Silicon Nanotubes Research Articles

Single-walled silicon nanotube as an exceptional candidate to eliminate SARS-CoV-2: a theoretical study

In this work, computational chemistry methods were used to study a silicon nanotube (Si192H16) as possible virucidal activity against SARS-CoV-2. This virus is responsible for the COVID-19 disease. DFT calculations showed that the structural parameters of the Si192H16 nanotube are in agreement with the theoretical/experimental parameters reported in the literature. The low energy gap value (0.29 eV) shows that this nanotube is a semiconductor and exhibits high reactivity. For nanomaterials to be used as virucides, they need to have high reactivity and high inhibition constant values. Therefore, the adsorption of 3O2 and H2O on the surface of Si192H16 (Si192H16@O2-H2O) was performed. In this process, the formation and activation energies were −51.63 and 16.62 kcal/mol, respectively. Molecular docking calculations showed that the Si192H16 and Si192H16@O2H-OH nanotubes bind favorably on the receptor-binding domain of the SARS-CoV-2 spike protein with binding energy of −11.83 (Ki = 2.13 nM) and −11.13 (Ki = 6.99 nM) kcal/mol, respectively. Overall, the results obtained herein indicate that the Si192H16 nanotube is a potential candidate to be used against COVID-19 from reactivity process and/or steric impediment in the S-protein. Communicated by Ramaswamy H. Sarma

An Environmental Sustainability Analysis Tool for Next Generation Lithium Ion Batteries of Electric Vehicles

Lithium-ion batteries (LIBs) are widely used in portable electronics and electric vehicles, but are limited in capacity and energy density. Tremendous efforts have been devoted to the research and development of next-generation LIBs with a high capacity and energy density, particularly through adoption of novel nano-structured materials in the LIB electrodes. The synthesis of nanomaterials, however, involves heavy use of toxic chemicals and nanoparticle emissions, which induce grave concerns on the environmental sustainability of next-generation LIBs. Silicon, with a high theoretical specific capacity, has been recognized as one of the most promising anode materials for next-generation LIBs. In this study, a comprehensive analysis tool is developed to evaluate the environmental sustainability of silicon-based LIBs for EVs by incorporating previously published data, and two nanostructured silicon materials, i.e., silicon nanowires (SiNWs) and silicon nanotubes (SiNTs) are chosen as examples. The purpose is to provide decision support for sustainable design of next-generation LIB technologies by providing overall environmental impact results and feedback to next-generation LIB designers to identify the tradeoffs between technical specifications and sustainability performance. Specifically, this tool based on an Excel spreadsheet comprises six modules, i.e., Dashboard, Material Consumptions, Gas and Aqueous Emissions, Nano Particle Emissions, Energy Consumption, and Life Cycle Impacts. The specifications of the battery packs are inputted in the Dashboard and the environmental impact assessment is conducted through the rest modules utilizing the inputted data to compute each modular results using the embedded formula from our previously published work. The conventional emissions and energy consumption data are characterized with the life cycle impact assessment method for design feedback, while the nanoparticle emission data are experimentally measured and directly used. This analysis tool provides insights into material consumptions and environmental impacts of SiNW-and SiNT-based LIBs and can be expanded for future analyses of other nanostructured next-generation LIB technologies for electric vehicles.

Computational study on encapsulation of 5-fluorouracil drug in nanotubes

<abstract><p>Cancer remains a major health concern worldwide, causing high rates of morbidity and mortality. Although chemotherapy with antitumor drugs is the most common treatment for cancer, certain disadvantages limit its usage, such as the damage caused to healthy cells, side effects, and toxicity. Owing to their geometric and mechanical properties, nanotubes are promising nanocarriers of anticancer drugs. Here, the interaction energies of the encapsulation of an anticancer drug by single-walled nanotubes were calculated through the application of the 6–12 Lennard-Jones function with a continuous approach. In particular, the interaction energies of the 5-fluorouracil drug entering three different nanotubes (carbon, silicon and boron nitride) and the offset equilibria inside the nanotubes were obtained. This study aimed at determining the appropriate type and favorable size of nanotubes that can be used to encapsulate the 5-fluorouracil drug. The results showed that the optimal radii of nanotubes for encapsulating the 5-fluorouracil drug were approximately 6.08, 6.05 and 5.98 Å for carbon, boron nitride and silicon nanotubes, corresponding to -16.55, -18.20 and -17.81 kcal/mol, respectively.</p></abstract>

Electron Delocalization on the Silicon Nanoparticles Surface

The specific properties of tubular and fullerenlike silicon nanoparticles depend on theirs electronic structure, which is directly related to the surface geometry. Using density functional approach, a novel dual nature of the surface structure of silicon nanotubes which depends on the type of nanotube have been revevaled. The rippled form of the surface has shown to be a favorable one for (n, n) type structure and the most stable form for (n, 0) Si NT is the nanotube with a smooth-walled graphene-like surface. The phenomenon is explained by the relative position of the non-hybridized p orbitals on the surface.

