Optimizing Conductive Adhesives for High-Efficiency PV Cells

An electrically conductive adhesive for photovoltaic modules that combines low silver content with high conductivity, adhesion, and reliability. The adhesive comprises a resin matrix of epoxy and urethane acrylates, reactive diluents, and silver flake and glass particles. The composition achieves optimal properties through a balanced formulation of oligomers, monomers, and fillers, and can be cured thermally. The adhesive is suitable for shingled and ribbon-attached photovoltaic modules, providing stable electrical contacts and reliable performance under thermal cycling and humidity conditions.

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The widely used adhesive joining technique suffers from the drawback of being unable to be dismantled to examine for degradation. To counteract this weakness, several structural health monitoring (SHM) methods have been proposed to reveal the joint integrity status. Among these, doping the adhesive with carbon nanotubes to make the joint conductive and monitoring its electrical resistance change is a promising candidate as it is of relatively low cost and easy to implement. In this work, resistance change to monitor fatigue debonding of composite single-lap adhesive joints has been attempted. The debonded area, recorded with a liquid penetrant technique, related linearly to the fatigue life expended. However, it correlates with the resistance change in two different trends. Scanning electron microscopy on the fracture surface reveals that the two trends are associated with distinct failure micromechanisms. Implications of these observations on the practical use of the resistance change for SHM are discussed.

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A method for bonding interconnection elements to photovoltaic cells that reduces adhesive consumption and improves reliability. The method involves successively depositing a first electrically conductive adhesive film on each interconnection element, then placing the elements on the photovoltaic cell with the adhesive film in contact. The second adhesive film is deposited simultaneously with the first, eliminating the need for additional adhesive layers.

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Abstract Our previous work highlighted how microscopic structural effects influence the sheet and contact resistance of electrically conductive adhesives (ECAs). Herein, we delve further by investigating how the contact and bulk resistivity of several ECAs that are based on the same formulation, but with different filler content, are correlated with the filler content. Additionally, two different filler geometries high and low surface area (HSA and LSA) fillers are combined in different ratios to maintain a similar viscosity and therefore processability. Hence, contact and bulk resistivities are also correlated with the different geometry ratios of these two fillers. As expected, it was found that the contact and bulk resistivities decreased when the filler content was increased. However, the magnitude of the decrease was found to depend strongly on the filler geometry ratio. At extreme filler geometry ratios, when the bulk is either mostly loaded with HSAfillers or mostly with LSAfillers, the impact of changes in the filler content on the bulk and contact resistivities is mark... Read More

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This work deals with shingle solar modules, in particular the interconnection of shingle solar cells by using an electrically conductive adhesive (ECA), as well as by simply overlapping the same type of shingle solar cells but omitting the ECA. For both types of interconnection, the resistance due to interconnection Rint and the corresponding cell-to-module (CTM) power loss PMPP in the case of a full-size shingle module are quantified, finding Rint 0.26 m and PMPP 0.4 W for the ECA-based interconnection, and Rint 0.86 m and PMPP 1.2 W for the ECA-free interconnection. The work mainly focuses on the methodology used to derive these numbers from small-format modules containing shingle strings of different lengths. An extensive error discussion is given, as well as a discussion on the advantages over a different approach to determine Rint.

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This article reports on the 11th Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells, which took place in May 2023 in Neuchtel, Switzerland. An important observation at the workshop was that, while screen printing is still dominating metallization, alternative pastes with increasing Cu content are starting to be implemented in the industry in response to the need to decrease cost and improve sustainability. Compared to previous workshops, interconnection topics were more prevalent in this edition because of the need for interconnection solutions that work at lower temperatures, as is needed for emerging solar cell technologies. Electrically conductive adhesives (ECA) have gained in importance in this respect. Understanding of reliability aspects and insight into proper characterization of ECAs are increasing, yet the challenge is here is to substantially further reduce cost and silver content.

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Abstract Anisotropic conductive adhesives (ACAs) are the preferred interconnection technology for applications that employ large dies, flexible substrates, and ultra finepitch interconnects. Conventional ACAs require relatively high bonding pressures and temperatures, and ultra finepitch applications challenge the tradeoff between low interconnect resistance and risk of short circuits. This study introduces an ACAlike interconnection technology that addresses these limitations, allowing for lowpressure, lowtemperature assembly processes with enhanced particle control at the interconnects. Conductive particles are deposited onto a patterned carrier and subsequently transferred to electrical pads using either nonconductive film or Ag sintering. The Ag sintering process is performed at a low temperature (140 C) and low bonding pressure (1 N for a 10 10 mm 2 chip). The capability of controlling the position and number of conductive particles within individual interconnects is demonstrated. This presents possibilities for achieving ultrafine pitch interconnects with negligible ... Read More

