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1.
Adv Mater ; 31(51): e1903448, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31682043

RESUMO

The emergence of cesium lead iodide (CsPbI3 ) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all-inorganic perovskite material, CsPbI3 :Br:InI3 , is prepared by defect engineering of CsPbI3 . This new perovskite retains the same bandgap as CsPbI3 , while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all-inorganic PSCs based on CsPbI3 :Br:InI3 and carbon electrode exhibit PCE and open-circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI3 can survive only a few days in air. The progress reported represents a major leap for all-inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.

2.
Nat Mater ; 18(12): 1273-1274, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31659290
3.
Small ; 15(39): e1901650, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31373741

RESUMO

Long-term instability and possible lead contamination are the two main issues limiting the widespread application of organic-inorganic lead halide perovskites. Here a facile and efficient solution-phase method is demonstrated to synthesize lead-free Cs2 SnX6 (X = Br, I) with a well-defined crystal structure, long-term stability, and high yield. Based on the systematic experimental data and first-principle simulation results, Cs2 SnX6 displays excellent stability against moisture, light, and high temperature, which can be ascribed to the unique vacancy-ordered defect-variant structure, stable chemical compositions with Sn4+ , as well as the lower formation enthalpy for Cs2 SnX6 . Additionally, photodetectors based on Cs2 SnI6 are also fabricated, which show excellent performance and stability. This study provides very useful insights into the development of lead-free double perovskites with high stability.

4.
Nat Commun ; 10(1): 2814, 2019 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-31249289

RESUMO

BiCuSeO oxyselenides are promising thermoelectric materials, yet further thermoelectric figure of merit ZT improvement is largely limited by the inferior electrical transport properties. The established literature on these materials shows only one power factor maximum upon carrier concentration optimization, which is typical for most thermoelectric semiconductors. Surprisingly, we found three power factor maxima when doping Bi with Pb. Based on our first-principles calculations, numerical modeling, and experimental investigation, we attribute the three maxima to the Fermi energy optimization, band convergence, and compositing effect due to in situ formed PbSe precipitates. Consequently, three ZT peaks of 0.9, 1.1, and 1.3 at 873 K are achieved for 4, 10, and 14 at.% Pb-doped samples, respectively, revealing the significance of complex electronic structure and multiple roles of Pb in BiCuSeO. The results establish an accurate band structure characterization for BiCuSeO and identify the role of band convergence and nanoprecipitation as the driving mechanism for high ZT.

5.
ACS Appl Mater Interfaces ; 11(13): 12777-12785, 2019 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-30854848

RESUMO

Metal-semiconductor contact has been a critical topic in the semiconductor industry because it influences device performance remarkably. Conventional metals have served as the major contact material in electronic and optoelectronic devices, but such a selection becomes increasingly inadequate for emerging novel materials such as two-dimensional (2D) materials. Deposited metals on semiconducting 2D channels usually form large resistance contacts due to the high Schottky barrier. A few approaches have been reported to reduce the contact resistance but they are not suitable for large-scale application or they cannot create a clean and sharp interface. In this study, a chemical vapor deposition (CVD) technique is introduced to produce large-area semiconducting 2D material (2H MoTe2) planarly contacted by its metallic phase (1T' MoTe2). We demonstrate the phase-controllable synthesis and systematic characterization of large-area MoTe2 films, including pure 2H phase or 1T' phase, and 2H/1T' in-plane heterostructure. Theoretical simulation shows a lower Schottky barrier in 2H/1T' junction than in Ti/2H contact, which is confirmed by electrical measurement. This one-step CVD method to synthesize large-area, seamless-bonding 2D lateral metal-semiconductor junction can improve the performance of 2D electronic and optoelectronic devices, paving the way for large-scale 2D integrated circuits.

6.
J Phys Condens Matter ; 31(18): 183002, 2019 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-30703759

RESUMO

Chemical bond hierarchy (CBH) depicts a unique structural type of solids, in which fractions of the materials are loosely bonded in a relatively rigid framework. The weak bonding in materials with CBH induces special atomic vibrational motions and has a significant influence on the thermoelectric transport properties. The architecture of compounds with CBH was first proposed by Slack in his 'phonon glass electron crystal' paradigm and has led to the discovery of numerous new thermoelectric compounds over the years. This review covers various types of thermoelectric materials with different levels of CBH, focusing on their lattice thermal conductivities (κ Ls). Caged compounds, with foreign impurities in the cages as the rattlers, are the first type of compounds stimulating the study of CBH. The fillers in both the clathrates and the filled skutterudites greatly reduce the κ L accompanied by abnormal temperature dependence. As reviewed herein, the reduced κ L is attributed to different mechanistic sources, i.e., the resonant scattering or the enhanced anharmonic phonon scatterings. Both may contribute to the κ L reductions. In recent years, more materials with different types of CBH have been discovered, some containing complex atomic clusters as the rattlers, and others having flowing atoms that cause multiple equilibrium sites and even liquid-like behaviors. All CBHs strongly interfere with the heat transport of the corresponding materials. Future perspectives and possible research directions for thermal transport in thermoelectric materials with CBH have also been summarized herein.

