Metal-free organic conductive adhesive materials for solar energy conversion

Abstract

Disclosed are materials, devices, systems, and methods for an intrinsically conductive adhesive (ICA) that can be used to interconnect solar modules. In some aspects, a method can include acquiring a material comprising an insulating epoxy matrix; synthesizing the ICA by replacing the insulating epoxy matrix with a conducting polymer matrix free of electronic filler material; and optimizing at least one functional property of the ICA by modifying one or more formulations of the ICA including incorporating one or more of a crosslinker, polar dopants, adhesion promoters, or carbon nanotubes into the ICA.

Description

METAL-FREE ORGANIC CONDUCTIVE ADHESIVE MATERIALS FOR SOLAR ENERGY CONVERSIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent document claims priority to and benefits of U.S. Provisional Application 63 / 556,358, entitled “SILVER-FREE, ALL-ORGANIC CONDUCTIVE ADHESIVES FOR SHINGLED SOLAR CELLS,” and filed on February 21, 2024. The entire content of the above noted patent application is incorporated by reference as part of the disclosure of this patent document.TECHNICAL FIELD

[0002] This patent document is generally related to the use of conductive adhesive materials for solar energy conversion technologies.BACKGROUND

[0003] Photovoltaic (PV) systems and techniques generate power using devices that absorb energy from sunlight and convert it into electrical energy through the use of semiconducting materials. These devices, commonly known as solar cells, are connected to form larger powergenerating units known as modules or panels (e.g., solar panels). PV systems generate power through the photovoltaic effect, which is a physical phenomenon where light is absorbed, causing excitation of an electron or other charge carrier to a higher-energy state. The excited charge carrier is contained within the material, by which an electric potential (or voltage) is produced due to the separation of charges.SUMMARY

[0004] Disclosed herein are methods, materials, compositions, formulations, products, and systems that pertain to conducting conjugated polymers as an intrinsically conductive adhesive (ICA) for a variety of energy conversion device applications. The disclosed conducting conjugated polymer ICA materials do not require metal (e g., silver (Ag)), thereby allowing replacement of silver-based electrically conductive adhesives (ECAs) to create interconnects in shingled solar modules for some example implementations of the disclosed technology.

[0005] In some aspects, a method of producing an intrinsically conductive adhesive (ICA) forinterconnecting solar modules in accordance with the present technology can include acquiring a material comprising an insulating epoxy matrix; synthesizing the ICA by replacing the insulating epoxy matrix with a conducting polymer matrix free of electronic filler material; and modifying one or more formulations of the ICA by incorporating at least one of a crosslinker, polar dopants, adhesion promoters, or carbon nanotubes into the ICA.

[0006] In some aspects, an engineered material for constructing solar apparatus in accordance with the present technology can include a ir-conjugated material comprising a conducting polymer matrix free of electronic filler material, wherein the 7t-conjugated material includes at least one of a crosslinked network, polar dopants, adhesion promoters, or carbon nanotubes, wherein the engineered material is electrically conductive.

[0007] In some aspects, a solar assembly system in accordance with the present technology can include a plurality of solar modules configured to receive solar radiation and convert the solar radiation to electrical power; and an intrinsically conductive adhesive (ICA) coupled to and interconnecting the plurality of solar modules such that the plurality of solar modules are in thermal and electrical communication with each other, wherein the ICA comprises art-conjugated material comprising a conducting polymer matrix.

[0008] These, and other, features and aspects are further disclosed in the present document.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIGS. 1A-1F show example data illustrating the impact of removing silver from electrically conductive adhesives for shingled solar modules.

[0010] FIG. 1G shows a diagram depicting a conducting polymeric matrix for an example embodiment of a conducting conjugated polymer ICA material in accordance with the present technology.

[0011] FIGS. 2A-2D show example properties and data of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-based formulations based on the disclosed technology.

[0012] FIGS. 3A-3F show example data plots illustrating some mechanical properties of PEDOT-based electrically conductive adhesives based on the disclosed technology.

[0013] FIGS. 4A-4E show example photovoltaic characteristics of shingled solar cells based on the disclosed technology.

[0014] FIGS. 5A and 5B show, respectively, example resistivity and conductivity data ofadhesives based on the disclosed technology.

[0015] FIGS. 6A-6E show example results obtained in a study performed in accordance with the disclosed embodiments.

