Showing papers on "Amorphous silicon published in 2014"
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TL;DR: In this paper, the state-of-the-art in organic field effect transistors (OFETs) are reviewed in light of requirements for demanding future applications, in particular active-matrix addressing for flexible organic light-emitting diode (OLED) displays.
Abstract: Over the past 25 years, organic field-effect transistors (OFETs) have witnessed impressive improvements in materials performance by 3–4 orders of magnitude, and many of the key materials discoveries have been published in Advanced Materials. This includes some of the most recent demonstrations of organic field-effect transistors with performance that clearly exceeds that of benchmark amorphous silicon-based devices. In this article, state-of-the-art in OFETs are reviewed in light of requirements for demanding future applications, in particular active-matrix addressing for flexible organic light-emitting diode (OLED) displays. An overview is provided over both small molecule and conjugated polymer materials for which field-effect mobilities exceeding > 1 cm2 V–1 s–1 have been reported. Current understanding is also reviewed of their charge transport physics that allows reaching such unexpectedly high mobilities in these weakly van der Waals bonded and structurally comparatively disordered materials with a view towards understanding the potential for further improvement in performance in the future.
1,992 citations
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TL;DR: The growth of a highly aligned meta-stable structure of 2,7-dioctyl[1]benzothieno[3,2-b][1] Benzothiophene (C8-BTBT) is described from a blended solution of C8- BTBT and polystyrene by using a novel off-centre spin-coating method, indicating their potential for transparent, high-performance organic electronics.
Abstract: One of the advantages of organic over inorganic semiconductors is they can be grown from solution, but their electrical mobility is often poor. Yuan et al. report a technique for fabricating organic transistors with mobilities far beyond that of amorphous silicon and close to that of polycrystalline silicon.
1,130 citations
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TL;DR: A structural relationship betweencarbon and silicon in biochars is proposed to explain the mutual protection between carbon and silicon under different pyrolysis temperatures, which contribute to the broader understanding of biochar chemistry and structure.
Abstract: Biochars are increasingly recognized as environmentally friendly and cheap remediation agents for soil pollution. The roles of silicon in biochars and interactions between silicon and carbon have been neglected in the literature to date, while the transformation, morphology, and dissolution of silicon in Si-rich biochars remain largely unaddressed. In this study, Si-rich biochars derived from rice straw were prepared under 150-700 °C (named RS150-RS700). The transformation and morphology of carbon and silicon in biochar particles were monitored by FTIR, XRD, and SEM-EDX. With increasing pyrolytic temperature, silicon accumulated, and its speciation changed from amorphous to crystalline matter, while the organic matter evolved from aliphatic to aromatic. For rice straw biomass containing amorphous carbon and amorphous silicon, dehydration (<250 °C) made silicic acid polymerize, resulting in a closer integration of carbon and silicon. At medium pyrolysis temperatures (250-350 °C), an intense cracking of carbon components occurred, and, thus, the silicon located in the inside tissue was exposed. At high pyrolysis temperatures (500-700 °C), the biochar became condensed due to the aromatization of carbon and crystallization of silicon. Correspondingly, the carbon release in water significantly decreased, while the silicon release somewhat decreased and then sharply increased with pyrolytic temperature. Along with SEM-EDX images of biochars before and after water washing, we proposed a structural relationship between carbon and silicon in biochars to explain the mutual protection between carbon and silicon under different pyrolysis temperatures, which contribute to the broader understanding of biochar chemistry and structure. The silicon dissolution kinetics suggests that high Si biochars could serve as a novel slow release source of biologically available Si in low Si agricultural soils.
382 citations
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TL;DR: In this article, the authors explore substoichiometric molybdenum trioxide (MoOx, x < 3) as a dopant-free, hole-selective contact for silicon solar cells.