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In this study, we aimed to develop and characterize Transparent Conductive Adhesive (TCA) materials for mechanically stacked tandem solar cell applications. The research objectives were to enhance the transparency, conductivity, and adhesive strength of TCAs to improve the efficiency and practicality of tandem solar cells. The TCA formulation comprises a combination of polymers and Ag-coated particles, with flexible poly-methyl methacrylate (PMMA) micro-spheres serving as conductive particles and SYLGARD 184 silicon elastomer poly-di-methyl-siloxane (PDMS), mixed in a 10:1 ratio of base to curing agent, serving as the transparent adhesive. We conducted systematic experiments with Ag-particle coverage areas ranging from 0.34 % to 21.61 % at temperatures of 80 C and 100 C, under 500 mb pressure. The optimal conductivity was achieved at 2 wt% Ag-particle coverage, measuring 5.26 10 S/m, with over 93 % transparency. These key results indicate the significant potential of the optimized TCA in enhancing the performance of mechanically stacked tandem solar cells, thus contributing to t... Read More

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The reduction of the series resistance in multijunction solar cells is of high importance for attaining peak efficiencies in concentrator photovoltaics. This study showcases strategies to reduce the sheet resistance of the uppermost subcell of a direct wafer bonded fourjunction devices, since it contributes significantly to the series resistance. Therefore, electron mobilities in ntype AlGaInP, lattice matched to GaAs, are investigated across bandgap energies between 1.9 and 2.1 eV and various doping concentrations. The sheet resistances for AlGaInP rear heterojunction cells are determined for the integration in a two terminal fourjunction solar cell. The rear heterojunction cell architecture effectively addresses the sheet resistance optimization because it features a thick ntype doped absorption layer. The sheet resistance of our current world record quadruplejunction solar cell with 47.6% efficiency under the 665fold concentrated AM1.5d spectrum is 550 sq 1 . Herein, it is shown that optimizing the nabsorption layer in the 1.90 eV GaInP top cell can reduce the sheet res... Read More

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A method for preparing photovoltaic cell strings and modules that reduces manufacturing costs by eliminating soldering and using adhesive films to connect cells. The method involves routing main grid lines to the back of cells, bonding them to an adhesive film, and then applying additional adhesive to secure the grid lines. This approach enables the use of thin silicon wafers and eliminates the need for soldering, reducing material costs and enabling the production of high-efficiency photovoltaic modules.

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Materials with high conductivity and low cost are urgently required for electronic products, particularly copper conductive adhesives. Developing reliable copper conductive adhesives (ECAs) remains a great challenge due to their low conductivity and easy oxidation. In this article, copper microflakes with surface passivation by formate ions and thiols were used to create an antioxidant copper adhesive. We demonstrate that the surface modification has no impact on the electrical conductivities, even in salt spray, acid, alkaline, high temperature, and humidity conditions. After being cured at 250 C for 30 min, the produced Cu ECAs displayed an ultralow resistivity of 65.12 cm1. Excellent stability enables its resistance to maintain a low level after 1000 h of aging at 200 C and 85%RH 85 C. This study establishes the enormous potential of Cu ECAs with antioxidants for low-cost microelectronics packaging.

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A conductive material for photovoltaic modules that enables accurate electrical connections between solar cells without the need for wide grid lines or soldering pads. The material features a conductive wire with a stepped or bent shape that passes through openings in an adhesive film, allowing for precise electrical connections between cells while minimizing material usage. The conductive material is prepared by fixing the wire to the film, heating the adhesive, and then melting the wire to secure it in place. The material is used to connect solar cells in series in a photovoltaic module, eliminating the need for traditional welding methods.

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In this work, the behavior of an electrically conductive adhesive (ECAs) was selected and studied, using shingled technology is a development in the connection of solar cells by means of superimposition with electrically conductive adhesives, thus obtaining higher powers than the previous welding process, also offers several advantages compared to standard photovoltaic modules, improving: efficiency, reduction of microcracks, better use of the surface, lower processing temperature, higher energy yield, and better aesthetics. The objective of this study was to analyze electrically conductive adhesives for use in the manufacture of photovoltaic modules to propose a technological development to obtain greater efficiency in energy capture. Polycrystalline cells and monocrystalline cells were studied. The photovoltaic module manufacturing set was made using the conventional fixing method to join solar cells, based on the union by welding with Sn-Cu connection tapes. Loctite Ablestik ICP 8282 adhesive was selected for use in the manufacture of the overlay prototype and the substitution of ... Read More

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This study presents a method to analyze the electrical resistance of planar contacts. The method can determine whether the contact resistance of the joint exhibits linear or non-linear behavior. By analyzing the current distribution over a planar contact, it can be determined whether an area-based contact resistance is justified or if other parameters define the contact resistance. Additionally, a quantitative evaluation of the factors that affect the measurement accuracy, including the positioning, the measurement equipment used, and the influence of the current injection on the sense pin was conducted. Based on these findings, the electrical contact resistance and the mechanical ultimate tensile force of a silver-filled epoxy-based adhesive are analyzed and discussed. The layer thickness and the lap joint length were varied. Overall, the investigated adhesive shows a low contact resistance and high mechanical strength of the same magnitude as that of well-established joining techniques, such as welding, press connections, and soldering. In addition to evaluating the mechanical and ... Read More

