Showing papers on "Fabrication published in 2016"

Aligned Single-Crystalline Perovskite Microwire Arrays for High-Performance Flexible Image Sensors with Long-Term Stability.

Abstract: A simple, low-cost blade-coating method is developed for the large-area fabrication of single-crystalline aligned CH3NH3PbI3 microwire (MW) arrays. The solution-coating method is applicable to flexible substrates, enabling the fabrication of MW-array-based photodetectors with excellent long-term stability, flexibility, and bending durability. Integrated devices from such photodetectors demonstrate high performance for high-resolution, flexible image sensors.

Layerless fabrication with continuous liquid interface production

Abstract: Despite the increasing popularity of 3D printing, also known as additive manufacturing (AM), the technique has not developed beyond the realm of rapid prototyping. This confinement of the field can be attributed to the inherent flaws of layer-by-layer printing and, in particular, anisotropic mechanical properties that depend on print direction, visible by the staircasing surface finish effect. Continuous liquid interface production (CLIP) is an alternative approach to AM that capitalizes on the fundamental principle of oxygen-inhibited photopolymerization to generate a continual liquid interface of uncured resin between the growing part and the exposure window. This interface eliminates the necessity of an iterative layer-by-layer process, allowing for continuous production. Herein we report the advantages of continuous production, specifically the fabrication of layerless parts. These advantages enable the fabrication of large overhangs without the use of supports, reduction of the staircasing effect without compromising fabrication time, and isotropic mechanical properties. Combined, these advantages result in multiple indicators of layerless and monolithic fabrication using CLIP technology.

Overcoming Short-Circuit in Lead-Free CH3NH3SnI3 Perovskite Solar Cells via Kinetically Controlled Gas-Solid Reaction Film Fabrication Process

Abstract: The development of Sn-based perovskite solar cells has been challenging because devices often show short-circuit behavior due to poor morphologies and undesired electrical properties of the thin films. A low-temperature vapor-assisted solution process (LT-VASP) has been employed as a novel kinetically controlled gas–solid reaction film fabrication method to prepare lead-free CH3NH3SnI3 thin films. We show that the solid SnI2 substrate temperature is the key parameter in achieving perovskite films with high surface coverage and excellent uniformity. The resulting high-quality CH3NH3SnI3 films allow the successful fabrication of solar cells with drastically improved reproducibility, reaching an efficiency of 1.86%. Furthermore, our Kelvin probe studies show the VASP films have a doping level lower than that of films prepared from the conventional one-step method, effectively lowering the film conductivity. Above all, with (LT)-VASP, the short-circuit behavior often obtained from the conventional one-step-fa...

Air-Stable, Efficient Mixed-Cation Perovskite Solar Cells with Cu Electrode by Scalable Fabrication of Active Layer

