Conventional Screen Printing Research Articles

Influence of the Aluminum Paste Surface Density on the Electrical Parameters of Silicon Solar Cells

The industrial process of silicon solar cells is mainly based on the aluminum back surface field (Al-BSF) performed by the conventional screen printing and firing in a belt furnace. The goal of this paper is to present the analysis of the influence of the amount of the Al paste on the electrical parameters and on the minority carrier diffusion length. The silicon solar cells were processed in p-type Czochralski solar grade wafers. The amount of Al paste deposited to form the BSF, denominated of Al paste surface density, was ranged from 2.8mg/cm2 to 8.8mg/cm2. The peak firing temperature for each amount of Al paste was optimized and the depth of the Al-BSF was estimated. The best results were found for the Al paste surface density of 3.5mg/cm2 and the peak firing temperature of 840°C, resulting in the efficiency of the solar cells of (15.0 ± 0.1) %. In this case, the depth of the Al-BSF was (5 ± 1) μm. Taking into account the peak firing temperature obtained for each Al paste surface density, we observed that the short-circuit current increased up to the average Al paste amount of 3.5mg/cm2. On the other hand, the fill factor decreased with the increasing of the Al paste surface density. The open circuit voltage was slightly affected by the Al paste amount. The minority carrier lifetime rose from 30μs to 120μs after the phosphorus diffusion. A strong improvement in the minority carrier diffusion length was observed after the firing process and depends on the Al paste amount. The measured average values were 500μm, 1280μm and 780μm for the Al paste surface density of about 2.8mg/cm2, 3.5mg/cm2 and 8.8mg/cm2, respectively.

Aerosol jet printing of two component thick film resistors on LTCC

Aerosol jet printing is a rather new technology for the deposition of thick film structures offering high line and space resolution. This offers a high potential for miniaturization for thick film structures. The advantages of this technology could be shown with inks carrying single solid powder (e.g. silver, platinum, ceramic or glass powder). Challenging is printing of solid powder mixtures due to the differences in the aerodynamic properties of different powders. Those differences result in changes of the mixing ratio within the aerosol jet and therefore poor reproducibility in the final film properties is obtained. In this work, thick film resistors consisting of RuO2 with particle size < 1 μm as the conducting phase and different glass powders with particle size around 1 μm as the isolating phase were investigated. One glass had a density rather close to RuO2, the other glass significantly lower. Inks were made from RuO2/glass powder mixtures, a solvent and organic additives. After manufacturing the inks are printed on LTCC and the microstructures of the dried and the fired films were visualized by FIB preparation and SEM. The resistances as well as the temperature coefficients of the resistors were measured and compared to resistor films with an identical solid composition manufactured by conventional screen printing. The results of the obtained resistors are presented and discussed in terms of powder properties, ink dispersion and printing parameters.

Aerosol Jet Printing of Two Component Thick Film Resistors on LTCC

Aerosol jet printing is a rather new technology for the deposition of thick film structures offering high line and space resolution. This method offers high potential for miniaturization for thick film structures. The advantages of this technology could be shown with inks carrying a single solid powder (e.g., silver, platinum, ceramic, or glass powder). One of the challenges in printing solid powder mixtures is the differences in the aerodynamic properties of different powders. Those differences result in changes of the mixing ratio within the aerosol jet and therefore poor reproducibility in the finished film. In this work, thick film resistors consisting of RuO2 with particle size <1 μm as the conducting phase and different glass powders with particle size around 1 μm as the isolating phase were investigated. One glass had a density rather close to RuO2, the other glass significantly lower. Inks were made from RuO2/glass powder mixtures, a solvent, and organic additives. After manufacturing, the inks are printed on LTCC and the microstructures of the dried and the fired films were visualized by FIB preparation and SEM. The resistances as well as the temperature coefficients of the resistors were measured and compared with resistor films with an identical solid composition manufactured by conventional screen printing. The results of the obtained resistors are presented and discussed in terms of powder properties, ink dispersion, and printing parameters.