[0016] FIGS. 7A-7F show additional example results obtained in a study performed in accordance with the disclosed embodiments.

[0017] FIG. 8 shows a flow diagram of an example method based on the disclosed technology.

[0018] FIG. 9 shows an example embodiment of a solar assembly system, in accordance with the present technology.

[0019] FIG. 10 shows a diagram comparing a conventional silver-based conductive adhesive material with an example embodiment of an ICA material in accordance with the present technology.

[0020] FIG. 11 shows an example plot of the annual percentage of silver used for solar PV relative to annual available supply.

[0021] FIGS. 12A and 12B show example viscosity data of disclosed embodiments of PEDOT:PSS solutions.

[0022] FIG. 12C shows example shear modulus data of some disclosed embodiments of PEDOTPSS solutions.

[0023] FIGS. 13A-13C show photographs of example PEDOT-based fdms which were investigated in an example study performed in accordance with the disclosed embodiments.

[0024] FIGS. 14A-14F show some example results obtained in a study performed in accordance with the disclosed embodiments.

[0025] FIG. 15 shows a diagram of an example fabrication scheme for shingled solar cells in accordance with the disclosed embodiments.

[0026] FIGS. 16A and 16B show images of example ribbons that can be used to form part of shingled solar cells based on the disclosed embodiments.

[0027] FIG. 17 shows an example I-V curve of obtained in an example study performed in accordance with the disclosed embodiments.

[0028] FIG. 18 shows exemplary series resistance data obtained in an example study performed in accordance with the disclosed embodiments.

[0029] FIGS. 19A and 19B shows microscope images of example PEDOT :PS S films obtained in an example study performed in accordance with the disclosed embodiments.

[0030] FIG. 20 shows microscope images of example embodiments of PEDOT:PSS films based on the disclosed technology.

[0031] FIGS. 21-26 shows images of example embodiments of PEDOT:PSS films stored under different relative humidity conditions and for different durations of the relative humidity conditions.

[0032] FIG. 27 shows a photograph depicting water-assisted delamination of an example embodiment of a PEDOT:PSS film based on the disclosed technology.

[0033] FIGS. 28A and 28B show some example results obtained in a study performed in accordance with the disclosed embodiments.

[0034] FIGS. 29A and 29B show photographs of an experimental setup of a three-point bend test performed in accordance with the disclosed embodiments. FIG. 29C shows photographs of example cells shingled with PEDOT-based ECAs after three-point bend tests. FIGS. 29D-29E show example results obtained from three-point bend performed in accordance with the disclosed embodiments.

[0035] FIG. 30A shows example images obtained during lap joint shear tests which were performed in accordance with the disclosed embodiments.

[0036] FIG. 30B shows example shear stress-strain curves from the lap joint tests.

[0037] FIG. 30C is an optical showing the thickness of an example lap joint of cells shingled using a disclosed embodiment of PEDOT:PSS.

[0038] FIGS. 31 A-3 IF show example results obtained in a study performed in accordance with the disclosed embodiments.

[0039] FIG. 32A shows a chemical structure of Block-6.

[0040] FIGS. 32B-32G show example results obtained in a study performed in accordance with the disclosed embodiments.

[0041] FIG. 33 shows an example plot comparing cost of silver required for busbar and shingled solar cell architectures that can be achieved in accordance with the disclosed embodiments.DETAILED DESCRIPTION

[0042] Silver is currently the most critical resource, both in terms of material scarcity and economic stability, required for scaling up installation of solar photovoltaic (PV) modules. Toreach the necessary installed capacity to achieve a net-zero emissions economy by 2050, projections estimate that >90% of global silver reserves would be required to be solely dedicated to solar PV. In a typical silicon solar cell, silver is used for metallization of both the front and back sides to form both fingers and busbars. To connect these cells together, copper connections are attached at the busbars to create a solar cell string. However, a more efficient way of connecting solar cells together is a shingling method, where cells are glued together like rooftop shingles (with an overlap), which allows for silver busbars to be removed. Though this reduces the silver required for metallization, the conductive adhesives used to connect cells typically employ silver as the electronic filler, which both contributes significantly to silver consumption and also makes the conductive adhesive expensive.