Stable nanotube construction conditions and electronic properties of possible Si double-walled nanotubes (nin,min)@(6,mout) (nin =3, 4) by SCC-DFTB calculations

The geometric structural optimization and electronic properties of double-walled silicon nanotubes (DWSiNTs) (nin,min)@(6,mout) (nin = 3, 4, min = 0 to nin, mout = 0 to 6) are studied in terms of the self-consistent charge density functional tight binding (SCC-DFTB) method. A suitable spacing range of initial model that can form a stable DWSiNT is explored. Most of the nanotubes present circular-like shapes of their cross-sectional configurations. When a DWSiNT has the same chiral angle, 0 or 30 in degree, in its inner and outer walls, a regular periodic structure develops. The bond length, inner and outer wall diameters, and wall spacing are also significantly affected by changes in the chiral index. The stability of the nanotube is affected by three factors: the configuration, the diameter, and the regularity of the atomic arrangements. The electrons in the inner wall are transferred to the outer wall, and the electron distribution of the atoms in the outer wall tube has the regional distribution of the interval between the electron-obtaining and the electron-losing regions. Among the seven tubes with fully commensurate inner and outer walls, DWSiNTs (3,2)@(6,4) exhibit semi-metallic characteristics; the others exhibit semiconductor-like properties with a narrow band gaps. The band gap of DWSiNTs is changed by tuning the chirality index, resulting in the transition between direct and indirect band gaps of nanotubes, which can be adjusted to match the performance needs of different devices, inducing a metal-semiconductor transition and direct-indirect band gap transition. These theoretical studies provide references for the preparation, and future application, of DWSiNTs.

DC and RF analysis of vertical 3D p-type silicon nanotube FET for low power applications

ABSTRACT A vertical p-type 3D silicon nanotube field effect transistor (p-type Si-NTFET) is designed and simulated by using the tool Sentaurus Technology computer-aided design (TCAD). To improve the performance with reduced short channel effects, Si-NTFET device is created with inner and outer gate structures. The performance of the proposed device is analysed in terms of outer gate length. The vertical 3D p-type Si-NTFET gives an on state current (I ON) of −2.084 × 10−3 A/µm, off state current of (I OFF) of −2.457 × 10−12A/µm and subthreshold swing of the p-type Si-NTFET device is 53 mV/dec at V DS of −0.3 V. The obtained I ON/I OFF ratio of the device is 109. The capacitances (C GD, C GG) and the transconductance (g m) and cutoff frequency (f t) of the device are also analysed. The simulated p-type Si-NTFET device has proved that the device is suitable for low-power applications.

Design of ultrafine silicon structure for lithium battery and research progress of silicon-carbon composite negative electrode materials

As demand for high-performance electric vehicles, portable electronic equipment, and energy storage devices increases rapidly, the development of lithium-ion batteries with higher specific capacity and rate performance has become more and more urgent. As the main body of lithium storage, negative electrode materials have become the key to improving the performance of lithium batteries. The high specific capacity and low lithium insertion potential of silicon materials make them the best choice to replace traditional graphite negative electrodes. Pure silicon negative electrodes have huge volume expansion effects and SEI membranes (solid electrolyte interface) are easily damaged. Therefore, researchers have improved the performance of negative electrode materials through silicon-carbon composites. This article introduces the current design ideas of ultra-fine silicon structure for lithium batteries and the method of compounding with carbon materials, and reviews the research progress of the performance of silicon-carbon composite negative electrode materials. Ultra-fine silicon materials include disorderly dispersed ultra-fine silicon particles such as porous structures, hollow structures, and core-shell structures; and ordered ultra-fine silicon, such as silicon nanowire arrays, silicon nanotube arrays, and interconnected silicon nano-films. The article analyzes and compares the composite method of ultrafine silicon and carbon materials with different structural designs, and the effect of composite negative electrode materials on the specific capacity and cycle performance of the battery. Finally, the research direction of silicon-carbon composite negative electrode materials is prospected.

