Microcrystalline Silicon Research Articles

Synergetic Effect of Gas Compositions on Material Properties of n‐Type Nanocrystalline Silicon Oxide Prepared by Plasma‐Enhanced Chemical Vapor Deposition

Hydrogenated nanocrystalline silicon oxide (nc‐SiOx:H) has drawn extensive attention during the past years for the utilization of silicon heterojunction (SHJ) solar cells. This material is demonstrated to be the key to the performance improvement of SHJ solar cells. Herein, the influence of the process gas compositions on the optical, electronic, chemical, and structural properties of n‐type nc‐SiOx:H films at the thickness of 38 nm is systematically investigated. The synergetic effect of CO2 and PH3 gas flow fraction ( and ) and the synergetic effect of CO2 and SiH4 gas flow fraction ( and ) on the growth of nc‐SiOx:H (n) films are demonstrated. Creatively combining the Fourier‐transform infrared, UV‐Raman scattering spectroscopy, spectroscopy ellipsometry, and photo‐thermal deflection spectroscopy measurement, the mechanism behind the synergetic effect of the gas compositions on the material properties is analyzed.

On the cogent formulation of an elastomeric silicone ink material for direct ink write (DIW) 3D printing

AbstractAdhesives and sealants show fine rheology with good physical and mechanical properties as viscous pastes, a possible starting point for developing direct ink writing (DIW) 3D printing ink. However, many commercial adhesives and sealants take days or weeks to cure fully. DIW 3D‐printed parts made directly from these sealants are not designed for a scalable manufacturing process and high‐volume production. Moreover, most of these adhesives and sealants have volume shrinkage during cure. A systematic understanding of formulation methods and design principles for an elastomeric silicone DIW ink can overcome these issues. This study presents the cogent formulation development of a 3D printable thermoset elastomer silicone that gels and cures isotropically in minutes, reducing cycle time for rapid ink development with no shrinkage during cure. More specifically, we outline the principles of raw material selection of a formulation to achieve excellent rheology, printability, synchronized working, and gel time fitting requirements closer to scalable manufacturing. The reaction kinetics and their corresponding 3D‐printed structural properties are also described. Interest in future work is toward a rational DIW 3D printing ink material development protocol and use of machine learning (ML).Highlights Formulation method flexibility and design principle of DIW ink. Raw material selection principle to achieve optimal rheology for DIW printing. Ink gel kinetics for large‐scale DIW manufacturing. Hydrosilylation conversion over time at different ambient temperatures. Structural properties of DIW 3D printed parts.

Development of n-Type, Passivating Nanocrystalline Silicon Oxide Films via Plasma-Enhanced Chemical Vapor Deposition

Nanocrystalline silicon oxide (nc-SiOx:H) is a multipurpose material with varied applications in solar cells as a transparent front contact, intermediate reflector, back reflector layer, and even tunnel layer for passivating contacts, owing to the easy tailoring of its optical properties. In this work, we systematically investigate the influence of the gas mixture (SiH4, CO2, PH3, and H2), RF power, and process pressure on the optical, structural, and passivation properties of thin n-type nc-SiOx:H films prepared in an industrial, high-throughput, plasma-enhanced chemical vapor deposition (PECVD) reactor. We provide a detailed description of the n-type nc-SiOx:H material development using various structural and optical characterization techniques (scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectroscopy, and spectroscopic ellipsometry) with a focus on the relationship between the material properties and the passivation they provide to n-type c-Si wafers characterized by their effective carrier lifetime (τeff). Furthermore, we also outline the parameters to be kept in mind while developing different n-type nc-SiOx:H layers for different solar cell applications. We report a tunable optical gap (1.8–2.3 eV) for our n-type nc-SiOx:H films as well as excellent passivation properties with a τeff of up to 4.1 ms (implied open-circuit voltage (iVoc)~715 mV) before annealing. Oxygen content plays an important role in determining the crystallinity and hence passivation quality of the deposited nanocrystalline silicon oxide films.

