ten previously reported materials. This product can be independently verified and decoupled to guide materials design and processing. OECTs can therefore be used as a tool for understanding and designing new organic mixed conductors.

Continuous Melt‐Drawing of Highly Aligned Flexible and Stretchable Semiconducting Microfibers for Organic Electronics

AbstractA scalable and green approach to manufacture semiconducting microfibers from polymer melts has been demonstrated. The polymer chains are highly aligned along the microfiber's long axis direction and exhibit highly anisotropic optical properties. In addition, the polymer microfibers show good flexibility and stretchability with a yield point around 10% under a reversible stress and can be stretched up to 180% without breaking. These features are desired for future flexible, stretchable, and conformable electronics. The origin of this stretchability is studied with diketopyrrolopyrrole derivatives using different conjugation break spacers and side chains. In addition, stretchable conducting microfibers can be obtained by doping with FeCl3, which are further evaluated as organic conductors and source/drain electrodes in organic field‐effect transistors.