Layered Crystalline Structure Research Articles

Enhanced broadband IR absorption and electrical characteristics of silicon variably hyperdoped by sulfur (1018-1021 cm−3) by ion implantation/pulsed laser annealing

Spectral range of crystalline silicon absorption could be extended to near- and even mid-infrared region by its hyperdoping via ion-implantation technology, requiring the following thermal annealing for removing ion-induced defects, recrystallizing the crystalline structure and activating the doping impurity. In this article, the crystalline structure, chemical and electrical characteristics of sulfur-hyperdoped silicon layers with broadly variable impurity concentration (1018-1021 cm−3) and annealed by a nanosecond laser were investigated for the first time by Raman, energy-dispersion x-ray and infrared spectroscopy, as well as by van der Paw and Hall measurements, respectively. The most preferable sulfur concentration for silicon hyperdoping from the point of view of impurity optical and electrical activation was found to be 1020 cm−3.

Impact of Cationic Stoichiometry on Physical, Optical and Electrical Properties of SrTiO3 Thin Films Grown on (001)-Oriented Si Substrates.

In this study, we investigate the changes in the crystalline structure of MBE-deposited SrTiO3 layers on Si with different deviations from Sr/Ti stoichiometry as deposited but also after annealing at high temperatures (>600 °C). We show that as-grown 15 nm thick non-stochiometric SrTiO3 layers present surprisingly lower FWHM values of the (002) omega diffraction peak compared to fully stoichiometric layers of similar thickness. This can misleadingly point to superior crystalline quality of such non-stochiometric layers. However, thermal post-deposition anneals of these layers at temperatures up to 850 °C in oxygen show strong detrimental effects on the crystalline structure, surface and interface with the Si (001) substrate. On the contrary, the post-deposition anneals applied to the stoichiometric samples strongly improve the physical, optical and electrical properties of the epitaxial SrTiO3 thin films.

Doping Regulation Stabilizing δ-MnO2 Cathode for High-Performance Aqueous Aluminium-ion Batteries.

δ-MnO2 is a promising cathode material for aqueous aluminium-ion batteries (AAIBs) for its layered crystalline structure with large interlayer spacing. However, the excellent Al ion storage performance of δ-MnO2 cathode remains elusive due to the frustrating structural collapse during the intercalation of high ionic potential Al ion species. Here, it is discovered that introducing heterogeneous metal dopants with high bond dissociation energy when bonded to oxygen can significantly reinforce the structural stability of δ-MnO2 frameworks. This reinforcement translates to stable cycling properties and high specific capacity in AAIBs. Vanadium-doped δ-MnO2 (V-δ-MnO2 ) can deliver a high specific capacity of 518mAhg-1 at 200mAg-1 with remarkable cycling stability for 400 cycles and improved rate capabilities (468, 339, and 285mAhg-1 at 0.5, 1, and 2Ag-1 , respectively), outperforming other doped δ-MnO2 materials and the reported AAIB cathodes. Theoretical and experimental studies indicate that V doping can substantially improve the cohesive energy of δ-MnO2 lattices, enhance their interaction with Al ion species, and increase electrical conductivity, collectively contributing to high ion storage performance. These findings provide inspiration for the development of high-performance cathodes for battery applications.

Trilithium salt of tetrahydroxyanthraquinone: A high-voltage and stable organic cathode material for rechargeable lithium metal and lithium-ion batteries

Organic cathode materials (OCMs) have drawn considerable attention for lithium batteries but suffer from unfavorable dissolution problem and thus inferior cycling performance. Salification is a simple approach to restrain the dissolution but most reported lithium-salt-type OCMs are still unable to achieve good cycling stability due to poorly conjugated and/or asymmetric structure. Herein, we report a novel air-stable, largely conjugated, and symmetric organic lithium salt synthesized from 1,4,5,8-tetrahydroxyanthraquinone (THAQ), namely Li3THAQ. It possesses a layered crystalline structure with large interlayer spacings, which is relatively stable in the reversible conversion between Li4THAQ and Li2THAQ. Benefiting from this, Li3THAQ exhibits exceptional electrochemical performance within 2.0–3.6 V, including high reversible capacity (192 mAh g−1), high discharge potential (2.93 V vs. Li+/Li), high rate capability (75 % capacity retention at 5000 mAh g−1 vs. 50 mAh g−1), and high cycling stability (95 % capacity retention after 500 cycles). Additionally, it can be also matched with natural graphite anode to construct a Li-ion full-cell, which was rarely reported for OCMs. In brief, Li3THAQ shows great advantages in structure stability, electrochemical performance, and practicability compared to its counterparts, and the in-depth mechanism understanding provides important insights into the development of lithium-salt-type OCMs.

