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1.
Adv Mater ; : e1906457, 2020 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-32048359

RESUMO

Thermoelectric (TE) research is not only a course of materials by discovery but also a seedbed of novel concepts and methodologies. Herein, the focus is on recent advances in three emerging paradigms: entropy engineering, phase-boundary mapping, and liquid-like TE materials in the context of thermodynamic routes. Specifically, entropy engineering is underpinned by the core effects of high-entropy alloys; the extended solubility limit, the tendency to form a high-symmetry crystal structure, severe lattice distortions, and sluggish diffusion processes afford large phase space for performance optimization, high electronic-band degeneracy, rich multiscale microstructures, and low lattice thermal conductivity toward higher-performance TE materials. Entropy engineering is successfully implemented in half-Huesler and IV-VI compounds. In Zintl phases and skutterudites, the efficacy of phase-boundary mapping is demonstrated through unraveling the profound relations among chemical compositions, mutual solubilities of constituent elements, phase instability, microstructures, and resulting TE properties at the operation temperatures. Attention is also given to liquid-like TE materials that exhibit lattice thermal conductivity at lower than the amorphous limit due to intensive mobile ion disorder and reduced vibrational entropy. To conclude, an outlook on the development of next-generation TE materials in line with these thermodynamic routes is given.

2.
ACS Appl Mater Interfaces ; 12(5): 6064-6073, 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-31912720

RESUMO

Interface interactions between perovskite materials and substrates are of great significance for the development of high-quality perovskite materials. Herein, we have successfully prepared Cs2AgBiBr6 double-perovskite films via a one-step spin-coating process and demonstrated a novel approach that modifies the surface of substrates with an ultrathin metal oxide (MOx) layer to promote the film quality and photoelectric performance. Characterization results strongly suggest that the improvement is attributed to the Bi-O interfacial interaction at substrate/perovskite interface. Benefiting from this interface interaction, the average grain size of Cs2AgBiBr6 films has remarkably risen up to ∼500 nm, which is nearly four times larger than the one directly deposited on a commercial fluorine-doped tin oxide substrate. Meanwhile, the pin hole surface area ratio has reduced from 2.61 to 0.60%. Furthermore, the corresponding photodetectors (PDs) have been fabricated and the performance has significantly improved owing to the enhanced Cs2AgBiBr6 film quality. The on-off ratio of the optimized PD has a boost of almost 10 times. In addition, the minimum detected irradiation has decreased from 9.7 × 10-8 to 1.9 × 10-9 W cm-2, as well as the maximum detectivity has increased from 3.3 × 1011 to 1.2 × 1013 Jones. These results suggest a feasible method for crystallization improvement of double-perovskite films and indicate promising promotion of photoelectric performance.

3.
Adv Mater ; 32(2): e1904634, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31736151

RESUMO

Organic semiconductors demonstrate several advantages over conventional inorganic materials for novel electronic and optoelectronic applications, including molecularly tunable properties, flexibility, low-cost, and facile device integration. However, before organic semiconductors can be used for the next-generation devices, such as ultrafast photodetectors (PDs), it is necessary to develop new materials that feature both high mobility and ambient stability. Toward this goal, a highly stable PD based on the organic single crystal [PtBr2 (5,5'-bis(CF3 CH2 OCH2 )-2,2'-bpy)] (or "Pt complex (1o)") is demonstrated as the active semiconductor channel-a material that features a lamellar molecular structure and high-quality, intraligand charge transfer. Benefitting from its unique crystal structure, the Pt-complex (1o) device exhibits a field-effect mobility of ≈0.45 cm2 V-1 s-1 without loss of significant performance under ambient conditions even after 40 days without encapsulation, as well as immersion in distilled water for a period of 24 h. Furthermore, the device features a maximum photoresponsivity of 1 × 103 A W-1 , a detectivity of 1.1 × 1012 cm Hz1/2 W-1 , and a record fast response/recovery time of 80/90 µs, which has never been previously achieved in other organic PDs. These findings strongly support and promote the use of the single-crystal Pt complex (1o) in next-generation organic optoelectronic devices.

