Lihua Chu

Glucose-assisted synthesis of the hierarchical TiO2 nanowire@MoS2 nanosheet nanocomposite and its synergistic lithium storage performance

A hierarchical nanocomposite of TiO2 nanowires decorated with molybdenum disulfide nanosheets (TiO2@MoS2) was synthesized by a facile and low-cost glucose-assisted hydrothermal approach. In this hierarchical nanocomposite, TiO2 nanowires served as an effective backbone for the nucleation and growth of few layered MoS2 nanosheets. Both glucose and the roughness of anatase-TiO2 (B) nanowires played important roles in the formation of the uniform TiO2 nanowire@MoS2 nanosheet (≤6 layers) nanocomposite. A synergistic effect was demonstrated on the nanocomposite of the TiO2 nanowire@MoS2 nanosheet. The one-dimensional robust TiO2 nanowire backbone provided a shortened and efficient pathway for electron and lithium ion transport and minimized the strain of the volume changes, while ultrathin MoS2 nanosheets offered high electrode/electrolyte interfacial contact areas, promoted rapid charge transfer and contributed to a high specific capacity. The favourable synergistic effect led to enhanced specific capacity, good cycling stability and superior rate capability of the nanocomposite, compared with either individual component. Such a TiO2 nanowire@MoS2 nanosheet nanocomposite is a promising anode material for high performance lithium ion batteries.

NH3-treated WO3 as low-cost and efficient counter electrode for dye-sensitized solar cells

A novel low-cost and efficient counter electrode (CE) was obtained by treating catalytic inert tungsten trioxide (WO3) nanomaterial in NH3 atmosphere at elevated temperatures. The formation of tungsten oxynitride from WO3 after NH3 treatment, as evidenced by X-ray photoelectron spectroscopy and X-ray diffraction, increases the catalytic activity of the CE. Correspondingly, the power conversion efficiency (PCE) of the DSC is significantly increased from 0.9% for pristine WO3 CE to 5.9% for NH3-treated WO3 CE. The photovoltaic performance of DSC using NH3-treated WO3 CE is comparable to that of DSC using standard Pt CE (with a PCE of 6.0%). In addition, it is also shown that NH3 treatment is more efficient than H2 or N2 treatment in enhancing the catalytic performance of WO3 CE. This work highlights the potential of NH3-treated WO3 for the application in DSCs and provides a facile method to get highly efficient and low-cost CEs from catalytic inert metal oxides.

High performance NiO microsphere anode assembled from porous nanosheets for lithium-ion batteries

3D NiO microspheres assembled from porous nanosheets are prepared and evaluated as an anode material for lithium-ion batteries, showing excellent electrochemical performance with high lithium storage capacity, and satisfactory cyclability and rate performance. The NiO microspheres deliver a first discharge capacity of 1242 mA h g−1 with a reversible capacity up to 820 mA h g−1 after 100 cycles at a current of 100 mA g−1 in a half cell, also exhibiting an ameliorative rate capacity of 634 mA h g−1 at the current of 1 A g−1. The high lithium storage performance can be mainly ascribed to the porous nanosheets, which improve lithium ion transfer, provide sufficient electrode/electrolyte contact areas, and more efficiently accommodate the volume change that occurs with the lithiation/delithiation process. Moreover, the 3D microsphere architecture is also helpful for enhancing the electrochemical performance of the lithium-ion battery. The results indicate the great potential of the 3D NiO microspheres assembled from porous nanosheets for use as an anode material for lithium-ion batteries.

Method to determine the optimal silicon nanowire length for photovoltaic devices

The length of the silicon nanowire (SiNW) is a key parameter in photovoltaic devices, as it dramatically decides the light-harvesting and carrier recombination. Here, we develop a method to determine the optimal SiNW length for photovoltaic devices, by comparing the light-harvesting efficiency of SiNWs with various lengths. The light-harvesting efficiency is measured by the light intensity in the SiNW, and the fraction of the length with high light intensity in its whole length. Under these criteria, we find that the optimal SiNW length is around 3 μm. This method is helpful in further optimization and application of SiNW-based solar cells.

Morphology control and fabrication of multi-shelled NiO spheres by tuning the pH value via a hydrothermal process

Controlling the morphology of nickel oxide (NiO) nanostructures is crucial to obtain excellent physical and chemical performance. Hence, the morphology of NiO was tuned by adjusting the pH value of the precursor solutions with NH3·H2O via a hydrothermal process and subsequent calcination. Different morphologies, including nanoparticles, porous structures and multi-shelled microspheres, were obtained with pH values varying from 8.30 to 10.90. The morphology evolution of as-synthesized NiO with the pH value indicates the important role of OH− in controlling the product morphology. Moreover, the formation mechanism of different NiO nanostructures at different pH values was discussed. Furthermore, the surface area and magnetic properties of NiO with different morphologies were also investigated, and indeed, these properties are very sensitive to the morphology. This work provides a facile way to control the morphology of NiO nanostructures, which also implies the potential application in modern science and technology with the modified magnetic properties.

