Silver Grid Research Articles

An optimization strategy for improving the aspect ratio of screen printing electronic paste based on rheological properties

The wide application of electronic pastes in the field of information electronics puts forward higher requirements for printability. As a key component to determine printability, there are few researches on the effect of organic vehicle components on printability of electronic paste. The purpose of the investigation was to explore the effects of different component contents on the properties of organic vehicles and then on the properties of electronic pastes. Experiments on the wettability of organic solvents to silicon wafers and solubility of adhesives were applied to screen organic solvents. The rheological properties of organic vehicles and electronic pastes in the optimization process were evaluated by the combined method of three interval thixotropy test (3ITT), oscillation amplitude sweep test and NMR relaxation time measurement. And the optimum ratio of adhesive, dispersant and coupling agent and the influence on rheological properties of electronic paste were determined. The optimized silver-aluminum paste as front-side paste was screen-printed and sintered to give a height/width (H/W) ratio of 0.4505 and an average resistivity of 5.06×10−6 Ω cm for the silver grid lines. The paste formulations developed in the investigation provide a new idea for the preparation and development of electronic pastes with excellent performance.

Influence of inverted pyramid texturization on front metallization and performance of crystalline silicon solar cells

The silicon surface texturing is an essential part for the fabrication of crystalline silicon solar cells to increase the conversion efficiency. By adjusting the etching texturing condition, inverted pyramid (IP) and upright pyramid (UP) texturization were prepared on crystalline silicon substrates for fabrication of PERC solar cells. The surface morphology not only affects the light trapping but also impacts electrode shading loss and front electrode contact interface. The IP texturization presents better anti-reflective performance due to more common light paths and narrower silver grids owing to less flow of Ag paste on concave blocked structure, both of which results in the higher short-circuit current density (Jsc). Yet in terms of front Ag/Si contact interface, the IP texturization causes more Ag crystallites and more surface recombination under the present condition suitable for UP texturization because of more edges on the upper part of IP, which leads to the lower open-circuit voltage (Voc). The final conversion efficiency of IP solar cells (23.61 %) is 0.06 % higher than that of UP solar cells (23.55 %). An improvement about 0.07 mA/cm2 of Jsc was achieved with IP samples and Voc has a decrease of 0.3 mV caused by the surface recombination on IP texturization. In summary, the structural characteristics of IP results in lower reflectivity and less electrode shading, while Ag/Si contact interface could be optimized by adjusting the processing condition, ultimately promising the higher efficiency.

Controlled in-situ reduction strategy for synthesis of transparent conductive metal meshes using tannic acid-based photoresists

Transparent conductive films (TCFs) that converge high transmittance and high conductive properties are essential for many optoelectronic devices, and efforts have been made to acquire films with high transmittance as well as low resistance of the thin layer by low-cost means. Here, we introduce a novel and simple strategy for the controlled in-situ templated synthesis of a transparent conductive metal mesh by utilizing the good reducibility to silver ions of the patterned tannic acid (TA)-based photoresists. To achieve this, mesh patterns with tunable line width were first printed using the TA-based negative photoresists by laser direct writing equipment. Within the patterned domains, the phenolic hydroxyl groups could interact with metal ions and act as reducing agents, thus accelerating the in-situ growth of silver nanoparticles to fabricate silver grids. By changing the line width of the designed patterns and the PH of the plating solution, the metal grids with a high transmission (T) of 91.5% and a thin-layer resistance (Rs) as low as 4.15 Ω sq.−1 are ultimately achieved after annealing treatment. Our description demonstrates a simple and effective approach that is potentially scalable to other materials as well.

