Electronic Transport Properties Research Articles

Polymerization of redox-active alizarin in biomass porous carbon with enhanced cycling stability for supercapacitor

Redox-active organic molecules have optimistic application prospects in energy storage due to their high theoretical capacitance, designable electrochemical activity and environmental friendliness. However, low conductivity and solubility in electrolyte severely hinder their redox activity. Here, alizarin molecules containing carbonyl and phenolic hydroxyl are encapsulated in biomass-derived porous carbon, and stable alizarin polymers are further grown on porous carbon substrate by electrochemical polymerization. Porous carbon as conductive network can improve electron transport properties, and provide suitable accommodation environment for confinement and polymerization of alizarin. The electrochemical polymerization strategy on carbon substrate allows alizarin to be connected by rigid C-O-C bond, which inhibits the dissolution of organic monomers while maintaining redox activity. The optimized polyalizarin/porous carbon composite (PAZ/PC-0.5) exhibits superior charge storage performance, with a specific capacitance of 355.8 F g−1 at 1 A g−1 and 220.8 F g−1 at high current density of 30 A g−1. Moreover, PAZ/PC electrode has more durable long-term charge-discharge stability (capacitance retention is 98 % after 10,000 charge and discharge cycles). The assembled symmetrical supercapacitor exhibits excellent energy-power characteristics (21.4 Wh kg−1 at 700 W kg−1) and durable cycle stability. This work sheds light on the design of stable organic electrode towards high-performance supercapacitor.

High thermoelectric performances of monolayer GeTe allotropes.

Aiming at finding wide-temperature-zone thermoelectric (TE) materials, five kinds of monolayer GeTe allotropes including the newly designedγ-,δ-, andɛ-GeTe monolayers and the usualα- andβ-GeTe ones are constructed. By using the density functional theory and the nonequilibrium Green's function method, all their electronic properties and TE transport properties are comparatively investigated. It is found that the room-temperature figure of meritZTof theγ-GeTe (ɛ-GeTe) along the armchair (zigzag) direction can amount to 4.5 (3.5), which is further increased to 7.15 (5.91) at 700 K. TheseZTvalues are much higher than the other IV-VI compounds usually withZT < 3, indicating that the armchairγ-GeTe and the zigzagɛ-GeTe we designed here can be used as superior wide-temperature-zone and high-performance TE materials in the temperature range from 300 K to 700 K. Moreover, with the increase of temperature, theZTpeaks will become wider in width and move towards the position of zero chemical potential, which will make the GeTe-based TE devices work at low bias voltages more efficiently. This work should be an important reference on the way to the stage ofZT⩾4, which will motivate more explorations into the high-performance TE materials working in a wider temperature scope.

First-principles studies of strain-tunable InN monolayer: Applications for switching and optoelectronic devices

Abstract Two-dimensional (2D) materials are attracting significant attention for their potential applications in the post-Moore era. In this work, we systematically investigate the effect of strains on the electronic structure, transport and optoelectronic properties of 2D indium nitride (InN) monolayer using density functional theory and non-equilibrium Green’s function methods. The results show that strains can modulate the electronic properties. Specifically, biaxial strain triggers the transition from semiconductor to metal and indirect to direct band gap. On this basis, the constructed InN-based nanodevice exhibits current switching ratios up to 10^10. In addition, the optoelectronic device based on InN monolayer exhibits a robust photoelectric response in the red light. Meanwhile, biaxial strain can improve the optoelectronic performance of InN-based optoelectronic devices. The compressive strains blue-shift the photocurrent peaks of the InN monolayer, which effectively modulates its detection range in the visible light region. These findings underscore the potential applications in nanotechnology, particularly in nano-switches and optoelectronic devices.&amp;#xD;

Ultrafast Charge and Exciton Diffusion in Monolayer Films of 9-Armchair Graphene Nanoribbons.

