Showing papers by "Deren Yang published in 2019"

Coupling PtNi Ultrathin Nanowires with MXenes for Boosting Electrocatalytic Hydrogen Evolution in Both Acidic and Alkaline Solutions

Abstract: Developing an efficient electrocatalyst for the hydrogen evolution reaction (HER) working in both acidic and alkaline solutions is highly desirable, but still remains challenging. Here, Ptx Ni ultrathin nanowires (NWs) with tunable compositions (x = 1.42, 3.21, 5.67) are in situ grown on MXenes (Ti3 C2 nanosheets), serving as electrocatalysts toward HER. Such Ptx Ni@Ti3 C2 electrocatalysts exhibit excellent HER performance in both acidic and alkaline solutions, with the Pt3.21 Ni@Ti3 C2 being the best one. Specifically, Pt3.21 Ni@Ti3 C2 achieves record-breaking performance in terms of lowest overpotential (18.55 mV) and smallest Tafel slope (13.37 mV dec-1 ) for HER in acidic media to date. Theory calculations and X-ray photoelectron spectroscopy analyses demonstrate that the coupling of MXenes with the NWs not only approaches the Gibbs free energy for hydrogen adsorption close to zero through the electron transfer between them in acidic media, but also provides additional active sites for water dissociation in alkaline solution, both of them being beneficial to the HER performance.

Designing superior solid electrolyte interfaces on silicon anodes for high-performance lithium-ion batteries

Abstract: The solid electrolyte interface (SEI) is a passivation layer formed on the surface of lithium-ion battery (LIB) anode materials produced by electrolyte decomposition. The quality of the SEI plays a critical role in the cyclability, rate capacity, irreversible capacity loss and safety of lithium-ion batteries (LIBs). The stability of the SEI is especially important for Si anodes which experience tremendous volume changes during cycling. Therefore, in this review we discuss the effect of the SEI on Si anodes. Firstly, the mechanism of formation, composition, and component properties of solid electrolyte interfaces (SEIs) are introduced, and the SEI of native-oxide-terminated Si is emphasized. Then the growth model and mechanical failure of SEIs are analyzed in detail, and the challenges facing SEIs of Si anodes are proposed. Moreover, we highlight several modification methods for SEIs on Si anodes, including electrolyte additives, surface-functionalization of Si, coating artificial SEIs or protective layers, and the structural design of Si-based composites. We believe that designing a high-quality SEI is of great significance and is beneficial for the improved electrochemical performance of Si anodes.

Silicon nanocrystals: unfading silicon materials for optoelectronics

Abstract: As the most fundamental material for microelectronics, silicon (Si) has bourgeoned in the past more than half a century. However, given the indirect bandgap of Si, the use of Si in optoelectronics is relatively limited due to its mediocre optical absorption and rather poor optical emission. During many years of efforts for extending the use of Si in optoelectronics Si nanocrystals (NCs) that are one type of the most important Si nanostructures have attracted significant attention owing to their remarkable electronic and optical properties. Si NCs are actually crystalline Si nanoparticles, which may be called Si quantum dots if their size is smaller than ∼10 nm. With the manipulation of the size, surface and doping of Si NCs great tunability for the light emission from Si NCs with the quantum yield of more than 60% has been realized. Based on the efficient light emission from Si NCs high-performance Si-NC light-emitting devices have been demonstrated. In the meantime, the efficient light emission from Si NCs has also been utilized for synaptic simulations in neuromorphic computing and down-shifting in photovoltaics. Broadband optical absorption ranging from the ultraviolet to mid-infrared has been recently obtained for Si NCs mainly by taking advantage of doping. This has enabled the use of Si NCs in novel solar cells, photodetectors and optoelectronic synaptic devices. The continuous improvement of the electronic and optical properties of Si NCs has made Si NCs unfading Si materials for optoelectronics, contributing to the development of Si-based optoelectronic integration.

