Ag Paste Research Articles

Characterization of front contact degradation in monocrystalline and multicrystalline silicon photovoltaic modules following damp heat exposure

Reliability and durability tests play a key role in the photovoltaic (PV) industry by minimizing potential failure risks for both existing and new cell and module technologies. In this work, a detailed study of contact degradation in monocrystalline and multicrystalline PV modules is performed. The modules are subjected to a sequence of damp heat (DH) exposures followed by electrical characterization after each step. Electroluminescence (EL) imaging shows different darkening patterns for monocrystalline modules compared to multicrystalline modules; the former shows darkening near the busbars and the latter shows it across virtually the entire cell surface. The primary loss mechanism is confirmed to be resistive after comparing the current-voltage ( I–V ) characteristics at each DH exposure step. Representative samples have been cored out from both the degraded modules and controls for materials characterization to gain further insights into the degradation mechanism. Top-down and cross-sectional scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and top-down high-resolution X-ray photoelectron spectroscopy (XPS) analysis performed on the cored samples confirm the degradation is due to metallization corrosion. Our study suggests that the difference in the darkening pattern can most likely be attributed to the different silver paste composition used for contacting each cell technology, particularly the composition of the glass frit. • Monocrystalline and multicrystalline PV modules show different cell darkening patterns in EL images after damp-heat exposure. • Performance losses are due to an increase in series resistance, not to any increase in the optical or recombination losses. • Primary reason for performance losses is the degradation of metal contacts, particularly the glass layer/metal-Si interface. • Sn migration from the interconnects to the metal contact surface plays a key role in accelerating the glass layer corrosion. • Difference in the darkening pattern can be attributed to the Ag paste composition used for contacting each cell technology.

Selective metallization of piezoelectric ceramics by laser-induced surface modification combined with electroless copper plating

Conventionally, the surface of piezoelectric ceramics has been selectively metallized by screen-printing of Ag pastes. However, the use of expensive Ag materials and high-temperature annealing increases the manufacturing costs and complicates the process. In this study, simple and economical method for the selective metallization of piezoelectric ceramics has been developed. Using this method, high-adhesion copper patterns were successfully formed on piezoelectric ceramics by combining laser-induced surface modification and electroless copper plating (ECP). Although a copper layer was uniformly deposited onto the piezoelectric ceramic surface at various laser parameters, the scanning speed of 200 mm/s ensured sufficiently high adhesion strength and minimum laser damage of the piezoelectric surfaces. The d33 and kp values of the piezoelectric ceramics with the attached ECP-processed copper and screen-printed silver electrodes were very close. These results demonstrate the possibility of fabricating low-cost copper electrodes on piezoelectric ceramics without high-temperature heat treatment or surface activation with expensive catalysts.

Laser-Induced Forward Transfer (LIFT) Technique as an Alternative for Assembly and Packaging of Electronic Components

Current trends in microelectronics chip bonding and assembly encompass ultra-fine pitch components with flexible form factors and advanced die-attach materials, which can sustain conformal strain without compromise in adhesion and reliability. These trends have highlighted the need for advanced microfrabrication technologies, which allow the on-demand digital fabrication of interconnections and die-attach bumps on chip carriers and interposers with challenging topographies. Laser printing, based on the laser induced forward transfer (LIFT) technique, has addressed such micromanufacturing challenges over the past decade. Several previous demonstrations of highly resolved and conformal interconnections for the bonding and packaging of micro and opto-electronic components are summarized in this paper. Latest advances in the laser printing and laser sintering of highly viscous nanopastes for achieving planar or three-dimensional (3D) structures consisting of Ag paste are demonstrated. The latter is achieved by stacking of arrays or bumps in a digital manner. The reported results verify that LIFT offers control over both the lateral and vertical dimensions. This control can facilitate the soldering process of heterogeneous components, whose pads have significant height and pitch dissimilarities. The applicability of LIFT in the fields of packaging and assembly of flexible and heterogeneous integration schemes, is further validated.

