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1.
    
Surface passivation is increasingly one of the most prominent strategies to promote the efficiency and stability of perovskite solar cells (PSCs). However, most passivation molecules hinder carrier extraction due to poorly conductive aggregation between perovskite surface and carrier transportation layer. Herein, a novel molecule: p‐phenyl dimethylammonium iodide (PDMAI) with ammonium group on both terminals is introduced, and its passivation effect is systematically investigated. It is found that PDMAI can mitigate defects at the surface and promote carrier extraction from perovskite to the hole transporting layer, leading to a lift of open‐circuit voltage of 40 mV. Profiting from superior PDMAI passivation, the average efficiency of PSCs has been elevated from 19.69% to 20.99%. As demonstrated with density functional theory calculations, PDMAI probably tends to anchor onto the perovskite surface with both ? NH3I tails, and enhances the adhesion and contact to perovskite layer. The exposed hydrophobic aryl core protects perovskite against detrimental environmental factors. In addition, the alkyl component between aryl and ammonium groups is demonstrated to be essentially vital in triggering passivation function, which offers the guidance for the design of passivation molecules.  相似文献   

2.
    
Stable oxide topological insulators (TIs) have been sought for years, but none have been found; whereas heavier (selenides, tellurides) chalcogenides can be TIs. The basic contradiction between topological insulation and thermodynamic stability is pointed out, offering a narrow window of opportunity. The electronic motif is first identified and can achieve topological band inversion in ABO3 as a lone‐pair, electron‐rich B atom (e.g., Te, I, Bi) at the octahedral site. Then, twelve ABO3 compounds are designed in the assumed cubic perovskite structure, which satisfy this electronic motif and are indeed found by density function theory calculations to be TIs. Next, it is illustrated that poorly screened ionic oxides with large inversion energies undergo energy‐lowering atomic distortions that destabilize the cubic TI phase and remove band inversion. The coexistence windows of topological band inversion and structure stability can nevertheless be expanded under moderate pressures (15 and 35 GPa, respectively, for BaTeO3 and RbIO3). This study traces the principles needed to design stable oxide topological insulators at ambient pressures as a) a search for oxides with small inversion energies; b) design of large inversion‐energy oxide TIs that can be stabilized by pressure; and c) a search for covalent oxides where TI‐removing atomic displacements can be effectively screened out.  相似文献   

3.
    
Considering the promising electrochemical performance of the recently reported pyrophosphate family in lithium ion batteries as well as the increasing importance of sodium ion batteries (SIBs) for emerging large‐scale applications, here, the crystal structure, electrochemical properties, and thermal stability of Na2FeP2O7, the first example ever reported in the pyrophosphate family for SIBs, are investigated. Na2FeP2O7 maintains well‐defined channel structures (triclinic framework under the P1 space group) and exhibits a reversible capacity of ≈90 mAh g?1 with good cycling performance. Both quasi‐equilibrium measurements and first‐principles calculations consistently indicate that Na2FeP2O7 undergoes two kinds of reactions over the entire voltage range of 2.0–4.5 V (vs Na/Na+): a single‐phase reaction around 2.5 V and a series of two‐phase reactions in the voltage range of 3.0–3.25 V. Na2FeP2O7 shows excellent thermal stability up to 500 °C, even in the partially desodiated state (NaFeP2O7), which suggests its safe character, a property that is very critical for large‐scale battery applications.  相似文献   

4.
Self‐assembled monolayers (SAMs) are fundamental building blocks of molecular electronics and find numerous applications in organic (opto)electronic devices. Their properties are decisively determined by their response to electric fields, which are either applied externally (e.g., when biasing devices) or originate from within the monolayer itself in case it consists of dipolar molecules (which are used to tune charge‐injection barriers). This response is typically described by the dielectric constant of the monolayer. In this work it is explicitly show that there is no “general” dielectric constant that simultaneously applies to both cases. This is first derived on the basis of density‐functional theory (DFT) calculations for substituted biphenyl‐thiol SAMs at varying packing densities. Depolarization effects, which play a crucial role for the dielectric properties of the monolayers, are subsequently analyzed on the basis of packing‐dependent charge rearrangements. Finally, the DFT results are rationalized using an electrostatic model. In this context, the importance of finite‐size effects is highlighted and a connection between the macroscopic dielectric properties and the molecular polarizability is established providing a monolayer equivalent to the Clausius–Mossotti relationship. This allows deriving general trends for the packing‐density dependent dielectric response of monolayers to both external and internal electric fields.  相似文献   

5.
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6.
    
