Conventional Screen Printing Research Articles

Screen printing approach for high throughput and flexible adhesive deposition in graphite bipolar plate production

The struggle against climate change necessitates innovative technologies for storing and utilizing renewable energy. Hydrogen is considered a promising solution for harnessing renewable energy in a wide range of applications. In addition to its application as a raw material in the steel and the chemical industry, hydrogen can also be utilized as an energy carrier in conjunction with fuel cells (e.g. with Polymer Electrolyte Membrane Fuel Cells PEMFC) for heavy-duty vehicles, emergency power supplies or the maritime sector. To achieve the required electrical voltages for these applications, several hundred cells are assembled to a stack. A crucial component of an individual cell alongside the Membrane Electrode Assembly (MEA) is the Bipolar Plate (BPP), consisting of two bonded Bipolar Half Plates (BPHP). The BPP enables an inflow of reactive media, the cooling of the cell and is also required for the electrical contacting of the stacked cells as well as the overall mechanical stability. According to previous studies, fully bonded BPPs, especially in the flow field, significantly improve both mechanical and electrical properties of the entire stack. The here presented innovative approach for adhesive deposition aims at bonding graphitic BPHPs to BPPs with a high throughput capability while maintaining high flexibility and process stability. The process is based on the conventional screen printing technique, which in this case is performed without a stencil, allowing for a high flexibility regarding the cell geometry. Furthermore, the range of usable adhesives can be expanded with minor adjustments, allowing for not only paste adhesives but also thermally activated powders. With the presented approach, the adhesive volume can be controlled precisely and applied uniformly by selecting a suitable screen. The feasibility of the approach was tested and initial parameter estimations for potential industrial implementation were determined.

Environmentally-Friendly Electroplating Process Using Solid Electrolyte Membranes

The automobile is a very broad industry, and consists of tens of thousands of parts. Many parts of automobile employ surface treatment to provide several functions such as electronic and anti-corrosion properties. Among several surface treatment process, plating is an important elemental technology for automobile industry. For the industrial perspective, interest in SDGs significantly increases, and efforts to reduce environmental impact are highly urgent. Recently, we have developed novel electroplating process, solid electrodeposition (SED), which is based on ion transfer through solid electrolyte membrane1). This process has unique deposition characteristics that the metal film can be deposited only on the contact area between cathode and the membrane, in a fashion similar to stamping deposition. The SED process has an advantage for reducing amounts of waste effluent and CO2 gas. Moreover, this process has a potential of high deposition rate due to utilization of thin electrolyte membrane, providing lower electrical resistance between electrodes1), 2). Therefore, in the environmental and economical perspective, we believe that SED is promising process to metallize the substrate surface as an alternative to the conventional electroplating, especially in the field of electronics manufacturing. In this study, we report on SED system in details and characterization of deposited copper and nickel films. We also introduce copper fine patterning technique combined with SED using hard mask. Figure 1 shows schematic of the present SED system. The head part composed of anode plate, electrolyte solution and membrane are placed on substrate under controlled temperature and pressure. The membrane mainly plays a role of selective cation transfer from electrolyte solution to the substrate, although a small amounts of electrolyte solution can also be transferred due to pressure difference between internal head part and atmosphere. This solution uniformly spread to the interface between membrane and substrate so that uniform metal deposition is continuously proceeded without adhering the membrane with the substrate. Additionally, the SED system allows one to shorten the distance between electrodes because membrane can act as a diaphragm. Therefore, the power consumption is smaller than that of conventional electroplating, owing to decrease in an internal electrical resistance, providing the decrease of exhaust CO2 gas. The deposited film has relatively uniform thickness as shown in Figure 2, the result of which is due to the short distance between electrodes as well as uniform current feeding to deposit metal films through the back side of the cathode. The deposited copper and nickel films are crystalline and highly conductive, the quality of which are being enough for application of the SED process in the current electronics device manufacturing. By combining the SED process with the conventional screen printing technique, copper circuit patterns with line width of below 50 μm could also be successfully fabricated.1) Akamatsu, S. Nakano, K. Kimura, Y Takashima, T. Tsuruoka, H. Nawafune, Y. Sato, J. Murai, H. Yanagimoto, ACS Appl. Mater. Interfaces, 13, 13896-13906 (2021)2) Narui, Y. Hoshi, I. Shitanda, M. Itagaki, H. Yanagimoto, M. Hiraoka and H. Iisaka, E01-920, 232nd ECS Meeting. Figure 1