Nano Ag sintering on Cu substrate assisted by self-assembled monolayers for high-temperature electronics packaging

Sintering of nano Ag paste on bare Cu has attracted more interests recently for high-temperature electronics packaging, which offers the advantages of high reliability, cost-effective and direct bonding process. However, the current bonding methods normally need a protective atmosphere or metallization on Cu substrate to avoid oxidation. In this study, self-assembled monolayers (SAMs) were deposited on Cu substrate to suppress oxidation prior to nano Ag sintering. Thermal-compression bonding process of Cu/nano Ag/Cu joints was conducted and analysed with and without SAMs treatment. The cross-sectional characterization and shear tests were conducted to evaluate the influence of SAMs treatment. When SAMs applied, shear strength of 12.72 MPa has been achieved in the ambient atmosphere, which is much higher than the value without SAMs treatment (3.77 MPa). It has been identified that the shear mode changed from the interfaces of sintered nano Ag/Cu to inside of sintered nano Ag due to the applied SAMs. This technological approach provides a tangible and cost-effective method for high-temperature electronics packaging.

IImproved performance of CdS powder-based hybrid solar cells through surface modification

The effects of surface modification of CdS through organic Eosin-Y, indoline D205, and Ru-based complex N719 and N3 dyes on CdS-based hybrid solar cells were studied. Chemical bath deposition (CBD) and doctor blade methods were in turn employed to fabricate the CdS specimens on Indium-Tin Oxide (ITO) covered glass substrates. P3HT material with and without dye coatings was covered through a spin-coater on the surface of CdS specimens. Ag paste was then deposited on the surface of P3HT to obtain hybrid solar cells. Structural analysis indicated that CdS powders showed a cubic growth with the preferred orientation of (111). Morphological analysis demonstrated that CdS powders exhibited hierarchical morphology and the morphology turned to granular structure with some porosity upon deposition of both N3 dye and P3HT layers. Absorption plots indicated that Eosin-Y dye loading led to a rise in the absorbance values of CdS specimens. After dye loading, photoluminescence data of CdS-based heterostructure illustrated a decrement in the luminescence intensity, implying that effective exciton dissociation was obtained. Current density-voltage (J-V) characteristics of the hybrid solar cells depicted that the best overall efficiency was observed for Eosin-Y-modified cell as 0.135%. This proved that surface modification by Eosin-Y dye led to a better interfacial contact between CdS and P3HT bilayer due to the enhancement in the charge separation.

Low temperature sintering of MOD assisted Ag paste for die-attach application

In this paper, we have developed a novel Ag paste containing MOD (metal organic decomposition) for assisting the sintering of nanoparticles. Based on the prepared Ag paste, the bonding joint can reach a maximum shear strength of 42.7 MPa at 175 °C. The effect of different amines on the performance of bonded joints was studied to elucidate the mechanism of MOD assisted sintering. Due to the advantage of high sintering performance, the new MOD assisted Ag paste is promising to be applied in the field of WBG device packaging.

Ag/GNS conductive laminated woven fabrics for EMI shielding applications

ABSTRACT In flexible electronics, a highly electroconductive, flexible, and durable material is important for various applications. This study describes the property changes in graphene nanosheets (GNSs) doped into a conductive silver (Ag) paste that is used to form a grid-style pattern on a polyurethane hot melt film (PU HMF) for electromagnetic wave shielding. Electrical conductivity, thermal conductivity, and bending tests were performed for materials fabricated by an electronic printing method. The results showed that the conductive paste with a loading of 0.3 wt% GNSs (3SC) had good electromagnetic shielding effectiveness (EMSE, 49.9 dB at 1800 MHz), much better electrical conductivity (4.63*104 S/cm) than the pure silver paste (1.38*104 S/cm), and an improved bending ability. The coefficient of variation of GNS loading (3.01% to 3.80%) under 1000 cyclic bending tests was better than that of the pure silver paste (6.94%) at 2.4% strain, but the results under 500 cyclic elongation tests at 10.0% strain did not exhibit the same pattern. The coefficients of variation (CVs) of all samples in the GNS group (8.3–13.3%) were worse than those of the pure silver group (6.3%) after the elongation test. The reason for the differences in the electrical conductivity and flexibility was explained by the SEM results, which indicated notable damage after the bending and elongation tests. Woven fabrics laminated with a PU/Ag/GNS conductive film that were doped with different amounts of fillers were successfully manufactured by electronic printing and can be used for Electromagnetic Interference (EMI) shielding materials, electrodes for sensor components, wearable elements, smart home textiles, and conductive materials, for example.