Abstract: We explore substoichiometric molybdenum trioxide (MoOx, x < 3) as a dopant-free, hole-selective contact for silicon solar cells. Using an intrinsic hydrogenated amorphous silicon passivation layer between the oxide and the silicon absorber, we demonstrate a high open-circuit voltage of 711 mV and power conversion efficiency of 18.8%. Due to the wide band gap of MoOx, we observe a substantial gain in photocurrent of 1.9 mA/cm2 in the ultraviolet and visible part of the solar spectrum, when compared to a p-type amorphous silicon emitter of a traditional silicon heterojunction cell. Our results emphasize the strong potential for oxides as carrier selective heterojunction partners to inorganic semiconductors.
358 citations
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TL;DR: To the best of the knowledge, this is the first report of all 2D transparent TFT fabricated on flexible substrate along with the highest mobility and current ON-OFF ratio.
Abstract: In this article, we report only 10 atomic layer thick, high mobility, transparent thin film transistors (TFTs) with ambipolar device characteristics fabricated on both a conventional silicon platform as well as on a flexible substrate. Monolayer graphene was used as metal electrodes, 3–4 atomic layers of h-BN were used as the gate dielectric, and finally bilayers of WSe2 were used as the semiconducting channel material for the TFTs. The field effect carrier mobility was extracted to be 45 cm2/(V s), which exceeds the mobility values of state of the art amorphous silicon based TFTs by ∼100 times. The active device stack of WSe2–hBN–graphene was found to be more than 88% transparent over the entire visible spectrum and the device characteristics were unaltered for in-plane mechanical strain of up to 2%. The device demonstrated remarkable temperature stability over 77–400 K. Low contact resistance value of 1.4 kΩ-μm, subthreshold slope of 90 mv/decade, current ON–OFF ratio of 107, and presence of both electr...
327 citations
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TL;DR: An amorphous (a) silicon nanoparticle backboned graphene nanocomposite for high-power lithium ion battery anodes was prepared and shows elastic behavior during lithium alloying and dealloying: the pristine particle size is restored after cycling, and the electrode thickness decreases during the cycles as a result of self-compacting.
Abstract: Although various Si-based graphene nanocomposites provide enhanced electrochemical performance, these candidates still yield low initial coloumbic efficiency, electrical disconnection, and fracture due to huge volume changes after extended cycles lead to severe capacity fading and increase in internal impedance. Therefore, an innovative structure to solve these problems is needed. In this study, an amorphous (a) silicon nanoparticle backboned graphene nanocomposite (a-SBG) for high-power lithium ion battery anodes was prepared. The a-SBG provides ideal electrode structures—a uniform distribution of amorphous silicon nanoparticle islands (particle size <10 nm) on both sides of graphene sheets—which address the improved kinetics and cycling stability issues of the silicon anodes. a-Si in the composite shows elastic behavior during lithium alloying and dealloying: the pristine particle size is restored after cycling, and the electrode thickness decreases during the cycles as a result of self-compacting. This...
176 citations
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TL;DR: A hybrid photovoltaic/photoelectrochemical (PV/PEC) water-splitting device with a benchmark solar-to-hydrogen conversion efficiency of 5.2% under simulated air mass (AM) 1.5 illumination is reported.
Abstract: A hybrid photovoltaic/photoelectrochemical (PV/PEC) water-splitting device with a benchmark solar-to-hydrogen conversion efficiency of 5.2 % under simulated air mass (AM) 1.5 illumination is reported. This cell consists of a gradient-doped tungsten–bismuth vanadate (W:BiVO_4) photoanode and a thin-film silicon solar cell. The improvement with respect to an earlier cell that also used gradient-doped W:BiVO4 has been achieved by simultaneously introducing a textured substrate to enhance light trapping in the BiVO4 photoanode and further optimization of the W gradient doping profile in the photoanode. Various PV cells have been studied in combination with this BiVO_4 photoanode, such as an amorphous silicon (a-Si:H) single junction, an a-Si:H/a-Si:H double junction, and an a-Si:H/nanocrystalline silicon (nc-Si:H) micromorph junction. The highest conversion efficiency, which is also the record efficiency for metal oxide based water-splitting devices, is reached for a tandem system consisting of the optimized W:BiVO_4 photoanode and the micromorph (a-Si:H/nc-Si:H) cell. This record efficiency is attributed to the increased performance of the BiVO_4 photoanode, which is the limiting factor in this hybrid PEC/PV device, as well as better spectral matching between BiVO_4 and the nc-Si:H cell.
