Electrochemical performances and volume variation of nano-textured silicon thin films as anodes for lithium-ion batteries.

Electrochemical behaviors of nano-textured silicon thin film (NTSTF) coated with Al2O3 or Cu layers as anodes for lithium-ion batteries have been investigated. The cyclic performance of NTSTF electrodes is superior to dense Si thin films. The NTSTF with a 5 nm thick Cu coating layer shows superior cyclic performance and rate performance to other NTSTF samples. The volume changes of NTSTF electrodes after the first cycle and the tenth cycle have been investigated. This series of electrodes shows an anisotropic volume variation: the height does not change but the diameter does expand. This finding shows the feasibility of dealing with the vertical expansion and contraction of Si-based powder electrodes in Li-ion batteries.

Unraveling Thermal Transport Correlated with Atomistic Structures in Amorphous Gallium Oxide via Machine Learning Combined with Experiments.

Thermal transport properties of amorphous materials are crucial for their emerging applications in energy and electronic devices. However, understanding and controlling thermal transport in disordered materials remains an outstanding challenge, owing to the intrinsic limitations of computational techniques and the lack of physically intuitive descriptors for complex atomistic structures. Here, it is shown how combining machine-learning-based models and experimental observations can help to accurately describe realistic structures, thermal transport properties, and structure-property maps for disordered materials, which is illustrated by a practical application on gallium oxide. First, the experimental evidence is reported to demonstrate that machine-learning interatomic potentials, generated in a self-guided fashion with minimum quantum-mechanical computations, enable the accurate modeling of amorphous gallium oxide and its thermal transport properties. The atomistic simulations then reveal the microscopic changes in the short-range and medium-range order with density and elucidate how these changes can reduce localization modes and enhance coherences' contribution to heat transport. Finally, a physics-inspired structural descriptor for disordered phases is proposed, with which the underlying relationship between structures and thermal conductivities is predicted in a linear form. This work may shed light on the future accelerated exploration of thermal transport properties and mechanisms in disordered functional materials.

Non-volatile optoelectronic memory based on a photosensitive dielectric.

Recently, the optoelectronic memory is capturing growing attention due to its integrated function of sense and memory as well as multilevel storage ability. Although tens of states have been reported in literature, there are still three obvious deficiencies in most of the optoelectronic memories: large programming voltage (>20 V), high optical power density (>1 mW cm-2), and poor compatibility originating from the over-reliance on channel materials. Here, we firstly propose an optoelectronic memory based on a new photosensitive dielectric (PSD) architecture. Data writing and erasing are realized by using an optical pulse to switch on the PSD. The unique design enables the memory to work with a programming voltage and optical power density as low as 4 V and 160 µW cm-2, respectively. Meanwhile, this device may be extended to different kinds of transistors for specific applications. Our discovery offers a brand-new direction for non-volatile optoelectronic memories with low energy consumption.

Solution-grown BiI/BiI3 van der Waals heterostructures for sensitive X-ray detection.

X-ray detectors must be operated at minimal doses to reduce radiation health risks during X-ray security examination or medical inspection, therefore requiring high sensitivity and low detection limits. Although organolead trihalide perovskites have rapidly emerged as promising candidates for X-ray detection due to their low cost and remarkable performance, these materials threaten the safety of the human body and environment due to the presence of lead. Here we present the realization of highly sensitive X-ray detectors based on an environmentally friendly solution-grown thick BiI/BiI3/BiI (BixIy) van der Waals heterostructure. The devices exhibit anisotropic X-ray detection response with a sensitivity up to 4.3 × 104 µC Gy-1 cm-2 and a detection limit as low as 34 nGy s-1. At the same time, our BixIy detectors demonstrate high environmental and hard radiation stabilities. Our work motivates the search for new van der Waals heterostructure classes to realize high-performance X-ray detectors and other optoelectronic devices without employing toxic elements.

Alternating BiI3-BiI van der Waals Photodetector with Low Dark Current and High-Performance Photodetection.

The emerging two-dimensional (2D) van der Waals (vdW) materials and their heterostructures hold great promise for optoelectronics and photonic applications beyond strictly lattice-matching constraints and grade interfaces. However, previous photodetectors and optoelectronic devices rely on relatively simple vdW heterostructures with one or two blocks. The realization of high-order heterostructures has been exponentially challenging due to conventional layer-by-layer arduous restacking or sequential synthesis. In this study, we present an approach involving the direct exfoliation of high-quality BiI3-BiI heterostructure nanosheets with alternating blocks, derived from solution-grown binary heterocrystals. These heterostructure-based photodetectors offer several notable advantages. Leveraging the "active layer energetics" of BiI layers and the establishment of a significant depletion region, our photodetector demonstrates a significant reduction in dark current compared with pure BiI3 devices. Specifically, the photodetector achieves an extraordinarily low dark current (<9.2 × 10-14 A at 5 V bias voltage), an impressive detectivity of 8.8 × 1012 Jones at 638 nm, and a rapid response time of 3.82 µs. These characteristics surpass the performance of other metal-semiconductor-metal (MSM) photodetectors based on various 2D materials and structures at visible wavelengths. Moreover, our heterostructure exhibits a broad-band photoresponse, covering the visible, near-infrared (NIR)-I, and NIR-II regions. In addition to these promising results, our heterostructure also demonstrated the potential for flexible and imaging applications. Overall, our study highlights the potential of alternating vdW heterostructures for future optoelectronics with low power consumption, fast response, and flexible requirements.