Highly thermally conductive Ag/SiO2 superhydrophobic coating for accelerated dropwise condensation

Due to the ability to promote dropwise condensation, superhydrophobic coatings are widely used to increase the heat transfer performance of functional surfaces. A higher thermal conductive coating is always required for maximum heat transfer. However, the traditional polymer or ceramic based coatings have poor thermal conductivity and weak adhesion, which will hinder the heat flow across the surface. As a candid attempt to improve the heat transfer, here we propose a smart method to fabricate a highly thermally conductive Ag/SiO2 superhydrophobic coating. The coating is obtained through screen printing Ag paste on Al surface followed by spray coating hydrophobic SiO2 nanoparticles and sintering at 600 °C. The Ag paste acted as a binder to hold the SiO2 particles and increased the thermal conductivity of the Ag/SiO2 coating up to 83.32 W/m⋅K, which was 40 times higher than that of the polyurethane/silica (PU/SiO2) coating. Because of the higher thermal conductivity, Ag/SiO2 coating showed quicker dropwise condensation compared to PU/SiO2 coating. Dropwise condensation of Ag/SiO2 coatings was also confirmed and compared with other metals, Al, Ag, Cu, and SUS. This work would give a solution to the existing design limitation of a coating when it is applied for heat transfer applications.

Fabrication and Characterization of Physical and Mechanical Properties of Carbon Nanotubes-Graphene-Based Sandwich Composite Pressure Sensor.

In this work, piezoresistive properties of graphene-multiwalled carbon nanotubes (MWCNTs) composites are investigated, characterized, and compared. Sandwich-type composite piezoresistive pressure-sensitive sensors (Ag/Graphene-MWCNT/Ag) with the same diameters, but different fabrication pressures and thicknesses were fabricated using the mortar and pestle/hydraulic press technique. To produce low-electrical-resistance contacts, both sides of the composite sensors were painted with silver (Ag) paste. All the sensors showed reductions in the direct current (DC) resistance ‘R’ with an increment in external uniaxial applied pressure. However, it was observed that higher fabrication pressure led to a lower resistance value of the composite, while the thicker samples give lower electrical conductivity and higher resistance than the thinner samples. The experimental data for all composite pressure sensors were in excellent agreement with the simulated results.

A Novel Preparation of Ag Agglomerates Paste with Unique Sintering Behavior at Low Temperature.

A novel bonding process using Ag agglomerates paste prepared by Ag2O reduction has been proposed, which solved the problem of Cu substrate oxidation in the conventional Ag2O sintering process for Cu–Cu bonding. By applying the Ag agglomerate paste to Ag–Ag bonding, a shear strength of 28.3 MPa at 150 °C was obtained. Further studies showed that the optimum sintering temperature was at 225 °C, and a shear strength of 46.4 MPa was obtained. In addition, a shear strength of 20 MPa was obtained at 225 °C for Cu–Cu bonding. Compared to common Ag pastes, the results in this paper revealed that the sintering behavior of Ag agglomerates was unique, and the sintering mechanisms for Ag–Ag and Cu–Cu bonding were also discussed.