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For the industrialization of large area perovskite silicon tandem solar cells a low-resistance and low-cost contact metallization needs to be established. On the one hand, curing or even firing temperatures as applied for screen-printing metallization of Si single junction cells are too high for perovskites. On the other hand, screen-printing pastes with very low curing temperatures have a reduced specific conductivity. Thus, they require wide Ag consuming contacts for a sufficiently low resistance. We present a concept which comprises screen-printing the front contacts onto an isolating layer located on the uppermost layer of the bottom cell before the perovskite top cell is applied. This allows higher curing temperatures and thus lower finger resistivities than in a low curing temperature screen-printing process on a perovskite solar cell. Furthermore, this concept avoids mechanical pressure on the soft perovskite material during cell interconnection. We expect that the latter aspect is beneficial to prevent shunting issues. The concept is shown for perovskite single junction solar... Read More

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Conductive adhesive joints were climatically aged with temperature pulses in the range of -40 to 115 C. The joints were made of two types of electrically conductive adhesives with isotropic electrical conductivity. The insulating matrix of the adhesives was bis-phenol formaldehyde epoxy resin, and the conductive filler was silver flakes. One adhesive was two-component and the other one-component. Adhesives were applied to the printed circuit board by stencil printing, and then zero-value resistors were mounted by adhesive mounting. Thus, adhesion bonds were formed. The joints were first exposed for 15 minutes in the hot chamber of the thermal pulse testing device, then moved within 8 seconds to the cold chamber and exposed again for 15 minutes. This cycle was repeated two hundred times and five hundred times. The connection resistance was measured using the four-point method. Exposure to temperature pulses was found to cause small changes only in junction resistance.

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The temperature dependence of the resistance of adhesive conductive joints and the thermal coefficient of longitudinal expansion of conductive adhesives are parameters that can significantly affect the properties of this type of conductive joining. The dependence of these parameters on temperature was investigated. Adhesive mounting zero-value resistors to the test PCB prepared adhesion joints. The adhesive was applied by stencil printing. The resistance of the joints was measured by the four-point method and the thermal expansion of used adhesives was measured by the thermomechanical analysis technique. The junction resistance was found to increase approximately linearly with temperature, but the joints were found to harden when measured. It was also found that the coefficient of thermal longitudinal expansion varies depending on the adhesive and also on the sample when all samples are made from the same adhesive. The reason is the not completely reproducible adhesive application technology for this measurement.

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With fast developments in the environmental-friendly industry, electrically conductive adhesive (ECA) composites with high electrical conductivity, mechanical strength, and electrochemical migration resistance as well as low cost are highly desirable for emerging power electronics applications. In this study, a category of ECAs, namely, size-controllable sonochemical low-melting-point-alloy (LMPA) particle-incorporated transient liquid-phase ECAs (TLP-ECAs), with excellent electrical conductivity, considerable mechanical strength, and high electrochemical migration resistance has been successfully demonstrated. Experimental results showed that the bulk resistivity of TLP-ECA decreased to a minimum value of 2.37 104 -cm with the remaining filler content at a low level (the total content of metallic fillers, i.e., 70 wt % in TLP-ECAs), while the mechanical shear strength increased considerably (by 55.4%) compared with pure silver ECA with the same filler content, demonstrating that addition of sonochemical LMPA particles into ECA can simultaneously and considerably improve the elec... Read More

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The objective of this paper is to add to the fundamental understanding of the conduction mechanisms and mechanical behavior of electrically conductive adhesives and their applications. Consequently, the research work to be presented involves two parts: (a) analysis of mechanical behavior, and (b) analysis of electrical behavior of conductive adhesives. Electrical and mechanical behaviors of both bulk conductive adhesives and single lap joints bonded with a conductive adhesive are studied. For bulk conductive adhesives, a model is established to predict the adhesive conductivity. The effect of film thickness on the conduction behavior of conductive adhesives is also presented, and it is shown that in thin flim adhesives the resistivity values in planar directions are much larger than those encountered in 3-D measurements for the same adhesive material. The thermal mismatch stress induced at the interface between the adhesive and the substrate is studied in closed form and by finite element analysis, and the mechanical properties of the filled adhesive composite are obtained for this p... Read More

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The contact resistivity of interfaces in solar module interconnects has a direct impact on the series resistance of the entire module and fill factor. Thus, this impacts the performance of entire photovoltaic systems. Accurate measurement of the contact resistance is a key component of optimizing the performance of such interconnects. However, this is difficult for electrically conductive adhesive (ECA) based interconnects. This work shows that transmission line method (TLM) test structures based on ECA display nonnegligible inhomogeneities leading to inaccuracies when determining the contact resistivity. Seven methods based on two models the front and endcontact TLM models (or a combination of both) were investigated for four commercially available ECAs used in solar modules and their impacts on the extrapolation of the contact resistivity were quantified. It was determined that even when macroscale inhomogeneities (e.g., variations in the thickness of the ECA) are not present, microscopic structural effects influence the sheet and contact resistance. In particular, variation... Read More