Determining the electronic transport properties of graphene nanoribbons is crucial for assessing their suitability for applications. So far, this has been highly challenging both through experimental and theoretical approaches. This is particularly the case for graphene nanoribbons that are prepared by chemical vapor deposition, which is a scalable and industry-compatible bottom-up growth method that results in closely packed arrays of ribbons with relatively short lengths of a few tens of nanometers. In this study, the experimental technique of spatiotemporal microscopy is applied to study monolayer films of 9-armchair graphene nanoribbons prepared using this growth method, and combined with linear-scaling quantum transport calculations of arrays of thousands of nanoribbons. Both approaches directly resolve electronic spreading in space and time through diffusion and give an initial diffusivity approaching 200 cm2 s-1 during the first picosecond after photoexcitation. This corresponds to a mobility up to 550 cm2 V-1 s-1. The quasi-free carriers then form excitons, which spread with a diffusivity of tens of cm2 s-1. The results indicate that this relatively large charge carrier mobility is the result of electronic transport not being hindered by defects nor inter-ribbon hopping. This confirms their suitability for applications that require efficient electronictransport.

Heteroatom‐Embedded Spiro[Fluorene‐9,9′‐Xanthene]‐Based Electron Transport Materials for Improved Driving Voltage and Efficiency in Phosphorescent Organic Light‐Emitting Diodes

AbstractThe organic material 9,9‐spirobifluorene (SBF) is a useful building block for the construction of organic light‐emitting diodes owing to its rigid molecular structure, good charge transport properties, and high triplet energy. However, the electron transport properties of the SBF‐derived electron transport materials (ETMs) are currently not good enough and should be improved. In this work, two ETMs derived from spiro[fluorene‐9,9′‐xanthene] (SFX) and spiro[cyclopenta[1,2‐b:5,4‐b′] dipyridine‐5,9′‐xanthene] (SPX) is developed to enhance the electron transport properties and triplet energy of the SBF‐derived ETMs. The SFX core can increase the triplet energy by disconnecting the conjugation on the xanthene part and SPX can improve the electron transport properties through the incorporation of two nitrogen atoms in the fluorene part of the SFX core. The SFX and SPX cores are substituted with diphenyltriazine to produce high mobility and high triplet energy ETMs. As a result, the SFX and SPX‐based ETMs showed high triplet energy of over 2.95 eV compared with 2.53 eV of the SBF‐derived ETM; in addition, the SPX‐derived ETM demonstrated higher mobility than the SBF‐derived ETM. As a result, the SPX‐derived ETM achieved lowered driving voltage and increased external quantum efficiency compared to other ETMs derived from SBF and SFX.

"V"-Shaped Changing Electronic Performance of Iodinene-Based Nanoflakes as a Function of Width.

Special structures and prominent performance make 2D iodinene more appealing and valuable at the molecular level. Here, new-type electronic devices have been constructed with iodinene-based nanoflakes in different sizes and are theoretically studied for electronic transport properties. Our findings reveal that iodinene-based nanoflakes possess great electron transport suppression, achieving the same function as SiO2 on single molecule scale. Such transport suppression shows surprisingly nonlinear "V"-shaped trend with the width of the iodinene-based nanoflake. The medium-width iodinene-based nanoflake exhibits the strongest electron transport suppression, while the narrowest and widest ones display the largest electron transmission coefficients due to delocalized transmission eigenstates. Essentially, the weakest electron transport originates from an extremely small DOS and wide HOMO-LUMO gap. Specifically, increasing the width would diminish the extension of electronic states for the dominant transport orbitals, resulting in more butterfly-like electronic states. In non-equilibrium, negative differential resistance effect can be observed in iodinene-based devices, caused by the weakening and staying away from the Fermi level of transmission peaks influenced by the bias. Our findings provide insights into the relationship between the width of iodinene-based nanoflake and electronic transport properties, and lay a foundation in the device design and applications in molecular insulators and controllable-functional devices.

Synergistic effect of lone-pair electron and atomic distortion in introducing anomalous phonon transport in layered PbXSeF (X= Cu, Ag) compounds with low lattice thermal conductivity