Study on the structures and electronic properties of double-walled silicon nanotubes (4,min)@(8,mout) under external electric field by SCC-DFTB calculations

The geometric structural optimization and electronic properties of double-walled silicon nanotubes (DWSiNTs) (4,min)@(8,mout) (min = 0 to 4, mout = 0 to 8) are studied in terms of the self-consistent charge density functional tight binding (SCC-DFTB) method. Calculations demonstrate that the regularity of the atomic arrangement, the diameter of the inner and outer walls, the degree of buckling, stability, energy gap, Fermi energy level, quantum molecular descriptors, and charge distribution strongly depend on the chiral index of the tube. In particular, the possibility of tuning the band structure by changing the chiral index has been demonstrated to help for the performance needs of different devices, inducing a metal–semiconductor transition and direct–indirect band gap transition. In addition, the influence of adding an external electric field on electronic properties of the zigzag DWSiNT (4,0)@(8,0) has been investigated. The tube applied electric field transforms from semiconductor to semi-metallic property. The tube becomes metallic upon the critical electric field strength of 0.7 V/nm and 1.0 V/nm. As increasing the external field strengths, the stability of the tube is reduced and the EF level is increased. The direction of charge transfer is always in the reverse of the field direction, which is different from the case of absent field.

Effect of different parameters on the heat transfer coefficient of silicon and carbon nanotubes

One of the most important properties of nanomaterials is their thermal conductivity, which is particularly needed by researchers in electronic equipment. In this research, the thermal conductivity properties of carbon nanotubes were first investigated. Next, the thermal conductivity of silicon nanotubes was investigated using the molecular dynamics method. For this purpose, five important effects were investigated: the effect of changing the potential function, the effect of changing the length of the heat bath region, the effect of changing the length, the effect of changing diameter, and the effect of changing the temperature of the nanotube. The results indicated that by changing the potential function, the thermal conductivity was decreased. Additionally, the result demonstrated that by increasing the length of the heat bath region, the thermal conductivity of silicon nanotubes was decreased, while in carbon nanotubes, the thermal conductivity was increased. Also, in both carbon nanotubes and silicon nanotubes, increasing temperature between 100 K and 300 K decreased kappa coefficient. On the other hand, increasing diameters, increased the kappa coefficient. Finally, as the length of the nanotubes was increased, no significant change was observed in the kappa coefficient of silicon nanotubes, while in carbon nanotubes, the kappa coefficient was increased.

Assessment of Novel Magnetic/Semiconducting Composites - FePt Nanoparticles Grown within Porous Silicon and Silicon Nanotubes

Porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures offering a hard magnetic behavior and resulting in novel magnetic/semiconducting composite systems. The difference of the magnetic characteristics between the two systems is figured out. Furthermore the FePt filled templates are compared with the same template materials filled with Ni/Co by electrodeposition.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution [1]. The morphology of the porous structure is achieved by the doping density of the silicon wafer and the choice of the electrochemical parameters such as electrolyte concentration, applied current density and temperature. In this case the morphology offers separated pores of about 60 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure and a wall of about 10 nm are used [2]. FePt nanoparticles (NPs) are deposited electroless inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.Ni and Co, both metals are electrodeposited within the nanostructured silicon. In the case of depositing Ni and Co from separate electrolytes, aqueous NiSO4 and CoSO4 solutions are used. The composition of the Ni-salt solution is 170g/l NiSO4 and 40 g/l H3BO3. For the Co deposition the electrolyte contains 120 g/l CoSO4 and 30 g/l H3BO3. An applied current density of 15 mA/cm2 and a frequency of 0.1 Hz are applied for 15 min. In the case of depositing Ni and Co from a single electrolyte, a solution in the ratio 1:1 of the Ni-salt to Co-salt is employed. Ni is deposited by applying a potential of 1.1 V and Co is deposited by changing to 1.8 V; the necessary deposition time of Co was three times longer than for Ni.Magnetic characterization of the samples is performed by VSM (Vibrating Sample Magnetometer), the structure is analyzed by SEM, TEM and EDX.The varying magnetic response of the different composite systems, porous silicon and silicon nanotubes is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.Porous silicon loaded with Ni/Co offers a different magnetic behavior, especially in the case of stacked deposition from two separate electrolytes. The achieved composite shows a two-slope hysteresis, which will be discussed in contrast to the single electrolyte deposition.By enabling an accurate control of the size and of the volume ratio of different metal structures such materials are promising for the fabrication of three-dimensional arrays of permanent nanomagnets.[1] K. Rumpf, P. Granitzer, H. Michor, NRL 11, 398 (2016).[2] K. Rumpf, P. Granitzer, R. Gonzalez-Rodriguez, J. Coffer, M. Reisser, Phys. Stat. Sol. A 217, 1901040 (2020). Figure 1

Investigation of PZT-5H and PZT-8 type piezoelectric effect on cycling stability on Si-MWCNT containing anode materials.