[0043] Solar modules typically require soldered busbars for connecting solar cells to one another, which poses several sources of inefficiencies. Shingling solar cells like rooftop shingles (i.e., overlapping) offers a considerable number of benefits, including increased efficiency. However, the conductive glues used to join these solar cells together are typically made by mixing a significant load of silver (70-80 wt%) into an epoxy or polymer matrix. As such, this composition makes these conductive adhesives extremely expensive, and they consume a lot of silver, which is a highly critical material.

[0044] The process of shingling solar cells is well known and researched. Likewise, silverbased conductive adhesives are already produced commercially, some specifically meant to be used for shingling solar cells. Other research focused on improving the conductive adhesive formulation typically does so by replacing or reducing silver with copper-based materials, carbon nanotubes, or hexagonal boron nitride. Additionally, other compositions have made modifications to the polymer matrix, solvent, or binders used to reduce the amount of electronic filler.

[0045] The projected silver consumption needed for the accelerating growth of solar photovoltaics (PV) is unsustainable and poses a critical materials challenge. Techniques related to the use of silver-free, intrinsically conductive adhesives designed from 7t-conjugated polymers offer a realistic and low-cost strategy for sustainably scaling up solar PV deployment using high- efficiency solar modules.

[0046] Disclosed herein are methods, materials, compositions, formulations, products, and systems that pertain to conducting conjugated polymers as an intrinsically conductive adhesive (ICA) for a variety of energy conversion device applications. The disclosed conducting conjugatedpolymer ICA materials do not require metal (e.g., Ag), thereby allowing replacement of silverbased electrically conductive adhesives (ECAs) to create interconnects in shingled solar modules for some example implementations of the disclosed technology.

[0047] The disclosed embodiments relate to the use of an all-organic (silver free, electronic filler-free) conductive adhesive for shingling solar cells. Some disclosed embodiments replace silver-based ECAs with a conductive polymer as the shingled interconnection, removing the need for silver filler entirely. The disclosed embodiments, among other features and benefits, offer an avenue for low-cost conductive adhesives that can be used for high efficiency shingled solar modules while drastically reducing the silver consumption, thus also conserving a critical resource. Furthermore, employing a conducting polymer as the ICA opens opportunities for tuning the electronic, mechanical, and adhesive properties for designing next-generation electronic interconnects. The all-organic (polymer) adhesives disclosed herein can replace silver-based adhesives and show similar performance in a shingled solar module.

[0048] The projected silver consumption needed for the accelerating growth of solar photovoltaics (PV) is unsustainable and poses a critical materials challenge. Techniques related to the use of silver-free, intrinsically conductive adhesives designed from ^-conjugated polymers offer a realistic and low-cost strategy for sustainably scaling up solar PV deployment using high- efficiency solar modules.

[0049] In some implementations, the disclosed silver-free conductive adhesives based on a conducting polymer matrix can be used to replace silver-based adhesives for shingled solar modules and can significantly reduce the silver demand as well as the material cost. Embodiments disclosed herein open the door to designing new n-conjugated materials that function as intrinsically conductive adhesives for solar PV applications.

[0050] Some example embodiments of the disclosed materials include all-organic (silver free, electronic filler-free) conductive adhesives for shingling solar cells can achieve similar performance compared to commercial silver-based conductive adhesives. This offers an avenue for low-cost conductive adhesives that can be used for high efficiency shingled solar modules while drastically reducing the silver consumption by solar photovoltaics, thus also conserving a critical resource. As will be described in further detail in the description that follows, some disclosed embodiments use an intrinsically conductive polymer interconnect as a replacement for conventional, silver-based ECAs.

[0051] 7t-Conjugated (semiconducting or conducting) polymers differ from conventional polymers in their chemical structure (i.e., an alternating double and single bond motif), which in turns allows for charge conduction and transport. As such, 7t-conjugated polymers can be rationally designed to function as intrinsically plastic (e.g., stretchable and flexible) electronics. However, considerably little focus has been dedicated to designing 71-conjugated materials to behave as conducting or semiconducting adhesives, particularly for electronic interconnects. Among the most common ^-conjugated materials is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which is a polyelectrolyte complex with low intrinsic conductivity, which can be doped with polar small molecules to significantly increase the bulk conductivity (e.g. ,>2500 S cm'1) and surface conductivity of the solid film. Recent efforts in polymer design and synthesis have also yielded the development of 7t-conjugated polymers with high intrinsic conductivities (e g., poly(benzodifurandione).