7.
Mol Med Rep ; 19(3): 2153-2163, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30628711

RESUMO

Hypoxia­induced apoptosis occurs in various diseases. Cobalt chloride (CoCl2) is a hypoxia mimic agent that is frequently used in studies investigating the mechanisms of hypoxia. Nuclear respiratory factor­1 (NRF­1) is a transcription factor with an important role in the expression of mitochondrial respiratory and mitochondria­associated genes. However, few studies have evaluated the effects of NRF­1 on apoptosis, particularly with regard to damage caused by CoCl2. In the present study, the role of NRF­1 in mediating CoCl2­induced apoptosis was investigated using cell viability analysis, flow cytometry, fluorescence imaging, western blotting analysis, energy metabolism analysis and reverse transcription­quantitative polymerase chain reaction. The present results revealed that the apoptosis caused by CoCl2 could be alleviated by NRF­1. Furthermore, overexpression of NRF­1 increased the expression of B­cell lymphoma­2, hypoxia inducible factor­1α and NRF­2. Also, cell damage induced by CoCl2 may be associated with depolarization of mitochondrial membrane potential, and NRF­1 suppressed this effect. Notably, the oxygen consumption rate (OCR) was reduced in CoCl2­treated cells, whereas overexpression of NRF­1 enhanced the OCR, suggesting that NRF­1 had protective effects. In summary, the present study demonstrated that NRF­1 protected against CoCl2­induced apoptosis, potentially by strengthening mitochondrial function to resist CoCl2­induced damage to H9C2 cells. The results of the present study provide a possible way for the investigation of myocardial diseases.


Assuntos
Apoptose/efeitos dos fármacos , Cobalto/farmacologia , Mitocôndrias/efeitos dos fármacos , Fator 1 Nuclear Respiratório/genética , Animais , Apoptose/genética , Hipóxia Celular/efeitos dos fármacos , Hipóxia Celular/genética , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Metabolismo Energético/efeitos dos fármacos , Metabolismo Energético/genética , Citometria de Fluxo , Regulação da Expressão Gênica/efeitos dos fármacos , Humanos , Mitocôndrias/patologia , Consumo de Oxigênio/efeitos dos fármacos , Ratos , Espécies Reativas de Oxigênio/metabolismo
8.
Nano Lett ; 19(1): 408-414, 2019 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-30532982

RESUMO

Single photon emission (SPE) by a solid-state source requires presence of a distinct two-level quantum system, usually provided by point defects. Here we note that a number of qualities offered by novel, two-dimensional materials, their all-surface openness and optical transparence, tighter quantum confinement, and reduced charge screening-are advantageous for achieving an ideal SPE. On the basis of first-principles calculations and point-group symmetry analysis, a strategy is proposed to design paramagnetic defect complex with reduced symmetry, meeting all the requirements for SPE: its electronic states are well isolated from the host material bands, belong to a majority spin eigenstate, and can be controllably excited by polarized light. The defect complex is thermodynamically stable and appears feasible for experimental realization to serve as an SPE-source, essential for quantum computing, with ReMoVS in MoS2 as one of the most practical candidates.

9.
ACS Appl Mater Interfaces ; 10(16): 13669-13674, 2018 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-29617559

RESUMO

We report a nonequilibrium fabrication method of n-type CoSb2.85Te0.15 skutterudites using selective laser melting (SLM) technology. A powder of CoSb2.85Te0.15 was prepared by self-propagating high-temperature synthesis (SHS) and served as the raw material for the SLM process. The effect of SLM processing parameters such as the laser power and scanning speed on the quality of the forming CoSb2.85Te0.15 thin layers was systematically analyzed, and the optimal processing window for SLM was determined. A brief postannealing at 450 °C for 4 h, following the SLM process, has resulted in a phase-pure CoSb2.85Te0.15 bulk material deposited on a Ti substrate. The Seebeck coefficient of the annealed SLM prepared bulk material is close to that of the sample prepared by the traditional sintering method, and its maximum ZT value reached 0.56 at 823 K. Moreover, a Ti-Co-Sb ternary compound transition layer of about 70 µm in thickness was found at a dense interface between CoSb2.85Te0.15 and the Ti substrate. The contact resistivity was measured as 37.1 µΩcm2. The results demonstrate that SLM, coupled with postannealing, can be used for fabrication of incongruently melting skutterudite compounds on heterogeneous substrates. This lays an important foundation for the follow-up research utilizing energy efficient SHS and SLM processes in rapid printing of thermoelectric modules.