Using first-principles calculations, self-consistent phonon theory and Boltzmann transport theory, the crystal structure, phonon and electronic transport, and thermoelectric (TE) properties of PbXSeF (X = Cu, Ag) compounds are comprehensive explored in the current work. The heterogeneous bonding characteristics along the in-plane and out-of-plane directions lead to low lattice thermal conductivities in PbXSeF (X = Cu, Ag) compounds. The low lattice thermal conductivity is primarily attributed to strong anharmonicity caused by the lone-pair electrons of Pb. Notably, the PbCuSeF compound, despite the lighter mass in comparison with PbAgSeF, exhibits relatively lower lattice thermal conductivity. Such finding can be attributed to the distortion introduced by Cu atom, which leads to strong quartic anharmonicity, and thereby suppressing the heat-carrying phonons through the rattling-like behavior of Cu atom. The lone-pair electrons of Pb2+ and the heterogeneous bonding characteristics in PbXSeF (X = Cu, Ag) compounds contribute the multi-valley band degeneracy, resulting the decoupling of Seebeck coefficient and electrical conductivity with carrier concentration while generating in a high power factor. Our current work not only illustrates the fundamental insights into the low lattice thermal conductivity and related anomaly of layered PbXSeF (X = Cu, Ag) compounds based on the four-phonon scattering and multiple carrier scattering rates, but also highlights the anisotropic feature of electronic and thermal transport properties.

Simulating graphene-based single-electron transistor: incoherent current effects due to the presence of electron–electron interaction

Carbon-based nanostructures have unparalleled electronic properties. At the same time, using an allotrope of carbon as the contacts can yield better device control and reproducibility. In this work, we simulate a single-electron transistor composed of a segment of a graphene nanoribbon coupled to carbon nanotubes electrodes. Using the non-equilibrium Green's function formalism we atomistically describe the electronic transport properties of the system including electron-electron interactions. Using this methodology we are able to recover experimentally observed phenomena, such as the Coulomb blockade, as well as the corresponding Coulomb diamonds. Furthermore, we separate the different contributions to transport and show that incoherent effects due to the interaction play a crucial role in the transport properties depending on the region of the stability diagram being considered.

Engineering of in-plane SnS2–SnO2 nanosheets heterostructures for enhanced H2S sensing

In-plane heterostructures has attracted considerable interest due to exceptional electron transport properties, high specific surface area, and abundant active sites. However, synthesis of in-plane SnS2–SnO2 heterostructures are rarely reported, and the deep investigation of the fine structure on reactivity is of great significance. Here, we propose partial in-situ oxidation strategy to construct the in-plane SnS2–SnO2 heterostructures and the surface properties, the ratio of two components can be finely tuned by precisely adjusting the treatment temperature. In particular, the SnS2–SnO2 heterostructures formed after annealing of SnS2 nanosheets at 350 °C exhibits a unique electronic structure and surface properties due to rich grain boundaries, which exhibits excellent gas sensing performance to H2S (Ra/Rg = 169.81 for 5 ppm H2S at 160 °C, fast response and recovery dynamic (41/101 s), excellent reliability (σ = 0.01) and sensing stability (φ = 0.11 %)). Notably, the in-plane heterostructures endow the material with abundant grain boundaries and effectively regulates the electronic structure of the Sn p-orbital, which facilitate the formation of active oxygen species (O−(ad)), thus contributing to the sensing performance. Our work provides a promising platform to design in-plane heterostructures for various advanced applications.

Coexistence of linear and non-linear thermoelectricity in graphene-superconductor tunnel junctions

We theoretically analyze the electronic transport properties of a monolayer graphene/insulator/superconductor (GIS) tunnel junction subject to a temperature gradient. For intrinsic graphene, the system shows always dissipative charge transport even in the presence of an electronic temperature difference between the two leads. Differently, the GIS produces a thermoelectric response when the graphene electrochemical potential is lifted to energies comparable to the zero-temperature gap of the superconductor, i.e., the system is particle–hole asymmetric. Indeed, the thermally biased GIS system is able to produce both a short-circuit Peltier current and an open-circuit Seebeck voltage. This thermoelectric effect is made of a linear conventional component, due to the intrinsic particle–hole asymmetry of the system, and a non-linear contribution, due to a further spontaneous particle–hole symmetry breaking. In most of the thermal and charge configurations of the GIS system, the linear component prevails. Concluding, the GIS system could be employed in the design of thermometers, electromagnetic radiation sensors, and heat engines with profound influence in superconducting quantum technologies.