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Adequate mechanical and electrical properties and long-term reliability are critical in conductive adhesive interconnects. In order to improve the electrical and mechanical properties of isotropic conductive adhesives (ICAs), reduce contact resistance and enhance the aging resistance of ICAs, the effects of low melting point SnBi58 alloy on the properties of ICAs were studied. The low melting point SnBi58 alloy formed metallurgical bonds between conductive fillers, as well as between the ICAs and a Cu substrate and not only improved the electrical conductivity and mechanical properties of ICAs, but also reduced the contact resistance shift of ICAs effectively. It was found that when the mass ratio of SnBi58 alloy in conductive fillers was maintained at 20 wt%, the bulk resistivity of ICAs reached 4.8 104 cm, the shear strength of ICAs was 27.71 MPa, and the contact resistance shift of ICAs was 7% after aging. In addition, better bulk resistivities and higher shear strengths of ICAs were achieved after aging at 85 C/85%RH.

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Accurate determination of the contact resistivity between electrically conductive adhesives (ECAs) and solar metallization paste is a key component of optimizing the electrical performance of bonds based on ECAs, such as shingled joints. This work proposed and validates a methodology that accounts for nonnegligible inhomogeneities of test structures based on ECAs and silver screen-printed metallization, such as changes in width of the ECA, to improve the accuracy in the calculation of the contact resistivity. The proposed validation uses statistical theory based on the central limit theorem and the law of large numbers showing that the contact resistivity of bonds based on two different commercially available ECAs can be clearly differentiated with a minimum confidence level of 95% and a maximum error margin of 5%. Moreover, the necessary sample size to achieve such requirements is calculated and shown to be equal to 24 test structures. The validation was done using an acryl-based adhesive loaded with silver flakes (104 cm), which was compared to an epoxide-based ECA filled with... Read More

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Enhancing the oxidation resistance of conductive silicone adhesive is crucial for long-term stability in rich oxygen and high-temperature environments. Coating thin film featuring low oxygen permeability on the adhesive has been considered a reliable solution. However, the current processes of coating film require extra precursor materials and post-treatment. Here we demonstrated a simple process with atmospheric pressure plasma-assisted to coat SiOxCy thin film on the conductive silicone adhesive within minutes. Our results indicated that the coated thin film has strong oxidation resistance that protects the conductive silicone adhesive from oxidation by 0.1 M HCl solution within 7 days and exposure to ozone for 20 min. The film presented a strong hydrophobic property with a contact angle of 120. The films chemical structure was detected mainly with Si3+: [Si(R)(-O-)-O] and Si4+: [Si(-O-)2O]. The coating process is simple, requires no precursor material, and does not change the original conductivity of the conductive adhesive.

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Abstract IIIV/silicon tandem solar cells simultaneously have the potential advantages of high efficiency and low cost. Bonding is an effective way to realize tandem at both ends. However, it is difficult to realize vacuum bonding in industrialized micrometersized pyramid silicon cells. Up to know, all bonding in IIIV/silicon tandem solar cells is based on planar silicon cells. Here, a transparent conductive adhesive (TCA) based on micron particle size is designed and implemented, which realizes the bonding of IIIV cell and textured silicon cell for the first time. The TCA consists of epoxy adhesive 301 (Epoxy301) as transparent adhesive and silvercoated flexible polymethylmethacrylate microspheres as conductive particles. The average contact resistance of TCA is 0.17 cm 2 , and the transmittance exceeds 91% in the range of 8001200 nm. In addition, TCA shows good stability in the etching process of GaAs substrates. Monolithic IIIV/silicon device exhibits 25.1% power conversion efficiency (PCE) on thin and textured silicon heterojunction solar cells, which enables flexible pr... Read More

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Electrically conductive adhesives (ECAs) are used widely to replace or reinforce lead soldering or conductive metal components in electronic packaging applications such as die attachment, solderless interconnections, component repair, display interconnections, and heat dissipation. Their conductive behavior as well as the associated behaviors such as heat conduction and mechanical behavior (strength, rigidity, deformation and viscoelastic behavior, which may be affected by moisture ingression) are affected by adhesive film thickness, volume fraction, size and shape of the conductive filler, as well as uncured base adhesive viscosity, substrate and filler surface treatment and the applied pressure (during bonding and during conduction). The adhesive resistivity decreases precipitously above a characteristic filler volume fraction called the percolation threshold. In general, micron-sized metal fillers mixed in an adhesive (often an epoxy) resulting with different film thicknesses exhibit thickness thresholds for transition from three-dimensional conductivity to two-dimensional conduc... Read More