10.
Adv Mater ; 30(1)2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29131432

RESUMO

Low-cost, environment-friendly aqueous Zn batteries have great potential for large-scale energy storage, but the intercalation of zinc ions in the cathode materials is challenging and complex. Herein, the critical role of structural H2 O on Zn2+ intercalation into bilayer V2 O5 ·nH2 O is demonstrated. The results suggest that the H2 O-solvated Zn2+ possesses largely reduced effective charge and thus reduced electrostatic interactions with the V2 O5 framework, effectively promoting its diffusion. Benefited from the "lubricating" effect, the aqueous Zn battery shows a specific energy of ≈144 Wh kg-1 at 0.3 A g-1 . Meanwhile, it can maintain an energy density of 90 Wh kg-1 at a high power density of 6.4 kW kg-1 (based on the cathode and 200% Zn anode), making it a promising candidate for high-performance, low-cost, safe, and environment-friendly energy-storage devices.

12.
J Phys Chem Lett ; 8(18): 4594-4599, 2017 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-28885849

RESUMO

Two-dimensional (2D) Dirac materials and boron sheets have attracted intensive interest recently. However, 2D Dirac materials remain rare and difficult to be realized experimentally, and 2D boron sheets generally have high dynamical instability. Stimulated by the experimental observation of Dirac cones in nongraphene-like ß12 boron sheets and based on the understanding of boron sheet electronic organization, we theoretically design new 2D Dirac materials ß12-XBeB5 (X = H, F, Cl) with high stability. We confirm ß12-HBeB5 as the global energy minimum among its 2D allotropes based on global structure search methods, a strong indication of its experimental feasibility. Our designed ß12-HBeB5 has not only a high Fermi velocity, but also a Dirac state very robust against extraordinary large tensile strains, an advantage for flexible electronics applications. Our work opens a new avenue to designing feasible 2D Dirac materials and stabilizing borophene sheets.

13.
Nature ; 549(7671): 247-251, 2017 09 13.
Artigo em Inglês | MEDLINE | ID: mdl-28905895

RESUMO

The ability to control chemical and physical structuring at the nanometre scale is important for developing high-performance thermoelectric materials. Progress in this area has been achieved mainly by enhancing phonon scattering and consequently decreasing the thermal conductivity of the lattice through the design of either interface structures at nanometre or mesoscopic length scales or multiscale hierarchical architectures. A nanostructuring approach that enables electron transport as well as phonon transport to be manipulated could potentially lead to further enhancements in thermoelectric performance. Here we show that by embedding nanoparticles of a soft magnetic material in a thermoelectric matrix we achieve dual control of phonon- and electron-transport properties. The properties of the nanoparticles-in particular, their superparamagnetic behaviour (in which the nanoparticles can be magnetized similarly to a paramagnet under an external magnetic field)-lead to three kinds of thermoelectromagnetic effect: charge transfer from the magnetic inclusions to the matrix; multiple scattering of electrons by superparamagnetic fluctuations; and enhanced phonon scattering as a result of both the magnetic fluctuations and the nanostructures themselves. We show that together these effects can effectively manipulate electron and phonon transport at nanometre and mesoscopic length scales and thereby improve the thermoelectric performance of the resulting nanocomposites.

14.
Adv Mater ; 29(42)2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28961340

RESUMO

High-performance thermoelectric materials require ultralow lattice thermal conductivity typically through either shortening the phonon mean free path or reducing the specific heat. Beyond these two approaches, a new unique, simple, yet ultrafast solid-state explosive reaction is proposed to fabricate nanoporous bulk thermoelectric materials with well-controlled pore sizes and distributions to suppress thermal conductivity. By investigating a wide variety of functional materials, general criteria for solid-state explosive reactions are built upon both thermodynamics and kinetics, and then successfully used to tailor material's microstructures and porosity. A drastic decrease in lattice thermal conductivity down below the minimum value of the fully densified materials and enhancement in thermoelectric figure of merit are achieved in porous bulk materials. This work demonstrates that controlling materials' porosity is a very effective strategy and is easy to be combined with other approaches for optimizing thermoelectric performance.