Nanocrystalline Silicon Layers for the Application in Silicon Heterojunction Solar Cells

After application in thin-film silicon tandem solar cells and in lab-scale silicon heterojunction (SHJ) devices, doped nanocrystalline silicon (nc) layers now arrived on the industrial stage. Despite their challenging deposition, the benefits they hold with respect to even higher device performance compared to their amorphous counterparts are significant and justify additional effort. In this contribution we report on developments towards industrially applicable processes for n- and p-doped silicon layers, nc-Si(n) and nc-Si(p), and their implementation in SHJ cells. Our investigation focuses on the impact of deposition temperature (Tdep) and the need for a thin oxide layer to promote fast nucleation of thin, sufficiently crystalline, doped nc-Si films in a single deposition chamber powered at 13.56 MHz. We identified main challenges for thin film and contact engineering and reached efficiencies of 23.0% with n- and 23.1% with p-type nc-Si approaching cell performances of our process of record based on amorphous Si (a-Si) layers.

Highly tailorable thermomechanical properties of nanograined silicon: Importance of grain size and grain anisotropy

Nanocrystalline silicon can have unique thermal transport and mechanical properties governed by its constituent grain microstructure. Here, we use phonon ray-tracing and molecular dynamics simulations to demonstrate the largely tunable thermomechanical behaviors with varying grain sizes (a0) and aspect ratios (ξ). Our work shows that, by selectively increasing the grain size along the heat transfer direction while keeping the grain area constant, the in-plane lattice thermal conductivity (kx) increases more significantly than the cross-plane lattice thermal conductivity (ky) due to anisotropic phonon–grain boundary scattering. While kx generally increases with increasing ξ, a critical value exists for ξ at which kx reaches its maximum. Beyond this transition point, further increases in ξ result in a decrease in kx due to substantial scattering of low-frequency phonons with anisotropic grain boundaries. Moreover, we observe reductions in the elastic and shear modulus with decreasing grain size, and this lattice softening leads to significant reductions in phonon group velocity and thermal conductivity. By considering both thermal and mechanical size effects, we identify two distinct regimes of thermal transport, in which anisotropic phonon–grain boundary scattering becomes more appreciable at low temperatures and lattice softening becomes more pronounced at high temperatures. Through phonon spectral analysis, we attribute the significant thermal conductivity anisotropy in nanograined silicon to grain boundary scattering of low-frequency phonons and the softening-driven thermal conductivity reduction to Umklapp scattering of high-frequency phonons. These findings offer insights into the manipulation of thermomechanical properties of nanocrystalline silicon via microstructure engineering, carrying profound implications for the development of future nanomaterials.

Evaluating the Practical Efficiency Limit of Silicon Heterojunction–Interdigitated Back Contact Solar Cells by Creating Digital Twins of Silicon Heterojunction Solar Cells with Amorphous Silicon and Nanocrystalline Silicon Hole Contact Layers

Improving power conversion efficiency (PCE) in photovoltaics has driven innovative approaches in solar cell design and technology. Silicon heterojunction (SHJ) solar cells exhibit advantages in PCE due to their effective passivating contact structures. SHJ–interdigitated back contact (SHJ–IBC) solar cells have the potential to surpass traditional SHJ cells, attributed to their advantage in short‐circuit current (JSC). Herein, Silvaco Atlas technology computer‐aided design is used to create digital twins of high‐efficiency SHJ solar cells with amorphous silicon and nanocrystalline silicon hole selective contact (HSC) layers. Using parameters from digital twins of SHJ solar cells, the practical efficiency limit of SHJ–IBC solar cells is assessed. The results show that SHJ–IBC cells can achieve potential efficiencies of 27.01% with amorphous HSC and 27.38% with nanocrystalline HSC. Further efficiency augmentation to 27.51% can be achieved by narrowing the gap from 80 to 20 μm. This study not only advances comprehension of SHJ–IBC solar cells but also provides insights into optimizing geometrical configurations for improved performance. The utilization of digital twins provides a valuable tool for predicting and evaluating the performance of SHJ–IBC solar cells, contributing substantively to the ongoing development of high‐efficiency photovoltaic technology.