Exploring highly efficient and inexpensive hydrogen evolution reaction (HER) electrocatalysts for various electrochemical energy conversion technologies is actively encouraged. Herein, a 3D urchin‐like Mo‐W18O49 nanostructure as an efficient HER catalyst is reported for the first time. The obtained Mo‐W18O49 catalyst exhibits excellent electrocatalytic activity toward HER with small onset potential and Tafel slope. The prepared Mo‐W18O49 electrode shows excellent durability after a long period. Density functional theory calculations reveal that the remarkably enhanced performance of Mo‐W18O49 can be due to the ability of Mo dopant to increase the number of active sites, leading to optimal hydrogen adsorption on the active sites because of the electronic and geometric modulation. In addition, the urchin‐like 3D morphology with a high surface area and abundant 1D nanowires promotes electron transfer, thereby ensuring fast interfacial charge transfer to improve electrocatalytic reactions. All these experimental and theoretical results clearly reveal that Mo‐W18O49 intrinsically improves HER activity and thus has potential applications in water splitting.  相似文献   

7.
    
Accurate complex dielectric functions are critical to accelerate the development of rationally designed metal alloy systems for nanophotonic applications, and to thereby unlock the potential of alloying for tailoring nanostructure optical properties. To date, however, accurate alloy dielectric functions are widely lacking. Here, a time‐dependent density‐functional theory computational framework is employed to compute a comprehensive binary alloy dielectric function library for the late transition metals most commonly employed in plasmonics (Ag, Au, Cu, Pd, Pt). Excellent agreement is found between electrodynamic simulations based on these dielectric functions and selected alloy systems experimentally scrutinized in 10 at% composition intervals. Furthermore, it is demonstrated that the dielectric functions can vary in very non‐linear fashion with composition, which paves the way for non‐trivial optical response optimization by tailoring material composition. The presented dielectric function library is thus a key resource for the development of alloy nanomaterials for applications in nanophotonics, optical sensors, and photocatalysis.  相似文献   

8.
    
Considering the high surface defects of polycrystalline perovskite, chemical passivation is effective in reducing defects-associated carrier losses. However, challenges remain in promoting passivation effects without compromising the carrier-extraction yield at the perovskite interfaces. In this work, interlayer molecules functionalized with different side groups are rationally designed to investigate the correlation between defect-passivation strength and interfacial carrier dynamics.  It is revealed that Cl-grafted molecules impose destructive effects on the perovskite structure due to its lower electronegativity and mismatched spatial configuration. The introduction of cyanide (CN) as a side group in molecules also leads to perovskite deformation and unfavorable hole collection. After the molecular optimization, the incorporation of carbonyl (C═O) as the side group (TPA─O) simultaneously promotes the carrier-collection yield as well as sufficient defect passivation. As a consequence, the devices based on TPA─O yield a champion PCE of 23.25%, along with remarkable stability by remaining above 88.5% of initial performance after 2544 h storage in the air. Furthermore, this interlayer based on TAP─O enables flexible devices to achieve a high efficiency of 21.81% and promising mechanical stability. This work paves the way for further improving the performance of perovskite solar cells.  相似文献   

9.
    