Silicon (Si) containing materials cannot be used in commercial lithium ion batteries due to the mechanical stress problem triggered by volume expansion during cycling. The high-volume change causes mechanical instability of Si anode materials during charging/discharging, resulting fast capacity fading. It is thought that piezoelectric materials can be a solution for the volume expansion problem because of their ability to generate electric field when pressure is applied on them. For this purpose, PZT-8 and PZT-5H type piezoelectric materials were mixed with silicon and multiwalled carbon nanotube (MWCNT) to obtain anode composites and tested electrochemically versus lithium metal. The piezoelectiric effect on the electrochemical activity of these anodes is investigated by preparing the anode composite without any piezoelectric material additive (Sample #3). At the end of the 50 charge/discharge cycles, the capacities reached 420 mAh/g, 300 mAh/g and 100 mAh/g for PZT-8-added, PZT-5H-added and no-PZT samples, respectively. These results showed that PZT addition improves capacity performance of Si-MWCNT anodes. Additionally, the obtained anode composites were characterized with X-ray diffraction and scanning electron microscopy.

Essential Electronic Properties of Silicon Nanotubes.

In this work, the various electronic properties of silicon nanotubes (SiNTs) were investigated by the density functional theory. The cooperative and competitive relationships between the chiral angle, periodic boundary conditions, and multi-orbital hybridizations create unusual narrow gaps and quasi-flat bands in the ultra-small armchair and zigzag tubes, respectively. The features varied dramatically with tube radii. Armchair SiNTs (aSiNTs) have an indirect-to-direct band gap transition as their radius is increased to a particular value, while zigzag SiNTs (zSiNTs) present a metal-semiconductor transition. The projected density of states was used to elucidate the critical transitions, and the evolution of p and s orbital mixing states during the process are discussed in detail. The information presented here provides a better understanding of the essential properties of SiNTs.

Effect of Diameter, Length, and Chirality on the Properties of Silicon Nanotubes

The mechanical properties of nanostructures are a researcher’s favorite topics. In the meantime, the mechanical and physical properties of the two dimensional structures and the nanotubes have attracted greater attention due to their wide application. Si (Si) nanotubes are structures consisting of Si atoms that are arranged as honeycombs. This structure has created some special properties in Si nanotubes. In this paper, Young’s modulus values and stress strain diagrams of Si nanotubes are investigated using molecular dynamics method and the Tersoff potential. Then, the changes effect of size and dimension was investigated for a closer look. For this purpose, the effect of nanotube diameter, length, and chirality shift from zigzag to armchair were studied. The results showed that the fracture stress of nanotube decreased with increasing the length of Si nanotube. It was also shown that the armchair structure was stronger than the zigzag. The effect of diameter change on the mechanical properties was also investigated and it was observed that no specific order could be found between the diameter changes with the Si nanotube strength. The results were in good agreement with other studies.

Design of a Capacitorless Dynamic Random Access Memory Based on Junctionless Dual-Gate Field-Effect Transistor with a Silicon-Germanium/Silicon Nanotube.

In this paper, a 1T-DRAM based on the junctionless field-effect transistor (JLFET) with a silicon-germanium (SiGe) and silicon (Si) nanotube structure was designed and investigated by using technology computer-aided design (TCAD) simulations. Utilizing bandgap engineering to make a quantum well in the core-shell structure, the storage pocket is formed by the difference in bandgap energy between SiGe and Si. By applying different voltage conditions at the inner gate and outer gate, excess holes are generated in the storage region by the band-to-band tunneling (BTBT) mechanism. The BTBT mechanism results in the floating body effect, which is the principle of 1T-DRAM. The varying amount of the accumulated holes in the SiGe region allows differentiating between state "1" and state "0." Additionally, the outer gate plays a role of the conventional gate, while the inner gate retains holes in the hold state by applying voltage. Consequently, the optimized SiGe/Si JLFET-based nanotube 1T-DRAM achieved a high sensing margin of 15.4 μA/μm, and a high retention time of 105 ms at a high temperature of 358 K. In addition, it has been verified that a single cycle of 1T-DRAM operations consumes only 33.6 fJ of energy, which is smaller than for previously proposed 1T-DRAMs.