Silicon Oxycarbide-Coated Bismuth for Enhanced Anode Stability in Lithium-Ion Batteries

The current state-of-the-art lithium-ion batteries (LIBs) with graphite as an anode foresees shortcomings to demands in energy storage and supplies with high energy and power densities for large-scale applications such as electric vehicles. Metallic Bi alloy is among the promising alternative alloy candidates to replace the graphitic anode owing to its high volumetric capacity (3765 mAh cm−3), relatively small volume expansion (~215%), and unique layered crystalline structure with large interlayer spacing along the c-axis (d 003 = 3.95 Å). Nevertheless, inevitable volume expansion during repetitive Li+-ion insertion/extraction build-ups localized mechanical strain, causing particle pulverization, cracking, and isolations, eventually leading to cell failure. Herein, to achieve decent reversibility of alloys, we introduce a polymer-derived ceramic silicon oxycarbide (SiOC) coating onto Bi nanoparticles (NPs) via facile dispersion of bismuth hydroxide in silicone oil and consecutive heat treatment. The SiOC coating layer alone is an active conversion material with a higher specific capacity but lower volumetric capacity than Bi. To promote the fabrication of high volumetric capacity Bi-based composites using higher tap density materials with a well-balanced specific capacity, the content of the metal precursor and silicone oil were varied. The sturdy SiOC matrix embedded with the Bi NPs cushions the stress cultivated upon (de)lithiation reactions, achieving stable capacity (507 mAh g−1 at 0.05 A g−1 after 150 cycles), high volumetric capacity (872 mAh cm−3), superb cyclic stability (380 mAh g−1 at 0.5 A g−1 after 500 cycles), and adequate cell integrity when tested as an anode in a half cell. In a full cell configuration coupled with a LiNi0.5Co0.2Mn0.3O2 cathode, high gravimetric and volumetric energy densities of 343 Wh kg−1 and 607 Wh L−1 can be estimated, respectively. The conducted kinetic and postmortem analyses provide additional insights into the effectiveness of amorphous SiOC as a protective layer in preventing excess solid electrolyte interface passivation and preserving the electrically conductive network for continuous transport of ions and electrons. Figure 1

Violet phosphorus transmission and photoconductance spectroscopy

Violet phosphorus is a semiconducting allotrope of phosphorus with a layered crystalline structure consisting of orthogonally oriented layers of phosphorus chains composed of P2[P8]P2[P9] repeating units. Here, we report optical transmission spectroscopy and photoconductivity measurements of exfoliated flakes of violet phosphorus in the thin-film bulk limit. The violet phosphorus was synthesized by chemical vapour transport, and subsequently protected from oxidation with an inert gas environment. A peak photoconductive responsivity of R = 7 mA W−1 at photon energy 2.8 eV was observed. The spectral dependence of optical transmission and photoconductivity of violet phosphorus leads us to identify optical transitions at van Hove singularities corresponding to energies E 1 = 1.80 ± 0.05 eV and E 2 = 1.95 ± 0.05 eV. Density functional theory was applied to the calculation of violet phosphorus (vP) bandstructure, and a dipole transition analysis shows that optical transitions at the Z and A 0 points of the Brillouin zone are in agreement with experimental observations. Exposure to ambient environmental conditions for several minutes is sufficient to significantly reduce vP photoconductivity, while longer exposure leads to blistering due to oxidation. Thus, a locally inert chemical environment is essential to accessing vP intrinsic optoelectronic properties.

Space‐ and Post‐Flight Characterizations of Perovskite and Organic Solar Cells

Perovskite and organic solar cells are promising for space applications for enabling higher specific powers or alternative deployment systems. However, terrestrial tests can only mimic space conditions to a certain extent. Herein, a detailed analysis of irradiation‐dependent photovoltaic parameters of perovskite and organic solar cells exposed to space conditions during a suborbital flight is presented. In orbital altitudes, perovskite and organic solar cells reach power‐conversion efficiencies of more than 13% and 6%, respectively. Based on postflight grazing‐incidence small‐angle and wide‐angle X‐ray scattering, the active layer morphology and crystalline structure of the returned space solar cells are studied and compared to those of reference solar cells that stayed in an inert atmosphere. Minor changes in the active layer morphology are induced by the sole transport, without causing significant performance loss. For the space solar cells, morphological changes are attributed to the flight experiment that includes rocket launch, spaceflight, and reentry, as well as short‐terrestrial environment exposure before and after launch. In contrast, no significant changes to the crystalline phase are observed. The notable performance during flight and high active layer stability, especially of perovskite solar cells, are promising results for further steps toward an orbital demonstration.