Fabrication of Durable and High-Performance Flat Tubular Anode-Supported Solid Oxide Cells for Stack Application

Solid oxide cell (SOC) technology is highly admissible for distributed power generation since it enables the most efficient and clean conversion of fuels into energy and heat. SOCs are also regarded as a potential technology for their decisive role in strengthening the hydrogen economy concept by storing renewable energy resources such as green hydrogen and synthetic fuels. In this work, high-performance and durable flat tubular anode-supported SOC is developed for SOC stack applications. NiO-8YSZ composite flat tubular anode support is fabricated by employing an extrusion process. Anode functional layer and electrolyte layers are deposited by the dip-coating technique, whereas the GDC diffusion barrier, LSCF-GDC composite cathode, and Ag-glass composite interconnect layers are fabricated by the conventional screen-printing process. Finally, the prepared flat tubular SOCs possess an active cathode area of 45 cm2 and demonstrated a high-power density of ~430 mW cm-2 at operating current density, voltage, and temperature conditions of 501 mA cm-2, 0.87 V, and 700 °C. During a long-term stability test at 700 °C for 1000 h, the SOC showed a voltage improvement of 0.013 % while operating at a fuel efficiency of 65%. The flat tubular anode-supported SOC’s high performance and durable operation showed its potential for commercial applications in distributed power generation and hydrogen production. Together with the research to further enhance the SOC’s performance and stability, the flat tubular SOC stack design and fabrication are also in progress.

Photocured, highly flexible, and stretchable 3D-printed graphene/polymer nanocomposites for electrocardiography and electromyography smart clothing

This work focuses on the development of photocured, highly flexible and stretchable 3D-printed graphene/polymer nanocomposites for electrocardiography and electromyography smart clothing. We combined acrylate monomers and oligomers in different proportions to prepare photocurable resins with good stretchability and resilience. Graphene was then added to introduce conductivity to the photocured resin and to enhance its flexibility. This resin was used to 3D print sample patterns with microneedle surface structures. The sample patterns were successfully used as sensing components for the detection of human body signals. Two methods were compared to avoid graphene aggregation: (1) the addition of styrene maleic anhydride (SMA) to enable physical adsorption via π–π interactions between the aromatic rings and graphene; and (2) the addition of polyetheramine (PEA), which creates steric effects with graphene. An amphiphilic dispersant was prepared by grafting SMA onto PEA, and the ideal dispersion ratio was determined. The dispersant was mixed with photocured resin to form a graphene/photocured resin nanocomposite material. By varying the graphene content, a nanocomposite material with the lowest resistance (approximately 3 × 103 Ω/sq) and mechanical strength (tensile strength: >4 MPa, elongation at break: 320 %) was obtained. The material also demonstrated good resilience under a 50 % cycle fatigue. Finally, flat base plates that differed from those produced by conventional screen printing were 3D-printed. Materials with surface microneedle structures with different length-to-diameter ratios and inter-needle spacings were prepared, and the differences in skin contact among these materials were experimentally investigated by measuring electrocardiography and electromyography signals in humans. Our results demonstrate that highly customized 3D-printed resins with diverse and complex structures can be successfully integrated into smart clothing to monitor the physiological status of humans.