Perovskite Bifunctional Device with Improved Electroluminescent and Photovoltaic Performance through Interfacial Energy-Band Engineering.

Abstract: Currently, photovoltaic/electroluminescent (PV/EL) perovskite bifunctional devices (PBDs) exhibit poor performance due to defects and interfacial misalignment of the energy band. Interfacial energy-band engineering between the perovskite and hole-transport layer (HTL) is introduced to reduce energy loss, through adding corrosion-free 3,3'-(2,7-dibromo-9H-fluorene-9,9-diyl) bis(n,n-dimethylpropan-1-amine) (FN-Br) into a HTL free of lithium salt. This strategy can turn the n-type surface of perovskite into p-type and thus correct the misalignment to form a well-defined N-I-P heterojunction. The tailored PBD achieves a high PV efficiency of up to 21.54% (certified 20.24%) and 4.3% EL external quantum efficiency. Free of destructive additives, the unencapsulated devices maintain >92% of their initial PV performance for 500 h at maximum power point under standard air mass 1.5G illumination. This strategy can serve as a general guideline to enhance PV and EL performance of perovskite devices while ensuring excellent stability.

Tuning Surface Structure of Pd 3 Pb/Pt n Pb Nanocrystals for Boosting the Methanol Oxidation Reaction.

Abstract: Developing an efficient Pt-based electrocatalyst with well-defined structures for the methanol oxidation reaction (MOR) is critical, however, still remains a challenge. Here, a one-pot approach is reported for the synthesis of Pd3Pb/Pt n Pb nanocubes with tunable Pt composition varying from 3.50 to 2.37 and 2.07, serving as electrocatalysts toward MOR. Their MOR activities increase in a sequence of Pd3Pb/Pt3.50Pb << Pd3Pb/Pt2.07Pb < Pd3Pb/Pt2.37Pb, which are substantially higher than that of commercial Pt/C. Specifically, Pd3Pb/Pt2.37Pb electrocatalysts achieve the highest specific (13.68 mA cm-2) and mass (8.40 A mgPt-1) activities, which are ≈8.8 and 6.8 times higher than those of commercial Pt/C, respectively. Structure characterizations show that Pd3Pb/Pt2.37Pb and Pd3Pb/Pt2.07Pb are dominated by hexagonal-structured PtPb intermetallic phase on the surface, while the surface of Pd3Pb/Pt3.50Pb is mainly composed of face-centered cubic (fcc)-structured Pt x Pb phase. As such, hexagonal-structured PtPb phase is much more active than the fcc-structured Pt x Pb one toward MOR. This demonstration is supported by density functional theory calculations, where the hexagonal-structured PtPb phase shows the lowest adsorption energy of CO. The decrease in CO adsorption energy and structural stability also endows Pd3Pb/Pt n Pb electrocatalysts with superior durability relative to commercial Pt/C.

Visible-blind short-wavelength infrared photodetector with high responsivity based on hyperdoped silicon

Abstract: Developing a low-cost, room-temperature operated and complementary metal-oxide-semiconductor (CMOS) compatible visible-blind short-wavelength infrared (SWIR) silicon photodetector is of interest for security, telecommunications, and environmental sensing. Here, we present a silver-supersaturated silicon (Si:Ag)-based photodetector that exhibits a visible-blind and highly enhanced sub-bandgap photoresponse. The visible-blind response is caused by the strong surface-recombination-induced quenching of charge collection for short-wavelength excitation, and the enhanced sub-bandgap response is attributed to the deep-level electron-traps-induced band-bending and two-stage carrier excitation. The responsivity of the Si:Ag photodetector reaches 504 mA· W−1 at 1310 nm and 65 mA ·W−1 at 1550 nm under −3 V bias, which stands on the stage as the highest level in the hyperdoped silicon devices previously reported. The high performance and mechanism understanding clearly demonstrate that the hyperdoped silicon shows great potential for use in optical interconnect and power-monitoring applications.