Effect of temperature on anti-corrosion properties of aluminum alloy anodized by sulphuric acid

Temperature is one of the most important parameters in anodizing treatments of aluminum alloys as it directly affects the quality of the anodic coatings. This research study has examined and investigated the effect of this important parameter on the anti-corrosion properties of the anodizing layers of aluminum alloy 5083.The morphology and crystalline structure of anodic oxide layers were characterized respectively by X-ray diffraction, scanning lectron microscopy and EDX analysis. The corrosion behaviour of the alloy, before and after anodization at different temperatures, was analyzed in chlorinated medium using different electrochemical techniques, namely open circuit potential measurement, potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that temperature has a significant influence on the quality of the anodic oxide layers. Therefore, for a relatively low treatment temperature, the developed anodic films show high surface roughness values and contain fewer pores and defects compared to the films obtained at 20°C. Electrochemical analysis indicates that these films also show good corrosion resistance in the chloride environment. This is reflected by relatively low corrosion current density values as well as relatively high polarization resistance values.

Calcium Phosphates-Chitosan Composite Layers Obtained by Combining Radio-Frequency Magnetron Sputtering and Matrix-Assisted Pulsed Laser Evaporation Techniques.

In this work, we report the synthesis of calcium phosphate-chitosan composite layers. Calcium phosphate layers were deposited on titanium substrates by radio-frequency magnetron sputtering technique by varying the substrate temperature from room temperature (25 °C) up to 100 and 300 °C. Further, chitosan was deposited by matrix-assisted pulsed laser evaporation technique on the calcium phosphate layers. The temperature at the substrate during the deposition process of calcium phosphate layers plays an important role in the embedding of chitosan, as scanning electron microscopy analysis showed. The degree of chitosan incorporation into the calcium phosphate layers significantly influence the physico-chemical properties and the adherence strength of the resulted layers to the substrates. For example, the decreases of Ca/P ratio at the addition of chitosan suggests that a calcium deficient hydroxyapatite structure is formed when the CaP layers are generated on Ti substrates kept at room temperature during the deposition process. The Fourier transform infrared spectroscopy analysis of the samples suggest that the PO43-/CO32- substitution is possible. The X-ray diffraction spectra indicated that the crystalline structure of the calcium phosphate layers obtained at the 300 °C substrate temperature is disturbed by the addition of chitosan. The adherence strength of the composite layers to the titanium substrates is diminished after the chitosan deposition. However, no complete exfoliation of the layers was observed.

Co-precipitation synthesis of nickel-rich cathodes for Li-ion batteries

The preparation of Ni-rich cathode materials is challenging due to the Ni2+ ion sensitivity to oxidation during synthesis. The synthesis conditions during the manufacture of Ni-rich materials such as LiNi0.8Mn0.1Co0.1O2 (NMC811) therefore require stringent control. The co-precipitation step, applied in the synthesis of the metal hydroxide precursor, determines the secondary particle assembly formation, where it is typically desirable to produce uniform, spherical, ∼10μm-diameter structures. A stirred tank reactor is often employed to maintain a constant temperature of 60 °C and a controlled pH of between 10.5 and 11.5 in an inert atmosphere to maintain a high Ni2+/Ni3+ ion ratio. This promotes the formation of an NMC hydroxide precursor (NixMnyCoz(OH)2) which is typically milled with a lithium salt and calcined to form LiNixMnyCozO2 with a layered α-NaFeO2 crystalline structure. This review outlines some of the critical synthetic parameters for the formation of spherical secondary assemblies of metal hydroxide precursors for nickel-rich layered cathodes.

Plastic Monolithic Mixed-Conducting Interlayer for Dendrite-Free Solid-State Batteries.