4.
ACS Appl Mater Interfaces ; 11(47): 44179-44185, 2019 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-31682399

RESUMO

In recent days, 2-dimensional (2D) niobium disulfide (NbS2) with near-zero Gibbs free energy and superlative acid electrolyte stability has provoked a great deal of interest toward hydrogen evolution reaction (HER) electrocatalyst due to its active basal and edge sulfur sites. Herein, we developed a single step method for the direct deposition of 2D-NbS2 on high-aspect-ratio topographies of silicon nanowires (NWs) by chemical vapor deposition for the applications in HER electrocatalyst. The resultant 2D-NbS2 electrocatalyst demonstrates the HER overpotential of ∼74 mV vs RHE (reversible hydrogen electrode) @ 1 mA/cm2 under acidic conditions and stable for more than 20 h. More importantly, we developed the Si NWs array based photoelectrochemical water-splitting system with the direct deposition of 2D-NbS2 as HER catalyst. The resultant 2D-NbS2-Si NWs photocathode system demonstrates improved charge transfer characteristics at the Si-NbS2 interfaces that leads to an enhanced turn on potential (from 0.06 to 0.34 V vs RHE) with the current density of -28 mA/cm2 at the 0 V vs RHE. The results evidence the synergistic effect of 2D-NbS2 electrocatalysts that addresses poor surface kinetics of Si toward solar water electrolysis. Our comprehensive studies reveal NbS2 as a new class of photoelectrochemical cocatalyst for efficient solar HER performance by promoting the charge transfer process with prolonged acid stability.

5.
Nat Commun ; 10(1): 5282, 2019 11 21.
Artigo em Inglês | MEDLINE | ID: mdl-31754117

RESUMO

Despite III-V semiconductors demonstrating extraordinary solar-to-hydrogen (STH) conversion efficiencies, high cost and poor stability greatly impede their practical implementation in photoelectrochemical (PEC) water splitting applications. Here, we present a simple and efficient strategy for III-V-based photoelectrodes that functionally and spatially decouples the light harvesting component of the device from the electrolysis part that eliminates parasitic light absorption, reduces the cost, and enhances the stability without any compromise in efficiency. The monolithically integrated PEC cell was fabricated by an epitaxial lift-off and transfer of inversely grown InGaP/GaAs to a robust Ni-substrate and the resultant photoanode exhibits an STH efficiency of ~9% with stability ~150 h. Moreover, with the ability to access both sides of the device, we constructed a fully-integrated, unassisted-wireless "artificial leaf" system with an STH efficiency of ~6%. The excellent efficiency and stability achieved herein are attributed to the light harvesting/catalysis decoupling scheme, which concurrently improves the optical, electrical, and electrocatalytic characteristics.

6.
ACS Nano ; 13(11): 12621-12629, 2019 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-31613089

RESUMO

Hot carrier (HC) cooling is a critical photophysical process that significantly influences the optoelectronic performance of hybrid perovskite-based devices. The hot carrier extraction at the device interface is very challenging because of its ultrashort lifetime. Here, ultrafast transient reflectance spectroscopy measurements and time-domain ab initio calculations show how the dielectric constant of the organic spacers can control and slow the HC cooling dynamics in single-crystal 2D Ruddlesden-Popper hybrid perovskites. We find that (EA)2PbI4 (EA = HOC2H4NH3+) that correspond to a high dielectric constant organic spacer has a longer HC cooling time compared to that of (AP)2PbI4 (AP = HOC3H6NH3+) and (PEA)2PbI4 (PEA = C6H5C2H4NH3+). The slow HC relaxation process in the former case can be ascribed to a stronger screening of the Coulomb interactions, a small nonradiative internal conversion within the conduction bands, as well as a weak electron-phonon coupling. Our findings provide a strategy to prolong the hot carrier cooling time in low-dimensional hybrid perovskite materials by using organic spacers with reduced dielectric confinement.

7.
Adv Mater ; 31(48): e1903841, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31621970

RESUMO

A titanium carbide (Ti3 C2 Tx ) MXene is employed as an efficient solid support to host a nitrogen (N) and sulfur (S) coordinated ruthenium single atom (RuSA ) catalyst, which displays superior activity toward the hydrogen evolution reaction (HER). X-ray absorption fine structure spectroscopy and aberration corrected scanning transmission electron microscopy reveal the atomic dispersion of Ru on the Ti3 C2 Tx MXene support and the successful coordination of RuSA with the N and S species on the Ti3 C2 Tx MXene. The resultant RuSA -N-S-Ti3 C2 Tx catalyst exhibits a low overpotential of 76 mV to achieve the current density of 10 mA cm-2 . Furthermore, it is shown that integrating the RuSA -N-S-Ti3 C2 Tx catalyst on n+ np+ -Si photocathode enables photoelectrochemical hydrogen production with exceptionally high photocurrent density of 37.6 mA cm-2 that is higher than the reported precious Pt and other noble metals catalysts coupled to Si photocathodes. Density functional theory calculations suggest that RuSA coordinated with N and S sites on the Ti3 C2 Tx MXene support is the origin of this enhanced HER activity. This work would extend the possibility of using the MXene family as a solid support for the rational design of various single atom catalysts.