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Abstract Electrically conductive tape (ECT) was characterized and used to assemble shingled cell strings at low temperature to achieve high reliability Pb and Agfree interconnections. The volume resistivity for two considered ECTs are 0.13 0.06 mcm and 0.47 0.20 mcm and specific contact resistances, 6.85 2.00 mcm 2 and 6.30 0.37 mcm 2 using the emerging IEC 6278881 Technical Specification for assessment of electrically conductive adhesives (ECA). Durability and performance of the technology in glassglass mini modules were evaluated with temperature cycling, damp heat testing, and combinedaccelerated stress testing (CAST). Through temperature cycling (40C to 85C) applying five times the mini module shortcircuit current in forward bias and in the multi climate CAST protocol, there was negligible degradation of fill factor after replacing connectors at the modules' cable leads; however, CAST resulted in short circuit current loss attributed to degradation in light collection by the cells, not the ECT. The IEC 612152 85C, 85% relative humidity damp heat testing... Read More

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Electrically conductive adhesives (ECAs) mainly comprise the resin matrix, conductive particles, dispersion additives, and other additives. ECAs can effectively bond various materials and have conductive properties. The conductive mechanism of ECAs is considered to be the contact between conductive particles to form an electrical path. ECAs are widely used for microelectronic assembly, including the connection of thin wires with printed circuits, electroplating bottom plates, metal layers of ceramic adhere and metal chassis, bonding wire and tube base, bonding elements, and plane hole passing through printed circuits, bonding waveguide tuning, and hole repair. At present, much research has been done in epoxy-based conductive adhesives, including categories, conduction mechanisms, fillers, and applications.

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High-performance conductive aramid fibers (PPTA) can be applied in many fields, while the poor interface compatibility between aramid fiber and conductive element restricted their practical applications. Herein, PPTA-based conductive fiber were fabricated by firstly functionalizing the PPTA surface to covalently attach some hyperbranched polyamidoamine (HPAMAM), then coating the crosslinked HPAMAM to constructing cross-linked HPAMAM interface. The stable cross-linked HPAMAM interface was constructed creatively by chemical method and it strongly strengthened interfacial bonding between Ag plated layer and PPTA. Meanwhile, the excellent mechanical property of PPTA was maintained, as the tensile strength of Ag-plated PPTA only had lowed 0.25 cN/dT compared to the original PPTA. The electrical resistance of prepared Ag-plated PPTA exhibited a very low value of 0.043 /cm. Moreover, the silver-plated PPTA presented high washing fastness that the resistance merely increased from 0.043 to 0.33 /cm after 6 cycles of washing. This research demonstrates a novelty and efficient path to fabrica... Read More

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Utilizing carbon-laminated electrodes on perovskite solar cells (PSCs) benefits from simple fabrication process and low-cost material, in addition to enhanced stability. In this method, carbon foils are laminated on the underlying hole transport layer (HTL), so the HTL/carbon electrode interface is of the utmost importance in achieving high-performance devices. Here, we develop a conductive adhesive ink, consisting of poly methyl methacrylate (PMMA), highly conductive carbon black (HCCB), and CuInS2 (CIS) nanoparticles, as the interfacial adhesive layer between the underlying CIS HTL and the top carbon electrode. Utilizing carbon foil, wetted by the proposed optimized adhesive ink layer, allows simply pressing the top carbon electrode on CIS HTL. The prepared optimized carbon-laminated PSCs lead to a maximum power conversion efficiency (PCE) of 17.2 % for the best PSC, as compared with the maximum PCE of 18.2 % for the best sample of conventional Au-based PSC. Furthermore, the average PCE of the fabricated optimized carbon-laminated PSCs has kept almost 92 % of the average maximum PC... Read More

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Electrically conductive adhesives (ECAs) are mainly used in integrated circuit (IC) packaging, light-emitting diode (LED) packaging and other electronic industries to replace traditional solders and lead-free solders. The electrical conductivity and mechanical properties are contradictory with an increase in the content of conductive fillers. Therefore, there is a continuous need to improve electrical conductivity without serious damage to the mechanical properties of ECAs. In this work, a tetra-functional polyurethane acrylate oligomer was used as the main composition of silver filled one-component ECAs to improve performance. By introducing the tetra-functional oligomer, low volume resistivity with good adhesion characteristics was achieved. The volume resistivity and lap shear strength of the silver flake filled ECAs were studied systematically. The ECA with 30.6 vol% content of silver flakes exhibits low volume resistivity of 1.02 107 m, with a lap shear strength of 8.995 MPa.

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In this work, we present results on various low-temperature approaches for the metallization and interconnection of high-efficiency solar cells as silicon heterojunction (SHJ) or perovskite silicon tandems. By using fine line screen printing for the cell metallization and Ag-free or -reduced interconnection technologies, we demonstrate the potential of these approaches both for SHJ and perovskite silicon tandem cells. Furthermore, low-temperature (LT, 200 C) or ultra-low-temperature (ULT, 150 C) processes are utilized for metallization and interconnection to treat these temperature-sensitive solar cells with a reduced energy consumption. We compare LT soldering of SHJ cells with Pb-free alloys to state-of-the-art soldering processes and interconnection with electrically conductive adhesives (ECAs). For successful module integration of perovskite silicon tandem solar cells, these findings provide the basis to build full-size tandem modules with different interconnection technologies.