Intermolecular forces and surface stress residual effects on the size-dependent performance analysis of nanocrystalline micro/nano gyroscopes

This work investigates an electrostatically-actuated vibrating beam micro/nano-gyroscope made of nanocrystalline silicon material. The comprehensive size-dependent micro/nanogyroscope model is developed by couple stress and surface elasticity theories. Then, considering the effects of intermolecular forces (Casimir force and van der Waals force) and surface stress residual, an in-depth investigation was conducted on the performance of the micro/nanogyroscope. The calculation results display that the maximum static deflection, pull-in voltage and natural frequency change obviously with the increase of surface stress residual as the scale varies from micrometer to nanoscale. However, the effect of intermolecular forces on the performance of gyroscopes is exactly the opposite, which improves the prediction of system structural softening deformation phenomenon. Considering the influence of the Casimir and van der Waals forces in micro/nano gyroscopic system will help gyroscopes to obtain reliability and functionality sensitivity, increase the accuracy of predicting static deformation, natural frequency and differential frequency. Moreover, a frequency-domain method using the difference between the two vibration natural frequencies is studied, with changing the scale of the gyroscope under the effect of the intermolecular forces. The numerical simulations exhibit that when considering smaller structure sizes of the gyroscope, strong coupling occurs between the intermolecular forces and surface stress residual, which is helpful for the design of micro/nano gyroscopes.

Fabrication of highly conductive phosphorous-doped nc-SiCx:H thin film on PET

Plasma enhanced chemical vapor deposition (PECVD) method has been utilized to fabricate phosphorous-doped hydrogenated nanocrystalline silicon carbide (P-doped nc-SiCx:H) thin films on polyethylene terephthalate (PET) substrate. With the aim at obtaining highly conductive thin films, H2/Ar mixed dilution has been applied for creating plasma during deposition, and the variation of structural, electrical and optical properties with H2/Ar flow ratio RH have been systemically investigated through a series of characterizations. Results show that the highly crystallized P-doped nc-SiCx:H thin film can be prepared while the properties are controllable through adjusting RH. In the case of RH = 0.75, the maximum dark conductivity (6.42 S cm−1) and a wide optical bandgap (1.93 eV) are attained. Finally, detail discussion has been made to illustrate the growth mechanism of the flexible P-doped nc-SiCx:H thin films.

Influence of Nanocrystalline Silicon Conductivity on the Structural and Optical Properties of Porous Silicon

Influence of Nanocrystalline Silicon Conductivity on the Structural and Optical Properties of Porous Silicon

Stable lithium storage with strong-grain sustained pinning-reinforced nanocrystalline silicon

Crystalline silicon has long been considered inferior to its amorphous form in lithium storage due to the anisotropy and post-cycling extinction of the crystal structure. However, the amorphous silicon is...

High conductivity characteristics of phosphorus-doped nanocrystalline silicon thin films by KrF pulsed excimer laser irradiation method.

The microstructure and high conductivity properties of phosphorus-doped nanocrystalline silicon films were investigated on samples prepared by a plasma-enhanced chemical vapor deposition technique and the KrF pulsed excimer laser irradiation method. The results of Fourier transform infrared spectroscopy and Raman spectroscopy show that Si nanocrystallites with an average diameter of 2 nm to 3 nm are formed in the film. The degree of crystallinity increases with the increase of laser radiation intensity, while the content of hydrogen decreases gradually. More phosphorus atoms are substitutionally incorporated into the nc-Si dots under higher laser irradiation fluence, which is responsible for the high dark conductivity. By controlling the laser fluence at 1.0 J cm-2, the dark conductivity as high as 25.7 S cm-1 can be obtained. Based on the measurements of temperature-dependent conductivity, the carrier transport processes are discussed. The phosphorus doping and the increase of electron concentration are considered to be the reason for high dark conductivity and extremely low conductivity activation energy.