Glutathione Coated Zinc Oxide Nanoparticles: A Promising Material for Pesticide Detection

Extensive research studies are being carried out to significantly improve the sensing characteristics of pesticide sensors (chloropyrifos, organophosphates (OP)) especially at ultra low concentrations using advance fabrication and characterization techniques. We report feasibility study of pesticide sensing, using nanostructured zinc oxide (ZnO) and acetylcholinesterase (AChE) immobilized ZnO films, at ultra low concentrations (10 to 1000 ppb). ZnO nanoparticles (NPs) were synthesized by non-aqueous sol–gel method. Reduced glutathione (GSH) was coated on as-synthesized ZnO NPs by physical mixing. FESEM observation revealed spherical particles of about 10–20 nm in diameter having fairly uniform shape distribution. Thick films of these powders were printed on pre-printed electrodes using conventional screen printing technique. AChE was immobilized on the films by physical adsorption method. It is found that bare ZnO NPs are insensitive to pesticides while GSH coated ZnO NPs exhibit monotonous increase of sensitivity as a function of OP concentration over the wide range (10 ppb to 1000 ppb) with sensitivity of 2.1 A/ppm/cm2, detection limit of 3 ppb and regression coefficient of 0.92. Electrochemical measurement indicated that sensors can be used for few times due to the known inhibitory nature of OP and AChE reaction.

Tattoo-based potentiometric ion-selective sensors for epidermal pH monitoring

This article presents the fabrication and characterization of novel tattoo-based solid-contact ion-selective electrodes (ISEs) for non-invasive potentiometric monitoring of epidermal pH levels. The new fabrication approach combines commercially available temporary transfer tattoo paper with conventional screen printing and solid-contact polymer ISE methodologies. The resulting tattoo-based potentiometric sensors exhibit rapid and sensitive response to a wide range of pH changes with no carry-over effects. Furthermore, the tattoo ISE sensors endure repetitive mechanical deformation, which is a key requirement of wearable and epidermal sensors. The flexible and conformal nature of the tattoo sensors enable them to be mounted on nearly any exposed skin surface for real-time pH monitoring of the human perspiration, as illustrated from the response during a strenuous physical activity. The resulting tattoo-based ISE sensors offer considerable promise as wearable potentiometric sensors suitable for diverse applications.

Multi-busbar Solar Cells and Modules: High Efficiencies and Low Silver Consumption

Ideally, future photovoltaic modules show higher power output without increasing costs during cell production or module interconnection. Today significant losses occur during stringing the cells in a module by using standard 3- busbar technology. In this paper an elegant approach for a front side design is discussed by using more busbars than the widely used 3-busbar design for the solar cell front electrode. Simulations demonstrated that the multi-busbar design allows higher cell and module efficiencies compared to a state of the art 3-busbar cell design, and in the same time reduces the amount of silver needed for the front electrode. “A conventional full area Al BSF and standard screen printing for the front contact was used for the 6” Cz-Si multi-busbar solar cells and efficiencies of up to 19.5% have been reached. The solar cells were analyzed on cell and module level and a reduction in Ag consumption for the front electrode of >50%abs could be achieved using the multi-busbar cell design. An additional silver reduction was achieved by replacing the rear side Ag/Al pads with tin pads for the soldering process. These changes in solar cell design reduce significantly the metallization costs and in the same time increase the efficiency.

Understanding the Effect of Flower Extracts on the Photoconducting Properties of Nanostructured TiO2

Here we report an easy method to improve the optoelectronic properties of commercially available TiO2 nanopowder using extracts of various flowers viz. Calendula Orange (CO), Calendula Yellow (CY), Dahlia Violet (DV), Dahlia Yellow (DY), Rabbit flower (RF), Sweet Poppy (SP), Sweet Williams (SW) and their Mixed Extracts (ME). Various analysis techniques such as UV-Vis, FTIR, FESEM, XRD, and Raman spectroscopy were used to characterize for elemental, structural and morphological properties of the unmixed/mixed TiO2 nanopowder. TiO2 nanopowder was also calcined at 550 degrees C. Thick films of the these unmixed/mixed powder were printed, using conventional screen printing method, on fluorine doped tin oxide (FTO) substrate with organic binders and dried at 45 degrees C. The photoconducting properties are investigated as a function of wavelength from ultra-violet (UV) to infra-red (IR) region at a constant illumination intensity. Photocurrent gradually decreases when irradiated from UV to IR region. In case of unmixed and uncalcined TiO2, conductance decreased continuously whereas when extracts are added, a flat region of conductance is observed. The overall effect of extracts (colour pigments) is seen as an increase in the photoconductance. Highest photoconductance is observed in case of DY flower extract. Anthocyanins, present in flowers are known to have antioxidative properties and hence can contribute in photoconduction by reducing the surface adsorbed oxygen. This investigation indicates the potential use of flower extracts for dye sensitized solar cell (DSSC).