Developing near-infrared quantum-dot light-emitting diodes to mimic synaptic plasticity

Abstract: The quantum-dot light-emitting diodes (QLEDs) that emit near-infrared (NIR) light may be important optoelectronic synaptic devices for the realization of artificial neural networks with complete optoelectronic integration. To improve the performance of NIR QLEDs, we take advantage of their low-energy light emission to explore the use of poly(3-hexylthiophene) (P3HT) as the hole transport layer (HTL). P3HT has one of the highest hole mobilities among organic semiconductors and essentially does not absorb NIR light. The usage of P3HT as the HTL indeed significantly mitigates the imbalance of carrier injection in NIR QLEDs. With the additional incorporation of an interlayer of poly [9,9-bis(3ʹ-( N , N -dimethylamino)propyl)-2,7-flourene]- alt -2,7-(9,9-dioctylfluorene)], P3HT obviously improves the performance of NIR QLEDs. As electroluminescent synaptic devices, these NIR QLEDs exhibit important synaptic functionalities such as short- and long-term plasticity, and may be employed for image recognition.

Ultra-small Rh nanoparticles supported on WO3−x nanowires as efficient catalysts for visible-light-enhanced hydrogen evolution from ammonia borane

Abstract: Hydrolysis of ammonia borane (AB) is a safe and convenient means of H2 production when efficient catalysts are used. Here we report a facile one-pot solvothermal method to synthesize Rh/WO3−x hybrid nanowires. Ultra-small Rh nanoparticles with an average size of ∼1.7 nm were tightly anchored on WO3−x nanowires. Rh/WO3−x catalysts exhibited substantially enhanced activity for hydrolytic dehydrogenation of AB under both dark and visible light irradiation conditions relative to mixed Rh nanoparticles and WO3−x nanowires (Rh + WO3−x), and Rh/C and WO3−x nanowires. X-ray photoelectron spectroscopy (XPS) analysis indicated that the synergistic effect between Rh nanoparticles and WO3−x nanowires was responsible for such an enhancement in activity. Specifically, Rh/WO3−x achieved the highest turnover frequency (TOF) with a value of 805.0 molH2 molRh−1 min−1 at room temperature under visible light irradiation. The H2 release rate as a function of reaction time exhibited a volcano plot under visible light irradiation, indicating that a self-activation process occurred in the hydrolytic dehydrogenation of AB due to additional oxygen vacancies arising from in situ reduction of WO3−x nanowires by AB, and thus an enhanced localized surface plasmon resonance (LSPR). Such a self-activation process was responsible for the enhanced catalytic activity under visible light irradiation relative to that under dark conditions, which was supported by the lower activation energy (45.2 vs. 50.5 kJ mol−1). In addition, Rh/WO3−x catalysts were relatively stable with only little loss in activity after five cycles due to the tight attachment between two components.

Solvation effect in precursor solution enables over 16% efficiency in thick 2D perovskite solar cells

Abstract: High-quality thick light harvesting film is important for two-dimensional (2D) perovskite solar cells (PVSCs). The relationship between the structure of the second spacer cation (SSC+) in the precursor solution and the morphology of the perovskite film was studied. By applying structurally symmetric guanidinium (GA+) as a SSC+ and utilizing the solvation effect of GA+ in N,N-dimethylformamide (DMF), the solvent of the precursor, we realized the fabrication of 2D BA2MA4Pb5I16 (BA+ = butylammonium, MA+ = methylammonium) perovskite film with oriented crystal grains grown throughout the 530 nm thick film on a PEDOT:PSS substrate, which favored the fast transport of the charge carriers. The inverted planar-structured PVSCs exhibit a hero PCE of 14.94%. The device efficiency was further improved to 16.26%, one of the highest efficiencies reported for 2D PVSCs, through interface optimization via adding MACl into the precursor solution. The unsealed device exhibits moisture stability by retaining 90% of its initial PCE after 800 hours of exposure to air with a humidity of 55 ± 5%. This work provides a new approach toward high-performance 2D PVSCs in terms of both PCE and stability.