[0052] In some example embodiments in accordance with the present technology, the disclosed conducting conjugated polymer ICA materials repurpose PEDOT:PSS as a silver-free conductive adhesive for interconnects between shingled solar cells. Replacing the insulating epoxy matrix with an intrinsically conductive matrix allows for the reduction or removal of electronic filler needed to achieve resistivities comparable to silver-based EC As, and thus achieve similar electronic performance in shingled solar modules. The use of a conducting polymer as the adhesive matrix additionally opens a wealth of opportunities for tuning the electronic properties, mechanical properties, and adhesive functionality to design next-generation, intrinsically conductive adhesives. Many of these strategies can be realized by rational design of the chemical structure or blending with a non-conductive polymer matrix. Most importantly, the removal of silver in the ECA formulation significantly reduces the demand for silver by solar PV, the increased cost associated with using silver-based ECAs, and the environmental footprint of the resulting module, offering an avenue forward to low-cost and sustainable conductive adhesives for shingled solar PV.

[0053] For example, solar cells shingled with PEDOT:PSS-based ICAs have similar photovoltaic (PV) performance metrics to those shingled with commerci ally-available silver-based ECAs, as well as similar stability when subjected to thermal cycling. While today’s dominant busbar-based module architectures require -15.8 mg / W of silver, shingling modules with ICAs can reduce silver consumption to -6.3 mg / W. These findings suggest that the design of jt-conjugated materials for intrinsically conductive adhesives could offer a realistic strategy for sustainable deployment of lower-cost, high-power solar modules.

[0054] FIGS. 1A-1F show example data to illustrate the impact of removing silver from electrically conductive adhesives for shingled solar modules. FIG. 1 A shows a diagram comparing conventional silver-based electrically conductive adhesives (ECAs) (left) to an example embodiment of all-organic (silver-free) conductive adhesive materials (right) for shingled solar cell applications. FIG. IB shows a comparison of bulk cost between common interconnect materials. FIG. 1C shows the annual supply and demand of silver, relative to the demand of silver from solar PV and price. FIG. ID shows the projected demand of silver relative to total PV capacity installed for busbar and shingled modules (both silver-based and silver-free). In FIG. ID, open circles represent median projected estimations— with dashed lines representing high and low projections— and the dotted horizonal line is the total global silver reserve. FIG. IE shows a comparison of silver consumption for busbar and shingled PV. FIG. IF shows a comparison of current silver consumption for common silicon cell architectures using busbar and shingled interconnects.

[0055] In contrast to conventional solar modules, which are connected by soldered busbars, shingled solar modules are glued together with an electrically conductive adhesive (ECA), as shown in FIG. 1A, where the electronic fdler is typically silver.

[0056] A high loading of silver is required to form a percolated matrix throughout the adhesive (where the percolation threshold is dependent on the material composition), as well as reduce the contact resistance with the electronic substrate. In contrast, the conductivity of a PEDOT:PSS matrix is dependent on the intrinsic conductivity of the conducting polymer, the morphology of the solid film, and doping effects from organic additives. As such, while silver-based ECAs transport charge through an insulating polymer matrix from particle-to-particle contact or electron tunneling, electronic and ionic conductive pathways are formed in PEDOT:PSS networks by charge transport along and between polymer chains.

[0057] Some advantages of replacing the silver-based ECA with an all-organic ECA are related to the material scarcity and price variability of silver. Due to the high filler loadings required, the price of silver-based ECAs is directly tied to silver, which has fluctuated between 300 $ kg’1and 1500 $ kg’1since 2006. In contrast, polymer-based materials can be far cheaper as shown in FIG. IB, with the current price of PEDOT:PSS roughly one-third that of silver, despitecurrent industrial use only for niche applications (e.g., antistatic coatings). The reason for this difference is obvious: while there is a finite supply of silver that can be mined, PEDOT:PSS (and other polymeric materials) can be manufactured synthetically at large scales. As such, significantly increasing demand of silver for solar PV will likely increase the price of the ECA (due to supply constraints), while doing the same for a conducting polymer adhesive will result in the opposite effect (due to economies of scale). Indeed, from historical reports, it can be seen that the annual supply of silver has remained relatively constant (~29 kt / yr), while the demand of silver for solar PV has been steadily increasing (FIG. 1C). As a result, silver demand by solar PV currently consumes -16% of the annual supply.