Depth of Laser Etching in Green State LTCC

Laser etching of green state LTCC is a useful rapid prototyping and precision manufacturing process. Laser etching allows selective removal of screen printed conductor layer, producing patterns with higher precision than conventional screen printing. Its usefulness for rapid prototyping is due to elimination of time consuming screen preparation process. The etching is performed using a near UV (355 nm), pulsed laser. The process is characterized by three parameters: laser power, pulse frequency, and etching speed. From the practical standpoint, we are interested in finding a combination of parameters which allows for achieving required etching depth at the maximum etching speed. We present an empirical mathematical model relating etching depth to process parameters, allowing to theoretically determine optimum processing parameters for a specified etching depth.

Tuning of size and luminescence of red Y(V,P)O4:Eu nanophosphors for their application to transparent panels of plasma display

Fabrication of transparent plasma display can be demonstrated by simply applying the scatter-less nanophosphors to the currently available plasma display panel (PDP) scheme. For this goal, the optimization of the nanophosphors with respect to size and luminescence is necessary to produce a uniform, transparent, bright emissive layer. To develop red-emitting nanophosphors suitable for transparent PDP fabrication, we hydrothermally synthesized red-emitting Y(V,P)O4:Eu nanophosphors having various V/P ratios and Eu concentrations and varied their subsequent annealing condition. When Y0.94(V0.5,P0.5)O4:Eu0.06 nanophosphor annealed at 1000 °C for 1 h was used, 1.1 μm thick, uniform emissive layer with a high visible transmittance value of 72% was generated on glass substrate by a conventional screen-printing. Mini-sized test panels of transparent red-emitting plasma display were constructed by combining the rear plate (Y(V,P)O4:Eu nanophosphor layer/glass) and the front plate used in alternating current (ac)-type PDP structure, and their discharge luminance characteristics were evaluated.

Fabrication of a HCHO gas sensor based on a MEMS heater and inkjet printing

We have developed In2O3 particle ink that can be applied in inkjet printing on a microelectromechanical systems (MEMS) heater and have fabricated semiconductor-type gas sensor based on that heater. The formaldehyde (HCHO) sensor prepared by inkjet printing showed comparable or even higher sensitivity compared to that of the sensor prepared from conventional screen printing when increasing the number of printings was increased. By virtue of its non-contact printing nature, this In2O3 ink as a sensing material could be deposited on the MEMS heater without damage to the heater membrane. We found that the sensor prepared on the MEMS heater by using the inkjet deposition technique showed response/recovery times of 7s/17s with a sensitivity of 0.63 at an 18 mW power and 60 ppb HCHO.

Stamp transfer electrodes for electrochemical sensing on non-planar and oversized surfaces

This article describes a new alternative approach to the fabrication of printed electrochemical sensors and biosensors based on the transfer of electrode patterns comprising common conductive and insulating inks from elastomeric stamps to a wide variety of rigid and flexible substrates. This simple, low cost, yet robust methodology is demonstrated to be well-suited for the formation of electrochemical sensors on non-planar substrates and large objects/structures, which have traditionally been off-limits to conventional screen printing techniques. Furthermore, the stamped electrode devices are shown to exhibit electrochemical performance that rivals that of their screen printed counterparts and display resilience against severe mechanical deformation. The stamp transfer approach is further extended to the demonstration of epidermal electrochemical sensors through the transfer of the electrode patterns directly onto the skin. The resulting sensors demonstrate a wide range of usability, from the detection of various physiological analytes, including uric acid on the skin, to the identification of residues originating from the handling of munitions and explosives. The migration of printable electrochemical sensors to non-conventional (non-planar and/or oversized) surfaces provides new opportunities within the personal healthcare, fitness, forensics, homeland security, and environmental monitoring domains.