Production and characterization of magnetic textiles

In this study, 100% cotton fabrics were imparted with magnetic field properties using a conventional screen printing method to obtain magnetic fabrics in the context of smart textiles. The magnetism in the fabrics was generated by using a Fe3O4 compound. In order to make this compound adhere more strongly to the fabric sample, printing method was used as a finishing application. The Fe3O4 compound was added to the printing paste without using any dyestuff since the Fe3O4 compound had a unique color itself. The washing durability of the printed functional textiles were investigated. The washing fastness, acidic sweat fastness, alkaline sweat fastness, water fastness, dry rubbing fastness, wet rubbing fastness, tear strength, pilling and degree of external magnetic induction of the fabrics were analyzed. In addition, the morphological analyzes of the fabrics were performed by scanning electron microscopy (SEM-EDX) and X-ray crystallography (XRD) to determine the crystallographic properties of the materials and the phases they contained. According to the result of quantitative evaluation of magnetic fields on textile surfaces, Fe3O4 microparticles were in the range of 25 mT when they constituted 50% of the weight.Thus, it was found that a magnetic field was successfully generated in the textiles. Moreover, the magnetic property of the fabric was durable after the washing process as the mT values were maintained even after 20 washing cycles, and the fastness and performance tests were also at the highest level. Increasing the Fe3O4 content in the formulations used in the study improved the tensile strength by 2-7%. Comparing the test results of the fabric sample with the optimum formulation with the untreated fabric sample, it was also determined that the tensile strength increased by 8-10% on average after 20 washes.

Water-based chitosan/reduced graphene oxide ink for extrusion printing of a disposable amperometric glucose sensor

Recently, developing appropriate printing techniques and conductive inks has received considerable attention in the field of (bio)sensors. Extrusion printing technology is an interesting alternative to conventional screen-printing for making flexible and disposable electronics due to its special features such as, direct printing, easy control of design, and manufacturing processes. Moreover, fabricating highly dispersed and stable graphene inks with appropriate conductivity and printability is always a challenge in (bio)sensors. Here, a water-based chitosan/reduced graphene oxide (CS/rGO) ink was obtained using extrusion printing to make conductive electrodes on paper. CS/GO ratio of 0.2 showed the best stability, electrochemical performance and hydrophilicity (water contact angle of 85° ± 6). The resulting sensor was a simple two-electrode device based on the chronoamperometry technique, representing a good potential for detecting glucose in the linear range of 0.5 to 4 mM and with a limit of detection (LOD) of 0.45 mM (S/N = 3). Furthermore, this non-enzymatic sensor showed proper selectivity against interfering substances, as well as an excellent stability during 28 days (2.9% response fall). Ultimately, the developed conductive ink can be considered as an innovative material with high stability and dispersivity of rGO for the future studies on disposable (bio)sensors and flexible electronics.

Design, Fabrication and Characterization of Inter-Layer Microheaters Using LTCC Technology

This paper presents design, fabrication and characterization of novel inter-layer microheaters based on low temperature co-fired ceramics (LTCC) technology. LTCC microheater structures (S1 to S3) with three different heater configurations has been presented. Microheater structure S1 has a heater pattern generated only on the top LTCC layer while S2 and S3 structures have inter-layer heater patterns. These structures have been simulated using COMSOL software to depict the temperature distribution over the active area. LTCC being a multilayer technology, heater patterns are generated in two different layers of LTCC tapes and connected through vias (3D interconnections) to fabricate inter-layer microheaters. By distributing the heater pattern of S1 equally in two LTCC tape layers (as in S3), this method allows possibility to develop miniature LTCC microheaters using conventional screen-printing process. The developed microheaters are characterized and the results are compared. At an input power of ∼1 W, structure S3 reaches a peak temperature of 316 °C as compared to 272 °C achieved with S1 configuration. Thermal imaging results shows better temperature uniformity in the active area for inter-layer microheaters as compared to microheater having heater pattern only on the top LTCC layer.