8.
J Phys Chem Lett ; : 5259-5264, 2019 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-31434482

RESUMO

By combining femtosecond transient reflectance (TR) spectroscopy and density functional theory (DFT) calculations, we reveal the impact of the length of the organic linkers (HOC2H4NH3+ and C6H5C2H4NH3+) and the number of inorganic layers (n = 1-3) on the hot carrier relaxation dynamics and coherent acoustic phonons in 2D Ruddlesden-Popper (RP) perovskites. We find that the interplay between the hot carriers and the coherent longitudinal acoustic phonons (CLAPs) can extend the oscillation of the TR kinetics to nanoseconds, which could lead to the higher thermal conductivities of 2D RP perovskites. Moreover, we find that the frequency of the acoustic phonon oscillation and phonon velocity decreases with the increasing number of layers due to the increased mass of the inorganic layers and reduced electron-phonon coupling. This finding provides new physical insights into how the organic spacers and number of inorganic layers control the overall carrier dynamics of 2D perovskite materials.

9.
Adv Mater ; 31(29): e1901300, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31148294

RESUMO

Memristive devices have been extensively demonstrated for applications in nonvolatile memory, computer logic, and biological synapses. Precise control of the conducting paths associated with the resistance switching in memristive devices is critical for optimizing their performances including ON/OFF ratios. Here, gate tunability and multidirectional switching can be implemented in memristors for modulating the conducting paths using hexagonal α-In2 Se3 , a semiconducting van der Waals ferroelectric material. The planar memristor based on in-plane (IP) polarization of α-In2 Se3 exhibits a pronounced switchable photocurrent, as well as gate tunability of the channel conductance, ferroelectric polarization, and resistance-switching ratio. The integration of vertical α-In2 Se3 memristors based on out-of-plane (OOP) polarization is demonstrated with a device density of 7.1 × 109 in.-2 and a resistance-switching ratio of well over 103 . A multidirectionally operated α-In2 Se3 memristor is also proposed, enabling the control of the OOP (or IP) resistance state directly by an IP (or OOP) programming pulse, which has not been achieved in other reported memristors. The remarkable behavior and diverse functionalities of these ferroelectric α-In2 Se3 memristors suggest opportunities for future logic circuits and complex neuromorphic computing.

10.
Opt Express ; 27(8): A352-A363, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-31052887

RESUMO

Photoelectrochemical water splitting is one of the viable approaches to produce clean hydrogen energy from water. Herein, we report MoS2/Si-heterojunction (HJ) photocathode for PEC H2 production. The MoS2/Si-HJ photocathode exhibits exceptional PEC H2 production performance with a maximum photocurrent density of 36.33 mA/cm2, open circuit potential of 0.5 V vs. RHE and achieves improved long-term stability up to 10 h of reaction time. The photocurrent density achieved by MoS2/Si-HJ photocathode is significantly higher than most of the MoS2 coupled Si-based photocathodes reported elsewhere, indicating excellent PEC H2 production performance.

11.
Small ; 15(19): e1901190, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30957964

RESUMO

Wearable electrochemical biosensors for sweat analysis present a promising means for noninvasive biomarker monitoring. However, sweat-based sensing still poses several challenges, including easy degradation of enzymes and biomaterials with repeated testing, limited detection range and sensitivity of enzyme-based biosensors caused by oxygen deficiency in sweat, and poor shelf life of sensors using all-in-one working electrodes patterned by traditional techniques (e.g., electrodeposition and screen printing). Herein, a stretchable, wearable, and modular multifunctional biosensor is developed, incorporating a novel MXene/Prussian blue (Ti3 C2 Tx /PB) composite designed for durable and sensitive detection of biomarkers (e.g., glucose and lactate) in sweat. A unique modular design enables a simple exchange of the specific sensing electrode to target the desired analytes. Furthermore, an implemented solid-liquid-air three-phase interface design leads to superior sensor performance and stability. Typical electrochemical sensitivities of 35.3 µA mm-1 cm-2 for glucose and 11.4 µA mm-1 cm-2 for lactate are achieved using artificial sweat. During in vitro perspiration monitoring of human subjects, the physiochemistry signals (glucose and lactate level) can be measured simultaneously with high sensitivity and good repeatability. This approach represents an important step toward the realization of ultrasensitive enzymatic wearable biosensors for personalized health monitoring.