Currently, known topological insulators (TIs) are limited to narrow gap compounds incorporating heavy elements, thus severely limiting the material pool available for such applications. It is shown via first‐principle calculations that a heterovalent superlattice made of common semiconductor building blocks can transform its non‐TI components into a topological nanostructure, illustrated by III–V/II–VI superlattice InSb/CdTe. The heterovalent nature of such interfaces sets up, in the absence of interfacial atomic exchange, a natural internal electric field that along with the quantum confinement leads to band inversion, transforming these semiconductors into a topological phase while also forming a giant Rashba spin splitting. The relationship between the interfacial stability and the topological transition is revealed, finding a “window of opportunity” where both conditions can be optimized. Once a critical InSb layer thickness above ≈1.5 nm is reached, both [111] and [100] superlattices have a relative energy of 1.7–9.5 meV Å–2, higher than that of the atomically exchanged interface and an excitation gap up to ≈150 meV, affording room‐temperature quantum spin Hall effect in semiconductor superlattices. The understanding gained from this study could broaden the current, rather restricted repertoire of functionalities available from individual compounds by creating next‐generation superstructured functional materials.  相似文献   

10.
    
Multi-heteroatoms co-doped carbon coating can significantly enhance the electronic conductivity and mass transfer rate of the electrode materials due to the synergistic effect. In this study N, S co-doped carbon coating is introduced on the surface of niobium oxides (GNO@NSC) by using a convenient thiourea evaporation method. Theory calculations and experimental results confirm the synergistic effect of N, S co-doping in GNO@NSC composite. N, S co-doping not only enlarges the layer distance of the carbon materials but also leads to more activation sites for lithium storage; meanwhile, the introduction of the co-doping carbon layer on GNO significantly enhances the bonding interaction with GNO, leading to excellent structural stability and conductivity of the composite. As a result, the GNO@NSC composite possesses excellent structural reversibility, a large specific capacity, and high-rate performance. GNO@NSC nanowires deliver a highly reversible capacity of 288 mAh g–1 and display excellent cycling stability, and its capacity retention is 78.9% after 6000 cycles at a high current density of 1 A g–1. This study reveals the functional mechanism of N, S co-doped carbon coating and the origin of performance improvement of niobium oxides, which can be used for reference to design and develop relevant materials.  相似文献   

11.
    
The band‐gap engineering of doped ZnO nanowires is of the utmost importance for tunable light‐emitting‐diode (LED) applications. A combined experimental and density‐functional theory (DFT) study of ZnO doping by copper (Zn2+ substitution by Cu2+) is presented. ZnO:Cu nanowires are epitaxially grown on magnesium‐doped p‐GaN by electrochemical deposition. The heterojunction is integrated into a LED structure. Efficient charge injection and radiative recombination in the Cu‐doped ZnO nanowires are demonstrated. In the devices, the nanowires act as the light emitters. At room temperature, Cu‐doped ZnO LEDs exhibit low‐threshold emission voltage and electroluminescence emission shifted from the ultraviolet to violet–blue spectral region compared to pure ZnO LEDs. The emission wavelength can be tuned by changing the copper content in the ZnO nanoemitters. The shift is explained by DFT calculations with the appearance of copper d states in the ZnO band‐gap and subsequent gap reduction upon doping. The presented data demonstrate the possibility to tune the band‐gap of ZnO nanowire emitters by copper doping for nano‐LEDs.  相似文献   

12.
In this article, density functional theory (DFT) based on generalized gradient approximation (GGA) and GGA+U, U is Hubbard term, is used to study the electronic properties of CdS doped with different dopants (Cr, Mn). The calculations are carried out for Mn-doped CdS, Cr-doped CdS, and co-doping of Mn/Cr in CdS simultaneously. It is found that hopping of electrons is possible with Cr:CdS and Mn:Cr:CdS while Mn:CdS does not allow the hopping of electrons. Moreover, double exchange interactions are observed in Cr:CdS and d-d super-exchange interactions are observed in Mn:CdS. Now the problem becomes interesting when one magnetic ion (Cr) supporting double exchange interactions and another ion (Mn) supporting d-d super-exchange interactions are doped simultaneously in the same system (CdS). The co-doped CdS is more stable even at high Curie temperature due to p-d double exchange interactions and d-d super exchange interactions. Furthermore, the Cr-3d and Mn-3d states present in-between the band gap are responsible for inner shell transitions and hence for optical properties. Therefore, the co-doped system is taken into account to enhance its applications in the field of spintronic and magneto-optical devices.  相似文献   

13.
    
