Excellent Transport Properties Research Articles

Comparison of the excellent thermoelectric properties of the half-Heusler compounds RbMgSb with a host-guest structure and LiMgSb

In this work, we systematically studied the thermoelectric (TE) transport properties of the half-Heusler compounds AMgSb (A = Li, Rb) based on an incorporation of first-principles calculations with self-consistent phonon theory and Boltzmann transport equations. We noted significant changes in the vibrational behavior of alkali metal atoms with a substantial increase in atomic mass. This alteration led to the formation of a host-guest structure in RbMgSb. In contrast, the stronger harmonic vibrations in LiMgSb results in it maintaining a Half-Heusler structure, without the pronounced anharmonicity found in RbMgSb. The calculation results reveal that RbMgSb has ultra-low lattice thermal conductivity κL, which is ten times lower than LiMgSb. We show that rattlers cause tenfold reductions in the thermal conductivity by increasing the phonon-phonon scattering probability, occurred in a wide frequency range. In addition, after careful consideration of multiple scattering mechanisms, the multiple valleys, high dispersion, flat band edges and band asymmetry near the Fermi level give both materials excellent electron transport properties. At the same time, LiMgSb itself already has a very low electron thermal conductivity κe, but the κe of RbMgSb is ten times smaller than that. As a consequence, remarkable ZT values of 2.51 and 3.45 at 900 K are captured in n-type LiMgSb and p-type RbMgSb, respectively. These findings reveal the promising potential of AMgSb in TE applications.

Surface Treatment with Tailored π-Conjugated Fluorene Derivatives Significantly Enhances the Performance of Perovskite Light-Emitting Diodes.

Surface defect passivation and carrier injection regulation have emerged as effective strategies for enhancing the performance of perovskite light-emitting diodes (Pero-LEDs). It usually requires two functional molecules to realize defect passivation and carrier injection regulation separately. In other words, developing one single molecule possessing these capabilities remains challenging. Herein, we utilized π-conjugated fluorene derivatives as surface treatment materials, 9,9-Spirobi[fluorene] (SBF), 9,9-Spirobifluoren-2-yl-diphenylphosphine oxide (SPPO1), and 2,7-bis(diphenylphosphoryl)-9,9'-spirobifluorene (SPPO13), to investigate the influence of their chemical structure on device optoelectronic performance, especially for defect passivation and carrier injection regulation. Consequently, the passivation capability of double-bonded SPPO13 surpassed single-bonded SPPO1 and nonbonded SBF, which all showed excellent electron transport properties, enhancing electron injection. The maximum external quantum efficiencies (EQE) for Pero-LEDs treated with SBF, SPPO1, and SPPO13 were 8.13, 17.48, and 22.10%, respectively, exceeding that of the derivative-free device (6.55%). Notably, SPPO13-treated devices exhibited exceptional reproducibility, yielding an average EQE of 20.00 ± 1.10% based on 30 devices. This result emphasizes the potential of tailored fluorene derivatives for enhancing the device performance of Pero-LEDs.

Gas Permeation through V2O5 Nanoribbons‐Based Membrane

AbstractMembrane separation processes play a crucial role in gas separation applications, with the need for ongoing development to fulfill new needs for today's challenges. For this purpose, novel 2D nanomaterials are progressively showing promise over conventional polymer‐based membrane material, exhibiting excellent molecular transport properties. Beyond the 2D materials already studied in this field, this article presents the first gas separation performances of vanadium pentoxide membrane. Brand new in gas separation topic, 2D van der Waals nanoribbons of V2O5 are successfully synthesized and layered on an anodic aluminum oxide substrate. Gas permeation analysis of He, N2, and CO2 are performed on various membranes made from different quantities of the nanomaterial. Gas permeance results suggest a deviation from an expected Knudsen diffusion mechanism of the V2O5‐based membrane for He separation. The ideal selectivities of He/N2 and He/CO2 are compared to Robeson's upper bound for polymeric membranes. V2O5 membranes, prepared with the highest V2O5 quantity, exceeded the upper bound from 2008 for He/N2 and 2019 (the most recent) for He/CO2, demonstrating the interesting potential of V2O5 2D materials for gas separation.