Effect of MoO3/WO3 modulation on high-temperature wettability and crystallization behavior of glass and its application in solar cell

The role of glass in the metallization contact of crystalline silicon solar cells is crucial. Numerous studies have been conducted to investigate the reaction between the main components in glass and SiNx antireflection layer during sintering. Additionally, the low content component in glass plays an indispensable role in etching and wetting silicon base. The present study investigated the impact of ionic radius on glass properties through manipulation of the elemental composition of transition metals Mo and W. The results indicated a significant decrease in the characteristic temperature point of glass and an increase in wettability after the addition of MoO3 and WO3. Furthermore, the thermal expansion of glass was observed to increase with higher WO3 content. Screen printing for the preparation of silver electrodes revealed that glass-silver pastes had optimal printing properties. When the quality ratio of MoO3 and WO3 was 7:3, it effectively enhanced the precipitation of Bi2WO6 and Pb7.90Mo0.10O12.15 crystals in the glass, leaded to a reduction in the band gap of the glass. This resulted in an increased imprint of silver crystals within the glass layer, with more nano-silver crystals were deposited near the pyramid. Consequently, an optimal metallization contact was established between the silver grid and emitter. The average aspect ratio of silver grid improved from 0.415 for AG-1 to 0.469 for AG-3, which enhanced the photoelectric conversion efficiency of crystalline silicon solar cells.

Breaking through the plasma wavelength barrier to extend the transparency range of ultrathin indium tin oxide films into the far infrared

Indium tin oxide (ITO) film, which is the most commonly used transparent conductive film (TCF), has traditionally been believed to be transparent in the visible spectrum but to reflect infrared (IR) light beyond the plasma wavelength (λp). However, our theoretical analysis challenges this notion by demonstrating that an ultrathin ITO TCF that is thinner than the light's penetration depth can overcome the transmission barrier at λp. To validate the theoretical modeling, we have successfully fabricated ultrathin ITO films that, despite having λp ≈ 1 μm, remain transparent from 400 nm to 20 μm. This represents the broadest transparency range ever reported for any In2O3-based TCF. The 10-nm-thick ITO TCFs have high visible transmittance (91.0% at 550 nm), low resistivity (5 × 10−4 Ω cm), and good IR transmittance (averaging 60% over 1.35–18.35 μm). Their IR transparency facilitates radiative cooling of the underlying circuitry. When an operational resistor is enclosed by commercial ITO TCFs that are 140 nm thick, its temperature increases. However, using 10-nm-thick ITO TCFs instead of the commercial ones can completely avoid this temperature rise. Moreover, attaching a silver grid to a 10-nm-thick ITO TCF can reduce the effective sheet resistance to ∼10 Ω/□ at the expense of only ∼3% transmittance. This development paves the way for large-scale applications that require low sheet resistance and far-IR transparency.

High-aspect-ratio silver grids of solar cells prepared by direct writing

Reducing the width of conductive silver wires, increasing the aspect ratio, improving the utilization rate of silver paste, and enhancing the uniformity of silver wires are key issues that need to be addressed in the manufacture of solar cells. This article explores the feasibility of using glass nozzles to directly write ultra-high viscosity silver paste containing micrometer-sized particles. By preparing a glass nozzle with a diameter of 45μm, conductive silver wires with an average width of about 43±2μm and an aspect ratio of up to 0.96 can be printed. After high-temperature sintering, the width of the silver wire is 32±2μm, the aspect ratio is 0.95, and the resistance of the finger line is 0.13 Ω/cm. In addition, the conductive silver paste is a Herschel–Bulkley (HB) non-Newtonian fluid. Combining the constitutive equation of the HB fluid, a mathematical model of the silver paste flow inside the nozzle is established. Therefore, the influence of characteristic parameters of the silver paste/nozzle on the printing process can be intuitively understood.

Longitudinal Through-Hole Architecture for Efficient and Thickness-Insensitive Semitransparent Organic Solar Cells.

Semi-transparent organic solar cells (ST-OSCs) have great potential for application in vehicle- or building-integrated solar energy harvesting. Ultrathin active layers and electrodes are typically utilized to guarantee high power conversion efficiency (PCE) and high average visible transmittance (AVT)simultaneously; however, such ultrathin parts are unsuitable for industrial high-throughput manufacturing. In this study, ST-OSCs are fabricated using a longitudinal through-hole architecture to achieve functional region division and to eliminate the dependence on ultrathin films. A complete circuit that vertically corresponds to the silver grid is responsible for obtaining high PCE, and the longitudinal through-holes embedded in it allow most of the light to pass through,where the overall transparency is associated with the through-hole specification rather than the thicknesses of active layer and electrode. Excellent photovoltaic performance over a wide range of transparency (9.80-60.03%), with PCEs ranging from 6.04% to 15.34% is achieved. More critically, this architecture allows printable 300-nm-thick devices to achieve a record-breaking light utilization efficiency (LUE) of 3.25%, and enables flexible ST-OSCs to exhibit better flexural endurance by dispersing the extrusion stress into the through-holes. This study paves the way for fabricating high-performance ST-OSCs and shows great promise for the commercialization of organic photovoltaics.