Abstract: However, fundamental solution to this problem still relies on fi nding another electrode material which is much less reactive with perovskite. Gold (Au) is chemically less active than Al and Ag, but the chemical reaction between Au and perovskite at the interface level is still observed, [ 19 ] not to mention the high price of Au. Here, we report the fabrication of compact, smooth at grain scale, and pure phase of mixed cation (formamidinium (FA) and methylammonium (MA)) perovskite fi lms by doctor-blade coating method. The mixed cation perovskite is chosen because of its lower bandgap for potentially higher device effi ciency, as demonstrated by previous studies using the nonscalable fabrication process. [ 2 ] The compositionally tuned perovskite layer extends the absorption onset to 850 nm, resulting in an increased PCE of over 18.0%, which is comparable to that of the spin-coated devices. In addition, we improved the devices stability substantially by replacing Al with Cu as cathode. The unsealed devices stored in ambient condition of ≈25 °C with 20%–60% relative humidity could maintain the performance without any PCE loss for up to 20–30 d. Figure 1 a illustrates the doctor-blade coating of mixed-cation perovskite FA x MA 1− x PbI 3 layer, modifi ed from our previous report. [ 12 ] Briefl y, PbI 2 , methylammonium iodide (MAI) and formamidinium iodide (FAI) were dissolved in N,N -dimethylformamide (DMF) at room temperature at a molar ratio of FAI:MAI:PbI 2 = x :(1x ):1. Then the solution was dropped on to preheated (100–145 °C) substrates on a hot plate, and swiped from the front to the end. The perovskite fi lms dried in seconds, and then were removed from the hot plate quickly. In this study, we fi rst demonstrate that the doctor-blade coating method provides a better control for the FAPbI 3 fi lm formation process due to its facile temperature controlling capability. FAPbI 3 has two phases, one is black, perovskite α-phase at 2 θ of 16° in X-ray diffraction (XRD) pattern by Co-Kα radiation ( λ = 1.788 Å), and the other one is yellow, nonperovskite δ-phase at 2 θ of 14.1°. It is well known that FAPbI 3 is thermodynamically stable in δ-phase at room temperature, and stable in α-phase at higher temperature. [ 15,22 ] The spun FAPbI 3 fi lms are often δ-phase (Figure 1 b), [ 15 ] which requires a high temperature annealing (150 °C, 10–30 min) process to convert them into α-phase (Figure 1 c). [ 15,23 ] The doctor-bladed FAPbI 3 fi lms have the desired α-phase perovskite which can be directly obtained without an additional thermal annealing process, because the precursor solution and the substrates can be heated in situ to the temperature that favors α-phase formation (Figure 1 c). Figure 1 d shows the X-ray diffraction patterns of pure FAPbI 3 ( x = 1) fi lms prepared at different doctor-blading Organic–inorganic halide perovskite solar cells have reached over 21.0% power conversion effi ciency (PCE) in only a few years of development due to their extraordinary and unique optoelectronic properties such as long carrier diffusion length. [ 1–3 ] Next big challenges to be addressed for perovskite solar cells are the scalable fabrication and long term stability before they can be considered for real products. One advantage of perovskite materials over Si and Gallium Arsenide (GaAs) for large area solar cell application is their solution process capability, which allows us to leverage the existing scalable solution deposition methods established in many other fi elds, such as slot-die coating and roll-to-roll fabrication, for large area perovskite solar cell fabrication. Though the stateof-the-art perovskite solar cells have multiple layers including charge transport layers, [ 4–6 ] the capability to fabricate a high quality perovskite layer by these scalable methods is crucial, because the fabrication of charge transport layers, including both organic and inorganic nanoparticle layers, have been wellestablished in the research of organic solar cells. [ 7,8 ] In the past couple of years, some efforts have been devoted to searching a good scalable deposition method for the perovskite layers, including spray-coating, [ 9 ] electrochemical deposition, [ 10 ] doctorblade coating, [ 11,12 ] slot-die coating, [ 13 ] etc. However the device effi ciencies from all these scalable deposition methods still lag far behind the state-of-the-art spin-coated devices by 30%–50%. The reasons include incomplete perovskite fi lm coverage, presence of pin-holes, and high roughness at grain scale caused by less controlled nucleation and/or crystal growth and the limited attempts of perovskite composition engineering in scalable fabrication methods. [ 14–16 ] In addition, scalable fabrication method should come with good long term stability to make perovskite solar cells a real solution to renewable energy conversion. Among many degradation mechanisms, [ 17,18 ] the interface deterioration by chemical reaction between the perovskite layer and the metal electrode (e.g., Al, Ag) in the ambient environment have been reported to dominate the initial degradation of perovskite solar cells, [ 19 ] which occurs far ahead of the degradation of perovskite grains by moisture or heat. Several recent studies showed that spatially separating the perovskite layer and metal

Relationships between Lead Halide Perovskite Thin-Film Fabrication, Morphology, and Performance in Solar Cells.

Abstract: Solution-processed lead halide perovskite thin-film solar cells have achieved power conversion efficiencies comparable to those obtained with several commercial photovoltaic technologies in a remarkably short period of time. This rapid rise in device efficiency is largely the result of the development of fabrication protocols capable of producing continuous, smooth perovskite films with micrometer-sized grains. Further developments in film fabrication and morphological control are necessary, however, in order for perovskite solar cells to reliably and reproducibly approach their thermodynamic efficiency limit. This Perspective discusses the fabrication of lead halide perovskite thin films, while highlighting the processing–property–performance relationships that have emerged from the literature, and from this knowledge, suggests future research directions.