High-Performance Hard X-Ray Imaging Detector Using Facet-Dependent Bismuth Vanadate.

Bismuth vanadate (BiVO4) exhibits large absorption efficiency for hard X-rays, which endows it with a robust capacity to attenuate X-ray radiation across a broad energy range. The anisotropic properties of BiVO4 allow for the manipulation of their physical and chemical characteristics through crystallographic orientation and exposed facets. In this study, the issue of heavy recombination caused by sluggish electron transport in BiVO4 is successfully addressed by enhancing the abundance of the (040) crystal face ratio using a Co2+ crystal face exposure agent. The facet-dependent modifications exhibit excellent and balanced intrinsic charge transport properties, and finely optimize both the sensitivity and detection limit of BiVO4 X-ray detectors. As a result, ultra-stable BiVO4 metal oxide X-ray detectors demonstrate a high sensitivity of 3164 µC Gyair -1 cm-2 and a low detection limit of 20.76 nGyair s-1 under 110 kVp hard X-rays, establishing a new benchmark for X-ray detectors based on polycrystalline Bi-halides and metal oxides. These findings highlight the significance of crystal orientation in optimizing materials for X-ray detection, setting a new sensitivity record for X-ray detectors based on polycrystalline Bi-halides and metal oxides, which paves the way for the development of advanced, low-dose, and highly stable imaging systems specifically for hard X-rays.

SiX2 (X = S, Se) Nanowire Gate-All-Around MOSFETs for Sub-5 nm Applications.

The gate-all-around (GAA) field-effect transistor (FET) holds great potential to support next-generation integrated circuits. Nanowires such as carbon nanotubes (CNTs) are one important category of channel materials in GAA FETs. Based on first-principles investigations, we propose that SiX2 (X = S, Se) nanowires are promising channel materials that can significantly elevate the performance of GAA FETs. The sub-5 nm SiX2 (X = S, Se) nanowire GAA FETs exhibit excellent ballistic transport properties that meet the requirements of the 2013 International Technology Roadmap for Semiconductors (ITRS). Compared to CNTs, they are also advantageous or at least comparable in terms of gate controllability, device dimensions, etc. Importantly, SiSe2 GAA FETs show superb gate controllability due to the ultralow minimum subthreshold swing (SSmin) that breaks "Boltzmann's tyranny". Moreover, the energy-delay product (EDP) of SiX2 GAA FETs is significantly lower than that of the CNT FETs. These features make SiX2 nanowires ideal channel material in the sub-5 nm GAA FET devices.

Exploring the ferroelectric photocatalytic potential of R3c-structured InVO3: A computational study

Ferroelectric oxides with large band gaps or band edge positions that are difficult to cross the water oxidation-reduction potential are not conducive to photocatalytic hydrogen production. This study systematically investigates the potential application of R3c-structured InVO3 in the field of photocatalysis through density functional theory calculations. The mechanical and phonon frequency stability of InVO3 is verified through stability analysis, followed by the confirmation of its excellent ferroelectric properties through first-principles calculations. The calculated optical properties of InVO3 are explored to reveal its strong absorption of visible light and high photoelectric conversion efficiency. InVO3 exhibits excellent charge carrier transport properties through calculations of electron mobility, promising efficient energy conversion in photocatalytic water splitting. The band edge positions of InVO3 can cross the water oxidation-reduction potential, providing theoretical support for its application in the field of photocatalysis. R3c-structured InVO3 is a potential high-performance ferroelectric photocatalytic material.