148 citations
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TL;DR: In this article, the authors use stacks of intrinsic amorphous silicon and amorphus oxide as front intrinsic buffer layers and show that this increases the short-circuit current density by up to 0.43 µm/cm2.
Abstract: In amorphous/crystalline silicon heterojunction solar cells, optical losses can be mitigated by replacing the amorphous silicon films by wider bandgap amorphous silicon oxide layers. In this article, we use stacks of intrinsic amorphous silicon and amorphous silicon oxide as front intrinsic buffer layers and show that this increases the short-circuit current density by up to 0.43 mA/cm2 due to less reflection and a higher transparency at short wavelengths. Additionally, high open-circuit voltages can be maintained, thanks to good interface passivation. However, we find that the gain in current is more than offset by losses in fill factor. Aided by device simulations, we link these losses to impeded carrier collection fundamentally caused by the increased valence band offset at the amorphous/crystalline interface. Despite this, carrier extraction can be improved by raising the temperature; we find that cells with amorphous silicon oxide window layers show an even lower temperature coefficient than referenc...
138 citations
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TL;DR: The results show that sputter-CVD is a viable method to synthesize large-area, high-quality, and layer-controlled MoS2 that can be adapted in conventional Si-based microfabrication technology and future flexible,high-temperature, and radiation hard electronics/optoelectronics.
Abstract: Two-dimensional MoS2 is a promising material for next-generation electronic and optoelectronic devices due to its unique electrical and optical properties including the band gap modulation with film thickness. Although MoS2 has shown excellent properties, wafer-scale production with layer control from single to few layers has yet to be demonstrated. The present study explored the large-scale and thickness-modulated growth of atomically thin MoS2 on Si/SiO2 substrates using a two-step sputtering–CVD method. Our process exhibited wafer-scale fabrication and successful thickness modulation of MoS2 layers from monolayer (0.72 nm) to multilayer (12.69 nm) with high uniformity. Electrical measurements on MoS2 field effect transistors (FETs) revealed a p-type semiconductor behavior with much higher field effect mobility and current on/off ratio as compared to previously reported CVD grown MoS2-FETs and amorphous silicon (a-Si) thin film transistors. Our results show that sputter–CVD is a viable method to synthes...
134 citations
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TL;DR: In this article, a comparative study is performed to obtain the energy performance of four different photovoltaic module technologies, when they are exposed to the same real sun conditions over a one-year period under the meteorological conditions of Southern Spain.
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TL;DR: An atomic-level study on the applicability of a Si anode in Na ion batteries using ab initio molecular dynamics simulations suggests that amorphous Si might be a competitive candidate for Na ion battery anodes.
Abstract: Despite the exceptionally large capacities in Li ion batteries, Si has been considered inappropriate for applications in Na ion batteries. We report an atomic-level study on the applicability of a Si anode in Na ion batteries using ab initio molecular dynamics simulations. While crystalline Si is not suitable for alloying with Na atoms, amorphous Si can accommodate 0.76 Na atoms per Si atom, corresponding to a specific capacity of 725 mA h g–1. Bader charge analyses reveal that the sodiation of an amorphous Si electrode continues until before the local Na-rich clusters containing neutral Na atoms are formed. The amorphous Na0.76Si phase undergoes a volume expansion of 114% and shows a Na diffusivity of 7 × 10–10 cm2 s–1 at room temperature. Overall, the amorphous Si phase turns out quite attractive in performance compared to other alloy-type anode materials. This work suggests that amorphous Si might be a competitive candidate for Na ion battery anodes.
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TL;DR: In this article, dual-function solar cells based on ultrathin dopant-free amorphous silicon embedded in an optical cavity that not only efficiently extract the photogenerated carriers but also display distinctive colors with the desired angle-insensitive appearances.