Structural and optical properties of phosphorous doped nanocrystalline silicon deposited using a VHF PECVD process for silicon heterojunction solar cells and optimization of a simple p-n junction cell using SCAP-1D tool.

Initially hydrogenated silicon (Si:H) thin films have been deposited using a plasma-enhanced chemical vapor deposition technique (PECVD) using silane (SiH4) as a precursor gas diluted in an inert gas argon (Ar) environment. Subsequently phosphine gas (PH3) was used as the n-type dopant and the deposition was carried out at a fixed substrate temperature of 200 °C. The PH3 flow rate was varied in the range of 0-1 sccm. The effect of PH3 flow rates on optical, electrical, and structural properties of hydrogenated amorphous and micro/nanocrystalline silicon films has been investigated and detailed analysis is presented. These films may find application in heterojunction solar cells as an emitter layer. Further, a crystalline silicon (c-Si) based simple p-n junction solar cell is simulated using an SCAP-1D tool to observe the effect of layer thickness and doping density on solar cell parameters.

3D-printable hydrophobic silicone inks for antiadhesion tough objects via molecular engineering

3D printable hydrophobic ink is highly desirable to simply print hydrophobic objects for various applications, such as oil/water separation. However, printable hydrophobic monomers/inks are limited which seriously restricts the fabrication and application of 3D printing hydrophobic objects. Herein, simulating the crown, trunk, and roots of trees from the molecular levels, coatings/objects were designed and prepared using a 6-functional hyperbranching polyurethane acrylate (PUA) monomer as the “trunk”, mono-acrylate terminated polydimethylsiloxane (Vi-PDMS) as the “leaf”, and tripropylene glycol diacrylate (TPGDA) as the “root”. The printed objects with excellent mechanical properties and stable hydrophobicity with CAs and SAs in the range of 80°–110° and 10°–30°, respectively, and could be used in a variety of environments (e.g., acid-based solution, seawater) for a month. Cylindrical, ladder, and mushroom-shaped micro-nano structures could be prepared to improve the hydrophobicity of the printed objects to achieve CAs up to ∼170°. The antiadhesion tough teeth and microchannels could be prepared facilely with the hydrophobic inks. This work demonstrates a simple and rapid method to manufacture various complex and sophisticated hydrophobic coatings/objects and a broader strategy for 3D printing technology.

Highly conductive p-type nc-SiOX:H thin films deposited at 130°C via efficient incorporation of plasma synthesized silicon nanocrystals and their application in SHJ solar cells

We present highly conductive and transparent p-type hydrogenated nanocrystalline silicon oxide (p-type nc-SiOX:H) layers produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) at 130°C and 150°C. We report on the crystalline volume fraction (XC), spectral broadening parameter C, and dark conductivity (σ) as functions of the growth temperature and RF power, and how these properties evolve with post-deposition annealing at 250°C and 300°C. Interestingly, we observe that the best layers in terms of crystalline volume fraction and conductivity are obtained at the lowest temperature and RF power, which we attribute to the soft landing of silicon nanocrystals synthesized in the plasma. The p-type nc-SiOX:H layers with the best properties on glass substrates are implemented as carrier-selective contacts in silicon heterojunction (SHJ) solar cells with the structure: (n) a-Si:H / (i) a-Si:H / n-type c-Si / (i) a-Si:H / (i) a-SiOX:H / (p) nc-SiOX:H / (p) nc-Si:H where all films are deposited by PECVD. The cells were completed with sputtered ITO on the front and rear sides plus Ag on the rear side, and Ag grid on the front, with the best devices showing conversion efficiencies of 21.8%, which, contrary to a-Si:H contact layers, are preserved or even slightly improved upon annealing at 240°C.