High-Performance Flexible Transparent Electrode with an Embedded Metal Mesh Fabricated by Cost-Effective Solution Process

Abstract: A new structure of flexible transparent electrodes is reported, featuring a metal mesh fully embedded and mechanically anchored in a flexible substrate, and a cost-effective solution-based fabrication strategy for this new transparent electrode. The embedded nature of the metal-mesh electrodes provides a series of advantages, including surface smoothness that is crucial for device fabrication, mechanical stability under high bending stress, strong adhesion to the substrate with excellent flexibility, and favorable resistance against moisture, oxygen, and chemicals. The novel fabrication process replaces vacuum-based metal deposition with an electrodeposition process and is potentially suitable for high-throughput, large-volume, and low-cost production. In particular, this strategy enables fabrication of a high-aspect-ratio (thickness to linewidth) metal mesh, substantially improving conductivity without considerably sacrificing transparency. Various prototype flexible transparent electrodes are demonstrated with transmittance higher than 90% and sheet resistance below 1 ohm sq(-1) , as well as extremely high figures of merit up to 1.5 × 10(4) , which are among the highest reported values in recent studies. Finally using our embedded metal-mesh electrode, a flexible transparent thin-film heater is demonstrated with a low power density requirement, rapid response time, and a low operating voltage.

Facile fabrication of stretchable Ag nanowire/polyurethane electrodes using high intensity pulsed light

Abstract: Silver nanowires (AgNWs) have emerged as a promising nanomaterial for next generation stretchable electronics. However, until now, the fabrication of AgNWbased components has been hampered by complex and time-consuming steps. Here, we introduce a facile, fast, and one-step methodology for the fabrication of highly conductive and stretchable AgNW/polyurethane (PU) composite electrodes based on a high-intensity pulsed light (HIPL) technique. HIPL simultaneously improved wire–wire junction conductivity and wire–substrate adhesion at room temperature and in air within 50 μs, omitting the complex transfer–curing–implanting process. Owing to the localized deformation of PU at interfaces with AgNWs, embedding of the nanowires was rapidly carried out without substantial substrate damage. The resulting electrode retained a low sheet resistance (high electrical conductivity) of <10 Ω/sq even under 100% strain, or after 1,000 continuous stretching–relaxation cycles, with a peak strain of 60%. The fabricated electrode has found immediate application as a sensor for motion detection. Furthermore, based on our electrode, a light emitting diode (LED) driven by integrated stretchable AgNW conductors has been fabricated. In conclusion, our present fabrication approach is fast, simple, scalable, and costefficient, making it a good candidate for a future roll-to-roll process.

One-dimensional photonic crystals: fabrication, responsiveness and emerging applications in 3D construction

Abstract: A one-dimensional photonic crystal (1DPC), which is a periodic nanostructure with a refractive index distribution along one direction, has been widely studied by scientists. In this review, materials and methods for 1DPC fabrication are summarized. Applications are listed, with a special emphasis on sensing platforms and photovoltaic devices together with full color display. After that, some typical 3D ordered structures with stacked layers are highlighted, fabrication methods are also described, and remaining problems are pointed out. Lastly, the possibility of building 3D stacked structures based on 1D layers through chemical routes is discussed; a relatively convenient and flexible method. We believe such a method is a promising way to conduct 3D fabrication.