Abstract: Most current solar panels are fabricated via complex processes using expensive semiconductor materials, and they are rigid and heavy with a dull, black appearance. As a result of their non-aesthetic appearance and weight, they are primarily installed on rooftops to minimize their negative impact on building appearance. The large surfaces and interiors of modern buildings are not efficiently utilized for potential electric power generation. Here, we introduce dual-function solar cells based on ultrathin dopant-free amorphous silicon embedded in an optical cavity that not only efficiently extract the photogenerated carriers but also display distinctive colors with the desired angle-insensitive appearances. Light-energy-harvesting colored signage is demonstrated. Furthermore, a cascaded photovoltaics scheme based on tunable spectrum splitting can be employed to increase power efficiency by absorbing a broader band of light energy. This study pioneers a new approach to architecturally compatible and decorative thin-film photovoltaics. Ultrathin solar cells that can also act as coloured signs and displays have been developed by scientists in the USA. Kyu-Tae Lee and co-workers from the University of Michigan fabricated them by embedding a very thin (10–30 nm) layer of amorphous silicon within a metal–semiconductor–metal optical cavity. The cavity acts as a Fabry–Perot resonator that reflects a particular colour; importantly, it is insensitive to the polarization state or angle (up to 60°) of the incident light. By combining cells of different thickness (and hence different colours), arbitrary patterns or images can be created. The design has yielded solar cells with power conversion efficiencies of around 3%, despite using an amorphous silicon layer that is ten times thinner than those usually found in solar cells.
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TL;DR: Amorphous silicon is a promising high-capacity anode material for the next generation of lithium-ion batteries as discussed by the authors, however, the enormous volume expansion of the active material during lithiation up to...
Abstract: Amorphous silicon is a promising high-capacity anode material for the next generation of lithium-ion batteries. However, the enormous volume expansion of the active material during lithiation up to...
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TL;DR: In this paper, a model of concurrent lithiation and rate-sensitive plasticity is developed for amorphous LixSi thin films, and the results have direct ramifications concerning the rate-capabilities of silicon electrodes: faster charging rates (i.e., strain rates) result in larger stresses and hence larger driving forces for fracture.
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TL;DR: In this article, a detailed structural characterization of silicon oxycarbide anodes is performed with complementary techniques with the aim of correlating the electrochemical behavior with the structure of the SiOC anodes.
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TL;DR: In this paper, an amorphous silicon (a-Si) film with a narrow band gap of 1.8 eV was deposited on the PZT/ITO/glass.
Abstract: Pb(Zr,Ti)O3 (PZT) film with a band gap of 3.6 eV was prepared on In2O3:Sn (ITO) coated glass, and then an amorphous silicon (a-Si) film with a narrow band gap of 1.8 eV was deposited on the PZT/ITO/glass. The short-circuit current of Ag/a-Si/PZT/ITO/glass sample is 2.56 mA cm−2, about 50 times greater than that of Pt/PZT/ITO/glass sample. The energy level of the a-Si film is well matched with that of PZT film, which is beneficial to the transport of UV-visible light-induced charges in the Ag/a-Si/PZT/ITO/glass sample. The photovoltaic output can be tuned by changing the dopant type of the a-Si film, and the maximum photoelectric conversion efficiency is measured to be up to 1.25% in the PZT film with an n-type a-Si film (phosphorus doped).
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TL;DR: In this paper, the authors report on the fabrication of back-contacted silicon heterojunction solar cells with conversion efficiencies above 21% using simple and size-scalable patterning methods.
Abstract: We report on the fabrication of back-contacted silicon heterojunction solar cells with conversion efficiencies above 21%. Our process technology relies solely on simple and size-scalable patterning methods, with no high-temperature steps. Using in situ shadow masks, doped hydrogenated amorphous silicon layers are patterned into two interdigitated combs. Transparent conductive oxide and metal layers, forming the back electrodes, are patterned by hot melt inkjet printing. With this process, we obtain high short-circuit current densities close to 40 mA/cm $^{2}$ and open-circuit voltages exceeding 720 mV, leading to a conversion efficiency of 21.5%. However, moderate fill factor values limit our current device efficiencies. Unhindered carrier transport through both heterocontact layer stacks, as well as higher passivation quality over the minority carrier-injection range relevant for solar cell operation, are identified as key factors for improved fill factor values and device performance.