Highly Stable and Sensitive (PEA)2PbBr4/CsPbBr3 Single‐Crystal Heterojunction X‐Ray Detector with Ultra‐Low Detection Limit

AbstractMetal halide perovskite (MHP) single crystals have shown great potential for high‐performance X‐ray detection due to their excellent carrier transport properties, tunable optical bandgap, and low‐temperature fabrication process. However, 3D perovskite single crystals suffer from severe ion migration, limiting the stability and sensitivity of X‐ray detectors. Herein, a lowing temperature crystallization (LTC) method for liquid‐phase epitaxial growth of 2D (PEA)2PbBr4 single‐crystal (SC) film on 3D CsPbBr3 substrate is demonstratedand a 2D/3D (PEA)2PbBr4/CsPbBr3 SC heterojunction is successfully constructed. The epitaxial (PEA)2PbBr4 layer shows a pronounced passivation effect on CsPbBr3 SC with a low trap density of 2.27 × 1010 cm−3. As such, the prepared 2D/3D heterojunction X‐ray detector achieves a record‐low detectable dose rate of 3.05 nGyair s−1 and high sensitivity of 34496 µC Gyair−1 cm−2 in 120 keV hard X‐ray detection, with a largely suppressed dark current drift of 2.49 × 10−4 nA cm−1 s−1 V−1. In addition, the heterojunction detector exhibits a self‐driven sensitivity of 44 µC Gyair−1 cm−2 due to its built‐in electric field. This work provides a simple strategy to controllable construct 2D/3D MHP SC heterojunction with excellent optoelectronic characteristic, which is conducive to promoting the development of MHP SC X‐ray detectors and other optoelectronic devices.

Strain-tunable elastic, electronic, and thermal transport properties of two-dimensional CaI2 monolayer: A first-principles study

Despite the increasing attention on two-dimensional (2D) metal iodides in recent years for their appropriate bandgaps and exceptional optical properties, there is limited understanding of their intriguing thermal transport properties. Here, the strain-tunable mechanic, electronic, and transport properties of the monolayer CaI2 are calculated in detail by combining first-principles calculations with Boltzmann transport theory. We have checked its thermal, dynamic, and mechanical stability by computing ab-initio molecular dynamics, phonon spectra and elastic constants, respectively. The calculation results from the PBE-GGA and HSE06 methods indicate that the monolayer CaI2 is an indirect semiconductor, with band gaps of 3.92 eV and 5.12 eV, respectively. Additionally, the effective masses and Fermi velocities for both holes and electrons are also obtained, which indicates that the monolayer CaI2 owns the excellent electronic transport property. These mechanical constants and electronic parameters are also highly sensitive to the external strain. The calculated real lattice thermal conductivity of the monolayer CaI2 at 300 K is about 1.01 W/mK, which is rather low among 2D materials, implying its potential application in heat insulation materials or thermal insulation material. With the biaxial tensile strain increasing, its lattice thermal conductivity would further decrease. The difference in lattice thermal conductivities between 0 % and 2 % strain, as well as between 4 % and 6 % strain, is much smaller than that between 2 % and 4 % strains. Subsequently, the group velocities, phonon scattering rates, and cumulative lattice thermal conductivities of the monolayer CaI2 are discussed under the different strains.

Wide‐Gap Perovskites for Indoor Photovoltaics

Organic–inorganic halide perovskite semiconductors have revolutionized next‐generation photovoltaics (PV) due to several characteristics such as solution‐processability, gap tunability, and excellent charge generation and transport properties. This has made them very adaptable for various applications in light harvesting and photodetection. One such rapidly growing application is indoor photovoltaics (IPV) which have the potential to power standalone Internet of Things devices. IPV requires wider optimal bandgaps than solar cells (1.8 vs 1.3 eV) due to the differences between the spectra of artificial lights versus solar radiation. For IPV applications, the active layer wide‐gap perovskite must be developed systemically considering all other components of the device, such as interlayers, electrodes, and scaling. This perspective provides an overview of the potential and challenges facing perovskite‐based IPV from a theoretical, material, and experimental perspective. Furthermore, accurate characterization of perovskite IPVs under simulated indoor conditions is discussed and candidate perovskite PV (PPV) systems are presented to provide insight into IPV development. These include IPV‐optimized formamidinium cesium‐based perovskite, wide‐gap p‐i‐n devices, and 2D perovskite devices, tested under spectrophotometrically calibrated LED illumination at various indoor‐relevant illuminances and benchmarked against thermodynamic predictions. Finally, strategies required to create stable, optimized PPV devices for indoor applications are discussed.