Intermetallic Pd3Pb square nanoplates as highly efficient electrocatalysts for oxygen reduction reaction

Abstract: Pd is generally regarded as an alternative catalyst material to Pt for the oxygen reduction reaction (ORR). However, its catalytic activity and durability are much lower than those of Pt. Here, we report a facile approach for the synthesis of intermetallic Pd3Pb square nanoplates enclosed by {100} facets. The use of oleylamine (OAm), oleic acid (OA), and 1-octadecene (ODE) played important roles in the formation of the Pd3Pb intermetallic square nanoplates in high-quality. The Pd3Pb square nanoplates exhibited substantially enhanced ORR properties in terms of activity and durability. In particular, such nanoplates showed higher mass activity (0.62 mA μgPd−1) and specific activity (3.59 mA cm−2), which were 10.3 and 32.6 times higher than those of the commercial Pt/C, respectively, due to ligand and geometry effects. Significantly, the Pd3Pb square nanoplates/C were highly stable with 23% loss in specific activity and 21% loss in mass activity after 10 000 cycles compared to the Pd3Pb alloy dendritic nanocrystals/C (over 50% loss in specific and mass activities) due to their unique intermetallic structure with high chemical stability.

Control of the formation and luminescent properties of polymorphic erbium silicates on silicon

Abstract: We report on the control of the formation and the luminescent properties of polymorphic forms of erbium (Er) silicates by the modification of annealing temperatures, annealing atmospheres and chemical compositions. Four Er silicate polymorphs, X1-Er2SiO5, y-Er­2Si2O7, α-Er2Si2O7 and β-Er2Si2O7, are fabricated in Er-doped SiO2 films. Higher annealing temperatures turn the Er silicates into more stable polymorphs, but the annealing in O2 and the deviation of chemical compositions from the stoichiometry of Er silicates will restrain this process. The luminescent properties of these polymorphs are quite different due to their strong correlation with the crystallographic structures. Photoluminescence spectra with the main peaks at 1530 nm, 1536 nm, 1529 nm, and 1539 nm are obtained for X1-Er2SiO5, y-Er­2Si2O7, α-Er2Si2O7 and β-Er2Si2O7, respectively, and the highest photoluminescence efficiency is associated to Er ions in y-Er2Si2O7.

Towards green antisolvent for efficient CH3NH3PbBr3 perovskite light emitting diodes: A comparison of toluene, chlorobenzene, and ethyl acetate

Abstract: Antisolvent engineering is one of the most widely used methods to obtain high quality perovskite films. This process involves the heavy use of toxic antisolvents, such as toluene (Tol) and chlorobenzene (CB). It is thus highly desirable to develop green antisolvents for the future manufacturing of perovskites. Though several green antisolvents have been developed for iodide perovskites, there are few reports about their application on bromide ones. Besides, the reported green antisolvents for iodide perovskites usually lead to a significant increase in the crystal size, which is not suitable for light emission due to reduced carrier confinement and radiative recombination. Here, we introduce green antisolvent ethyl acetate (EA) to prepare CH3NH3PbBr3 (MAPbBr3) perovskite films. In contrast to previously reported iodide perovskites, EA engineered MAPbBr3 only shows a slight increase in the crystal size. A systematic study on the structural, morphological, and optoelectronic properties of MAPbBr3 prepared with Tol, CB, and EA was carried out. With the benefits of relatively high polarity and low boiling point compared with Tol and CB, EA could extract the solvent more efficiently. This gives rise to MAPbBr3 films with increased crystallinity, improved morphology, and reduced defects, boosting the performance of the corresponding light emitting diodes (LEDs). Our study provides an environmentally friendly way to the manufacturing of efficient MAPbBr3 perovskite LEDs as well as other optoelectronic devices.