Influence of the textured pyramid size on the performance of silicon heterojunction solar cell

By adjusting the KOH/H2O texturing condition intendedly, different random pyramidal textures with the average pyramid size of 8 μm (large), 4 μm (medium) and 1.5 μm (small) were prepared on N type M2 monocrystalline silicon substrates for the fabrication of silicon heterojunction (SHJ) solar cell. It was evidenced that the pyramid morphology not only impacted the reflection of incident light and the heterojunction interface passivation quality but also affected the interface contact property between transparent conductive oxide (TCO) layer and Ag electrode. The texture with small pyramids presented the best anti-reflective and passivation performance due to the pyramidal size distribution uniformity, which brought the SHJ solar cell the highest short-circuit current density (JSC) and open-circuit voltage (VOC). However, the texture with small pyramids also led to the worst fill factor (FF). As a result, there was no obvious difference on the conversion efficiency for the textures with different pyramidal size. By characterizing the TCO/Ag contact, the FF reduction induced by the small pyramid texture could be attributed to the increased specific contact resistance of the TCO/Ag contact, which resulted from the fact that there were lots of voids between the TCO layer and Ag electrode, since Ag particles with a larger size than the small pyramids could not fill into the limited space between the adjacent pyramids. As a result, in order to realize the potential to enhance the SHJ solar cell conversion efficiency by adopting the texture with small pyramids, new Ag paste with smaller Ag particles should be adopted.

On the dependence of interfacial resistance on contact materials between cathode and interconnect in solid oxide fuel cells

The dependence of interfacial contact resistance (ICR) on contact materials between cathode and interconnect is systematically studied under both isothermal oxidation and thermal cycling conditions. Three kinds of cathode current-collecting layer (CCCL) are used, (La,Sr) (Co,Fe)O3 (LSCF), LSCF+10%Ag, and Ag, and tested in a SUS430/CCCL/SUS430 sandwich structure to simulate the actual operation of the solid oxide fuel cells (SOFCs). Experimental results show that the ICR of LSCF+10%Ag exhibits the smallest value, in comparison with the specimens with LSCF and Ag paste, as well as the sample without a CCCL. For LSCF+10%Ag contact, the ICR increases from 0.0069 mΩ cm2 to 3.74 mΩ cm2 under an isothermal condition for 150 h, then increases from 3.74 mΩ cm2 to 10.79 mΩ cm2 after 15 thermal cycles. This work provides information for the understanding of possible mechanisms of performance degradation of SOFCs.

A Review of Sintering-Bonding Technology Using Ag Nanoparticles for Electronic Packaging.

Metal nanoparticles (NPs) have attracted growing attention in recent years for electronic packaging applications. Ag NPs have emerged as a promising low-temperature bonding material owing to their unique characteristics. In this study, we mainly review our research progress on the interconnection of using polyol-based Ag NPs for electronic packaging. The synthesis, sintering-bonding process, bonding mechanism, and high-temperature joint properties of Ag NP pastes are investigated. The paste containing a high concentration of Ag NPs was prepared based on the polyol method and concentration. A nanoscale layer of organic components coated on the NPs prevents the coalescence of Ag NPs. The effects of organic components on the bondability of the Ag NP paste were studied. Compared to the aqueous-based Ag NP paste, the polyol-based Ag NP with the reduction of organic component can improve the bondability, and the coffee ring effect was successfully depressed due to the increased Marangoni flow. The sintering behaviors of Ag NPs during the bonding process were investigated using the classical sphere-to-sphere approach. The mechanical property of joints using this Ag paste was better than that using Pb95Sn5 solders after storage at high temperatures. The sintering–bonding technology using polyol-based Ag NPs was helpful to the low-temperature interconnection for electronic packaging applications.

Low-temperature sintered Ni\u2013Zn\u2013Co\u2013Mn\u2013O spinel oxide ceramics for multilayer NTC thermistors

The phase formation, sintering behavior and electrical properties of Ni–Co–Zn–Mn spinel NTC thermistor ceramics of the series Ni0.5ZnzCo0.5Mn2−zO4 with 0 ≤ z ≤ 1 were studied. In contrast to NiMn2O4, which exhibits limited stability in air below 730 °C and above 970 °C, the Zn–Co-substituted nickel manganite spinels are stable at T < 730 °C and decompose at Td > 900 °C, with Td increasing with decreasing Zn Content z. The samples were sintered at 900 °C with addition of 3 wt% Bi2O3 as sintering aid and densities of above 92% were achieved. The room temperature resistivity and thermistor B-constants are almost independent of composition at 0 ≤ z ≤ 0.6 and start to increase at higher Zn concentrations. A multilayer NTC thermistor was fabricated using green tapes of a spinel of composition z = 0.75, commercial Ag paste, and cofiring at 900 °C. The firing behavior, microstructure formation and electrical properties of the multilayer thermistor are reported.