[0058] To compare the silver required for scaling up solar PV and achieving a net-zero emission economy, FIG. ID shows projections of silver consumption as demanded from busbar architectures, shingled architectures with silver-based ECAs, and shingled architectures with silver-free ECAs. In FIG. ID, a linear projection was used for solar growth rather than a realistic timeline (which others have already modeled) for simplicity. Regardless, the findings provide a clear conclusion: despite shingled solar cells outperforming conventional modules in terms of efficiency, using silver-based ECAs to do so is unsustainable, as the demand of silver required far exceeds the global supply. However, a similar conclusion holds true for conventional busbar modules, which would (in optimistic projections) essentially consume the entire silver reserve. In both cases, the projected silver consumption required to fulfill a 75 TW transition to solar PV by 2050 is unsustainable. While recycling is an option, recycling silver from photovoltaic modules remains a challenge, as the current supply of end-of-life modules does not make it economically viable to scale up recycling efforts. In this sense, the long lifespan of silicon solar modules actively hinders recycling efforts by making the demand for doing so lag (by -25 years) behind the necessity of doing so.

[0059] Using silver-free ECAs for shingled connections significantly reduces the amount of silver required for metallization (as silver busbars can be removed from the cell architecture), and removes the silver contribution entirely from the ECA. Using work described elsewhere, it was assumed this corresponded to a 60% decrease in silver consumption in comparison to conventional busbar modules. With a current silver consumption of roughly 15.8 mg / W, this approximation suggests that only -6.32 mg / W is required for current (p-type, PERC) shingled modules using silver-free ECAs as shown in FIG. IE. Assuming the silver learning curve applies for shingledmodules using silver-free interconnects, a complete and immediate (but unrealistic) transition to such architectures prevents silver usage from exceeding global supply (FIG. ID). The silver learning curve, calculated elsewhere, suggests that a -5 mg / W silver consumption rate is projected to be achieved around 2050. An approximation of -6.3 mg / W for modules shingled with silver- free ECAs immediately accelerates placement of the disclosed adhesives on the learning curve by two decades (-2040) (FIG. IE). As such, development of silver-free, intrinsically conductive adhesives offers an avenue forward for decreasing the unsustainability of silver consumption by solar PV. Likewise, calculations also suggest that a switch from busbar modules to shingled modules likely has greater benefits for high efficiency n-type (particularly TOPCon and SHJ) cells in comparison to p-type PERC (which currently dominates the photovoltaic market) as shown in FIG. IF. The reason for this is because roughly the same amount of ECA is necessary to glue cells together, regardless of type, but metallization of high efficiency n-type cells demands far greater silver consumption than p-type cells.

[0060] As of 2023, the silver required for installing new solar PV accounts for -15-19 mg W’ which at the scale of current PV production totals -15% of the annual supply. Coupled with the growing rate of solar PV installation, the Ag demand in PV is projected to grow, as achieving the net-zero goals set out by the International Energy Agency and Paris Agreement requires continued PV installation growth of 25-30% annually for the next decade. However, at the current rate of Ag consumption, solar PV would require -98% of the annual silver supply by 2030. While research to reduce silver consumption in solar technologies is advancing, the scarcity of silver may inhibit short-term growth required by making solar modules more expensive to produce. This immediate challenge is further overshadowed by the long-term growth of solar required for this task, with extended projections suggesting a total installed capacity of -60-75 TW needed by 2050. To accelerate the transition to a decarbonized electrical grid, reducing the silver required for solar PV is a priority.

[0061] The current photovoltaic market is dominated by crystalline silicon, totaling >95% of the global market. These silicon solar modules are made from solar cells connected by soldered ribbons and wired together in a string. This configuration poses several sources of inefficiency, including: (1) Busbars shade the frontside of the cell; (2) Metal ribbons require gaps between cells, which further reduces the active area of the module; (3) Ribbons are subject to mechanical and thermal stresses that can result in substantial power losses (e.g., solder bond failure, damage tosoldered joints). In contrast, shingled solar modules are formed using slightly-overlapping strings of solar cells that are glued together using an electrically conductive adhesive (EC A), in a manner resembling rooftop shingles. Here, resistive losses remain along the finger length, but the areal power output is typically increased in shingled modules compared to conventional busbar designs and with better resilience to partial shading. On the other hand, shingled modules can be at a cost disadvantage because more cells are used per area in a shingled module and greater loadings of silver are used per watt.