The path of mass transfer during Au thin film-assisted chemical etching by designed surface barriers

The mass transfer in metal-assisted chemical etching between the interfaces has been revealed directly by an epoxy protection method. The results show that the dissolution of Si occurs in the Au film surface instead of the Au–Si interface. A mass transfer path inside the Au film is proposed, in which the Si atoms dissolve in the Au film, and then diffuse across the Au lattice, and are oxidized and etched away at the Au film/solution interface. This model is proved by the oxidation products of Si atoms (SiO2 and SiF62−) on the surface of the Au thin film. In addition, the abnormal emission of H2 at the Au–Si interface indicates the probability of the diffusion of H atoms inside the Au film during the etching. This work provides a further insight into the mechanism of metal-assisted chemical etching.

Multishelled NiO Hollow Spheres Decorated by Graphene Nanosheets as Anodes for Lithium-Ion Batteries with Improved Reversible Capacity and Cycling Stability

Graphene-based nanocomposites attract many attentions because of holding promise for many applications. In this work, multishelled NiO hollow spheres decorated by graphene nanosheets nanocomposite are successfully fabricated. The multishelled NiO microspheres are uniformly distributed on the surface of graphene, which is helpful for preventing aggregation of as-reduced graphene sheets. Furthermore, the NiO/graphene nanocomposite shows much higher electrochemical performance with a reversible capacity of 261.5 mAh g−1 at a current density of 200 mA g−1 after 100 cycles tripled compared with that of pristine multishelled NiO hollow spheres, implying the potential application in modern science and technology.

Computational Study of Ternary Devices: Stable, Low-Cost, and Efficient Planar Perovskite Solar Cells

Although perovskite solar cells with power conversion efficiencies (PCEs) more than 22% have been realized with expensive organic charge-transporting materials, their stability and high cost remain to be addressed. In this work, the perovskite configuration of MAPbX (MA = CH3NH3, X = I3, Br3, or I2Br) integrated with stable and low-cost Cu:NiOx hole-transporting material, ZnO electron-transporting material, and Al counter electrode was modeled as a planar PSC and studied theoretically. A solar cell simulation program (wxAMPS), which served as an update of the popular solar cell simulation tool (AMPS: Analysis of Microelectronic and Photonic Structures), was used. The study yielded a detailed understanding of the role of each component in the solar cell and its effect on the photovoltaic parameters as a whole. The bandgap of active materials and operating temperature of the modeled solar cell were shown to influence the solar cell performance in a significant way. Further, the simulation results reveal a strong dependence of photovoltaic parameters on the thickness and defect density of the light-absorbing layers. Under moderate simulation conditions, the MAPbBr3 and MAPbI2Br cells recorded the highest PCEs of 20.58 and 19.08%, respectively, while MAPbI3 cell gave a value of 16.14%.

Ion‐Migration Inhibition by the Cation–π Interaction in Perovskite Materials for Efficient and Stable Perovskite Solar Cells

Migration of ions can lead to photoinduced phase separation, degradation, and current-voltage hysteresis in perovskite solar cells (PSCs), and has become a serious drawback for the organic-inorganic hybrid perovskite materials (OIPs). Here, the inhibition of ion migration is realized by the supramolecular cation-π interaction between aromatic rubrene and organic cations in OIPs. The energy of the cation-π interaction between rubrene and perovskite is found to be as strong as 1.5 eV, which is enough to immobilize the organic cations in OIPs; this will thus will lead to the obvious reduction of defects in perovskite films and outstanding stability in devices. By employing the cation-immobilized OIPs to fabricate perovskite solar cells (PSCs), a champion efficiency of 20.86% and certified efficiency of 20.80% with negligible hysteresis are acquired. In addition, the long-term stability of cation-immobilized PSCs is improved definitely (98% of the initial efficiency after 720 h operation), which is assigned to the inhibition of ionic diffusions in cation-immobilized OIPs. This cation-π interaction between cations and the supramolecular π system enhances the stability and the performance of PSCs efficiently and would be a potential universal approach to get the more stable perovskite devices.

Excellent Infrared Nonlinear Optical Crystals BaMO(IO3)5 (M = V, Ta) Predicted by First Principle Calculations

Two nonlinear optical crystals, BaVO(IO3)5 and BaTaO(IO3)5, are designed by substituting Nb with V and Ta, respectively, in BaNbO(IO3)5, which is itself a recently synthesized infrared nonlinear optical (NLO) material. The designs of BaVO(IO3)5 and BaTaO(IO3)5 from BaNbO(IO3)5 are based on the following motivation: BaVO(IO3)5 should have a larger second-harmonic generation (SHG) coefficient than BaNbO(IO3)5, as V will result in a stronger second-order Jahn-Teller effect than Nb due to its smaller ion radius; at the same time, BaTaO(IO3)5 should have a larger laser-damage threshold, due to the fact that Ta has a smaller electronegativity leading to a greater band-gap. Established on reliable first-principle calculations, it is demonstrated that BaVO(IO3)5 has a much larger SHG coefficient than BaNbO(IO3)5 (23.42 × 10−9 vs. 18.66 × 10−9 esu); and BaTaO(IO3)5 has a significantly greater band-gap than BaNbO(IO3)5 (4.20 vs. 3.55 eV). Meanwhile, the absorption spectra and birefringences of both BaVO(IO3)5 and BaTaO(IO3)5 are acceptable for practice, suggesting that these two crystals can both be expected to be excellent infrared NLO materials.