Nanostructure formation and passivation of large-area black silicon for solar cell applications.

Nanoscale textured silicon and its passivation are explored by simple low-cost metal-assisted chemical etching and thermal oxidation, and large-area black silicon was fabricated both on single-crystalline Si and multicrystalline Si for solar cell applications. When the Si surface was etched by HF/AgNO(3) solution for 4 or 5 min, nanopores formed in the Si surface, 50-100 nm in diameter and 200-300 nm deep. The nanoscale textured silicon surface turns into an effective medium with a gradually varying refractive index, which leads to the low reflectivity and black appearance of the samples. Mean reflectance was reduced to as low as 2% for crystalline Si and 4% for multicrystalline Si from 300 to 1000 nm, with no antireflective (AR) coating. A black-etched multicrystalline-Si of 156 mm × 156 mm was used to fabricate a primary solar cell with no surface passivation or AR coating. Its conversion efficiency (η) was 11.5%. The cell conversion efficiency was increased greatly by using surface passivation process, which proved very useful in suppressing excess carrier recombination on the nanostructured surface. Finally, a black m-Si cell with efficiency of 15.8% was achieved by using SiO(2) and SiN(X) bilayer passivation structure, indicating that passivation plays a key role in large-scale manufacture of black silicon solar cells.

Quasi-Epitaxial Growth of ß-Ga2O3-Coated Wide Band Gap Semiconductor Tape for Flexible UV Photodetectors.

The epitaxial growth of technically important ß-Ga2O3 semiconductor thin films has not been realized on flexible substrates due to the limitations of high-temperature crystallization conditions and lattice-matching requirements. We demonstrate the epitaxial growth of ß-Ga2O3(-201) thin films on flexible CeO2(001)-buffered Hastelloy tape. The results indicate that CeO2(001) has a small bi-axial lattice mismatch with ß-Ga2O3(-201), inducing simultaneous double-domain epitaxial growth. Flexible photodetectors are fabricated on the epitaxial ß-Ga2O3-coated tape. Measurements reveal that the photodetectors have a responsivity of 4 × 104 mA/W, with an on/off ratio reaching 1000 under 254 nm incident light and 5 V bias voltage. Such a photoelectrical performance is within the mainstream level of ß-Ga2O3-based photodetectors using conventional rigid single-crystal substrates. More importantly, it remained robust against more than 20,000 bending test cycles. Moreover, the technique paves the way for the direct in situ epitaxial growth of other flexible oxide semiconductor devices in the future.

Room-Temperature Ozone Sensing Capability of IGZO-Decorated Amorphous Ga2O3 Films.

In present work, we report a room-temperature ozone sensor using InGaZnO (IGZO)-decorated amorphous Ga2O3 (a-Ga2O3) thin films. The gas sensing tests demonstrate that the topmost IGZO modification can significantly promote the sensors' responsivity. Intriguingly, the sensing capability presents a first increasing and then decreasing tendency as the surface morphology of IGZO develops from dispersed particles to a continuous film. Finite difference time domain (FDTD) simulation results prove that IGZO nanoparticles can remarkably increase the surface density of photogenerated electrons, clearly manifesting a strong dependence on IGZO particle size and contributing to the boosted responsiveness. However, once IGZO particles coalesce into a thin film, the ozone sensor's responsivity starts to decrease even though the number of photogenerated carriers still increases. The smaller specific surface area of IGZO thin film is believed to be responsible for this phenomenon. The proposed ozone gas sensors own the merits of low cost, room-temperature detection, easy integration, and mass production, significantly expanding the application fields of a-Ga2O3 thin film.

Interface Engineering of High Efficiency Organic-Silicon Heterojunction Solar Cells.

Insufficient interface conformity is a challenge faced in hybrid organic-silicon heterojunction solar cells because of using conventional pyramid antireflection texturing provoking the porosity of interface. In this study, we tested alternative textures, in particular rounded pyramids and inverted pyramids to compare the performance. It was remarkably improved delivering 7.61%, 8.91% and 10.04% efficiency employing conventional, rounded, and inverted pyramids, respectively. The result was interpreted in terms of gradually improving conformity of the Ag/organic/silicon interface, together with the gradually decreasing serial resistance. Altogether, the present data may guide further efforts arising the interface engineering for mastering high efficient heterojunction solar cells.