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A back contact solar cell module with improved efficiency and reduced manufacturing cost. The module comprises small back contact solar cells with doped regions arranged in a specific pattern to prevent electrical shorts, and a conductive adhesive on the back plate to connect the cells. The cells are electrically isolated using a reflection-enhancing laminated passivation film, eliminating the need for additional insulating materials and process steps. The module is fabricated by stacking and laminating the cells, eliminating the need for welding belts and integrally molded back plates.

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A new concept for anisotropic conductive adhesive (ACA) based on a predefined number of electrically conductive particles captured at individual interconnects is introduced. Capillary assembly method is applied to deposit conductive particles on a patterned polydimethylsiloxane (PDMS) carrier. These particles are transferred to electrical pads on a substrate whose surface is laminated with a non-conductive adhesive film. A die is then aligned and thermocompression bonded to the substrate. A yield as high as 97.8% is obtained for the particle deposition process while the yield of transferring particle process is almost 100%. Bonded samples achieve 63% of interconnects having the exact predefined number of conductive particles. The measurements of electrical resistance and contact area between particles and substrate indicate the formation of electrical paths between the electrical pads and conductive particles. This work has demonstrated the feasibility of ACA interconnects with conductive particles localized only between mating electrical pads on the die and substrate, but not outsid... Read More

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The effect of the chemical factors on electrical resistivity and interfacial electrical resistivity between silver-plated aluminum filled electrically conductive adhesives composed of polyhydroxyurethane-based binders and metal electrodes was investigated. Three types of polyhydroxyurethanes having different average molecular weights were used for the adhesives. The effect of the isocyanate cross-linker on the electrical resistivity differs depending on the difference in the average molecular weight in the binders. The interfacial electrical resistivity was increased by decreasing the molecular weight of the polyurethane binder. In addition, the isocyanate cross-linker was found to affect the interfacial electrical resistivity with copper electrodes. These results suggest that the binder chemistry of flexible electrically conductive adhesives influence both of electrical resistivity and interfacial electrical resistivity with metal electrodes.

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Conductive adhesive joints were created from two types of electrically conductive adhesives with isotropic electrical conductivity by the adhesive mounting of resistors with "zero" resistance on the test board with copper pads. Both adhesives were from the same manufacturer, one was one-component and the other two-component. Joints were loaded first climatically, and then by current pulses. Climatic loading was carried out for one group of joints at normal temperature and 99 % relative humidity, for the other group of joints in an environment with a temperature of 85 C and relative humidity of 85 %. The exposure time was always 300 hours. Then the joints were loaded with current pulses with a frequency of 50 Hz for 20, 50, and 100 minutes. The amplitudes of the current pulses were 5, 15, and 40 A, respectively. The semi-wide pulse was 2 .s The resistance of joins was measured in the four-point arrangement. Climatic loading of joints made of two-component glue caused, in the case of both types of loading, only small changes in the resistance of the joints. With one-component adhesiv... Read More

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Dicing tapes are commonly employed in semiconductor processing, and acrylic pressure-sensitive adhesive (PSA) tapes play an essential role. Since the semiconductor products are quite sensitive to electrostatic discharge (ESD) problems, high quality with anti-static properties are required for dicing tapes. The general dicing tapes can easily accumulate electrostatic charge at voltage up to 10kV or so. Such high electrostatic voltage may cause severe product defects due to ESD in the following semiconductor manufacturing processes. In this study, we developed a new acrylic based composite PSA by incorporating a modified reduced graphene oxide into the acrylic copolymer system via in situ polymerization strategy. The dicing tapes prepared by the composite PSA exhibited high performance of traditional non-UV tape and highly efficient anti-static properties with low surface resistivity.

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Integration of dissimilar materials is an important technology for future space solar cells. Adhesive bonding is used to integrate dissimilar materials while widely spaced, reactive conducting particles are used to achieve electrical conduction. Indium is shown to be highly reactive with Au leading to alloyed junctions. This reactive anisotropic conducting adhesive structure reliably achieves low resistance III-V and Si bonded structures with low bow and without cracking.

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Silicon heterojunction (SHJ) cells have shown record efficiencies of 23-25% in recent years and continue to show a promising pathway towards high-efficiency solar cells [1][3]. The efficiencies of these cells are typically limited by their series resistance, which results from the high resistivity of the low-temperature silver paste front-grid metallization that are required in SHJ cells. Using reactive silver ink (RSI) and dispense printing offers an alternative to fabricate solar cell front-grids with a low-resistivity compatible with low-temperature processes and all while using 97% less silver. Here we present latest results of our RSI metallization for use on TCO surfaces. We will show how these perfectly metallic inks allow us to redefine the form factor needed in advanced metallization.