First-principles studies on the electronic and thermal transport properties of twin graphene and its analogues

The novel two-dimensional (2D) carbon allotropes with various carbon networks have provided an unprecedented platform to explore fascinating device applications beyond graphene. In this work, the electronic and thermal transport properties of the twin graphene and its structural analogues, i.e., γ-graphyne, twin T-graphene, and twin 4–8 graphene, have been systematically revealed through first-principles calculations. Our results confirm the energetic and dynamical stability of the twin graphene family, and the intrinsic semiconducting nature of these 2D carbon sheets superior to graphene. Based on the solution of the phonon Boltzmann transport equation, the evaluated thermal conductivity of the considered 2D carbon sheets indicates that the absence of acetylenic linkages in carbon networks leads to a relatively enhanced heat transfer capacity, i.e., a higher thermal conductivity in the twin graphene family than the γ-graphyne case. More interestingly, a way to effectively tune thermal transport properties in the twin graphene family has been proposed via the utilization of atom-embedded carbon nanocages. Our results indicate that a notable 63.8% reduction in thermal conductivity can be achieved for twin graphene through the embedding of Ti atoms into the nanocages, exhibiting great potential for robust thermal management in low-dimensional carbon networks.

Matched Electron-Transport Materials Enabling Efficient and Stable Perovskite Quantum-Dot-Based Light-Emitting Diodes.

Light-emitting diodes (LEDs) based on perovskite quantum dots (QDs), abbreviated as P-QLEDs have been regarded as significantly crucial emitters for lighting and displays. Efficient and stable P-QLEDs still lack ideal electron transport materials (ETM), which could efficiently block hole, transport electron, reduce interface non-radiative recombination and possess high thermal stability. Here, we report 2,4,6-Tris(3'-(pyridine-3-yl) biphenyl-3-yl)-1,3,5-triazine (TmPPPyTz, 3P) with strong electron-withdrawing moieties of pyridine and triazine to modulate the performance of P-QLEDs. Compared with commonly used 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), the pyridine in 3P have a strong interaction with perovskites, which can effectively suppress the interface non-radiative recombination caused by the Pb2+ defects on the surface of QDs. In addition, 3P have deep highest occupied molecular orbital (HOMO) (enhancing hole-blocking properties), matched lowest unoccupied molecular orbital (LUMO) and excellent electron mobility (enhancing electron transport properties), realizing the carrier balance and maximizing the exciton recombination. Furthermore, high thermal resistance of 3P obviously improves the stability of QDs under variable temperature, continuous UV illumination, and electric field excitation. Resultantly, the P-QLEDs using the 3P as ETM achieved an outstanding performance with a champion EQE of 30.2 % and an operational lifetime T50 of 3220 hours at an initial luminance of 100 cd m-2, which is 151 % and about 11-fold improvement compared to control devices (EQE=20 %, T50=297 hours), respectively. These results provide a new concept for constructing the efficient and stable P-QLEDs from the perspective of selective ETM.

Characteristics of a heavy metal resistant heterotrophic nitrification–aerobic denitrification bacterium isolated from municipal activated sludge

The heterotrophic nitrification-aerobic denitrification (HNAD) is a new biological denitrification technology, the present study isolated a new HNAD strain named Cupriavidus metallidurans TX6 with heavy metal resistance. The gene expression, electron transport, enzyme activity and nitrogen removal property of strain TX6 were studied with different influencing factors. Strain TX6 has five nitrogen metabolism pathways (NH4+ → NH2OH → NO → NO2− → NH4+ → GOGAT/GDH; NH4+-N → NH2OH → NO → N2O → N2; NH4+ → NH2OH → NO → NO2− → NO3−; NO3− → NO2− → NH4+ → GOGAT/GDH; NO3−→ NO2− → NH4+ → GOGAT/GDH). Nitrogen balance analysis shows that 29 ± 4 mg/L of N was converted to intracellular nitrogen by assimilation and 50 ± 3 mg/L N loss may be attributed to aerobic denitrification. The results provide a theoretical basis for the HAND bacteria application in nitrogen removal from wastewaters containing heavy metals.

Structural-modulated substrate of MXene for surface-enhanced Raman scattering sensing.

The distinctive structure of MXene offers exceptional electron transport properties, abundant surface chemistry, and robust mechanical attributes, thereby bestowing it with remarkable advantages and promising prospects in the realm of surface-enhanced Raman scattering (SERS). This review comprehensively outlines the evolution, synthesis methodologies, and characterization techniques employed for MXene-based SERS substrates. It delves into the intricacies of its SERS enhancement mechanism, substrate variants, and performance metrics, alongside showcasing its diverse applications spanning molecular detection, biosensing, and environmental monitoring. Furthermore, it endeavors to pinpoint the research bottlenecks and chart the future research trajectories for MXene-based SERS substrates.