15.
Nano Lett ; 17(7): 4109-4115, 2017 07 12.
Artigo em Inglês | MEDLINE | ID: mdl-28585826

RESUMO

Transition metal dichalcogenides, such as MoS2 and VSe2 have emerged as promising catalysts for the hydrogen evolution reaction (HER). Substantial work has been devoted to optimizing the catalytic performance by constructing materials with specific phases and morphologies. However, the optimization of adsorption/desorption process in HER is rare. Herein, we concentrate on tuning the dynamics of the adsorption process in HER by applying a back gate voltage to the pristine VSe2 nanosheet. The back gate voltage induces the redistribution of the ions at the electrolyte-VSe2 nanosheet interface, which realizes the enhanced electron transport process and facilitates the rate-limiting step (discharge process) under HER conditions. A considerable low onset overpotential of 70 mV is achieved in VSe2 nanosheets without any chemical treatment. Such unexpected improvement is attributed to the field tuned adsorption-dynamics of VSe2 nanosheet, which is demonstrated by the greatly optimized charge transfer resistance (from 1.03 to 0.15 MΩ) and time constant of the adsorption process (from 2.5 × 10-3 to 5.0 × 10-4 s). Our results demonstrate enhanced catalysis performance in the VSe2 nanosheet by tuning the adsorption dynamics with a back gate, which provides new directions for improving the catalytic activity of non-noble materials.

16.
Diabetes Obes Metab ; 19(8): 1071-1077, 2017 08.
Artigo em Inglês | MEDLINE | ID: mdl-28191913

RESUMO

AIMS: To assess the effect of LY2409021 on systolic blood pressure (SBP) in patients with type 2 diabetes. MATERIALS AND METHODS: This 6-week, randomized, crossover study evaluated the effects of once-daily administration of LY2409021 20 mg vs those of placebo on SBP, diastolic BP (DBP), and mean arterial pressure (MAP) using 24-hour ambulatory BP monitoring (ABPM) in 270 subjects treated with diet/exercise ± metformin. Other measures included changes in glycemic control, serum lipids, and hepatic safety markers. RESULTS: At 6 weeks of LY2409021 treatment, 24-hour mean SBP was increased, with a least squares mean (LSM) difference of 2.26 mm Hg vs placebo (95% CI: 1.11, 3.40; P < .001). The 24-hour mean DBP and MAP also increased, with LSM differences of 1.37 mm Hg (95% CI: 0.66, 2.08; P < .001) and 1.67 mm Hg (95% CI: 0.86, 2.47; P < .001) vs placebo, respectively. At week 6, LY2409021 treatment reduced glycated hemoglobin (HbA1c) levels, with an LSM difference of -0.49% (-5.4 mmol/mol) (95% CI: -0.56%, -0.42% [-6.1, -4.6 mmol/mol]; P < .001) vs placebo. Mean HbA1c at baseline was 7.3% (56 mmol/mol). Small but significant changes in serum lipid and aminotransferase levels were observed with LY2409021 treatment (all P < .05 vs placebo). CONCLUSIONS: Statistically significant increases in BP, MAP and serum lipid levels were observed with LY2409021 treatment at a dose that lowered HbA1c and glucose levels. These effects may limit the clinical utility of LY2409021 as a chronic treatment for type 2 diabetes.


Assuntos
Compostos de Bifenilo/efeitos adversos , Diabetes Mellitus Tipo 2/tratamento farmacológico , Angiopatias Diabéticas/induzido quimicamente , Hipertensão/induzido quimicamente , Hipoglicemiantes/efeitos adversos , Receptores de Glucagon/antagonistas & inibidores , Administração Oral , Idoso , Biomarcadores/sangue , Compostos de Bifenilo/administração & dosagem , Compostos de Bifenilo/uso terapêutico , Pressão Sanguínea/efeitos dos fármacos , Monitorização Ambulatorial da Pressão Arterial , Estudos Cross-Over , Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/complicações , Método Duplo-Cego , Feminino , Seguimentos , Hemoglobina A Glicada/análise , Humanos , Hiperglicemia/prevenção & controle , Hiperlipidemias/induzido quimicamente , Hiperlipidemias/complicações , Hipertensão/complicações , Hipoglicemia/induzido quimicamente , Hipoglicemia/prevenção & controle , Hipoglicemiantes/administração & dosagem , Hipoglicemiantes/uso terapêutico , Masculino , Pessoa de Meia-Idade
17.
J Am Chem Soc ; 139(7): 2630-2638, 2017 02 22.
Artigo em Inglês | MEDLINE | ID: mdl-28112933