Cost-effective fabrication of high-performance flexible all-solid-state carbon micro-supercapacitors by blue-violet laser direct writing and further surface treatment

Abstract: A facile and cost-effective method for the fabrication of all-solid-state flexible carbon micro-supercapacitors (MSC) was demonstrated by laser direct writing on polyimide (PI) sheets with a compact and low-cost 405 nm semiconductor blue-violet laser, the beam of which was almost totally absorbed in the PI sheet. The obtained MSCs exhibit high performances due to the hierarchical porous structures and large thickness. Furthermore, surface treatment by air-plasma etching was employed to improve the contact interface between the carbon structures and the electrolyte, which may also influence pore structures, thus largely enhancing the MSC performance. The typical MSCs after plasma treatment for 100 s show an improved specific capacitance as high as 18.3 mF cm−2 at a scan rate of 10 mV s−1 and 31.9 mF cm−2 at a current density of 0.05 mA cm−2, both of which are higher than most of the carbon material-based MSCs reported till now. Moreover, the MSCs show good flexibility, long-time cycle stability, as well as temperature tolerance up to 80 °C. In addition, the voltage and capacitance can be scaled up by simply connecting a single MSC in series, parallel or both. The facile fabrication, low cost, and good performance make carbon-based MSCs fabricated by semiconductor laser direct writing promising candidates for on-chip energy storage devices.

Fully Tunable Silicon Nanowire Arrays Fabricated by Soft Nanoparticle Templating.

Abstract: We demonstrate a fabrication breakthrough to produce large-area arrays of vertically aligned silicon nanowires (VA-SiNWs) with full tunability of the geometry of the single nanowires and of the whole array, paving the way toward advanced programmable designs of nanowire platforms. At the core of our fabrication route, termed “Soft Nanoparticle Templating”, is the conversion of gradually compressed self-assembled monolayers of soft nanoparticles (microgels) at a water–oil interface into customized lithographical masks to create VA-SiNW arrays by means of metal-assisted chemical etching (MACE). This combination of bottom-up and top-down techniques affords excellent control of nanowire etching site locations, enabling independent control of nanowire spacing, diameter and height in a single fabrication route. We demonstrate the fabrication of centimeter-scale two-dimensional gradient photonic crystals exhibiting continuously varying structural colors across the entire visible spectrum on a single silicon subs...

A 3D printable diamond polymer composite: a novel material for fabrication of low cost thermally conducting devices

Abstract: The development of a thermally conducting composite material that can be rapidly 3D printed into prototype objects is presented. The composite structures containing 10, 20, 25 and 30% (w/v) of 2–4 micron sized synthetic diamond microparticles added to the acrylate polymer were produced using a low cost stereolithographic 3D printer. The prepared materials were characterised according to heat transfer rates, thermal expansion co-efficients and contact angles, and analysed using high resolution electron microscopy, thermogravimetric analysis and thermal imaging. The composites displayed minor enhancements in heat transfer rates with incrementing diamond content upto 25% (w/v), however a significant improvement was observed for the 30% (w/v) polymer–diamond composite, based on an interconnected diamond aggregate network, as confirmed by high resolution scanning electron microscopy. The developed material was used in the fabrication of prototype 3D printed heat sinks and cooling coils for thermal management applications in electronic and fluidic devices. Infrared thermal imaging performed on 3D printed objects verified the superior performance of the composite compared to the inherent polymer.

Light and Strong SiC Networks

Abstract: The directional freezing of microfiber suspensions is used to assemble highly porous (porosities ranging between 92% and 98%) SiC networks. These networks exhibit a unique hierarchical architecture in which thin layers with honeycomb‐like structure and internal strut length in the order of 1–10 μm in size are aligned with an interlayer spacing ranging between 15 and 50 μm. The resulting structures exhibit strengths (up to 3 MPa) and stiffness (up to 0.3 GPa) that are higher than aerogels of similar density and comparable to other ceramic microlattices fabricated by vapor deposition. Furthermore, this wet processing technique allows the fabrication of large‐size samples that are stable at high temperature, with acoustic impedance that can be manipulated over one order of magnitude (0.03–0.3 MRayl), electrically conductive and with very low thermal conductivity. The approach can be extended to other ceramic materials and opens new opportunities for the fabrication of ultralight structures with unique mechanical and functional properties in practical dimensions.