Fabrication of submicron linewidth silver grid/ionogel hybrid films for highly stable flexible transparent electrodes via asymmetric wettability template-assisted self-assembly

High-performance flexible transparent electrodes are the basis for the continuous upgrading of optoelectronic devices. Silver grids are attractive for replacing traditional indium tin oxide (ITO) as the premier transparent electrode materials, due to their high transmittance, excellent conductivity, and low cost. However, large linewidth and oxidation of silver grids are limiting the practical application of the resulting optoelectronic devices. Here, we report an effective and scalable solution-based method to prepare highly stable flexible transparent silver grid electrodes with submicron linewidth by the asymmetric wettability template-assisted self-assembly of silver nanoparticles (AgNPs), which is then encapsulated by a thin transparent conductive ionogel as protective layer. It is demonstrated that the linewidth of silver grids can be precisely controlled by the concentration of the AgNP dispersion. Wrapping with the ionogel nanolayer have no deterioration for conductivity and transmittance of the grid electrodes. The optimized hybrid grid electrodes exhibit low sheet resistance of 24.6 Ω sq−1 and high transparency of 99%. More importantly, the introduction of the iongel nanolayer endows the hybrid grid electrodes with excellent mechanical flexibility and thermal, electrical, and chemical stability. As a proof of concept demonstration, the submicron linewidth silver grid/ionogel hybrid films are successfully used to fabricate flexible smart windows and transparent touch panel. We envision that this work will shed new light on the development of next-generation optoelectronic applications which need ultrahigh resolution displays.

High Performance Transparent Silver Grid Electrodes for Organic Photovoltaics Fabricated by Selective Metal Condensation.

We report silver grid electrodes on glass and flexible plastic substrates with performance that exceeds that of commercial indium-tin oxide (ITO) coated glass and show their suitability as a drop-in replacement for ITO glass in solution processed organic photovoltaics (OPVs). When supported on flexible plastic substrates these electrodes are stable towards repeated bending through a small radius of curvature over tens of thousands of cycles. The grid electrodes are fabricated by the unconventional approach of condensation coefficient modulation using a perfluorinated polymer shown to be far superior to the other compounds used for this purpose to date. The very narrow line-width and small grid pitch that can be achieved also opens the door to the possibility of using grid electrodes in OPVs without a conducting PEDOT:PSS layer to span the gaps between grid-lines. This article is protected by copyright. All rights reserved.

Design of a transparent and flexible broadband omnidirectional antenna using characteristic mode analysis

An optically-transparent, mechanically flexible, monopole-radiation-characteristic, broadband omnidirectional antenna is proposed in this work. The radiator layer of the sandwich-structured antenna consists of a circular central patch with 16 circular satellite patches, and the characteristic mode analysis (CMA) was used to guide the detailed design process. We first analyzed the different modes of the 3×3 circular patch array, further reduced the size of the surrounding patch to increase the required omnidirectional mode bandwidth, further reduced the cross-polarization by adjusting the distance between the four corner patch and the central patch, and finally increased the number of surrounding patches to increase the bandwidth and gain. The entire analysis and optimization process uses the CMA. The antenna was excited by a single probe, with good omnidirectionality, low cross-polarization, and broad operating bandwidth in (5-12.7) GHz, achieving 87% relative bandwidth and peak gain of 4.1 dBi. The antenna has a radius of 27 mm and a thickness of 4.5 mm. A transparent and flexible antenna sample was fabricated on a flexible polydimethylsiloxane (PDMS) substrate using electrohydrodynamic (EHD) printing technology. The optical transmittance of the horseshoe-structured metal grids fabricated by EHD was investigated, as well as the equivalent surface resistance evaluation method. The theoretical optical transmittance of the horseshoe-structured single-layer silver grid on the PDMS substrate was 81.2%, versus 80.8% measured value, with an equivalent surface resistance of roughly 5 Ω/◻. The proposed antenna was bent on a 50 mm-radius cylinder surface and retained excellent omnidirectionality.