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TL;DR: In this paper, optically stable amorphous silicon nanowires with both high nonlinear figure of merit (FOM) of ~5 and high non linearity Re({\gamma}) = 1200W-1m-1.
Abstract: We demonstrate optically stable amorphous silicon nanowires with both high nonlinear figure of merit (FOM) of ~5 and high nonlinearity Re({\gamma}) = 1200W-1m-1. We observe no degradation in these parameters over the entire course of our experiments including systematic study under operation at 2 W coupled peak power (i.e. ~2GW/cm2) over timescales of at least an hour.
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TL;DR: In this paper, the authors show that the enhanced surface energetics at a high growth temperature improved the amorphous structural network of e-beam a-Si and removed TLSs.
Abstract: The ubiquitous low-energy excitations, known as two-level tunneling systems (TLSs), are one of the universal phenomena of amorphous solids. Low temperature elastic measurements show that e-beam amorphous silicon (a-Si) contains a variable density of TLSs which diminishes as the growth temperature reaches 400 °C. Structural analyses show that these a-Si films become denser and more structurally ordered. We conclude that the enhanced surface energetics at a high growth temperature improved the amorphous structural network of e-beam a-Si and removed TLSs. This work obviates the role hydrogen was previously thought to play in removing TLSs in the hydrogenated form of a-Si and suggests it is possible to prepare "perfect" amorphous solids with "crystal-like" properties for applications.
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TL;DR: In this paper, degradation analysis of three different photovoltaic technology modules namely a-Si (amorphous single junction silicon), HIT (hetro-junction intrinsic thin layer silicon) and m-C-Si(multi-crystalline silicon) is carried out after 28 months of outdoor exposure at Solar Energy Centre, India.
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19 Dec 2014TL;DR: In this paper, a method and apparatus for cleaning a substrate having a plurality of high-aspect ratio openings is described, where the substrate can include a silicon oxide layer over a damaged or amorphous silicon layer.
Abstract: Method and apparatus for cleaning a substrate having a plurality of high-aspect ratio openings are disclosed. A substrate can be provided in a plasma processing chamber, where the substrate includes the plurality of high-aspect ratio openings, the plurality of high-aspect ratio openings are defined by vertical structures having alternating layers of oxide and nitride or alternating layers of oxide and polysilicon. The substrate can include a silicon oxide layer over a damaged or amorphous silicon layer in the high-aspect ratio openings. To remove the silicon oxide layer, a bias power can be applied in the plasma processing chamber at a low pressure, and a fluorine-based species can be used to etch the silicon oxide layer. To remove the underlying damaged or amorphous silicon layer, a source power and a bias power can be applied in the plasma processing chamber, and a hydrogen-based species can be used to etch the damaged or amorphous silicon layer.
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TL;DR: In this article, the role of mechanical properties of the current collector on this characteristic delamination behavior during electrochemical cycling was investigated and it was shown that current collectors with low elastic modulus such as graphite can completely suppress interfacial delamination.
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TL;DR: In this article, the authors investigated the crystallization of amorphous silicon nanoparticles in nonthermal plasmas using a tandem plasma configuration and found that the nanoparticles reach temperatures as high as 750-850 K in the secondary plasma, which is well above the gas temperature and sufficient for complete nanoparticle crystallization.
Abstract: While the formation of nanoparticles in nonthermal plasmas is well known, the heating mechanism leading to their crystallization is poorly understood. In this study, we investigate the crystallization of amorphous silicon nanoparticles in nonthermal plasmas using a tandem plasma configuration. Amorphous silicon nanoparticles with diameters of 3, 4 or 5 nm are formed in a low-power nonthermal upstream plasma, and injected directly into a second separate downstream plasma. Crystallization of the amorphous silicon nanoparticles is investigated as a function of the power used to maintain the second plasma. This approach allows for the decoupling of nanoparticle synthesis and heating. The nanoparticle properties and plasma conditions are examined to obtain a comprehensive understanding of nanoparticle heating and crystallization. The particle crystallinity was studied using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. We discovered a threshold power for complete crystallization of the particles. A combination of comprehensive plasma characterization with a nanoparticle heating model reveals the underlying plasma physics leading to crystallization. Here we found that the nanoparticles reach temperatures as high as 750–850 K in the secondary plasma, which is well above the gas temperature and sufficient for complete nanoparticle crystallization. While we demonstrate this method of predicting nanoparticle temperature using silicon, the approach can be applied broadly to other plasma-synthesized nanomaterials.