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High-power and lightweight photovoltaic (PV) modules are suitable for building-integrated photovoltaic (BIPV) systems. Due to the characteristics of the installation sites, the BIPV solar modules are limited by weight and installation area. In this study, we fabricated glass-free and shingled-type PV modules with an area of 1040 mm 965 mm, which provide more conversion power compared to conventional PV modules at the same installed area. Further, we employed an ethylene tetrafluoroethylene sheet instead of a front cover glass and added an Al honeycomb sandwich structure to enhance the mechanical stability of lightweight PV modules. To optimize the conversion power of the PV module, we adjusted the amount of dispensed electrically conductive adhesives between the solar cells. Finally, we achieved a conversion power of 195.84 W at an area of 1.004 m2, and we performed standard reliability tests using a PV module that weighed only 9 kg/m2.

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To investigate the effect of surface treatment agents on electrical resistivity in an 85C/85%RH environment, copper (Cu) fillers surface-treated with oleic acid and triethanolamine were mixed with a resol-type phenolic resin to obtain the conductive adhesives. When the cured samples were exposed to 85C/85%RH, the electrical resistivity increased significantly when oleic acid and triethanolamine were individually used for the surface treatment of the fillers. However, the increase in resistivity was greatly suppressed when these surfactants were simultaneously used for the surface treatment. This suggests that interfacial chemistry is a key for designing advanced Cu-filled adhesives.

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In this study, Electro-Adhesive Gel Sheet (EAGS) was fabricated. It is suggested that the electrical resistance characteristics of EAGS could be applied as slip detection sensors or contact detection sensors. EAG is a functional elastomer which can change surface adhesiveness depending on an electric field, and EAGS is a sheet of EAG fabricated on a flexible electrode sheet. It was found that slipping on the surface when grasping an object or contact with a grounded conductor changes the resistance inside the EAGS, and the mechanism was analyzed from an engineering point of view.

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The effects of temperature and time (200, 250 and 300 C for 15 h in total) on the electrical resistivity and phases of conductive adhesives were studied. Also, the effect of filler content (70 to 85 wt%) and graphite addition (2 to 15 wt%) on the performance of conductive adhesives in terms of electrical resistivity were investigated. These adhesives were prepared from [email protected] particles containing 20 and 50 wt% of silver. Two-point conductivity measurements, SEM, XRD, and TG/DSC analyses were used to evaluate the properties of the adhesives. The results showed that at a constant filler content, the electrical resistivity of adhesives prepared from powder containing 20 wt% silver increases with exposure time. However, the majority of the adhesives prepared from powder containing 50 wt% of silver under similar oxidation conditions had almost constant electrical resistivity. Moreover, the results of temperature change on the electrical resistivity showed that the electrical resistivity of adhesives prepared from powder containing 20 wt% of silver increases with temperature, a... Read More

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The conductive adhesives were made using Ag-coated Cu and V2CTx + Ag + MWCNTs + Ag composites as fillers. The effects of V2CTx + Ag + MWCNTs + Ag composites content on the conductivity and microstructural properties of the conductive adhesives were investigated using two-point resistance measurements, scanning electron microscopy and XRD, respectively. The results showed that when the Ag package Cu content was 70%, the resistivity increased inversely with the V2CTx + Ag + MWCNTs + Ag (0.3%0.6%) content. Two-dimensional V2CTx + Ag + MWCNTs + Ag composites were obtained by solution mixing, offering the possibility to build up a large number of conductive networks. The synergistic effect of the Ag-claded Cu and V2CTx + Ag + MWCNTs + Ag composites significantly reduces the percolation threshold and conductivity of the conductive glue. In particular, the resistivity of the conductive glue is only 3.52 106 m at a content of 70% Ag-coated Cu and 0.3% V2CTx + Ag + MWCNTs + Ag composites. Inside the epoxy resin Ag-coated Cu is connected to each other to form a conductive pathway and V2C... Read More

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Electrically conductive adhesives (ECAs) are an alternative to soldering technology for solar cell interconnection, offering low-temperature and lead-free processing. ECAs are especially relevant for novel, often temperature sensitive high-efficiency cell types such as silicon heterojunction technology (SHJ). ECA suppliers offer a large number of products with different characteristics. In the current work most important ECA properties and their thresholds relevant for industrial string production are identified. They are compiled into an efficient testing scheme, which allows quick pre-selection of products suitable for further tests in the production environment. The proposed scheme includes determination of curing time with differential scanning calorimetry (DSC), investigation of the mechanical stability of the bond with a 90 peel test, one-cell modules production and their I-V and EL measurements to assess initial ECA performance, damp heat (DH) and accelerated thermocycling (aTC) testing for early determination of severe material or design flaws. In order to illustrate the app... Read More