Delayed Lubricant Depletion of Slippery Liquid Infused Porous Surfaces Using Precision Nanostructures.

Slippery liquid infused porous surfaces (SLIPS) are an important class of repellent materials, comprising micro/nanotextures infused with a lubricating liquid. Unlike superhydrophobic surfaces, SLIPS do not rely on a stable air-liquid interface and thus can better manage low surface tension fluids, are less susceptible to damage under physical stress, and are able to self-heal. However, these collective properties are only efficient as long as the lubricant remains infused, which has proved challenging. We hypothesized that, in comparison to a nanohole and nanopillar morphology, the "hybrid" morphology of a hole within a nanopillar, namely a nanotube, would be able to retain and redistribute lubricant more effectively, owing to capillary forces trapping a reservoir of lubricant within the tube, while lubricant between tubes can facilitate redistribution to depleted areas. By virtue of recent fabrication advances in spacer defined intrinsic multiple patterning (SDIMP), we fabricated an array of silicon nanotubes and equivalent arrays of nanoholes and nanopillars (pitch, 560 nm; height, 2 μm). After infusing the nanostructures (prerendered hydrophobic) with lubricant Krytox 1525, we probed the lubricant stability under dynamic conditions and correlated the degree of the lubricant film discontinuity to changes in the contact angle hysteresis. As a proof of concept, the durability test, which involved consecutive deposition of droplets onto the surface amounting to 0.5 L, revealed 2-fold and 1.5-fold enhancements of lubricant retention in nanotubes in comparison to nanopillars and nanoholes, respectively, showing a clear trajectory for prolonging the lifetime of a slippery surface.

Electrochemical Conversion of Silica Nanoparticles to Silicon Nanotubes in Molten Salts: Implications for High-Performance Lithium-Ion Battery Anode

Electrochemical Conversion of Silica Nanoparticles to Silicon Nanotubes in Molten Salts: Implications for High-Performance Lithium-Ion Battery Anode

Fabricating Silicon Nanotubes by Electrochemical Exfoliation and Reduction of Layer-Structured CaSiO3 in Molten Salt.

Silicon nanotubes (SNTs) are very attractive in the fields of energy, catalysis, and sensors, but a facile template- and/or catalyst-free preparation method is still absent. Herein, we study a controllable and cost-effective approach for preparing SNTs by electrochemically reducing layer-structured calcium silicate (CaSiO3) in molten CaCl2/NaCl without any template and catalyst. The underlying mechanism of the SNT formation is uncovered: the layer-structured CaSiO3 is first electrochemically exfoliated into SiOx (0 < x < 2) sheets while releasing CaO into the molten salts, and then the SiOx sheets are electrochemically reduced and simultaneously crimped into SNTs. The diameter (120-312 nm) and wall thickness (∼40 nm) of the SNTs can be tailorable by manipulating the reduction potential between -1.28 and -1.48 V (vs Ag/AgCl). Lastly, the electrolytic SNTs show a high lithium storage capacity of 3737 mAh g-1 at 0.2 A g-1, a high rate capability of 1371 mA h g-1 at 10 A g-1, and stable cycling with a capacity of 974 mAh g-1 after 600 cycles at 1 A g-1. Overall, the template- and catalyst-free electrochemical method provides a straightforward and facile way to prepare SNTs with a brand-new mechanism that can be applied to other tubular structure materials.