Laser fabrication of crystalline silicon nanoresonators from an amorphous film for low-loss all-dielectric nanophotonics

Abstract: The concept of high refractive index subwavelength dielectric nanoresonators, supporting electric and magnetic optical resonance, is a promising platform for waveguiding, sensing, and nonlinear nanophotonic devices. However, high concentration of defects in the nanoresonators diminishes their resonant properties, which are crucially dependent on their internal losses. Therefore, it seems to be inevitable to use initially crystalline materials for fabrication of the nanoresonators. Here, we show that the fabrication of crystalline (low-loss) resonant silicon nanoparticles by femtosecond laser ablation of amorphous (high-loss) silicon thin films is possible. We apply two conceptually different approaches: recently proposed laser-induced transfer and a novel laser writing technique for large-scale fabrication of the crystalline nanoparticles. The crystallinity of the fabricated nanoparticles is proven by Raman spectroscopy and electron transmission microscopy, whereas optical resonant properties of the nanoparticles are studied using dark-field optical spectroscopy and full-wave electromagnetic simulations.

Solution-Processable High-Purity Semiconducting SWCNTs for Large-Area Fabrication of High-Performance Thin-Film Transistors.

Abstract: For the large-area fabrication of thin-film transistors (TFTs), a new conjugated polymer poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl] is developed to harvest ultrahigh-purity semiconducting single-walled carbon nanotubes. Combined with spectral and nanodevice characterization, the purity is estimated up to 99.9%. High density and uniform network formed by dip-coating process is liable to fabricate high-performance TFTs on a wafer-scale and the as-fabricated TFTs exhibit a high degree of uniformity.

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

Abstract: Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

Rapid fabrication of microfluidic PDMS devices from reusable PDMS molds using laser ablation

Abstract: The conventional fabrication methods for microfluidic devices require cleanroom processes that are costly and time-consuming. We present a novel, facile, and low-cost method for rapid fabrication of polydimethylsiloxane (PDMS) molds and devices. The method consists of three main fabrication steps: female mold (FM), male mold (MM), and chip fabrication. We use a CO2 laser cutter to pattern a thin, spin-coated PDMS layer for FM fabrication. We then obtain reusable PDMS MM from the FM using PDMS/PDMS casting. Finally, a second casting step is used to replicate PDMS devices from the MM. Demolding of one PDMS layer from another is carried out without any potentially hazardous chemical surface treatment. We have successfully demonstrated that this novel method allows fabrication of microfluidic molds and devices with precise dimensions (thickness, width, length) using a single material, PDMS, which is very common across microfluidic laboratories. The whole process, from idea to device testing, can be completed in 1.5 h in a standard laboratory.

Replacement metal gate and fabrication process with reduced lithography steps

Abstract: Embodiments of the present invention provide a replacement metal gate and a fabrication process with reduced lithography steps. Using selective etching techniques, a layer of fill metal is used to protect the dielectric layer in the trenches, eliminating the need for some lithography steps. This, in turn, reduces the overall cost and complexity of fabrication. Furthermore, additional protection is provided during etching, which serves to improve product yield.

A review on fabrication processes for electrochromic devices

Abstract: Electrochromism is a phenomenon involving change of colors under an externally applied voltages Because its importance is rising today, various fabrication processes have been used to manufacture electrochromic devices (ECDs). In this review, solution-, vapor-, and solid particle-based processes are introduced and compared in terms of process parameters. The seven representative fabrication processes discussed in this paper are electrodeposition, sol-gel, spray pyrolysis, chemical vapor deposition (CVD), thermal evaporation deposition, sputtering, and nanoparticle deposition systems (NPDS). Temperature and vacuum conditions for each process are compared. Electrodeposition and sol-gel processes can be performed under atmospheric pressure. Most sputtering and NPDS processes are conducted at room temperature. Although many fabrication processes are reviewed here, commercialization, environmental issues, cost, improvement of performance, and enhancement of product size will be studied for future ECDs.

Organic and perovskite solar modules innovated by adhesive top electrode and depth-resolved laser patterning

Abstract: We demonstrate an innovative solution-processing fabrication route for organic and perovskite solar modules via depth-selective laser patterning of an adhesive top electrode. This yields unprecedented power conversion efficiencies of up to 5.3% and 9.8%, respectively. We employ a PEDOT:PSS–Ag nanowire composite electrode and depth-resolved post-patterning through beforehand laminated devices using ultra-fast laser scribing. This process affords low-loss interconnects of consecutive solar cells while overcoming typical alignment constraints. Our strategy informs a highly simplified and universal approach for solar module fabrication that could be extended to other thin-film photovoltaic technologies.