(Invited) Conformal Printing for Advanced Electronic Devices

Different electronic devices are ubiquitous in our daily lives. These devices keep on improving daily, and their evolution contributes to the enrichment of our lives. However, two factors remain, that is, little or no progress at all has been introduced in the field of electronics for a long time. First, the use of a printed circuit board (PCB) to drive electronic-device circuits has not been improved. The PCB remains thick and hard. Second, the PCB is enclosed in a cabinet for finished products. Generally, device engineers and product designers design electronic circuits and cabinets, respectively. In this case, engineers emphasize that they cannot change the circuit size and arrangement of the lead-out wiring, whereas designers insist that they must realize an attractive cabinet beyond the restriction of the circuit designs.To overcome this issue, conformal printing using a soft blanket has attracted much attention as a technique that can form wires/electrodes on objects with complex shapes. Although the cabinets of electronic devices often have a curved surface, printing that uses a soft blanket can simply and easily form patterns on these electronic devices. At least, wires/electrodes can be formed on a cabinet with a complex shape. Among the many printing methods, the screen-printing-based technology is the most practical. The wires/electrodes of various commercially available electronic devices are fabricated using this printing method. Thus, we are developing screen-printing-based conformal-printing techniques such as screen-offset and screen-pad printing.Screen-offset printing involves screen printing onto a blanket made of silicone and transfer printing from the blanket to a substrate [Fig. 1(a)]. In this process, the organic solvents in conductive ink are absorbed by the silicone. Therefore, collapse of the patterns due to cohesion failure during transfer printing can be prevented. In addition, solvent absorption prevents ink from smudging caused by its fluidity, which subsequently means that fine patterns can be formed compared with those obtained using the conventional screen printing. The width of the patterns formed by screen-offset printing can be as fine as 10 µm, whereas the minimum width obtained by screen printing in mass-produced products is approximately 40–50 µm.Furthermore, the surface free-energy of silicone is low, indicating that screen-offset printing can form patterns even on an adhesive. For example, a material sticks to a screen mask when conventional screen printing is employed. Although heat-applied soldering is often employed for electronic-component mounting, non-heated interconnection can be performed by fixing the electronic components on a screen-offset-printed adhesive substrate using an alignment of component and substrate electrodes.Another feature of the screen-offset printing is that the silicone blanket can deform along the shape of a substrate owing to its softness, which indicates that the conductive ink can be transcriptionally formed on the surface of an object with a complex shape. For example, we developed printed wire-bonding techniques using screen-offset printing [Fig. 1(b)]. A 200-µm-thick Si chip with face-up-type electrodes was arranged on a PCB. Using screen-offset printing, the conductive-ink patterns could climb over the cleaved sidewall of the Si chip because silicone can deform along the steric structure. Thus, wiring connections between the PCB pads and Si-chip pads were successfully performed.Furthermore, screen-offset printing can properly form conductive patterns on textiles [Fig. 1(c)]. For example, plain-woven cotton, which is often used for clothes such as shirts, has a bumpy and porous surface, implying that forming wires/electrodes without breaking is very difficult. However, the silicone blanket can deform along the textured surface. In addition, dried ink caused by organic-solvent absorption of the blanket can bridge the air gap. This wiring technique can contribute to the e-textile technology as a platform for wearable electronics.Applying screen-offset printing on a surface with a large step on the order of millimeters is difficult. To overcome this problem, we need to employ a much softer and thicker blanket to drastically deform along the substrate surface. In contrast, screen printing ink onto such a softer blanket becomes difficult. To address this issue, we have developed screen-pad printing, which is composed of the following: (i) screen printing to a normal blanket, (ii) picking ink to a soft pad from the blanket, and (iii) transcriptionally forming ink patterns on a substrate from the pad. Patterns can be formed even on bumpy surfaces with a large step owing to the soft pad, although the number of processes increases.Common objects generally do not have a flat surface but have a complicated shape. We are currently attempting to fabricate such object-sensor devices by forming functional-material patterns using our developed conformal-printing technique. Figure 1

Red ZnGa2O4:Cr3+ powder electroluminescence co-generating sounds with a longer lifetime and no thermal quenching behaviors

The ZnGa2O4:Cr3+ powder electroluminescence (PEL) device has been demonstrated through a conventional screen printing method. The phosphor powder was prepared by a solid-state reaction in an air ambient and dispersed in an ethyl cellulose binder before screen printing in ITO glass. The PEL device consists of 20 μm-thick BaTiO3 as an insulating layer and 30 μm-thick ZnGa2O4:Cr3+ as an active layer. It has a comparatively lower threshold voltage (40 V) than the previous PEL device. It generates the red light peaking at 696 nm and 708 nm attributed to the forbidden transition of Cr3+ ions and the sound depending on the applied frequency due to the BaTiO3 layer. Its EL intensity was exponentially increased with voltage and linearly increased with the frequency before saturating at a frequency of 3 kHz, which is consistent with the 1/10 decay time. It has the best luminous efficiency of 0.74 lm/W and the maximum EL luminance of 1.64 cd/m2. In particular, it was not thermally quenched even at a higher temperature due to the anti-thermal quenching effect. Moreover, it shows high reliability under ultrasonic frequency (>20 kHz) and is long-lived in an accelerated aging environment (>740 min, temperature of 60 °C and humidity of 50%).