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Polymeric nanocomposites composed of an organic matrix and inorganic nanoparticles makes a useful union of the polymer functionalities, such as low weight and moldability, with the good mechanical, thermal and electrical properties of the nanofillers. The possibilities to improve mechanical or thermal properties, developing a new material, by nanoparticles, have found applications in both academia and industry. To increase the application of adhesive bonding, many researchers have developed special hybrid welding technologies to improve bonding properties. Although epoxy resins have presented the disadvantage of not being electrically conductive as a matrix for adhesives electrical conductivity is a necessary property for hybrid joints of adhesive and resistance spot welding techniques. In the way to promote the weldability in adhesive joints, the objective of this paper is to develop a conductive structural adhesive by adding nanoparticles in a well-established structural adhesive. The results show that multiwalled carbon nanotubes can be the desirable filler to improve the elec... Read More

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This article addresses the research and development of a reliable interconnection technique for mounting surface mounted device components onto newly developed conductive stretchable textile ribbons. The alternative nonconductive adhesive bonding in which electrical contact is realized only by mechanical pressure and fixed by an adhesive and the conventional soldering technique were selected for examination. Assessment of the performance of these techniques and their usability for interconnecting components on conductive textile ribbons was also our research goal. Reliability tests of the electrical and mechanical properties of realized interconnections (dry heat, damp heat, washing, electrical current load, jerk, and stretch tests) were realized. The results show that the nonconductive adhesive technique results in good mechanical properties and acceptable median electrical resistance of less than 2 even after 90 washing cycles. It is also very gentle and fully compatible with textile production due to the maximal processing temperature lower than 70C, without the risk of short c... Read More

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Ohmic contacts are of great importance in the quality and reliability of electronic circuits and also in the photovoltaic field. To characterize the electrical performance of such contacts, the contact resistivity is a well-known figure of merit applicable for such a task. However, its determination is still a difficult topic due to an observed dependence of the contact resistivity on the contact size for test structures in the nano-, micro-or millimeter scale, which should not be the case. The Transmission Line Method is the most prevalent and widely used method to determine the contact resistivity of planar devices, such as the joints based on conductive adhesives reviewed in this study. However, its reliability is questionable when the adhesive bulk is considerably more resistive than the contact itself, hence, the Contact End Resistance method is also reviewed. This method uses the same test structures but a different model of the contact, which improves the determination of the contact resistivity. According to our results, both methods still exhibit a dependence on contact area... Read More

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The addition of V2CTx two-dimensional materials as auxiliary fillers in conductive adhesives can increase the contact area between conductive particles inside the matrix effectively reducing the resistivity of epoxy resin conductive adhesives. The V2CTx/Ag/rGO/MWCNTs fillers inside the epoxy resin will connect more Ag-clad Cu particles to form a conductive pathway, but its excessive content will be aggregated inside and thus increase the resistivity of the conductive adhesive. The volume resistivity of ECAs increases from 4.4 106 m to 1.15 105 m when the V2CTx/Ag/rGO/MWCNTs content of 0.1% increases to 0.34%. The Ag-clad Cu particles are interconnected inside the epoxy resin to form an electron transfer network. Inside the epoxy resin substrate Ag-clad Cu particles and V2CTx/Ag/rGO/MWCNTs interconnects to form a larger conductive network, so that the conductive adhesive shows good conductive properties.

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The addition of V2CTx two-dimensional materials as auxiliary fillers in conductive adhesives can increase the contact area between conductive particles inside the matrix effectively reducing the resistivity of epoxy resin conductive adhesives. It is mainly because V2CTx/Ag/rGO/MWCNTs auxiliary fillers inside the epoxy resin will connect more Ag-clad Cu to form a conductive pathway, but its excessive content will be aggregated inside and thus increase the resistivity of the conductive adhesive. The volume resistivity of ECAs increases from 4.410-6 m to 1.1510-5 m when the V2CTx/Ag/rGO/MWCNTs content of 0.1% increases to 0.34%. The Ag-clad Cu is interconnected inside the epoxy resin to form an electron transfer network. Inside the epoxy resin substrate Ag-clad Cu and V2CTx/Ag/rGO/MWCNTs interconnects to form a larger conductive network, so that the conductive adhesive has good conductive properties.

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Shingled solar cells based on electrically conductive adhesive (ECA) interconnection have emerged as a commercially viable option for photovoltaic (PV) modules with attractive attributes including no soldering process (lead-free), tight packing with no gap between cells, and resulting efficiency gains. Reliability of such modules is, however, less certain due to the lack of long-term outdoor performance data. Here we report numerical simulation of thermo-mechanical stress in shingled solar cells using finite element modelling, and identify stress concentration in silicon in the interconnect region not anticipated from simpler analytical models. We also present design and fabrication of samples using ECA interconnection with geometry and characteristics that closely match production modules for realistic fatigue testing under cyclic loading. The setup is combined with real-time electrical measurements that permit monitoring of fatigue-induced changes in the electrical resistance of ECA joint. Detailed measurements are presented using samples with different types ECA and varying patter... Read More

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