Hard Magnetic Composite: FePt Nanoparticles Grown within Nanostructured Silicon

In this work porous silicon (PSi) and silicon nanotubes (SiNTs) are presented as a platform for filling with FePt nanostructures which offer a hard magnetic behavior. The difference of the magnetic characteristics between the two systems is figured out.The porous silicon is produced by anodization of a highly doped n-type silicon wafer in a 10 wt% HF solution [1]. The morphology offers separated pores of about 60 nm and a mean distance between the pores of 50 nm. The SiNTs are fabricated in using an array of ZO wires as template, subsequent silicon deposition and finally etching off the ZO [2]. The inner diameter of the tubes and also the wall thickness can be tuned by the fabrication process. In this work SiNTs with comparable inner diameter to the PSi structure are used. FePt nanoparticles (NPs) are chemically grown inside the pores and the tubes, respectively whereat the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). For this purpose a 3 component solution consisting of H2PtCl6, Fe(NO3)3 and citric acid is used, whereas the ratio of the components is modified.Magnetic characterization of the samples is performed by VSM (Vibrating Sample Magnetometer), the structure is analyzed by SEM, TEM and EDX.The magnetic response of the two different composite systems is investigated. PSi/FePt shows a higher coercivity and remanence than SiNTs/FePt and thus a higher hard magnetic performance. The variation of the coercivities between SiNTs/FePt and PSi/FePt is about 57%.Considering the FePt deposits with different molar ratio of Fe the coercivities vary in a range of 5% in the case of both template types. Comparing FePt loaded samples with Co loaded samples in all cases an increase of the coercivity and of the remanence is observed for FePt, whereat in the case of PSi as template material the increase is significantly stronger than in the case of SiNTs samples. Figure 1 shows the comparison of the hysteresis of PSi and SiNTs filled with FePt NPs.Hard magnetic materials within nanostructured silicon give rise for on-chip applications using 3 dimensional arrays of nanomagnets.Figure 1: Field dependent magnetization measurements of PSi and SiNTs filled with FePt NPs, respectively showing a higher coercivity in the case of PSi.[1] K. Rumpf, P. Granitzer, H. Michor, NRL 11, 398 (2016).[2] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Comm. 49, 5760 (2013). Figure 1

(Invited) Nafion/CNT Passivated Carrier Selective Contacts for Silicon Photovoltaics

In the past, the application of carbon nanotube-silicon solar cell technology to industry has been limited by the use of a metallic frame to define the active area in the middle of a silicon wafer. In our work, we use industry standard device geometries with a front- and back-junction design which allow for the entire wafer to be used as the active area. These are enabled by the use of an intermixed Nafion layer which simultaneously acts a passivation, antireflective and physical blocking layer as well as a nanotube dopant. This leads to the formation of a hybrid nanotube/Nafion passivated charge selective contact (PCSC) and solar cells with active areas of 1 – 16 cm2 are fabricated. Record maximum power conversion efficiencies of 15.2% and 18.9% are reported for front- and back-junction devices for 1 cm2 and 3 cm2 active areas, respectively. By placing the nanotube film on the rear of the device in a back-junction architecture many of the design related challenges for carbon nanotube silicon solar cells are addressed and their future application to industrialized processes are discussed.Additionally, traditional silicon solar cells extract holes and achieve interface passivation with the use of a boron dopant and dielectric thin films such as silicon oxide or hydrogenated amorphous silicon. Without these two key components, few technologies have realized power conversion efficiencies above 20%. We now develop a carbon nanotube/Nafion ink that can be spin coated directly onto a silicon wafer to serve simultaneously as a hole extraction layer, but also to passivate interfacial defects. This enables a low-cost fabrication process that is absent of vacuum equipment and high-temperatures. Power conversion efficiencies of 21.4% on an device area of 4.8 cm2 and 20% on an industrial size (245.71 cm2) wafer are obtained.[1] D. D. Tune, N. Mallik, H. Fornasier, B. S. Flavel, Adv. Energy Mater. 10, 2020, 1903261. DOI: 10.1002/aenm.201903261[2] J. Chen, D. D. Tune, K. Ge, H. Li, B. S. Flavel, Adv. Funct. Mater. 2020, 30 2000484. DOI: 10.1002/adfm.202000484[3] J. Chen, L. Wan, H. Li, J. Yan, J. Ma, B. Sun, F. Li, B. S. Flavel, Adv. Funct. Mater. 30, 2020, 202004476. DOI: 10.1002/adfm.202004476[4] L. Wieland, H. Li, C. Rust, J. Chen, B. S. Flavel, Adv. Energy Mater. 2020 just accepted manuscript. DOI: 10.1002/aenm.202002880 Figure 1

The possible structure and electronic structure of zigzag silicon nanotubes doped with group V elements

We performed spin-polarized density functional theory (DFT) calculations to study the stable structures and electronic structure of X-doped (X = N, P, As, Sb and Bi) single-walled silicon nanotubes (SiNTs). Intrinsic SiNTs with small diameters can exist stably and maintain a smooth surface structure. However, due to the addition of impurities, small-diameter nanotubes cannot maintain a stable tube structure. In addition to Bi, the doping of group five elements can effectively improve the stability of (14, 0) SiNTs. Moreover, the addition of group V elements makes SiNTs produce impurity levels at the Fermi level, thereby reducing the band gap. The doping of P, As, Sb, and Bi even led to the transformation of SiNTs from semiconductors to metals, and the energy level shift appears in N-doped SiNTs.