Performance Enhancement of the Digital Printed Cotton Fabric through Ecofriendly Finishes

ABSTRACT Digital textile printing has emerged as a sustainable alternative to the conventional screen printing. Similar to other forms of coloration, digitally printed cotton fabric also needs finishing to overcome the inherent drawbacks of the cotton fabric. However, research on the finishing of the digital printed fabric is very limited and focused on non-sustainable finishes. In the first instance, this paper optimizes the recipe of the pre-printing process. Then, this paper investigates the performance of the digitally printed cotton fabric using three sustainable and formaldehyde free cross-linkers, three different softeners, C8-free oil and water repellent, and halogen free flame-retardant. This study applies these finishes on the steamed and non-steamed digitally printed fabric samples. The paper tests the performance of the finished digitally printed fabric in terms of key finishing properties. The results show that the proposed sustainable finishes have significantly improved the performance of the digitally printed fabric as compared to the reference non-finished digitally printed sample.

A simple process to create micro-gaps in printed copper electrodes by sintering induced stress in flexible PET substrates

A new simple low-cost technique for fabricating micro-gaps of less than 50 µm in copper electrodes is reported, which combines conventional screen printing of copper paste and intense pulsed light (IPL) sintering. The micro-gap is created via a two-step IPL sintering. First, a continuous printed copper stripe is half sintered along its length with another half blocked by an opaque mask. Then, the second sintering is performed over the entire length of copper stripe with the opaque mask removed. At the joint between two sintering steps, a micro-gap is formed across the copper stripe due to thermal contraction of underlying polyethylene terephthalate substrate. The width of copper micro-gaps can be adjusted by IPL energy. Simple light emitting diode circuits have been made by the micro-gap electrodes, demonstrating its feasibility for practical applications.

Development of TOPCon tunnel-IBC solar cells with screen-printed fire-through contacts by laser patterning

Interdigitated back contact (IBC) solar cells featuring passivated contacts are promising candidates to achieve record-efficiency single-junction silicon-based solar cells. However, they usually require processes that are not amenable for industrial mass production and involve great process complexity associated with patterning and alignment. In this work, we present a novel TOPCon tunnel-IBC solar cell architecture, minimizing the complexity of patterning and alignment. By adopting a local poly-Si(n+)/poly-Si(p+)/SiOx tunnel junction, this cell architecture only requires full-area deposition of various thin-film layers and is compatible with conventional fire-through screen printing. The cell architecture is realized by sequential laser patterning steps and hence no shadow masks are needed. As a critical building block, we develop a working poly-Si(n+)/(SiOx)/poly-Si(p+)/SiOx tunnel junction with implied open-circuit voltage of 727 mV and a tunnel resistivity of 0.52 Ω cm2. We also establish the required laser patterning and damage-removal processes. Finally, we demonstrate that both the electron-selective and hole-selective regions can be contacted by conventional high-temperature fire-through screen printing, hence being compatible with industrial solar cell processing. Using realistic input parameters measured on test samples, we demonstrate by computer simulation that the proposed TOPCon tunnel-IBC cells favour IBC geometry with small pitches up to the technological limit. Corresponding full device integration is currently ongoing.