RESUMO

Hybrid organic-inorganic halide perovskites with the prototype material of CH3NH3PbI3 have recently attracted intense interest as low-cost and high-performance photovoltaic absorbers. Despite the high power conversion efficiency exceeding 20% achieved by their solar cells, two key issues-the poor device stabilities associated with their intrinsic material instability and the toxicity due to water-soluble Pb2+-need to be resolved before large-scale commercialization. Here, we address these issues by exploiting the strategy of cation-transmutation to design stable inorganic Pb-free halide perovskites for solar cells. The idea is to convert two divalent Pb2+ ions into one monovalent M+ and one trivalent M3+ ions, forming a rich class of quaternary halides in double-perovskite structure. We find through first-principles calculations this class of materials have good phase stability against decomposition and wide-range tunable optoelectronic properties. With photovoltaic-functionality-directed materials screening, we identify 11 optimal materials with intrinsic thermodynamic stability, suitable band gaps, small carrier effective masses, and low excitons binding energies as promising candidates to replace Pb-based photovoltaic absorbers in perovskite solar cells. The chemical trends of phase stabilities and electronic properties are also established for this class of materials, offering useful guidance for the development of perovskite solar cells fabricated with them.

18.
Nat Nanotechnol ; 12(1): 55-60, 2017 01.
Artigo em Inglês | MEDLINE | ID: mdl-27723733

RESUMO

How to suppress the performance deterioration of thermoelectric materials in the intrinsic excitation region remains a key challenge. The magnetic transition of permanent magnet nanoparticles from ferromagnetism to paramagnetism provides an effective approach to finding the solution to this challenge. Here, we have designed and prepared magnetic nanocomposite thermoelectric materials consisting of BaFe12O19 nanoparticles and Ba0.3In0.3Co4Sb12 matrix. It was found that the electrical transport behaviours of the nanocomposites are controlled by the magnetic transition of BaFe12O19 nanoparticles from ferromagnetism to paramagnetism. BaFe12O19 nanoparticles trap electrons below the Curie temperature (TC) and release the trapped electrons above the TC, playing an 'electron repository' role in maintaining high figure of merit ZT. BaFe12O19 nanoparticles produce two types of magnetoelectric effect-electron spiral motion and magnon-drag thermopower-as well as enhancing phonon scattering. Our work demonstrates that the performance deterioration of thermoelectric materials in the intrinsic excitation region can be suppressed through the magnetic transition of permanent magnet nanoparticles.

19.
J Chem Phys ; 144(19): 194502, 2016 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-27208953

RESUMO

Quite a few interesting but controversial phenomena, such as simple chemical composition but complex structures, well-defined high-temperature cubic structure but intriguing phase transition, coexist in Cu2Se, originating from the relatively rigid Se framework and "soft" Cu sublattice. However, the electrical transport properties are almost uninfluenced by such complex substructures, which make Cu2Se a promising high-performance thermoelectric compound with extremely low thermal conductivity and good power factor. Our work reveals that the crystal structure of Cu2Se at the temperature below the phase-transition point (∼400 K) should have a group of candidate structures that all contain a Se-dominated face-centered-cubic-like layered framework but nearly random site occupancy of atoms from the "soft" Cu sublattice. The energy differences among those structures are very low, implying the coexistence of various structures and thus an intrinsic structure complexity with a Se-based framework. Detailed analyses indicate that observed structures should be a random stacking of those representative structure units. The transition energy barriers between each two of those structures are estimated to be zero, leading to a polymorphous phase transition of Cu2Se at increasing temperature. Those are all consistent with experimental observations.

20.
Sci Rep ; 6: 21712, 2016 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-26880667

RESUMO

Non-radiative recombination plays an important role in the performance of optoelectronic semiconductor devices such as solar cells and light-emitting diodes. Most textbook examples assume that the recombination process occurs through a single defect level, where one electron and one hole are captured and recombined. Based on this simple picture, conventional wisdom is that only defect levels near the center of the bandgap can be effective recombination centers. Here, we present a new two-level recombination mechanism: first, one type of carrier is captured through a defect level forming a metastable state; then the local defect configuration rapidly changes to a stable state, where the other type of carrier is captured and recombined through another defect level. This novel mechanism is applied to the recombination center Te(cd)(2+) in CdTe. We show that this two-level process can significantly increase the recombination rate (by three orders of magnitude) in agreement with experiments. We expect that this two-level recombination process can exist in a wide range of semiconductors, so its effect should be carefully examined in characterizing optoelectronic materials.

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