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TL;DR: Cross-phase modulation is utilized to observe all-optical switching in microring resonators fabricated with hydrogenated amorphous silicon (a-Si:H), which exhibits substantially higher switching speeds due to reduced impact of free-carrier processes.
Abstract: We utilize cross-phase modulation to observe all-optical switching in microring resonators fabricated with hydrogenated amorphous silicon (a-Si:H). Using 2.7-ps pulses from a mode-locked fiber laser in the telecom C-band, we observe optical switching of a cw telecom-band probe with full-width at half-maximum switching times of 14.8 ps, using approximately 720 fJ of energy deposited in the microring. In comparison with telecom-band optical switching in undoped crystalline silicon microrings, a-Si:H exhibits substantially higher switching speeds due to reduced impact of free-carrier processes.
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TL;DR: A low-cost and scalable approach to achieve perfectly ordered i-cone arrays is demonstrated to demonstrate a viable and convenient route toward scalable fabrication of nanostructures for high-performance thin film PV devices based on a broad range of materials.
Abstract: Thin film photovoltaic (PV) technologies are highly attractive for low-cost solar energy conversion and possess a wide range of potential applications from building-integrated PV generation to portable power sources. Inverted nanocones (i-cones) have been demonstrated as a promising structure for practical thin film PV devices/modules, owning to their antireflection effect, self-cleaning function, superior mechanical robustness, and so forth. In this work, we have demonstrated a low-cost and scalable approach to achieve perfectly ordered i-cone arrays. Thereafter, thin film amorphous silicon (a-Si:H) solar cells have been fabricated based on various i-cone substrates with different aspect ratios and pitches to investigate the impact of geometry of i-cone nanostructures on the performance of the as-obtained PV devices. Intriguingly, the optical property investigations and device performance characterizations demonstrated that the 0.5-aspect-ratio i-cone-based device performed the best on both light absorption capability and energy conversion efficiency, which is 34% higher than that of the flat counterpart. Moreover, the i-cone-based device enhanced the light absorption and device performance over the flat reference device omnidirectionally. These results demonstrate a viable and convenient route toward scalable fabrication of nanostructures for high-performance thin film PV devices based on a broad range of materials.
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TL;DR: In this paper, a light-weight three dimensional soft silicon anodes for flexible and stretchable lithium ion batteries are presented. But the authors employ a coaxial flexible Ni/Ni/PVDF nanofiber network as the freestanding current collector and active amorphous silicon coating to form a core-shell structure of Si/Ni, PVDF and nanofibers.
Abstract: We present novel light weight three dimensional soft silicon anodes for flexible and stretchable lithium ion batteries. We employ a coaxial flexible Ni/PVDF nanofiber network as the freestanding current collector and active amorphous silicon coating to form a core–shell structure of Si/Ni/PVDF nanofibers. The soft silicon anodes show high specific capacities and good cycling life. We have demonstrated that a soft battery with the freestanding Si/Ni/PVDF membrane as an anode is capable of powering a LED at different bending states.
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TL;DR: In this article, the amorphous silicon/carbon (a-Si/C) multilayer thin films were synthesized by magnetic sputtering method and the bonding characteristics and phase identification were investigated by X-ray diffraction (XRD) and Raman spectrum.
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TL;DR: In this article, a study on recycling silicon and silicon carbide powders from wire-saw slurry containing silicon carbides, silicon kerfs, polyethylene glycol (PEG), and iron fragments in the slicing silicon ingots process was conducted.
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TL;DR: In this article, the authors studied the fracture resistance of amorphous silicon micropillars (∼2.3mm tall) after electrochemical lithiation and delithiation.