Digital Textile Printing: A New Alternative to Short-Run Textile Printing in Ghana

This paper is a part of a broader research into textile design technology and trends across the world and their reflection on the local Ghanaian textile industry. It places conventional manual screen printing and digital textile printing technologies side by side and discusses the various drawbacks of screen printing as against the advantages of digital textile printing to illustrate a path for a wider consideration of the latter in Ghanaian small to medium scale textile production. Short-run textile printing commissions are the main source of jobs for small to medium scale textile producers in Ghana. And manual screen printing is the main process employed by these small-scale textile printers. However, screen printing has various layers of limitations such as poor registration of the design, stains, pinholes, colour correctness, colour consistency, colour smear, dye migration, scorching, improper curing, amongst others. These layers of limitations negatively affect the overall outcome of the prints. So, as it stands now, short-run textile printing commissions are either produced manually, of course, with several inconsistencies or outsourced to China and other countries at a higher production cost. This is because, the large-scale textile factories in Ghana could print a minimum of 2400 yards due to their machine settings, calibration and running cost to make the least returns. This study highlights some of the milestones in the development of digital textiles print machines and examines some of the key aspects of their tremendous production aptitudes for short-run textile commissions. The case study research method is used because data comes largely from documentation, archival records, interviews and physical artefacts.
 Keywords: Textile Design, Digital Textile Printing, Screen Printing, Short-run Prints.

Fabrication of group IV semiconductor alloys on Si substrate applying Al paste with screen-printing

We investigated the influence of Sn and Ge ratio in Al paste to fabricate Si-based alloy semiconductor on large-area Si substrate using a conventional screen-printing process and high-temperature treatment steps. From the X-ray diffraction patterns, crystalline SiSn peaks with applying Al-Sn paste have been detected and Sn content in the SiSn layer was estimated around 0.35%, close to the level of solid solubility of Sn in Si. In addition, the Sn depth profile showed similar behavior with Al, which confirms the concept of a liquid epitaxial growth using Al. On the other hand, the SiGe peaks with applying Al–Sn–Ge paste were clearly observed and their main peaks were shifted to a higher angle linearly with decreasing the Ge ratio in the paste. It was suggested that Sn was segregated easily to the surface if in coexistence with Ge due to its lower solubility in SiGe systems.

Resistance variation of conductive ink applied by the screen printing technique on different substrates

AbstractThis research study focuses on the application of conductive ink by the screen printing technique to evaluate the potential of creating printed electrodes and to investigate the effect of washing upon electrical resistance and flexibility. Two conductive inks were applied by a conventional screen printing method on four different textile substrates, 100% cotton, 50%/50% cotton/polyester, 100% polyester and 100% polyamide. The inks were also applied on a multifibre fabric. Atmospheric plasma treatment was applied to improve the adhesion to the samples, and the resistance values were compared with those of non‐treated samples. The values were measured before and after cleaning and washing tests, which were performed to simulate domestic treatment for garments to predict the behaviour of the inks after normal usage of the fabrics. Comfort properties like stiffness of the fabrics were also evaluated after five and 10 washing cycles. It was observed that PE 825 ink forms a thicker film on the fabric surface, contributing to the loss of flexibility of the textile. However, PE 825 ink also produced the best results in terms of durability and lower values of resistance. Polyamide fabrics lost their conductive property after five washing cycles due to weak bonding between the ink and the fibres, whereas cotton fibres provided the best results.

Fabrication of Si1-xSnx Layer on Si Substrate by Screen-Printing of Al-Sn Paste

Single-crystalline Si1-xSnx thick layers on large area Si substrates are fabricated by applying Al-Sn paste using conventional screen-printing process and high temperature treatment step. The impact of the Al and Sn ratio in the Al-Sn pastes are investigated. From the XRD patterns, the crystalline Si1-xSnx peak has been detected and the Sn content in the Si1-xSnx films is increased with increasing annealing temperature reaching approximately 0.35% at 900°C.

Modified Sn-doped LaCrO3 nanostructures: focus on their characterization and applications as ethanol sensor at a lower temperature

The present work emphasizes the effect of the use of Sn, with different concentrations, over the structural properties and sensing applications of LaCrO3. In this work, LaCrO3 nanostructures were modified with different concentration of Sn (0.2 M %, 0.4 M %, 0.6 M % and 0.8 M %).Different modified Sn-doped LaCrO3 was synthesized by sol–gel method and followed by preparation of thick films via a conventional screen printing approach. The characterizations done by means of X-ray diffraction (XRD), energy-dispersive X-ray (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the confirmation of a Sn-doped LaCrO3 crystal structure and its morphology, respectively. These oxides were formulated to identify various air pollutants such as CO2, ethanol, H2S, NH3, NO2, and acetone. The Sn-doped LaCrO3 with 0.4 M % Sn displayed higher gas response to ethanol vapor at the range of 150–250 °C. The sensors additionally demonstrated proper recovery and acceptable stability.Graphic abstractThe graphical abstract demonstrates the in situ synthesis of Sn-doped LaCrO3 by sol–gel method. Similarly, it shows its characterization and finally, the thick films of doped Sn demonstrate best selectivity for ethanol.