MoOx work function, interface structure, and thermal stability analysis of ITO/MoOx/a-Si(i) stacks for hole-selective silicon heterojunction solar cells

Silicon heterojunction (SHJ) solar cells are gaining prevalence owing to their high conversion efficiency and simple, low-cost, and industrially compatible fabrication process. However, the high parasitic absorption exhibited by the doped amorphous silicon a:Si(p/n) layer substantially limits their performance. This can be alleviated by substituting traditional amorphous doped p/n layers with alternative materials such as transition metal oxides. MoOx is one of the most promising candidates for replacing the a:Si(p) layer, and it has yielded impressive results in recent studies; however, the thermal instability of MoOx-based devices is a major limitation. In this work, the MoOx work function, thermal stability of the ITO/MoOx/a-Si(i) interface, and the effect of MoOx thickness variation on the performance of a MoOx SHJ solar cell were thoroughly studied. The MoOx composition and work function were analyzed using X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and ultraviolet photoelectron spectroscopy. The O2-treated MoOx film showed minimal oxygen deficiencies accompanied by a higher work function of 6.22 eV compared with those of H2-, N2-, and Ar-treated MoOx films. The ITO/MoOx/a-Si(i) stacks have a clear contact interface up to 150 °C and in-out diffusion between the layers is initiated upon further increase of the annealing temperature. Thus, 150 °C was proposed as the optimal temperature and used for Ag paste sintering without degrading the device performance. Additionally, a thin sub-stoichiometric SiOx layer was formed on a-Si(i) during MoOx deposition, irrespective of the annealing environment, temperature, and thickness of MoOx. The fabricated SHJ solar cell with an optimized thickness of MoOx (7 nm) exhibited an efficiency of 19.86% with a Voc of 716 mV, Jsc of 37.50 mA/cm2, and FF of 74.01%. The achieved Jsc is 1.40 mA/cm2 higher and the external quantum efficiency in the range of 300–600 nm is 13%–15% higher than those for the reference SHJ solar cell. Therefore, our results show that MoOx is an efficient and convenient alternative emitter material for Si solar cells, and the proposed optimized parameters for MoOx processing pave the way for more efficient SHJ solar cells.

Mechanism investigation on effects of glass composition on Ag/Si contact for crystalline silicon solar cells

Pb–Te–Li oxide glasses have been widely applied in front silver (Ag) paste metallization of crystalline silicon (c-Si) solar cells. In practical application, some other important glass compositions, such Bi2O3, SiO2, ZnO and so on, are often added into Pb–Te–Li oxide glasses to improve the quality of Ag/Si contact. In this paper, the significant effects of these glass compositions on the Ag/Si contact are demonstrated by discussing their influences on the formation of Ag colloids in the interface, the erosion of glass to Si, the glass phase conductivity, and the glass passivation performance at the contact interface. The results show that the addition of Bi2O3 or SiO2 into the glass may reduce the Ag/Si contact resistivity, because Bi2O3 can promote the formation of Ag colloid in the interface glass layer and increase the interface glass phase conductivity, and SiO2 can weaken the erosion ability of the glass to keep relatively high dopant concentration in the contacted Si surface. The addition of ZnO into the glass may aggravate the erosion to Si and decrease the glass phase conductivity. It is inferred that increasing Bi2O3 and SiO2 or reducing ZnO can improve the glass passivation performance at the contact interface. Through the application in Ag paste metallization, the important effects of the glass compositions on the electrical properties of solar cells are shown that Bi2O3 and SiO2 in the glasses are helpful to increase the open-circuit voltage and short-circuit current, while ZnO is very useful for raising fill factor.