Electroluminescence from light-emitting devices based on erbium-doped ZnO/n-Si heterostructures: Enhancement effect of fluorine co-doping

Abstract: We report on erbium (Er) related electroluminescence (EL) in the visible and near infrared (NIR) regions from the light-emitting device (LED) based on the Er-doped ZnO (ZnO:Er)/n-Si isotype heterostructure formed by sputtering ZnO:Er film on n-Si/n+-Si epitaxial wafer. Herein, the ZnO:Er film exhibits n-type in electrical conduction. The aforementioned LED is electroluminescent only under sufficiently high forward bias with the negative voltage connecting to n+-Si substrate. Such forward bias enables the electrons from n-Si to enter into the ultra-thin SiOx (x ≤ 2) layer inherently existing between the ZnO:Er film and n-Si via Poole-Frenkel conduction mechanism and, subsequently, to drift into the ZnO:Er film thus becoming hot electrons, which impact-excite the Er3+ ions to emit characteristic visible and NIR light. Furthermore, the Er-related EL from the aforementioned LED can be significantly enhanced through adopting the strategy of co-doping F− ions into the ZnO host, which brings about twofold primary effects. Firstly, due to the atomic size compensation between F− and Er3+ ions, the ZnO crystal grains become larger to accommodate much more optically active Er3+ ions. Secondly, the partial substitution of F− ions for O2- ions around the Er3+ ion reduces the symmetry of pseudo-octahedral crystal field of Er3+ ion, thus increasing the probabilities of intra-4f transitions of Er3+ ions. We believe that this work sheds light on developing efficient silicon-based LEDs using the Er-doped oxide semiconductors.

Interface engineering of C60/ fluorine doped tin oxide on the photovoltaic performance of perovskite solar cells using the physical vapor deposition technique

Abstract: Fullerene (C60) has been demonstrated, using vapor deposition, to be a good electron transport layer (ETL) and different thicknesses have been utilized in n-i-p configuration perovskite solar cells. However, an underlying reason for the variation in thicknesses, which hinders the reproducibility of perovskite solar cells employing a C60 ETL, has not been well-examined. This study reveals that the surface roughness of the conducting glass, such as fluorine doped tin oxide (FTO), affects the photovoltaic performance while optimizing the thickness of the vacuum deposited compact C60 ETL. A low-thickness C60 ETL retains a surface roughness and Ohmic behavior similar to bare FTO due to physical defects at the C60/FTO interface. Increasing the thickness further reduces the defects at the C60/FTO interface and facilitates an enhanced electron extraction from a vacuum co-deposited methyl-ammonium lead iodide perovskite light absorber. As a result, a perovskite solar cell with a homogenously covered C60 ETL on an FTO substrate delivers a power conversion efficiency of 14.63%. These comprehensive characterizations support the finding that suppression of defects at the C60/FTO interface results in an improved photovoltaic performance. This work demonstrates that the surface roughness of FTO needs to be considered for a decisive compact ETL for enhanced photovoltaic performance and reproducibility.

Intermetallic Pd3Pb ultrathin nanoplate-constructed flowers with low-coordinated edge sites boost oxygen reduction performance.

Abstract: Although tremendous efforts have been devoted to exploring non-Pt based electrocatalysts toward the oxygen reduction reaction (ORR), achievements in both catalytic activity and durability are still far from satisfactory. Here, we report a facile approach for the synthesis of intermetallic Pd3Pb ultrathin nanoplate-constructed flowers. Such highly opened hierarchical nanostructures with an ordered phase and low-coordinated edge sites exhibited a substantially enhanced activity toward the ORR. Especially, the intermetallic Pd3Pb nanoflowers achieved a record-breaking mass activity (1.14 mA μgPd−1) in an alkaline solution at 0.9 V vs. a reversible hydrogen electrode among the reported Pd-based ORR electrocatalysts to date, which was 1.8, 3.9 and 11.4 times higher than those of intermetallic Pd3Pb nanocubes, Pd3Pb dendrites and commercial Pt/C, respectively. More importantly, the intermetallic Pd3Pb nanoflowers also showed a higher durability with only 23.7% loss in mass activity after 10 000 cycles compared to the commercial Pt/C (35% loss in mass activity) due to their chemically stable intermetallic structures.