Metallic support films reduce optical heating in cryogenic correlative light and electron tomography

Super-resolved cryogenic correlative light and electron tomography is an emerging method that provides both the single-molecule sensitivity and specificity of fluorescence imaging, and the molecular scale resolution and detailed cellular context of tomography, all in vitrified cells preserved in their native hydrated state. Technical hurdles that limit these correlative experiments need to be overcome for the full potential of this approach to be realized. Chief among these is sample heating due to optical excitation which leads to devitrification, a phase transition from amorphous to crystalline ice. Here we show that much of this heating is due to the material properties of the support film of the electron microscopy grid, specifically the absorptivity and thermal conductivity. We demonstrate through experiment and simulation that the properties of the standard holey carbon electron microscopy grid lead to substantial heating under optical excitation. In order to avoid devitrification, optical excitation intensities must be kept orders of magnitude lower than the intensities commonly employed in room temperature super-resolution experiments. We further show that the use of metallic films, either holey gold grids, or custom made holey silver grids, alleviate much of this heating. For example, the holey silver grids permit 20× the optical intensities used on the standard holey carbon grids. Super-resolution correlative experiments conducted on holey silver grids under these increased optical excitation intensities have a corresponding increase in the rate of single-molecule fluorescence localizations. This results in an increased density of localizations and improved correlative imaging without deleterious effects from sample heating.

An analytical investigation on characterizing the properties of glass composition for crystalline silicon solar cells based on the digital microsystem measurement technology

As a significant component of silver paste, glass frit has a nonnegligible effect on crystalline silicon solar cells. The purpose of this research is to obtain an analysis method to explore the performance of glass frit for solar cells. The samples were measured by digital microscopic system, and the three-dimensional layered tinting model was established. Moreover, the longitudinal cutting was carried out. The data of cross section was analyzed to obtain the information of melt height, wetting base angle, and melting included angle, to further infer the relationship between thermal stability, fluidity, wettability with mathematical model of glass frit through theoretical derivation. The curve fitting method was introduced in detail and the law was summarized. Based on relationship of them, the melting characteristics of glass frit could be quantitatively tested. The vertical view and surface topography were measured by the digital microscope and found that the glass frit underwent shrinkage, softening, wetting, spreading, and equilibrium during sintering. Combined with the image, abundant information was detected from the macroscopic structure of glass surface. Meanwhile, the mechanism of spreading was explained. Finally, the screen-printing technology combined with the 3D microscopic view of the silver grid line proved that glass frit with satisfactory performance can effectively reduce the contact resistance of solar cells, improve the photovoltaic conversion efficiency, verify the feasibility and accuracy of the simulation method equally. This study not only enriches the understanding of glass frit for crystalline silicon solar cells, but also provides a theoretical guidance for the research and determination of its performance. • Digital microscope system was used to record the shape changes of glass samples and more wetting parameters. • This investigation used a combination of mathematical simulation and physical simulation. • The essence of the technology to characterize glass is to combine the fixed droplet technology with optical measurement.

Fabrication and performances of silver grid transparent conducting films and heaters on glass and PET substrates based on fractal periodic grid pattern design

A metal grid transparent conducting film (TCF) requires an excellent trade-off between optical transparency and electrical conductivity, both of which are affected by grid patterns and parameters. In this work, the fractal geometry was introduced to design fractal periodic grid patterns, which were employed to fabricate fractal periodic Ag grid TCFs with different grid periods, pitches and thicknesses on glass substrates by magnetron sputtering Ag films and laser localized removal. By comparing with the corresponding conventional periodic Ag grid, the fractal periodic Ag grid was confirmed to enable a significant improvement in trade-off between optical transparency and electrical conductivity, and thus excellently improving the comprehensive properties of the TCFs. The optimal fractal periodic Ag grid TCF achieved a figure of merit of 15.04 × 10–2 Ω–1, which was higher than that of the optimal conventional periodic Ag grid TCF (11.38 × 10–2 Ω–1). In addition, transparent heaters were prepared by using the optimal fractal periodic Ag grid TCFs on glass and flexible PET substrates, and showed excellent heating performances, good performance stability and deicing availability. This work provides a simple and extendable method for tailoring optical transmittance and electrical conductivity to fabricate high-performance TCFs.