12.
Angew Chem Int Ed Engl ; 58(43): 15206-15226, 2019 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-30785665

RESUMO

Hybrid organic-inorganic materials have been considered as a new candidate in the field of thermoelectric materials since the last decade owing to their great potential to enhance the thermoelectric performance by utilizing the low thermal conductivity of organic materials and the high Seebeck coefficient, and high electrical conductivity of inorganic materials. Herein, we provide an overview of interfacial engineering in the synthesis of various organic-inorganic thermoelectric hybrid materials, along with the dimensional design for tuning their thermoelectric properties. Interfacial effects are examined in terms of nanostructures, physical properties, and chemical doping between the inorganic and organic components. Several key factors which dictate the thermoelectric efficiency and performance of various electronic devices are also discussed, such as the thermal conductivity, electric transportation, electronic band structures, and band convergence of the hybrid materials.

13.
ACS Nano ; 13(2): 1168-1176, 2019 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-30588789

RESUMO

3D organic-inorganic hybrid halide perovskites have attracted great interest due to their impressive optoelectronic properties. Recently, the emergence of 2D layered hybrid perovskites, with their excellent and tunable optoelectronic behavior, has encouraged researchers to develop the next generation of optoelectronics based on these 2D materials. However, device fabrication methods of scalable patterning on both types of hybrid perovskites are still lacking as these materials are readily damaged by the organic solvents in standard lithographic processes. We conceived the orthogonal processing and patterning method: Chlorobenzene and hexane, which are orthogonal to hybrid perovskites, are utilized in modified electron beam lithography (EBL) processes to fabricate perovskite-based devices without compromising their electronic or optical characteristics. As a proof-of-concept, we used the orthogonal EBL technique to fabricate a 2D layered single-crystal (C6H5C2H4NH3)2PbI4 photodetector featuring nanoscale patterned electrodes and superior photodetection ability with responsivity of 5.4 mA/W and detectivity of 1.07 × 1013 cm Hz1/2/W. Such orthogonal processing and patterning methods are believed to fully enable the high-resolution, high-throughput fabrication of complex perovskite-based electronics in the near future.

14.
Nat Commun ; 9(1): 5196, 2018 12 05.
Artigo em Inglês | MEDLINE | ID: mdl-30518919

RESUMO

Two dimensional layered organic-inorganic hybrid perovskites (2D perovskites) are potential candidates for next generation photovoltaic device. Especially, the out-of-plane surface perpendicular to the superlattice plane of 2D perovskites (layer-edge surface) has presented several exotic behaviors, such as layer-edge states which are found to be crucial for improving the efficiency of 2D perovskite solar cells. However, fundamental research on transport properties of layer-edge surface is still absent. In this report, we observe the electronic and opto-electronic behavior in layer-edge device of 2D perovskites. The dark and photo currents are demonstrated to strongly depend on the crystallographic orientation in layer-edge device, and such anisotropic properties, together with photo response, are related to the thickness of inorganic layers. Finally, due to the abundant hydroxyl groups, water molecules are easy to condense on the layer-edge surface, and the conductance is extremely sensitive to the humidity environment, indicating a potential application of humidity sensor.

15.
Chem Sci ; 9(40): 7727-7745, 2018 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-30429982

RESUMO

Ever since two dimensional-transition (2D) metal dichalcogenides (TMDs) were discovered, their fascinating electronic properties have attracted a great deal of attention for harnessing them as critical components in novel electronic devices. 2D-TMDs endowed with an atomically thin structure, dangling bond-free nature, electrostatic integrity, and tunable wide band gaps enable low power consumption, low leakage, ambipolar transport, high mobility, superconductivity, robustness against short channel effects and tunneling in highly scaled devices. However, the progress of 2D-TMDs has been hampered by severe charge transport issues arising from undesired phenomena occurring at the surfaces and interfaces. Therefore, this review provides three distinct engineering strategies embodied with distinct innovative approaches to optimize both carrier injection and transport. First, contact engineering involves 2D-metal contacts and tunneling interlayers to overcome metal-induced interface states and the Fermi level pinning effect caused by low vacancy energy formation. Second, dielectric engineering covers high-k dielectrics, ionic liquids or 2D-insulators to screen scattering centers caused by carrier traps, imperfections and rough substrates, to finely tune the Fermi level across the band gap, and to provide dangling bond-free media. Third, material engineering focuses on charge transfer via substitutional, chemical and plasma doping to precisely modulate the carrier concentration and to passivate defects while preserving material integrity. Finally, we provide an outlook of the conceptual and technical achievements in 2D-TMDs to give a prospective view of the future development of highly scaled nanoelectronic devices.