Area-selective atomic layer deposition (AS-ALD) offers tremendous advantages in comparison with conventional top-down patterning processes that atomic-level selective deposition can achieve in a bottom-up fashion on pre-defined areas in multi-dimensional structures. In this work, a method for exploiting substrate-dependent selectivity of aminosilane precursors for oxides versus nitrides through chemo-selective adsorption is reported. For this purpose, AS-ALD of SiO2 thin films on SiO2 substrates rather than on SiN substrates are investigated. Theoretical screening using density functional theory (DFT) calculations are performed to identify Si precursors that maximize adsorption selectivity; results indicate that di(isopropylamino)silane (DIPAS) has the potential to function as a highly chemo-selective precursor. Application of this precursor to SiN and SiO2 substrates result in inherent deposition selectivity of ≈4 nm without the aid of surface inhibitors. Furthermore, deposition selectivity is enhanced using an ALD-etch supercycle in which an etching step inserts periodically after a certain number of ALD SiO2 cycles. Thereby, enlarged deposition selectivity greater than ≈10 nm is successfully achieved on both blanket- and SiO2/SiN-patterned substrates. Finally, area-selective SiO2 thin films over 4–5 nm are demonstrated inside 3D nanostructure. This approach for performing inherent AS-ALD expands the potential utility of bottom-up nanofabrication techniques for next-generation nanoelectronic applications.  相似文献   

14.
    
Carrier mobility is a key parameter for the operation of electronic devices as it determines the ON state current and switching speed/frequency response of transistors. 2D phosphorene is considered as a potential candidate for field‐effect transistors due to its high mobility. Here it is proposed to further enhance the carrier mobility of phosphorene and device performance via strain engineering. A systematic ab initio investigation on the anisotropic electronic structure of few‐layer phosphorene reveals that the monolayer under 7.5–10% strain along zigzag direction shows an exceptional carrier mobility of ≈106 cm2 V−1 s−1, which is 10 times higher than the strain‐free case. The simulated device performance shows that strain‐engineered phosphorene–based field‐effect transistors demonstrate a cut‐off frequency of ≈1.14 THz with a gate length of 1.0 micron and 112 THz with a sub‐10 nm gate length.  相似文献   

15.
The uses of self‐assembled monolayers (SAMs) of dipolar molecules or of adsorbed molecular acceptors on electrode materials are common strategies to increase their work function, thereby facilitating hole injection into an organic semiconductor deposited on top. Here it is shown that a combination of both approaches can surpass the performance of the individual ones. By combined experimental and theoretical methods it is revealed that in a three‐component system, consisting of an indium‐tin‐oxide (ITO) electrode, a carbazole‐based phosphonic acid SAM, and a molecular acceptor layer on top of the SAM, charge transfer occurs from the ITO through the SAM to the acceptor layer, resulting in an electrostatic field drop over the charge‐neutral SAM. This result is in contrast to common expectations of either p‐doping the carbazole of the SAM or charge transfer complex formation between the carbazole and the acceptor molecules. A high work function of 5.7 eV is achieved with this combined system; even higher values may be accessible by exploiting the fundamental charge redistribution mechanisms identified here with other material combinations.  相似文献   

16.
制备了Al/Al_2O_3/InP金属氧化物半导体(MOS)电容,分别采用氮等离子体钝化工艺和硫钝化工艺处理InP表面。研究了在150、200和300 K温度下样品的界面特性和漏电特性。实验结果表明,硫钝化工艺能够有效地降低快界面态,在150 K下测试得到最小界面态密度为1.6×1010 cm-2·eV-1。与硫钝化工艺对比,随测试温度升高,氮等离子体钝化工艺可以有效减少边界陷阱,边界陷阱密度从1.1×1012 cm-2·V-1降低至5.9×1011 cm-2·V-1,同时减少了陷阱辅助隧穿电流。氮等离子体钝化工艺和硫钝化工艺分别在降低边界陷阱和快界面态方面有一定优势,为改善器件界面的可靠性提供了依据。  相似文献   

17.
    