A three-terminal ultraviolet photodetector constructed on a barrier-modulated triple-layer architecture.

We report a novel three-terminal device fabricated on MgZnO/ZnO/MgZnO triple-layer architecture. Because of the combined barrier modulation effect by both gate and drain biases, the device shows an unconventional I-V characteristics compared to a common field effect transistor. The photoresponse behavior of this unique device was also investigated and applied in constructing a new type ultraviolet (UV) photodetector, which may be potentially used as an active element in a UV imaging array. More significantly, the proper gate bias-control offers a new pathway to overcome the common persistent photoconductivity (PPC) effect problem. Additionally, the MgZnO:F as a channel layer was chosen to optimize the photoresponse properties, and the spectrum indicated a gate bias-dependent wavelength-selectable feature for different response peaks, which suggests the possibility to build a unique dual-band UV photodetector with this new architecture.

Fluorine doping: a feasible solution to enhancing the conductivity of high-resistance wide bandgap Mg0.51Zn0.49O active components.

N-type doping of high-resistance wide bandgap semiconductors, wurtzite high-Mg-content MgxZn1-xO for instance, has always been a fundamental application-motivated research issue. Herein, we report a solution to enhancing the conductivity of high-resistance Mg0.51Zn0.49O active components, which has been reliably achieved by fluorine doping via radio-frequency plasma assisted molecular beam epitaxial growth. Fluorine dopants were demonstrated to be effective donors in Mg0.51Zn0.49O single crystal film having a solar-blind 4.43 eV bandgap, with an average concentration of 1.0 × 10(19) F/cm(3).The dramatically increased carrier concentration (2.85 × 10(17) cm(-3) vs ~10(14) cm(-3)) and decreased resistivity (129 Ω · cm vs ~10(6) Ω cm) indicate that the electrical properties of semi-insulating Mg0.51Zn0.49O film can be delicately regulated by F doping. Interestingly, two donor levels (17 meV and 74 meV) associated with F were revealed by temperature-dependent Hall measurements. A Schottky type metal-semiconductor-metal ultraviolet photodetector manifests a remarkably enhanced photocurrent, two orders of magnitude higher than that of the undoped counterpart. The responsivity is greatly enhanced from 0.34 mA/W to 52 mA/W under 10 V bias. The detectivity increases from 1.89 × 10(9) cm Hz(1/2)/W to 3.58 × 10(10) cm Hz(1/2)/W under 10 V bias at room temperature.These results exhibit F doping serves as a promising pathway for improving the performance of high-Mg-content MgxZn1-xO-based devices.

Maskless inverted pyramid texturization of silicon.

We discovered a technical solution of such outstanding importance that it can trigger new approaches in silicon wet etching processing and, in particular, photovoltaic cell manufacturing. The so called inverted pyramid arrays, outperforming conventional pyramid textures and black silicon because of their superior light-trapping and structure characteristics, can currently only be achieved using more complex techniques involving lithography, laser processing, etc. Importantly, our data demonstrate a feasibility of inverted pyramidal texturization of silicon by maskless Cu-nanoparticles assisted etching in Cu(NO3)2 / HF / H2O2 / H2O solutions and as such may have significant impacts on communities of fellow researchers and industrialists.

[Properties of the stimulated emission in the ZnO thin film].

ZnO thin film is a promising material for short-wave laser and LED etc, due to its high excition binding energy, intense stimulated emission, low lasing threshold, and high working temperature. ZnO thin films were prepared by laser molecular beam epitaxy (L-MBE) in our work. At room-temperature we reported the measurements of absorption spectra and emission spectra of ZnO thin films excited by various optical pumping intensities. High structural perfection of our sample was shown in these figures. We studied the properties and mechanism of stimulated emission in ZnO thin films. The relation between emission intensity and pumping intensity was obtained. Time behaviors of the stimulated emission under relatively high pumping intensity, spontaneous emission, and laser pulses were compared, and hence the stimulated emission of ZnO thin films was proved.

Probing defects in nitrogen-doped Cu2O.

Nitrogen doping is a promising method of engineering the electronic structure of a metal oxide to modify its optical and electrical properties; however, the doping effect strongly depends on the types of defects introduced. Herein, we report a comparative study of nitrogen-doping-induced defects in Cu2O. Even in the lightly doped samples, a considerable number of nitrogen interstitials (Ni) formed, accompanied by nitrogen substitutions (NO) and oxygen vacancies (VO). In the course of high-temperature annealing, these Ni atoms interacted with VO, resulting in an increase in NO and decreases in Ni and VO. The properties of the annealed sample were significantly modified as a result. Our results suggest that Ni is a significant defect type in nitrogen-doped Cu2O.