Effect of Sn on Physical and Optical Properties of Lithium Zinc Borate Glasses

22.5 Li2O3-(20-x) ZnO-57.5B2O3 – xSnCl2 (x = 0, 0.5. 1) glasses were synthesized using the conventional melt quench technique. Glass composition with larger concentration of lithium oxide exhibits excellent transport properties. Introducing intermediate element like zinc into the matrix will lead towards slight modification in structure by not varying much in its intrinsic properties. Thus, incorporation of Sn as dopant into the matrix has tailored the physical and optical properties of glasses. In this study, it is interesting to note that, the density of the glass has reduced for 0.5 mol % SnCl2 in the matrix and on the contrary, the density of glass was found to be increased for the SnCl2 with 1 mol % concentration. It indicates that, there could be a possibility of slight modification in the structure of glasses which eventually leads towards tuning of the optical bandgap due to existence of Sn.

High-performance intrinsically stretchable organic solar cells based on flexible spacer incorporated dimerized small-molecule acceptors

High power conversion efficiency (PCE), long-term stability, and mechanical robustness are important requirements for the practical applications of organic solar cells (OSCs). Herein, we develop a series of flexible spacer (FS)-incorporated dimerized small-molecule acceptors (DSMAs; DYBT-C0, DYBT-C4, and DYBT-C8) and demonstrate high-performance OSCs with a high PCE of 18.6%, excellent mechanical robustness (crack-onset strain (COS) = 32%) and photostability (t80% lifetime = 1735 h under 1-sun illumination). The incorporation of aliphatic FS units with optimal length effectively reduces the backbone rigidity of the DSMAs and increases the fraction of intermixed domains in the blend films, while maintaining excellent electron transport properties. The DYBT-C4-based OSCs demonstrate higher PCE (18.6%) and stretchability (COS = 32%) compared to the OSCs based on the monomer acceptor (MYT; PCE = 15.9% and COS = 10%) and DSMA without FS units (DYBT-C0; PCE =17.2% and COS = 17%). In addition, due to the reduced diffusion coefficient and higher glass transition temperature of DYBT-C4, the DYBT-C4-based OSCs exhibit photostability significantly higher than that of the OSCs fabricated using MYT (t80% lifetime= 36 h). Consequently, DYBT-C4-based intrinsically stretchable (IS)-OSCs exhibit high device stretchability (strain at PCE80% = 36%) and PCE of 14.3%, demonstrating potential for wearable applications.

Enhancement of thermoelectric performance in monolayer AlP3 via Ga and In doping: A first-principles study

Recently, two-dimensional (2D) triphosphides have attracted much attention in the thermoelectric field due to their semiconductor properties and excellent electronic transport properties. In our study, the performances of AlP3, Al0.5Ga0.5P3, and Al0.5In0.5P3 doped monolayers in the thermoelectric transport are studied. First, the dynamic structural stabilities of the three monolayers are verified through phonon dispersion curves. Moreover, all monolayers are indirect band-gap semiconductors, which can be used as thermoelectric materials. The results show that larger electronic relaxation time and carrier mobilities of doped monolayers lead to larger electronic transport parameters and higher dimensionless thermoelectric figure-of-merit (ZT). It is found that after doping via Ga and In, the thermoelectric performances of AlP3 are increased by 1.31–1.79 times. Our findings show that AlP3 and its doped monolayers hold significant promise as thermoelectric materials within the temperature span of 300–700 K and the doping mechanism could significantly improve the thermoelectric properties of 2D structures.

Carbon nanotube integrated circuit technology: purification, assembly and integration

Abstract As the manufacturing process of silicon-based integrated circuits (ICs) approaches its physical limit, the quantum effect of silicon-based field-effect transistors (FETs) has become increasingly evident. And the burgeoning carbon-based semiconductor technology has become one of the most disruptive technologies in the post-Moore era. As one-dimensional nanomaterials, carbon nanotubes (CNTs) are far superior to silicon at the same technology nodes of FETs because of their excellent electrical transport and scaling properties, rendering them the most competitive material in the next-generation ICs technology. However, certain challenges impede the industrialization of CNTs, particularly in terms of material preparation, which significantly hinders the development of CNT-based ICs. Focusing on CNT-based ICs technology, this review summarizes its main technical status, development trends, existing challenges, and future development directions.