Three new heteroleptic iridium complexes that combine two approaches, one leading to a high stability and the other yielding a high luminescence efficiency, are presented. All complexes contain a phenyl group at the 6‐position of the neutral bpy ligand, which holds an additional, increasingly bulky substituent on the 4‐position. The phenyl group allows for intramolecular π–π stacking, which renders the complex more stable and yields long‐living light‐emitting electrochemical cells (LECs). The additional substituent increases the intersite distance between the cations in the film, reducing the quenching of the excitons, and should improve the efficiency of the LECs. Density functional theory calculations indicate that the three complexes have the desired π–π intramolecular interactions between the pendant phenyl ring of the bpy ligand and the phenyl ring of one of the ppy ligands in the ground and the excited states. The photoluminescence quantum efficiency of concentrated films of the complexes improves with the increasing size of the bulky groups indicating that the adopted strategy for improving the efficiency is successful. Indeed, LEC devices employing these complexes as the primary active component show shorter turn‐on times, higher efficiencies and luminances, and, surprisingly, also demonstrate longer device stabilities.  相似文献   

18.
    
Semiconductor photocatalysis technology has aroused great interest in photocatalytic degradation, but it suffers from the drawbacks of fast electron‐hole recombination and unsatisfactory degradation efficiency. Herein, a novel photocatalyst Ag3PO4@NC with excellent photocatalytic activity is successfully prepared, characterized, and evaluated for the efficient removal of organic pollutants. After visible light irradiation for 5, 8, and 12 min, the photocatalytic degradation efficiency of norfloxacin, diclofenac, and phenol on the composite catalyst reaches 100%, and the apparent rate constant of which is 19.2, 48.7, and 23.2 times than that of the pure Ag3PO4, respectively. The density functional theory calculation results indicate that there is a built‐in electric field from N‐doped carbon (NC) to Ag3PO4 at the interface of the composite catalyst. Driven by the electric field, the photogenerated electrons of Ag3PO4 can be readily transferred to the NC, leading to the efficient separation of photogenerated carriers and the significant improvement of the catalytic performance. The results of radical trapping experiments and electron spin resonance analysis show that photogenerated holes and O2? play an important role in the photodegradation process. This work provides a universal strategy of construction built‐in electric field through coupling with NC to improve the photocatalytic performance of photocatalysts.  相似文献   

19.
    
In the architecture described, cuprous oxide (Cu2O) is tamed to be highly (111) plane oriented nanostructure through adjusting the deposition postulate by glancing angle deposition technique. In the controlled atmosphere oxygen vacancy is introduced into the Cu2O crystal subsequently fostering an impurity energy state (Eim) close to the conduction band. Our model of Cu2O electronic structure using density functional theory suggests that oxygen vacancies enhance the electron donating ability because of unshared d‐electrons of Cu atoms (nearest to the vacancy site), allowing to pin the work function energy level around 0.28 eV compared to the bulk. This result is also complemented by Kelvin probe force microscopy analysis and X‐ray photoelectron spectroscopy method. Oxygen vacancy in Cu2O (Cu2O1‐δ) exhibits promising field emission properties with interesting field electron tunneling behavior at different applied fields. The films show very low turn‐on and threshold voltages of value 0.8 and 2.4 V μm?1 respectively which is influenced by the oxygen vacancy. Here, a correlation between the work function modulation due to the oxygen vacancy and enhancement of field emission of Cu2O1–δ nanostructure is demonstrated. This work reveals a promising new vision for Cu2O as a low power field emitter device.  相似文献   

20.
    
By means of theory and experiments, the application capability of nickel ditelluride (NiTe2) transition‐metal dichalcogenide in catalysis and nanoelectronics is assessed. The Te surface termination forms a TeO2 skin in an oxygen environment. In ambient atmosphere, passivation is achieved in less than 30 min with the TeO2 skin having a thickness of about 7 Å. NiTe2 shows outstanding tolerance to CO exposure and stability in water environment, with subsequent good performance in both hydrogen and oxygen evolution reactions. NiTe2‐based devices consistently demonstrate superb ambient stability over a timescale as long as one month. Specifically, NiTe2 has been implemented in a device that exhibits both superior performance and environmental stability at frequencies above 40 GHz, with possible applications as a receiver beyond the cutoff frequency of a nanotransistor.  相似文献   

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