Surface Passivation Studies on n+pp+ Bifacial Solar Cell

Bifacial solar cell is a specially designed solar cell for the production of electricity from both sides of the solar cell. It is an active field of research to make photovoltaics (PV) more competitive by increasing its efficiency and lowering its costs. We developed an n+pp+ structure for the bifacial solar cell. The fabrication used phosphorus-oxy-trichloride (POCl3) diffusion to form the emitter and Al diffusion using conventional screen printing to produce the back surface field (BSF). The n+pp+ bifacial solar cell was a sandwiched structure of antireflective coatings on both sides, Argentum (Ag) as a front contact and Argentum/Aluminum (Ag/Al) as a back contact. This paper reports the solar cell performance with different surface passivation or antireflecting coatings (ARC). Silicon nitride (SiN) deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD), thermally grown silicon dioxide (SiO2), PECVD-SiO2, and SiO2/SiN stack were used as ARC. The efficiency obtained for the best bifacial solar cell having SiN as the ARC is 8.32% for front surface illumination and 3.21% for back surface illumination.

Direct Etch through SiNx, Selective Dope, and Seed Layer Dispense with Inert Piezoelectric Inkjet Print Head for Solar Cell Fabrication

The solar photovoltaic industry is driven towards increasing cell efficiency while reducing cost. Ink jet process offers an attractive, non-contact method enabling reduced capital equipment cost, fewer process steps and higher throughput. This study focuses on inkjet processes development of directly etching through a Silicon Nitride layer (anti-reflection layer), selectively doping and precisely dispensing a seed layer, also their combination at a shot to prepare for conventional screen printing afterwards or for low cost electroplating for the “selectiveemitter” solar cell fabrication.

Front Side Metallization Issues of a Solar Cell with Ink-jet Printing

The metallization of a multi-crystalline silicon solar cell has been challenged because the thickness reduction of a solar cell wafer decreases the breaking force of a solar cell wafer. Therefore, ink-jet printing has drawn attention of researchers in the art in place of conventional screen printing which requires the direct contact with a solar cell wafer to transfer silver paste. In this study, a preliminary study for the front side metallization of a solar cell wafer with ink-jet printing was conducted. Firstly, multicrystalline silicon solar cell wafers, the size of which is 156 mm by 156 mm, were coated with a 0.2 wt% fluorocarbon solution. After laser-patterning to selectively remove the SiNx layer and prepare for the surface energy patterned finger electrode regions, silver nanoparticulate ink was delivered with a piezo Drop-On-Demand ink-jet print head and baked at the peak temperature of 830 °C after drying at 100 °C. The measured cell efficiency of an ink-jet metallized solar cell was about 12.1% and the cause of the low cell efficiency is addressed here.

The fabrication of front electrodes of Si solar cell by dispensing printing

Abstract The dispensing printing was applied to fabricate the front electrodes of silicon solar cell. In this method, a micro channel nozzle and normal Ag paste were employed. The aspect ratio and line width of electrodes could be controlled by the process variables such as the inner diameter of nozzle, dispensing speed, discharge pressure, and the gap between wafer and nozzle. For the nozzle with the inner diameter of 50 μm, the line width and aspect ratio of electrode were under 90 μm and more than ∼0.2, respectively. When comparing the efficiency of solar cell prepared by conventional screen printing and the dispensing printing, the latter exhibited 19.1%, which is 0.8% absolute higher than the former even with the same Ag paste. This is because the electrode by dispensing printing has uniform aspect ratio and narrow line width over the length of electrode.

Improving of Silk Printability by Atmospheric Air Plasma Treatment

Plasma surface treatment of silk has been carried out in atmospheric air under experimental conditions at different discharge powers and plasma exposure times. The treated fabric samples are printed with reactive dye using a conventional silk screen printing technique. After drying, the samples are steam fixed at 102°C for 15 min, washed and air dried. Before and after printing, both treated and untreated samples are subjected to different investigations. The wetting time is found to depend upon the treatment time and discharge power. The colour strength of the treated samples printed with reactive dye is improved to a large extent compared with the untreated samples. An improvement in the fastness properties of the printed samples to washing, rubbing and perspiration is also noticed.