Doping-induced electronic transport properties in tetracene-based molecular device

Doping-induced electronic transport properties in tetracene-based molecular device

Electronic, optical, and thermoelectric behaviour of KCuX (X = S, Se, Te) monolayers.

In the past few decades, two-dimensional (2-D) materials gained huge deliberation due to their outstanding electronic and heat transport properties. These materials have effective applications in many areas such as photodetectors, battery electrodes, thermoelectrics, etc. In this work, we have calculated structural, electronic, optical, and thermoelectric properties of KCuX (X = S, Se, Te) monolayers (MLs) with the help of first-principles-based calculations and semi-classical Boltz- mann transport equation (BTE). The phonon dispersion calculations demonstrate the dynamical stability of the KCuX (X = S, Se, Te) MLs. Our results show that the monolayers of KCuX (X = S, Se, Te) are semiconductors with band gaps of 0.193 eV, 0.26 eV, and 1.001 eV respectively, and therefore they are suitable for photovoltaic applications. The optical analysis illustrates that the maximum absorption peaks of the KCuX (X = S, Se, Te) MLs are located in visible and ultraviolet (UV) regions, which may serve as a promising candidate for designing advanced optoelectronic devices. Furthermore, thermoelectric properties of the KCuS and KCuSe MLs, including See- beck coefficient, electrical conductivity, electronic thermal conductivity, power factor, and figure of merit, are calculated at different temperatures 300 K, 600 K, and 800 K. Additionally, we also focus on the analysis of Gru ̈neisen parameter and various scattering rates to further explain their ultra-low thermal conductivity. Our results show that KCuS and KCuSe possess ultra-low lattice thermal conductivity value of 0.15 Wm-1K-1 and 0.06 Wm-1K-1 respectively, which is lower than those of recently reported KAgSe (0.26 Wm-1K-1 at 300 K) and TlCuSe (0.44 Wm-1K-1 at 300 K), indicating towards the large value of ZT. These materials are found to possess desirable thermoelectric and optical properties, making them suitable candidates for efficient thermoelectric and optoelectronic device applications.

Low lattice thermal conductivity induced by rattling-like vibration in Zintl phase Na2CaCdSb2 compound with high ZT from two-channel model

Zintl phase compounds, characterized by the traits of a phonon-glass and electron-crystal, stand out as promising candidates for thermoelectric applications. This study delves into the thermoelectric properties of Zintl phase Na2CaCdSb2 compound through a synergy of first-principles calculations, machine learning interatomic potential approach based on the two-channel model, and high-throughput screening calculations. With an indirect bandgap of 1.02 eV, Na2CaCdSb2 compoundpossesses an high carrier mobility. The high valence band degeneracy and anisotropic band (light-heavy band) lead to a high power factor for the p-type Na2CaCdSb2 compound. The strong fourth-order anharmonicity of the rattling-like Na atom manifests the low lattice thermal conductivity on the basis of two-channel model. The loosely bonding Na atom displays random rotations and dynamically disordered orientations, leading to the weakly disordered nature of Na2CaCdSb2 compound. The unique crystal structure of Na2CaCdSb2 compound coupled with the abundance of diffusion-like phonons play a pivotal role in the phonon transport. Considering the low lattice thermal conductivity and high power factor with the framework of two-channel model, the n-type and p-type Na2CaCdSb2 compounds exhibit optimal figure-of-merits (ZT) of 1.0 and 2.0 at 600 K, showcasing excellent thermoelectric performance. Meanwhile, an optimal ZT of 2.3 is achieved for p-type Na2CaCdSb2 compound at the same temperature along the x-direction. Our present study not only provides fundamental insights into the thermal and electronic transport properties of Na2CaCdSb2 compound under the two-channel model in combination with the four-phonon scattering and multiple carrier scattering rates, but also rationalizes the high-order phonon interactions and thermal transport properties under two-channel model.