Scalable Fabrication of Integrated Nanophotonic Circuits on Arrays of Thin Single Crystal Diamond Membrane Windows

Abstract: Diamond has emerged as a promising platform for nanophotonic, optical, and quantum technologies. High-quality, single crystalline substrates of acceptable size are a prerequisite to meet the demanding requirements on low-level impurities and low absorption loss when targeting large photonic circuits. Here, we describe a scalable fabrication method for single crystal diamond membrane windows that achieves three major goals with one fabrication method: providing high quality diamond, as confirmed by Raman spectroscopy; achieving homogeneously thin membranes, enabled by ion implantation; and providing compatibility with established planar fabrication via lithography and vertical etching. On such suspended diamond membranes we demonstrate a suite of photonic components as building blocks for nanophotonic circuits. Monolithic grating couplers are used to efficiently couple light between photonic circuits and optical fibers. In waveguide coupled optical ring resonators, we find loaded quality factors up to 66 0...

Maskless Fabrication of Highly Robust, Flexible Transparent Cu Conductor by Random Crack Network Assisted Cu Nanoparticle Patterning and Laser Sintering

Abstract: A novel maskless fabrication method for highly flexible Cu random network transparent conductor has been developed by random nanocrack generation and subsequent Cu nanoparticle ink filling, transfer, and oxidation-free laser sintering without the aid of conventional photolithography or vacuum metal deposition steps. Use of random nanocrack on a silicon as a transfer printing template enables large area, high resolution network patterning, and fabrication in a simple maskless manner. At the same time, the laser sintering process allows low temperature, fast processing time, and oxidation suppression of Cu nanoparticle under ambient atmosphere. The fabricated Cu metal network establishes strong adhesion to plastic substrates, thus mechanical stability against tensile and compressive bending is attainable. Moreover, the template-assisted Cu metal network fabrication method minimizes waste of Cu nanoparticle as compared with other methods. A simple touch screen using Cu metal network-based transparent conductor is also demonstrated.

Fabrication of graphite film/aluminum composites by vacuum hot pressing: Process optimization and thermal conductivity

Abstract: Effective thermal management is becoming increasingly important for high power density electronic devices, which requires materials with high thermal conductivity. A novel graphite film/aluminum composite material with ultrahigh thermal conductivity was fabricated by vacuum hot pressing process to meet this requirement. The effects of fabrication parameters on microstructures and thermal conductivities of these composites were investigated. As a result, the composites with graphite volume fraction of 17.4–69.4% sintered at 655 °C/45 MPa for 100 min exhibit in-plane thermal conductivities of 380–940 W/mK, over 90% of the predictions by rule of mixture. These composites possess higher in-plane thermal conductivities than graphite flake/aluminum composites due to well-controlled graphite orientation and fabrication parameters, which indicates that these composites are promising materials for effective thermal management.

Transversally Extended Laser Plasmonic Welding for Oxidation-Free Copper Fabrication toward High-Fidelity Optoelectronics

Abstract: Laser direct processing is a promising approach for future flexible electronics because it enables easy, rapid, scalable, and low-temperature fabrication without using expensive equipment and toxic material. However, its application for nanomaterials with high chemical susceptibility, such as representatively Cu, is limited because severe oxidation occurs under ambient conditions. Here, we report the methodology of a transversally extended laser plasmonic welding process, which outstandingly improves the electrical performance of a Cu conductor (4.6 μΩ·cm) by involving the spatially concurrent laser absorption to the surface oxide-free Cu nanoparticles (NPs). Physical/chemical properties of fabricated Cu conductors are fully analyzed in perspectives of the mechanism based on the thermo-physical-chemical interactions between photon energy and pure Cu NPs. The resultant Cu conductors showed an excellent durability in terms of bending and adhesion. Furthermore, we successfully demonstrated a single layer Cu-...