16.
Adv Mater ; 30(46): e1804372, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30276878

RESUMO

Despite the remarkable progress of optoelectronic devices based on hybrid perovskites, there are significant drawbacks, which have largely hindered their development as an alternative of silicon. For instance, hybrid perovskites are well-known to suffer from moisture instability which leads to surface degradation. Nonetheless, the dependence of the surface effect on the moisture stability and optoelectronic properties of hybrid perovskites has not been fully investigated. In this work, the influence of the surface effect of 2D layered perovskites before and after mechanical exfoliation, representing rough and smooth surfaces of perovskite crystals, are studied. It is found that the smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current, which outperforms the rough perovskites by 23.6 times in terms of photodetectivity. The superior moisture stability of the smooth perovskites over the rough perovskites is demonstrated. Additionally, ethanolamine is employed as an organic linker of the 2D layered perovskite, which further improves the moisture stability. This work reveals the strong dependence of the surface conditions of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties, which are of utmost importance to the design of practical optoelectronic devices based on hybrid perovskite crystals.

17.
Adv Mater ; : e1801972, 2018 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-30019787

RESUMO

Optical resonance formed inside a nanocavity resonator can trap light within the active region and hence enhance light absorption, effectively boosting device or material performance in applications of solar cells, photodetectors (PDs), and photocatalysts. Complementing conventional circular and spherical structures, a new type of multishelled spherical resonant strategy is presented. Due to the resonance-enhanced absorption by multiple convex shells, ZnO nanoshell PDs show improved optoelectronic performance and omnidirectional detection of light at different incidence angles and polarization. In addition, the response and recovery speeds of these devices are improved (0.8 and 0.7 ms, respectively) up to three orders of magnitude faster than in previous reports because of the existence of junction barriers between the nanoshells. The general design principles behind these hollow ZnO nanoshells pave a new way to improve the performance of sophisticated nanophotonic devices.

18.
Adv Mater ; 30(28): e1705385, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29806141

RESUMO

Transforming thermal energy into electric energy and vice versa needs the decoupling of electrical transport from thermal transport. An innovative strategy is proposed by forming/disrupting electrically triggered conductive nanofilaments within semiconducting thin films to switch thermoelectric properties between two states without further material modification and manufacturing processes. It can also controllably adjust the degree of decoupling, providing a potential resolution and performance adjustability for heat/coldness control or power consumption reduction on demand.

19.
ACS Nano ; 12(5): 4976-4983, 2018 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-29694024

RESUMO

Piezoelectric materials have been widely used for sensors, actuators, electronics, and energy conversion. Two-dimensional (2D) ultrathin semiconductors, such as monolayer h-BN and MoS2 with their atom-level geometry, are currently emerging as new and attractive members of the piezoelectric family. However, their piezoelectric polarization is commonly limited to the in-plane direction of odd-number ultrathin layers, largely restricting their application in integrated nanoelectromechanical systems. Recently, theoretical calculations have predicted the existence of out-of-plane and in-plane piezoelectricity in monolayer α-In2Se3. Here, we experimentally report the coexistence of out-of-plane and in-plane piezoelectricity in monolayer to bulk α-In2Se3, attributed to their noncentrosymmetry originating from the hexagonal stacking. Specifically, the corresponding d33 piezoelectric coefficient of α-In2Se3 increases from 0.34 pm/V (monolayer) to 5.6 pm/V (bulk) without any odd-even effect. In addition, we also demonstrate a type of α-In2Se3-based flexible piezoelectric nanogenerator as an energy-harvesting cell and electronic skin. The out-of-plane and in-plane piezoelectricity in α-In2Se3 flakes offers an opportunity to enable both directional and nondirectional piezoelectric devices to be applicable for self-powered systems and adaptive and strain-tunable electronics/optoelectronics.

20.
Nat Commun ; 9(1): 1229, 2018 03 26.
Artigo em Inglês | MEDLINE | ID: mdl-29581419

RESUMO

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS2, WS2, MoSe2, and WSe2) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device.

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