Electronic Properties of ZnO Nanowires: A First-Principles Analysis Using Two-Probe Methodology

In this study, the electrical characteristics of pure ZnO nanowires are investigated using density functional theory (DFT) inside the non-equilibrium Green's function (NEGF) paradigm. We clarify the underlying electronic behaviours by a thorough analysis of I-V curves, density of states (DOS) spectra, and transmission spectra. All calculations are carefully carried out using the Quantum Wise Atomistic Tool Kit programme and the Generalised Gradient Approximation (GGA). Our results show that localised d orbitals dominantly contribute to ZnO nanowire transmission properties. We also investigate the effect of doping with copper on these characteristics. Gradual doping from pristine to 2 and 4 Cu atoms shows significant enhancements, indicating a clear relationship between electrical properties and doping concentration. Notably, the device's potential as a resistor is highlighted by the greater linearity of current with copper doping, demonstrating adherence to Ohm's law. Moving beyond basic research, we tackle real-world issues in sensing applications, including the quick identification of copper molecules in water. We provide light on the Au-ZnO-Au structure's potential for sensor applications by thoroughly discussing its electron transport properties. In conclusion, this study advances our knowledge of the electrical characteristics of ZnO nanowires and how doping modifies them, opening the door to their application in a variety of electronic and sensing devices.

Optimizing electron transport layers for high-efficiency perovskite solar cells using impedance spectroscopy

The best interface for a perovskite solar cell is designed to facilitate effective charge transport to achieve a high-power conversion efficiency. Tin dioxide (SnO2) is widely recognized as an electron transport material for perovskite solar cells, offering advantages such as low hysteresis, low defect concentration, and low fabrication temperature. However, the low conduction band edge of SnO2 restricts the built-in potential of the solar cell device. In this study, we designed a double layer of electron transport by applying zinc oxide (ZnO) on SnO2 to improve the electron transport properties in perovskite solar cells. The bilayer of electron transport enhances the interfaces between the perovskite and the electron transport layer, leading to an improvement in the efficiency and stability of solar cell devices up to 11.71 % compared to a single SnO2 layer device with a PCE of 9.06 %. The introduction of ZnO reduces charge recombination, resulting in a lower recombination resistance (Rrec). Also, charge transfer resistance (Rct) of ZnO/SnO2 increased to 16.6KΩ compared to a single SnO2 layer device with a Rct of 5.29KΩ. Our findings provide valuable insights into the design of electron transport layers for perovskite solar cells and highlight the importance of electrochemical impedance spectroscopy in understanding the dynamic processes that govern their performance.

Numerical optimization of cesium tin-germanium triiodide/antimony selenide perovskite solar cell with fullerene nanolayer

SCAPS-1D platform was used to simulate a solar cell with FTO/CdS/Sb2Se3/CuInSe2/Au structure which was recently fabricated by Liu et al. (2022) [1] [Journal of Energy Chemistry68 521–528 (2022)] and a very similar result was obtained. Reported parameters were Fill Factor (FF) = 53.60 %, short circuit current density (JSC) = 26.18 mA/cm2, open circuit voltage (VOC) = 0.37 V, and power conversion efficiency (PCE) = 5.19 %, while simulated parameters were FF of 54.68 %, JSC of 27.54 mA/cm2, VOC of 0.36 V, and PCE = 5.55 %. The advancements have been evaluated by analyzing FTO/CdS/Sb2Se3/CuInSe2/Au and FTO/C60/Sb2Se3/CuInSe2/Au configurations, serving as the reference cells. To improve the cell performance, the CdS layer was replaced with another layer (C60) which shows excellent electron transport properties. Replacing the CdS layer with C60 led to an increase in the power conversion efficiency by 65 % (from 5.55 % up to 9.20 %). In photovoltaic systems, the PCE constitutes a pivotal parameter that can be enhanced through the absorption of a broad spectrum of incident photons. Consequently, the implementation of two absorber layers within a solar cell, each characterized by a graded band gap energy, enables the capture of solar photons over a more extensive spectral range. Therefore, a perovskite containing a band gap of 1.5 eV, lead-free, and Sn-based was used as the second absorber layer in the device. Therefore, a solar cell with FTO/C60/CsSn0.5Ge0.5I3/Sb2Se3/CuInSe2/Au structure was simulated, and significant results were achieved. Results showed that inserting the CsSn0.5Ge0.5I3 layer led to an increase in PCE up to 11.42 %.