Printing and Laser Curing of Ag and Cu Paste - Prospects and Challenges in Additive Manufacturing

This study depicts substantial characteristics of copper and silver pastes, dispensed and cured by oven processing. Different analyses, such as second electron microscopy (SEM), rheometry, thermogravimetric analysis (TGA), UV-VIS-NIR-spectroscopy and 4-point measurement were used. This work also will illustrate some results of computational design of experiment (DOE) and regression analyses for jet and mechanical printing processes.

Low Recombination Firing-Through Al Paste for N-Type Solar Cell with Boron Emitter

A kind of low recombination firing-through screen-printing aluminum (Al) paste is proposed in this work to be used for a boron-diffused N-type solar cell front side metallization. A front side fire-through contact (FTC) approach has been carried out for the formation of local contacts for a front surface passivated solar cell. With a low contact resistivity (ρc) of 1.0 mΩ·cm2, good ohmic contact between the boron-doped front surface of the silicon sample and the Al paste was realized. To obtain a good energy conversion efficiency, a balance can be achieved between the open circuit voltage (Voc) and contact resistivity (ρc) of the cell by combining suitable Al powders and appropriate additives. The detailed micro-contact difference in Si/metallization between the firing-through Al paste and silver-aluminum (Ag-Al) paste was analyzed. The dark saturation current density beneath the metal contact (J0, metal) of the Si/metallization region using our firing-through Al paste was discussed, which was proven to be 61% lower than using Ag-Al paste. The pseudo energy conversion efficiency of the cell using Al paste measured by Suns-VOC was also higher than using Ag-Al paste. The role of Al paste in low surface metal recombination is discussed. The utilization of this new kind of Al paste was much cheaper and more convenient, compared to the traditional process using Ag or Ag-Al paste.

A Novel Method to Fabricate a Thick-Film Cu Electrode Fired in Air Through Printing Al Electrode and Reduction-Oxidation Substitution Reaction

The thick-film conductor pastes that are applied most widely are Ag and Cu due to their high conductivity. Ag paste can be sintered in air to have high conductivity, but its disadvantage is the overly high cost. Contrarily, although Cu thick paste is not expensive in terms of materials, Cu thick-film paste must be sintered in a reducing atmosphere to obtain high conductivity, which leads to high processing costs. A novel method for fabricating the base metal electrode Cu in an air atmosphere for high-temperature firing was successfully developed based on thick-film screen-printing Al pastes utilizing a reduction-oxidation substitution reaction. To make an excellent Cu electrode that can be substituted for a thick-film Al electrode, Al paste with high solid content, a large Al powder particle size, a CuSO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> solution with low pH, high temperature, and proper soaking time are all positive parameters. The first thick-film screen-printing Cu electrode with high conductivity ( > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6 </sup> Ω), which is comparable with a thick-film Ag electrode, was successfully fabricated in air firing instead of reducing atmosphere firing.

Corrosion of novel reactive silver ink and commercial silver-based metallizations in diluted acetic acid

Silver-based metallizations in photovoltaic modules are susceptible to corrosion by acetic acid generated in ethylene vinyl acetate encapsulated modules, resulting in power losses over time. Here, three silver-based metallizations are exposed to diluted acetic acid, in concentrations representative of that found in field-exposed modules. Compositional, morphological, and structural changes of the metallizations are studied over 3000 h of exposure to diluted acetic acid using Raman spectroscopy mapping, X-ray diffraction, and scanning electron microscopy. The three metallizations studied are: 1) a commercial high-temperature fire-through Ag paste, commonly used for Si diffused junction solar cells; 2) a commercial low-temperature paste normally used for silicon heterojunction cells; and 3) a novel low-temperature reactive silver ink shown to be suitable for photovoltaic applications. We find distinct corrosion rates for the high-temperature silver paste and reactive silver ink in the presence of diluted acetic acid. On the other hand, the low-temperature silver paste appears to be more corrosion resistant, likely due to a polymer layer that protects the silver particles.