Solid‐state electrolytes (SSEs) hold a critical role in enabling high‐energy‐density and safe rechargeable batteries with Li metal anode. Unfortunately, nonuniform lithium deposition and dendrite penetration due to poor interfacial solid–solid contact are hindering their practical applications. Here, solid‐state lithium naphthalenide (Li‐Naph(s)) is introduced as a plastic monolithic mixed‐conducting interlayer (PMMCI) between the garnet electrolyte and the Li anode via a facile cold process. The thin PMMCI shows a well‐ordered layered crystalline structure with excellent mixed‐conducting capability for both Li+ (4.38 × 10–3 S cm–1) and delocalized electrons (1.01 × 10–3 S cm–1). In contrast to previous composite interlayers, this monolithic material enables an intrinsically homogenous electric field and Li+ transport at the Li/garnet interface, thus significantly reducing the interfacial resistance and achieving uniform and dendrite‐free Li anode plating/stripping. As a result, Li symmetric cells with the PMMCI‐modified garnet electrolyte show highly stable cycling for 1200 h at 0.2 mA cm–2 and 500 h at a high current density of 1 mA cm–2. The findings provide a new interface design strategy for solid‐state batteries using monolithic mixed‐conducting interlayers.

Nonlinear microscopy of lead iodide nanosheets.

Lead iodide (PbI2) is a van der Waals layered semiconductor with a direct bandgap in its bulk form and a hexagonal layered crystalline structure. The recently developed PbI2 nanosheets have shown great promise for high-performance optoelectronic devices, including nanolasers and photodetectors. However, despite being widely used as a precursor for perovskite materials, the optical properties of PbI2 nanomaterials remain largely unexplored. Here, we determine the nonlinear optical properties of PbI2 nanosheets by utilising nonlinear microscopy as a non-invasive optical technique. We demonstrate the nonlinearity enhancement dependent on excitonic resonances, crystalline orientation, thickness, and influence of the substrate. Our results allow for estimating the second- and third-order nonlinear susceptibilities of the nanosheets, opening new opportunities for the use of PbI2 nanosheets as nonlinear and quantum light sources.

Growth and optical characterization of Sn0.6Sb0.4Se layer single crystals for optoelectronic applications

SnSe compound is an attractive semiconductor material due to its usage in photovoltaic applications. The substitution of Sb in the SnSe compound presents a remarkable advantage especially in point of tuning optical characteristics. The present paper reports the structural and optical properties of Sn1-xSbxSe (x = 0.4) layered single crystals grown by the vertical Bridgman method. To the best of our knowledge, this work is the first investigation of the Sn0.6Sb0.4Se crystal grown with the vertical Bridgman technique. X-ray diffraction (XRD) pattern of the grown crystal indicated the well crystalline structure of the grown crystals. Lattice strain and interplanar spacing of the crystal structure were determined using the XRD pattern. Scanning electron microscope images allowed to the observation of the layer crystal structure. The layer crystalline structure shows 2D material properties and provides 2D applications. Optical properties were revealed by carrying out Raman, ellipsometry and transmission measurements. Raman modes, refractive index, extinction coefficient, and dielectric spectra, band gap energy of the crystal were presented throughout the paper. The obtained results indicated that Sn1-xSbxSe (x = 0.4) layer single crystals may be an alternative potential for photovoltaic and optoelectronic applications.

Deuterium Retention and Release Behavior from Beryllium Co-Deposited Layers at Distinct Ar/D Ratio

Beryllium-deuterium co-deposited layers were obtained using DC magnetron sputtering technique by varying the Ar/D2 gas mixture composition (10/1; 5/1; 2/1 and 1:1) at a constant deposition rate of 0.06 nm/s, 343 K substrate temperature and 2 Pa gas pressure. The surface morphology of the layers was analyzed using Scanning Electron Microscopy and the layer crystalline structure was analyzed by X-ray diffraction. Rutherford backscattering spectrometry was employed to determine the chemical composition of the layers. D trapping states and inventory quantification were performed using thermal desorption spectroscopy. The morphology of the layers is not influenced by the Ar/D2 gas mixture composition but by the substrate type and roughness. The increase of the D2 content during the deposition leads to the deposition of Be-D amorphous layers and also reduces the layer thickness by decreasing the sputtering yield due to the poisoning of the Be target. The D retention in the layers is dominated by the D trapping in low activation binding states and the increase of D2 flow during deposition leads to a significant build-up of deuterium in these states. Increase of deuterium flow during deposition consequently leads to an increase of D retention in the beryllium layers up to 300%. The resulted Be-D layers release the majority of their D (above 99.99%) at temperatures lower than 700 K.