Embossed transparent electrodes assembled by bubble templates for efficient flexible perovskite solar cells

Flexible perovskite solar cells are promising power source candidates in wearable and portable electronics. However, the performance of flexible perovskite solar cells still lags the values reported in rigid devices. This issue is mainly due to the lack of suitable electrodes which possess low sheet resistance, high optical transmittance, and smooth surface. Here, we proposed a flexible electrode based on solution-processed silver grids. With the patterned micro-bubbles as templates, high-resolution sliver grids electrodes were fabricated, which showed a sheet resistance of 7.9 Ω/sq and optical transmittance over 85% (including the substrate, from 375 nm to 900 nm). Besides, the embossed sliver grids can assist the growth of perovskite crystals and provide localized channels for charge carrier transport. The corresponding flexible perovskite solar cells based on these flexible sliver grids electrodes achieved a power conversion efficiency of 18.49% with remarkable flexibility, which enhanced about 20% compared to the control devices.

Femtosecond laser trapping nanoprinting of silver micro/nanostructures

In this paper, silver micro/nanostructures composed of sintered nanoparticles were printed by capturing silver nanoparticles in water with 800 nm femtosecond laser trapping. Relationships of laser power, scanning speed, nanoparticle concentration, and the width and morphology of fabricated silver wire were systematically investigated. It is found that low scanning speed and high nanoparticle concentration favor the printing of silver wire with good morphology. A silver wire with width of 305 nm was printed. Electrical resistivities of printed wires are about 24 times that of bulk silver. Silver grid structures and dot arrays were printed by using this technology. Several three-dimensional silver cuboid structures were also printed. This work provides a protocol for printing of three-dimensional metallic micro/nanostructures using laser trapping. These printed structures have great application prospects in metamaterials, flexible electronics, and SERS.

A deep residual neural network identification method for uneven dust accumulation on photovoltaic (PV) panels

Uneven dust accumulation can significantly influence the thermal balance between different regions of photovoltaic (PV) panels, leading to a sharp decrease in power generation efficiency and service life. In this paper, a new identification method for uneven dust accumulation on the surface of PV panels is developed to analyze the dust state (concentration and distribution) quantitatively. First, a novel deep residual neural network (DRNN) is proposed to obtain the regional dust concentration. The residual elements in the model are connected in the form of skipping layers to reduce the order of the weight matrices and improve the network flexibility and the feature learning accuracy. Second, an image preprocessing method is designed to classify the dust accumulation. It includes transformation and correction, removal of the silver grid, nonlinear interpolation, equivalent segmentation, and clustering. A new error evaluation method, error loop, is proposed to analyze the consistency between the measured and the experimental results. The results show that the DRNN has better prediction accuracy than other methods. The R2 and mean absolute error (MAE) of the DRNN are 78.7% and 3.67, respectively. In addition, three conditions are used to verify the performance of the identification method for determining uneven dust accumulation. The average evaluation coefficients of the error loop are 1.19, 0.77, and 1.10, respectively, meeting the design requirements. The proposed method can provide theoretical support for the intelligent operation and maintenance of PV systems.

Fabrication of the Silver Grids by Interfacial Interaction

Silver (Ag) grid is one of the most competitive alternatives for transparent conductors because of its optical transparency, high conductivity, and cost competitiveness. Although printing, self‐assembly, and other combination strategies are widely adopted for the fabrication of Ag grids, the size/morphology accuracy adjustments and structural complexity design in micro/nanodimension are still challenges. Herein, adjustable Ag grid patterns at the micro/nanoscale are obtained by the combination of template printing and self‐assembly method. The strategy generates air‐filled uniform concave meniscus between silicon pillars helped by coating polymer solutions. The experimental results demonstrate that the concave meniscus’ features strongly influence the stick‐slip motion of the triple‐phase contact line (TCL), which is the key factor for the construction of different Ag grid patterns, and the morphologies of the patterns affect the application of the Ag grid accordingly. By selection of the surface interaction, the proper Ag grids at the micro/nanoscale have good transmittance (85.3%) and low sheet resistance (7.6 Ω sq−1) on the glass substrate, and Ag grids on polyethylene terephthalate (PET) substrate have also been investigated which are important for its application in flexible transparent electronics.