Enhanced electrochemical properties of Bi-layer La 0.5Sr 0.5CoO 3− δ cathode prepared by a hybrid method

Bi-layer La 0.5Sr 0.5CoO 3− δ (LSCO) cathodes are processed by a hybrid method that combines a seed layer prepared by a pulsed laser deposition (PLD) technique and a conventional cathode layer (∼7 μm in thickness) by a screen printing method. By inserting the PLD seed layer with the thickness of ∼500 nm or less, robust cathode films with desired microstructure and excellent adhesion properties with the underlying electrolyte layer, are successfully fabricated. The area specific resistance (ASR) of the hybrid cathode layers decreases about 5 times compared with that of the single layer cathode films prepared by the conventional screen printing method. The hybrid approach provides a cost-effective way to fabricate thick cathode films with significantly enhanced electrochemical properties for solid oxide fuel cells (SOFCs).

Advanced metallization of rear surface passivated metal wrap through silicon solar cells

Abstract We present metal wrap through passivated emitter and rear cells (MWT-PERC) on p-type Czochralski silicon (Cz-Si) using advanced metallization approaches. Front surface metallization is performed either with a one-step approach (conventional thick film screen printing) or with a more advanced two-step approach, consisting of aerosol printing of a silver seed layer and subsequent silver electroplating. High short circuit current densities of up to 39.9 mA/cm 2 indicate excellent light trapping and decreased front side shading due to the absence of busbars as well as high quality surface passivation. Both metallization technologies allow for conversion efficiencies of 18.7% for 125 x 125 mm 2 sized Cz-Si MWT-PERC solar cells. Furthermore, we show the possibility of via metallization by the use of two-step seed and plate technology. Via resistances similar to those for screen printed via metallization are achieved. The seed and plate technology therefore forms a promising approach for via metallization of next generation MWT-PERC solar cells.

An improved planar-gate triode with CNTs field emitters by electrophoretic deposition

An improved planar-gate triode with carbon nanotubes (CNTs) field emitters has been successfully fabricated by conventional photolithography, screen printing and electrophoretic deposition (EPD). In this structure, cathode electrodes and ITO arrays linked with gate electrodes were interdigitated and paralleled on the same plane although the gate electrodes and cathode electrodes were isolated by dielectric layer, a so-called improved planar-gate triode structure. An electrophoretic process was developed to selectively deposit CNTs field emitters onto cathode electrodes in the CNTs suspension by an applied voltage between the gate electrodes and cathode electrodes. The optical microscopy and FESEM image showed that the CNTs emitters with the uniform packing density were selectively defined onto the cathode electrodes. In addition, field emission characteristics of an improved planar-gate triode with CNTs field emitters were investigated. The experiment results indicated that the turn-on voltage of this triode structure at current density of 1μA/cm2 was approximately 55V. The anode current and gate current came to 396μA and 325μA, at gate voltage and anode voltage of 100V and 4000V, respectively and at the anode–cathode spacing of 2000μm. The emission image became brighter and the luminous image with dot matrix on the anode plate obviously increased with the increase of the gate voltage. Moreover, the emission current fluctuation was smaller than 5% for 11h, which indicated that the improved planar-gate triode has a good field emission performance and long lifetime.

Disposable amperometric biosensors based on xanthine oxidase immobilized in the Prussian blue modified screen-printed three-electrode system

The screen-printed three-electrode system was applied to fabricate a new type of disposable amperometric xanthine oxidase biosensor. Carbon-working, carbon-counter and Ag/AgCl reference electrodes were all manually printed on the polyethylene terephthalate substrate forming the screen-printed three-electrode system by the conventional screen-printing process. As a mediator, Prussian blue could not only catalyze the electrochemical reduction of hydrogen peroxide produced from the enzyme reaction, but also keep the favorable potential around 0 V. The optimum operational conditions, including pH, potential and temperature, were investigated. The sensitivities of xanthine and hypoxanthine detections were 13.83 mA/M and 25.56 mA/M, respectively. A linear relationship was obtained in the concentration range between 0.10 μM and 4.98 μM for xanthine and between 0.50 μM and 3.98 μM for hypoxanthine. The small Michaelis-menten constant value of the xanthine oxidase biosensor was calculated to be 3.90 μM. The results indicate that the fabricated xanthine oxidase biosensor is effective and sensitive for the detection of xanthine and hypoxanthine.