Graphene coating-modified LiCoO2 films as high-performance cathode material in quasi-solid-state thin-film lithium batteries

LiCoO2 (LCO) films were successfully prepared using a radio frequency magnetron sputtering method, and the interface between the LCO cathode films and Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte was modified by a graphene (G) buffer layer. The composition and morphology of the thin-film samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The LCO thin film annealed at 600 °C had excellent charge transport properties, respectively delivering initial charge and discharge specific capacities of 162.7 mAh·g−1 and 124.5 mAh·g−1 at 0.1C in a half-cell structure. Relaxation time distribution reconstruction impedance analysis and rate characteristic analysis of an LCO/G/LAGP/G/LCO symmetric cell demonstrated that the flexible graphene buffer layer effectively improved the contact impedance of the interface and structure stability of the active materials. After cycling for 1000 h at current densities of 0.02 mA·cm−2 and 0.5 mA·cm−2, the LCO/G/LAGP/G/LCO symmetric cell still maintained stable polarization voltages of 0.05 V and 0.7 V, respectively. In addition, an assembled LCO/G/LAGP/Li quasi-solid-state film lithium battery presented an initial discharge specific capacity of 109.53 mAh·g−1 at 0.1C, with a capacity retention rate of 71.86 % after 100 cycles.

Local Structure in Disordered Melilite Revealed by Ultrahigh Field 71Ga and 139La Solid-State Nuclear Magnetic Resonance Spectroscopy.

Multinuclear Nuclear Magnetic Resonance (NMR) spectroscopy of quadrupolar nuclei at ultrahigh magnetic field provides compelling insight into the short-range structure in a family of fast oxide ion electrolytes with La1+xSr1-xGa3O7+0.5x melilite structure. The striking resolution enhancement in the solid-state 71Ga NMR spectra measured with the world's unique series connected hybrid magnet operating at 35.2 T distinctly resolves Ga sites in four- and five-fold coordination environments. Detection of five-coordinate Ga centers in the site-disordered La1.54Sr0.46Ga3O7.27 melilite is critical given that the GaO5 unit accommodates interstitial oxide ions and provides excellent transport properties. This work highlights the importance of ultrahigh magnetic fields for the detection of otherwise broad spectral features in systems containing quadrupolar nuclei and the potential of ensemble-based computational approaches for the interpretation of NMR data acquired for site-disordered materials.

Integration of One-Dimensional (1D) Lead-Free Perovskite Microbelts onto Silicon for Ultraviolet-Visible-Near-Infrared (UV-vis-NIR) Heterojunction Photodetectors.

Lead-free perovskites are considered to be candidates for next-generation photodetectors, because of their excellent charge carrier transport properties and low toxicity. However, their application in integrated circuits is hindered by their inadequate performance and size restrictions. To aim at the development of lead-free perovskite-integrated optoelectronic devices, a CsAg2I3/silicon (CAI/Si) heterojunction is presented in this work by using a spatial confinement growth method, where the in-plane growth of CAI microbelts with high-quality single-crystal characteristics is primarily dependent on the concentration of surrounding precursor solution. The fabricated photodetectors based on the CAI/Si heterojunctions exhibit a broad-spectrum detection capability in the ultraviolet-visible-near-infrared (UV-vis-NIR) range. In addition, the photodetectors show good photoelectric detection performance, including a maximum responsivity of 48.5 mA/W and detectivity of 1.13 × 1011 Jones, respectively. Besides, the photodetectors have a rapid response of 6.5/224 μs and good air stability for over 2 months. This work contributes a new idea to design next-generation optoelectronic devices with high integration density.

All-Inorganic Hydrothermally Processed Semitransparent Sb2S3 Solar Cells with CuSCN as the Hole Transport Layer.