Parameterization of Metallic Grids on Transparent Conductive Electrodes for the Scaling of Organic Solar Cells

AbstractIntense research interest in organic photovoltaic (OPV) devices has resulted in steadily improving figures of merit in recent years. Typically, these devices are fabricated by processing active and buffer layers on transparent conductive electrodes (TCEs). Superlative OPV devices are small (<≈0.1 cm2). The sheet resistance of available monolithic transparent conductive oxide (TCO) materials limits the performance of larger devices and hence the practically attainable cell area. Here, the use of metallic grids in combination with TCOs to create composite TCEs as a means of scaling solution‐processed photovoltaics devices to practical sizes is parameterized. Finite element modeling is used to investigate the relevant design parameters and to estimate figures of merit for realistic organic solar cells. It is shown that the scalability of devices with metallic grids improves significantly when grids are implemented at micrometer scales. Representative silver grids are fabricated and the optical and electrical properties of the resulting structures are measured. Overall, these findings indicate that metallic grids can be designed to develop large‐area solution‐processed solar cells with currently available fabrication techniques.

Direct Single-Step Printing of Conductive Grids on Curved Surfaces Using Template-Guided Foaming.

Advanced transparent conductors have been studied intensively in the aspects of materials, structures, and printing methods. The material and structural advancements have been successfully accomplished with various conductive nanomaterials and spring-like structures for better electrical conductivity and high mechanical flexibility of the transparent conductors. However, the capability to print submicrometer conductive patterns directly and conformally on curved surfaces with low processing cost and high throughput remains a technological challenge to achieve, primarily because of the original two-dimensional (2D) nature of conventional lithography processes. In our study, we exploit a liquid-mediated patterning approach in the development of flexible templates, enabling printing of curvilinear silver grids in a single-step and strain-free manner at a submicrometer resolution within several minutes with minimum loss of noble metals. The template can guide arrays of receding liquid-air interfaces on curved substrates during liquid evaporation, thereby generating ordered 2D foam structures that can confine and assemble silver nanoparticles in grid patterns. The printed silver grids exhibit suitable optical, electrical, and Joule-heating performances, enabling their application in transparent heaters. Our technique has the potential to extend the existing 2D micro/nanofluidic liquid-mediated patterning approach to three-dimensional (3D) control of liquid-air interfaces for low-cost all-liquid-processed functional 3D optoelectronics in the future.

Performance of PV modules using co-extruded backsheets based on polypropylene

Due to the general price pressure PV modules experienced in the last decade, a variety of alternative polymer materials and new backsheet designs were developed and introduced into the market, amongst others also extruded backsheets based on polypropylene (PP). The production of co-extruded films represents a backward integration of backsheet manufacturers, allowing for easy material and design modifications regarding additive formulation, fillers and geometry. The main objective of this paper was to describe the influence of the special properties of PP-based backsheets on the performance and reliability of PV modules. The higher reflectance of the PP backsheet compared to a reference polyester (PET) based laminate led to an increase in power output between 1.5 and 2.5%. Test modules using PP and PET backsheets were exposed to 3000 h of damp heat testing. No changes in power output for either of the test modules was observed. However, the selective permeation properties of PP backsheets prevent humidity from entering the module (similarly to PET based backsheets) but allow for significantly higher diffusion of acetic acid out of the PV module. Therefore, in contrast to test modules using Ethylene Vinyl Acetate (EVA) encapsulants and PET backsheets, no silver grid corrosion was observed for modules using PP backsheets. Co-extruded backsheets based on PP show great potential to be a valid replacement of standard PET based backsheets in PV modules. On the one hand, the PP backsheet so far proved excellent stability, exhibiting no severe material degradation after extended exposure to temperature, humidity and irradiation. On the other hand, its improved functional properties (optical properties; selective permeability) lead to increased performance and improved long-term stability of the tested PV modules.