Improved interface microstructure between crystalline silicon and nanocrystalline silicon oxide window layer of silicon heterojunction solar cells

N-type hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) is potential to enhance the performance of silicon heterojunction solar cells, but the raised plasma damage on underlying layer during the nc-SiOx:H deposition with a high-volume fraction of hydrogen is a burning issue. The underlying intrinsic hydrogenated amorphous silicon (i-a-Si:H) bilayer between n-type crystalline silicon (c-Si) and n-type nc-SiOx:H has been investigated by modulating silane (SiH4) gas flow rate (GFR) of interface porous layer. It has been found that the initial H-rich i-a-Si:H bilayer deposited by interfacial 1600 sccm GFR with relatively stable larger voids diameter and less voids number density can not only withstand hydrogen ions bombardment but also passivate c-Si surface well. Meanwhile, it also has been verified that the optimal n-seed deposition can further enhance both total hydrogen content and hydrogen content in compact structure to promote c-Si surface passivation and carrier transportation. The optimized SiH4 GFR for the interfacial i-a-Si:H growth and the appropriate deposition time of n-seed layer have been applied into the front passivation layer of silicon heterojunction solar cells, thus a high efficiency of approximate 25 % with high VOC and FF has been achieved.

Utilizing 3D Printing Technology to Create Prosthetic Irises: Proof of Concept and Workflow.

There are currently limited treatment options for aniridia. In this context, 3D printed iris implants may provide a cost-effective, cosmetically acceptable alternative for patients with aniridia. The purpose of this study was to develop a proof-of-concept workflow for manufacturing 3D printed iris implants using a silicone ink palette that aesthetically matches iris shades, identified in slit lamp images. Slit lamp iris photos from 11 healthy volunteers (3 green; 4 blue; 4 brown) were processed using k-means binning analyses to identify two or three prominent colors each. Candidate silicone inks were created by precisely combining pigments. A crowdsourcing survey software was used to determine color matches between the silicone ink swatches and three prominent iris color swatches in 2 qualifying and 11 experimental workflows. In total, 54 candidate silicone inks (20 brown; 16 green; 18 blue) were developed and analyzed. Survey answers from 29 individuals that had passed the qualifying workflow were invited to identify "best matches" between the prominent iris colors and the silicone inks. From this color-match data, brown, blue, and green prototype artificial irises were printed with the silicone ink that aesthetically matched the three prominent colors. The iris was printed using a simplified three-layer five-branch starburst design at scale (12.8 mm base disc, with 3.5 mm pupil). This proof-of-concept workflow produced color-matched silicone prosthetic irises at scale from a panel of silicone inks using prominent iris colors extracted from slit lamp images. Future work will include printing a more intricate iris crypt design and testing for biocompatibility.

The Impact of P-Type Layer on Performance and Stability of Thin Film Silicon Solar Cells in Relation to Third Generation: A review Analysis

Thin-film Silicon (Si) Solar Cells (SCs) have emerged as a promising candidate for next-generation photovoltaic devices due to their potential for cost-effectiveness and versatility. However, achieving high efficiency and long-term stability remains a significant challenge in their development. The primary challenges with thin-film Si SCs have been the poor infrared light absorption of Hydrogenated Microcrystalline Silicon (c-Si: H) and the light-induced metastability of Hydrogenated Amorphous Silicon (a-Si: H). This study reviewed the influence of the p-type layer, a key component in thin-film Si SCs, on both performance and stability. Third generation SCs are optimized for high Power Conversion Efficiency (PCE) at low manufacturing costs. According to the review of the comparison analysis, Patel K. et al., (2021) obtained the highest PCE of 30.17% with the a-Si/MoTe2 material (Photocurrent Density Jsc = 32.41mA/cm2, An Open-Circuit Voltage Voc = 1.093V, and Fill Factor (FF) = 85.12%) of the state-of-the-art previous works. The findings presented here contribute valuable insights toward the development of efficient and durable SC technology, crucial for advancing the adoption of renewable energy sources in our ever-growing energy demand.