Conformal Printing of Graphene for Single‐ and Multilayered Devices onto Arbitrarily Shaped 3D Surfaces

AbstractPrinting has drawn a lot of attention as a means of low per‐unit cost and high throughput patterning of graphene inks for scaled‐up thin‐form factor device manufacturing. However, traditional printing processes require a flat surface and are incapable of achieving patterning onto 3D objects. Here, a conformal printing method is presented to achieve functional graphene‐based patterns onto arbitrarily shaped surfaces. Using experimental design, a water‐insoluble graphene ink with optimum conductivity is formulated. Then single‐ and multilayered electrically functional structures are printed onto a sacrificial layer using conventional screen printing. The print is then floated on water, allowing the dissolution of the sacrificial layer, while retaining the functional patterns. The single‐ and multilayer patterns can then be directly transferred onto arbitrarily shaped 3D objects without requiring any postdeposition processing. Using this technique, conformal printing of single‐ and multilayer functional devices that include joule heaters, resistive deformation sensors, and proximity sensors on hard, flexible, and soft substrates, such as glass, latex, thermoplastics, textiles, and even candies and marshmallows, is demonstrated. This simple strategy promises to add new device and sensing functionalities to previously inert 3D surfaces.

Non-volatile free silver paste formulation for front-side metallization of silicon solar cells

We present a versatile, cost-effective formulation platform for highly conductive silver pastes used in front-side metallization of silicon (Si) solar cells. Pastes based on the capillary suspension concept include silver particles, glass frit and two immiscible fluids. Capillary forces inferred from the second fluid added only in small fractions induce the formation of a percolating particle network. This provides extended shelf-life and distinct flow properties adjustable in a wide range as demanded by the respective printing process, thus yielding residual-free sintered electrodes. Si-wafers are successfully metallized with such pastes using conventional screen-printing, knotless screen and Pattern Transfer Printing™. Paste spreading is studied via high-speed imaging during screen-printing on glass plates. Morphology of printed lines is analyzed using laser scanning microscopy. Electrical properties of the cells are characterized employing a solar simulator and electroluminescence spectroscopy. Results are compared to those obtained using commercial pastes including the same silver particles and glass frits. Paste performance strongly depends on the selected secondary fluid. Aspect ratios ≈0.4–0.5 can be reached and cell efficiencies ηeff ≈ 21% on Cz- and 18.6% on mc Si-wafers are obtained. Additional investigations are necessary to further reduce paste spreading and line interruptions thus improving cell performance.

Pd/Ag thin film deposited on negative temperature coefficient (NTC) ceramics by direct current magnetron sputtering

Metallization of Negative Temperature Coefficient (NTC) thermistors deposited via direct current magnetron sputtering had been the main subject of this extensive research. A variety of multi-layered thin films, namely Pd (35 nm–1200nm)/Ag(400 nm), were utilized as a multilayer structure electrode materials. On the other hand, a conventional screen printing silver paste electrode was used for a comparative study. In general, the Pd/Ag experimental results had shown that the electrode had a good ohmic contact with ceramics. The resistance of electrodes using Pd/Ag was constantly lower than that of using traditional screen-printed electrodes (29.9–33.7 < 34.1 kΩ). To elaborate, its tensile strength intensifies as the width of the transition layer (Pd) expanded. The tensile strength also reached its maximum at 7.17 MPa as the transition layer width extended up to 800 nm. In addition, it can be concluded from the SEM and EDS mapping image that the newly electrode prevented Ag from diffusing into the ceramic.