An inorganic wide-bandgap hole transport layer (HTL), copper(I) thiocyanate (CuSCN), is employed in inorganic planar hydrothermally deposited Sb2S3 solar cells. With excellent hole transport properties and uniform compact morphology, the solution-processed CuSCN layer suppresses the leakage current and improves charge selectivity in an n-i-p-type solar cell structure. The device without the HTL (FTO/CdS/Sb2S3/Au) delivers a modest power conversion efficiency (PCE) of 1.54%, which increases to 2.46% with the introduction of CuSCN (FTO/CdS/Sb2S3/CuSCN/Au). This PCE is a significant improvement compared with the previous reports of planar Sb2S3 solar cells employing CuSCN. CuSCN is therefore a promising alternative to expensive and inherently unstable organic HTLs. In addition, CuSCN makes an excellent optically transparent (with average transmittance >90% in the visible region) and shunt-blocking HTL layer in pinhole-prone ultrathin (<100 nm) semitransparent absorber layers grown by green and facile hydrothermal deposition. A semitransparent device is fabricated using an ultrathin Au layer (∼10 nm) with a PCE of 2.13% and an average visible transmittance of 13.7%.

HBN‐Encapsulated Graphene Coupled to a Plasmonic Metasurface via 1D Electrodes for Photodetection Applications

It is shown here how encapsulated graphene devices can be laterally coupled to plasmonic metasurfaces via 1D edge contacts, preserving the high mobility of encapsulated graphene while enhancing optical coupling. The device is used for photodetection applications where high responsivities in the range of 100 A W−1 for most of the visible spectrum are reported. The device exhibits a photogating effect which is attributed to defect states in the encapsulating hBN layers. The results highlight a new configuration to couple graphene with plasmonic structures and points to a new type of device based on defect states and graphene's excellent transport properties to achieve photodetectors with ultrahigh responsivities.

Strain-Driven High Thermal Conductivity in Hexagonal Boron Phosphide Monolayer.

Two-dimensional graphenelike material, hexagonal boron phosphide (h-BP), is a promising candidate for electronic and optoelectronic devices because of its suitable band gap and high carrier mobility. Especially from the ultrahigh lattice thermal conductivity (κl), it exhibits great potential to solve the challenges of future thermal management applications. Here, the excellent lattice thermal transport properties of the h-BP monolayer are systematically analyzed at the atomic level based on the first-principles method. The results show that the ultrahigh κl value of the h-BP monolayer is attributed to its high phonon group velocity and long phonon lifetime and the strong phonon hydrodynamic effect. We further explore the influence of the tensile strain on the thermal transport properties of the h-BP monolayer. As the strain increases from 0 to 8%, the κl value shows a trend of first increasing and then decreasing due to the coeffect of strain-driven changes for phonon harmonicity and anharmonicity. Under a strain of 6%, the κl value of the h-BP monolayer is as high as 795 W/mK at 300 K, which is about 2.22 times larger than that of 357 W/mK without strain. Such a significant increase in the κl value is mainly due to the increased phonon group velocity and decreased Grüneisen parameter caused by strain. This work is helpful to understand the critical role of tensile strain in lattice thermal transport of two-dimensional graphenelike materials. It is conducive to promoting the thermal management application of the h-BP monolayer.

Surface Transfer Doping in MoO3-x/Hydrogenated Diamond Heterostructure.

Surface transfer doping is proposed to be a potential solution for doping diamond, which is hard to dope for applications in high-power electronics. While MoO3 is found to be an effective surface electron acceptor for hydrogen-terminated diamond with a negative electron affinity, the effects of commonly existing oxygen vacancies remain elusive. We have performed reactive molecular dynamics simulations to study the deposition of MoO3-x on a hydrogenated diamond (111) surface and used first-principles calculations based on density functional theory to investigate the electronic structures and charge transfer mechanisms. We find that MoO3-x is an effective surface electron acceptor and the spatial extent of doped holes in hydrogenated diamond is extended, promoting excellent transport properties. Charge transfer is found to monotonically decrease with the level of oxygen vacancy, providing guidance for engineering of the surface transfer doping process.