High reversibility of layered oxide cathode enabled by direct Re-generation

Recently, lithium-ion batteries (LIBs) play an increasingly important role in daily life, and recycle of LIBs material has also become a hotspot. Herein, the degradation mechanisms of layered transition metal oxide, LiNi0.5Co0.2Mn0.3O2 (NCM523) single crystal particles, are comprehensively investigated by the atomic analysis and simulations of Aberration-corrected scanning transmission electron microscope (STEM) and Density Functional Theory (DFT). Based on understanding the degradation mechanisms, a direct regeneration technology is adopted to recover the degraded cathode materials (≈ 10% capacity retains) by hydrothermal treatment combined with a solid-state eutectic Li+ molten-salt solutions sintering step. The regenerated cathodes present a layered crystalline structure in the whole phase region and the capacity of pouch cell (1.7 Ah) remains 90.8% after 500 cycles with the mass loading of cathode around 21 ± 0.5 mg cm−2. In addition, the modified strategies are applied in the regenerations of different degraded samples such as LiNi1/3Co1/3Mn1/3O2 and commercially-purchased spent samples, which show the capacity maintain more than 90% after 500 cycles. Therefore, the direct regeneration technology supported with experiments and simulation affords a foundational direction for the sustainable development of energy materials.

Synthesis of Hybrid Organic-Inorganic Hydrotalcite-Like Materials Intercalated with Duplex Herbicides: The Characterization and Simultaneous Release Properties.

In this study, a controlled-release formulation of duplex herbicides, namely, 2,4,5-trichlorophenoxybutyric acid (TBA) and 3,4-dichlorophenoxy-acetic acid (3,4D), was simultaneously embedded into Zn-Al-layered double hydroxides (LDHs). The resulting nanohybrid Zinc-Aluminium-3,4D-TBA (ZADTX) was composed of a well-ordered crystalline layered structure with increasing basal spacing from 8.9 Å to 20.0 Å in the Powder X-ray Diffraction (PXRD) with 3,4D and TBA anions located in the gallery of LDHs with bilayer arrangement. The release of 3,4D and TBA fit the pseudo-second-order model. This duplex nanohybrid possessed a well-controlled release property (53.4% release from TBA and 27.8% release from 3,4D), which was highly effective, requiring the use of a small quantity and, hence, environmentally safer.

Layered 2H-MoTe2: A novel anode material for lithium-ion batteries

Transition metal dichalcogenides with well-developed two-dimensional layers and high structural stability provide superior Li+ storage property in lithium-ion batteries (LIBs). For this study, the MoTe2 polycrystalline powder sample is prepared using a facile solid-state route. Transmission electron microscopy (TEM) along with selected area diffraction (SAD) patterns, Field emission scanning electron microscopy (FE-SEM) combined with energy dispersive X-ray spectroscopy (EDX) have been performed to obtain crystallographic, morphological, and chemical information of the as-prepared MoTe2 powder. SAD patterns and the high-resolution transmission electron microscopy (HRTEM) study reveal the well-developed crystalline layered structure of the MoTe2 powder. The as-prepared MoTe2 electrode showed an initial specific discharge capacity of ~ 452 mAh g−1 versus lithium metal and a corresponding specific discharge capacity of ~ 279 mAh g−1 is achieved after 40 cycles at 1.0 A g−1 current density.

Enabling the fast lithium storage of large-scalable γ-Fe2O3/Carbon nanoarchitecture anode material with an ultralong cycle life

Two-dimensional (2D) materials are generally expected to have superior lithium-ion (LIBs) performances compare with their bulk counterpart as they display superior specific surface area. In this context, the development of 2D maghemite would be of great interest owing to its high theoretical specific capacity, natural abundance, and relatively low cost and toxicity; however, maghemite do not have a layered crystalline structure. Herein, to overcome this hindrance, γ-Fe2O3 has been enclosed within a 2D carbon matrix via a simple and facile synthesis strategy based on the complexation of ethylene glycol with aqueous iron species by hydrolysis and condensation reactions followed by its carbonization. As obtained 2D carbon γ-Fe2O3 nanosheet composite (CEG-Fe) is composed of 41.3 wt.% carbon and 10.2 wt.% Fe. When used as anode materials in LIBs, CEG-Fe demonstrated the enhanced initial discharge capacity of 1589 mAh g−1 at 100 mA g−1, and outstanding ultralong cycling performance with the significant stable capacity of 700 mAh g−1 and 230 mAh g−1 at the higher current rate of 0.5 A g−1 and 10 A g−1 for more than 300 and 6000 cycles, respectively. These results enable a promising avenue to design the large-scale production of 2D CEG-Fe sheets-based nanostructured anode materials for next-generation LIBs for large‐scale energy storage applications.