The synergistic and reinforcement mechanism of SiC nanostructures on the ablation properties of silicone rubber composites

With improvements to the performance of ramjets, the ablation environment in afterburning chambers has become more severe, leading to an urgent demand for high-performance thermal protection materials (TPMs). In this study, the reinforcing effects of silicon carbide (SiC) nanowhiskers and nanopowders on silicone rubber composites and their synergistic effects were investigated. Both SiC nanowhiskers and nanopowders improved the thermal stability of the TPMs. SiC nanowhiskers enhanced the thermal conductivity of the TPMs by forming thermal conductivity pathways. Furthermore, SiC nanofillers can reinforce the ablation resistance of the TPM. The best performance was demonstrated by the TPM formulated with five parts SiC nanowhiskers and five parts SiC nanopowders. The ablation rate was reduced by 72.7% relative to the TPM with a basic formulation, and the back temperature increased by only 27.1%. In this study, the SiC nanofiller improved the ablation resistance of composites by densifying the pore structure and strengthening the skeleton of the char layer. Furthermore, the more compact char layer improved the thermal conductivity of the composites. The increase in the thermal conductivities of the composites and the char layer led to a decrease in the thermal insulation properties of the composites.

Radio frequency-assisted curing of on-chip printed CNT/silicone heatsinks produced by material extrusion 3D printing

With the rapid development of high-power integrated electronic devices, many polymer-based thermal management devices have been developed to address the problem of overheating and to improve the reliability and lifetime of electronic devices. Here we demonstrate the material extrusion 3D printing of carbon nanotube (CNT)/silicone heatsinks directly onto electronic devices. CNTs were used as a conductive nanofiller and a rheological modifier to improve thermal and electrical conductivities and the printability of the silicone inks, respectively. Additionally, CNTs are also a radio frequency (RF) susceptor, so the integration of CNTs into the silicone matrix allowed for rapid out-of-oven curing by applying RF heating. Specifically, at a CNT loading of 14 wt%, the CNT/silicone heatsinks could be printed and RF cured with shape retention; the heatsinks’ performance was comparable to that of commercial heatsinks. More importantly, the CNT/silicone heatsinks could be printed and cured directly onto a chip attached to a circuit board. This printing approach can eliminate the use of thermal interface materials and the step of heatsink assembly while reducing the number of thermal interfaces between the chip and the heatsink. The results suggest that material extrusion 3D printing combined with RF-assisted curing can be an effective approach to fabricate high-performance polymer-based heatsinks with reduced production time and energy requirements.

Rheological formulation of room temperature vulcanizing silicone elastomer ink for extrusion-based 3D printing at room temperature

Silicone elastomer is a versatile material that is widely used in various industries due to its exceptional properties such as resistance to extreme temperatures, thermal conductivity, and bioinert. However, conventional fabrication methods of silicone are limited by molding which has design restrictions and makes it unsuitable for highly customized applications. This study presents a novel room temperature vulcanizing (RTV) silicone formulation that enables three-dimensional printing using an extrusion-based method. The study identifies that rheological measurements such as static yield stress are critical in determining the success of 3D silicone printing. Chemical additives, including nano-silica and plasticizers, have a significant impact on the static yield stress of the silicone ink, enabling the printing of complex structures. By adding 7 wt% of nano-silica and 10 wt% of plasticizers, a static yield stress of 400 Pa was achieved, which allowed the printing of complex 3D structures, including supportless macro-porous scaffolds. The newly formulated silicone ink demonstrated printability and the ability to achieve complex structures, reducing fabrication time, improving scalability, and allowing flexibility in the scaffold's design and specifications. This novel approach opens up new possibilities for the development of highly customized and cost-effective silicone-based 3D printing ink for the fabrication of complex silicone articles and macro-porous scaffolds. The potential applications of this approach include tissue engineering and biomedical devices.