Plasmon-Coupled Förster Resonance Energy Transfer between Silicon Quantum Dots

Abstract: The distance dependence of localized surface plasmon (LSP)-coupled Forster resonance energy transfer (FRET) between Si quantum dots (QDs) is experimentally and theoretically investigated utilizing ...

Negatively charged silicon nitride films for improved p-type silicon surface passivation by low-temperature rapid thermal annealing

Abstract: The effect of post-deposition rapid thermal annealing (RTA) on p-type Czochralski silicon surface passivation by plasma-enhanced chemical vapor deposited nitrogen-rich silicon nitride (SiN x ) films has been investigated. The effective carrier lifetime is significantly improved after annealing at low temperature (400 °C–450 °C) for 15–30 s. This improvement is associated with a decrease of N–H and Si–H bond densities in SiN x films and, a resultant decreased density of states at the SiN x /Si interface. More importantly, the polarity of fixed charges is converted from positive to negative in the annealed SiN x films. It is demonstrated that a release of hydrogen atoms to the SiN x /Si interface combined with a tuning of charges during low-temperature RTA, is very beneficial for p-type silicon surface passivation.

Effects of n-butyl amine incorporation on the performance of perovskite light emitting diodes.

Abstract: The efficiency of perovskite light emitting diodes (PeLEDs) is crucially limited by leakage current and nonradiative recombination. Here we introduce n-butyl amine (BA) to modulate the growth of perovskite films as well as improve the performance of PeLEDs, and investigate in detail the effects of BA incorporation on the structural, optical, and electrical characteristics of perovskite films. The results indicate that BA would terminate the grain surface and inhibit crystal growth, leading to increased radiative recombination. However, BA overload would make the films loose and recreate shunt paths. The electrical detriment of BA overload outweighs its optical benefit. As a result, optimal PeLEDs can be obtained only with moderate BA incorporation.

Synthesis of Co/SnO 2 core-shell nanowire arrays and their electrochemical performance as anodes of lithium-ion batteries

Abstract: The Co/SnO2 core-shell nanowire arrays were synthesized via a simple hydrothermal approach and subsequently the deposition of amorphous SnO2 layer. When used as anode materials of lithium-ion batteries, the Co/SnO2 core-shell nanowire arrays maintain at 667.9 mAh g−1 with the capacity retention of 85.7% after 100 cycles at the current density of 200 mA g−1. For comparison, the discharge capacity of the planar SnO2 electrodes shows the capacity of 196.3 mAh g−1 with the capacity retention of 22.6% after 100 cycles under the same condition. The enhanced electrochemical performance is attributed to the core-shell array nanostructures that can improve the conductivity and buffer the volume changes of tin-based anode during the charge/discharge process.

Litchi-structural core–shell Si@C for high-performance lithium–ion battery anodes

Abstract: Silicon is regarded as the next-generation alternative anode material of lithium–ion battery due to the highest theoretical specific capacity of 4200 mAh g−1. Nevertheless, the drastic volume expansion/shrink (~ 300%) during the lithiation/delithiation process and the poor electrical conductivity obstruct its commercial application. Herein, we report a novel design of litchi-structural Si@C nanoparticles (L-S Si@C) as long cycle life anode material for lithium–ion battery. The L-S Si@C with nanosized (~ 50 nm) SiC dispersed in the inner surface and ~ 6 wt% carbon layer covering the outer surface delivers a specific capacity of 1145 mAh g−1 in the initial cycle and maintains a specific capacity of 570 mAh g−1 after 300th cycling times, which can be attributed to the specially structurally stable L-S Si@C nanoparticles.