Formation and Characterization of Ge1–x–ySixSny/Ge Heterojunction Structures for Photovoltaic Cell Application

Group-IV alloy semiconductor materials are much attractive for photovoltaic application, as those realizes multijunction photovoltaic with multi-heterostructure like group-III-V compound semiconductors [1]. In addition, group-IV alloy materials are expected to be familiar to Si integrated electronics. Ge1–x–ySixSny is one of candidate materials suitable for multijunction photovoltaic, since ternary alloy semiconductor provides energy band design independent on the lattice constant. The energy band gap of Ge1–x–ySixSny can be controlled from 0.66 eV to 1.0 eV with the epitaxial layer whose lattice is matching to Ge substrate.We previously reported the epitaxial growth of Ge1–x–ySixSny layers and also investigated the crystalline and electronic properties of them [2, 3]. However, the junction properties of Ge1–x–ySixSny/Ge heterostructure have not been well understood and it is necessary to clarify the crystalline and electronic properties of group-IV ternary alloy hetero junctions. In this study, we examined the crystal growth of pseudomorphic epitaxial layers of Ge1–x–ySixSny ternary alloy on Ge(001) substrates to form heterojunction structure for photovoltaic application. We also investigated the electronic and optoelectronic properties of these Ge1–x–ySixSny/n-Ge heterojunction diodes.Substrate used was n-type Ge(001) wafer. After chemical cleaning of substrate, a 200 nm-thick undoped Ge1–x–ySixSny layer was grown at 150–350 °C on substrate using molecular beam epitaxy system in ultrahigh vacuum chamber. Ge and Sn were deposited using Knudsen cells and Si was done using electron gun evaporation. Then, we prepared a mesa-shaped structure with wet etching. A 300 nm-thick SiO2 layer was deposited with coating of spin-on-glass and annealing at 450 °C. Finally, an Al electrode was prepared on contact holes to form heterojunction diode structure.We confirmed the crystalline structure of epitaxial layers with X-ray diffraction reciprocal space mapping. A Ge1–x–ySixSny layer with a high Sn content of 12% can be prepared with lattice matching epitaxy on Ge at a low temperature below 250 °C. It is also found that the small misfit between Ge1–x–ySixSny and Ge effectively impacts on the high crystalline quality and high thermal stability of substitutional Sn atoms in Ge matrix.Absorption spectroscopy and current-voltage characteristics of undoped Ge1–x–ySixSny/n-Ge heterojunction diodes were also performed. We observed good rectifying property of the diodes meaning that the majority carrier of these undoped Ge1–x–ySixSny ternary alloy layers is hole unintentionally generated due to defects. We also found the extension of the energy band gap of Ge1–x–ySixSny layer with Si and Sn contents. Photovoltaic property of Ge1–x–ySixSny/Ge heterojunction diodes were also measured. We can see the increasing of the open circuit voltage, Voc from 0.08 to 0.12 V for undoped Ge/n-Ge to undoped Ge0.54Si0.36Sn0.10/Ge heterojunction photovoltaic cell structure, which indicates the enhancement of Voc with increasing the energy bandgap of epitaxial layer. We also achieved the improvement of Voc by 0.14 V with 500 °C-annealing in hydrogen (H2) ambient, which suggests the annihilation or termination of point defect in the heterojunction structure.In conclusions, heterojunction structure with Ge1–x–ySixSny ternary alloy semiconductor layer provides the energy band engineering for photovoltaic applications. Understanding and controlling the defect properties in epitaxial growth and heterojunction formation should be key factors for the enhancement of performance of group-IV multijunction photovoltaic.

Progress and perspectives of bismuth oxyhalides in catalytic applications

Bismuth oxyhalides are characterized by their open two-dimensional layered crystalline structures which endow bismuth oxyhalides with high specific surface areas, large amount of surface exposed atoms and some other unique physical and chemical properties. Owing to these abundant features, bismuth oxyhalides have great potential in serving as excellent photocatalysts and electrocatalysts and have received enormous research interest in addressing serious global environmental pollution and energy shortage crisis recent years. In this review, we first discuss the superior structural characteristics of bismuth oxyhalides, comprehensively summarize the efficient strategies including metal/non-metal incorporation, modulating strain, constructing vacancies, constructing heterostructures and constructing moiré superlattice to improve the photocatalytic activities, and then introduce current progress on bismuth-oxyhalides-templated electrocatalysts for CO2 reduction. At the end of this article, we propose some perspectives for the future development of bismuth oxyhalides as photocatalysts and templates of electrocatalysts, aiming at constructing superior photoelectrochemical devices and promoting this bifunctional material into industrial application.