[0062] Specifically, the ECAs used for shingled modules typically include conductive filler (e.g., silver particles) blended in an insulating adhesive polymer to form a paste, where a 70-80 wt% of silver is required to achieve conductivities >104S cm'1. The use of silver in ECA compositions poses several economic and engineering problems. First, the scarcity of silver means that the price is sensitive to supply constraints. Likewise, high loadings of electronic filler mean the cost of the ECA, and thus the shingled module, are directly tied to the price of silver. Increasing demand of silver also poses ethical and sustainability concerns, as silver mining contributes to environmental destruction and pollution. From an engineering standpoint, the composition of silver-based ECAs yield a tradeoff between the physical properties of the polymer matrix and electronic filler, potentially compromising either the mechanical performance of the adhesive or the electronic performance of the silver. This tradeoff can be exacerbated by external (e.g., thermal) stresses due to the mechanical mismatch between the metal particles and polymer matrix. Finally, from a manufacturing standpoint, silver-based ECAs can have poor shelf lives, typically due to phase segregation (from e.g., gravity or solvent volatility) resulting in non-uniform distribution of electronic filler, and thus, non-uniform conductivity and / or adhesion.

[0063] The unsustainable demand of silver creates an obstacle to the adoption of shingled architectures, as employing silver-based ECAs further exacerbates this demand. Recent research has been focused on reducing or removing silver filler in ECAs, as well as the silver needed throughout the rest of the module. Formulations have replaced silver with e.g., silver-copper composites, all-copper formulations, or carbon nanotubes. Some have developed a cost-effective formulation of silver paste with an extended shelflife by employing a capillary suspension. Some others fabricated high-efficiency silicon heterojunction solar cells with copper and tin oxide contacts. Other work has explored the use of adhesive-free interconnects, particularly by busbarbusbar lamination or laser welding aluminum foil between shingles. Some others showed thatshingled solar modules could be made from cells with busbar-free electrode layouts, reducing the silver needed for metallization by -61%. Likewise, emerging research in solar cell technology has yielded busbar-less (OBB) configurations for solder-based architectures, which is expected to significantly reduce silver demand. Similarly, recent advancements in soldered module design have also applied gapless or tiling technology to reduce active area losses.

[0064] Embodiments disclosed herein relate to the use of a conducting conjugated polymer as an intrinsically conductive adhesive (ICA) to create interconnects between solar cells.

[0065] Some advantages of the disclosed embodiments include an all-organic (silver free, electronic filler-free) conductive adhesive for shingling solar cells which can be made at low cost point due to reduced silver consumption. Furthermore, employing a conducting polymer as the ICA opens opportunities for tuning the electronic, mechanical, and adhesive properties for designing next-generation electronic interconnects. Additionally, solar cells shingled with conjugated polymer-based ICAs have similar photovoltaic (PV) performance metrics to those shingled with commercially-available silver-based electrically conductive adhesives (ECAs), as well as similar stability when subjected to thermal cycling.Example Embodiments

[0066] In an example embodiment, a silver-free conductive adhesive is formed using the 7t- conjugated polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The electrical conductivity of PEDOT:PSS may be controlled through doping. Various ICA formulations comprising PEDOT:PSS can be made by incorporating a crosslinker, polar small molecules, or multiwalled carbon nanotubes into PEDOT:PSS.

[0067] In some example embodiments, a silver-free conductive adhesive is formed using a conducting polymer matrix that is intrinsically electrically conductive. In conventional silverbased conductive adhesives, the adhesive matrix is completely insulating. This means that a high loading of silver must be added to achieve good electrical properties. In the present example embodiment, a conducting polymer matrix that is intrinsically electrically conductive is used. Instead of using an electronic filler (such as silver, silver particles, plated copper particles, etc.), polar small molecules are added (e.g., conjugated) to the conducting polymer matrix to promote morphological changes that increase the conductivity. A crosslinker is added to stabilize the polymer film and improve the cohesive strength of the material. As such, the need of any metalbased or carbon-based electronic filler is removed. This all-organic adhesive can then be depositedfrom solution onto a solar cell. To shingle solar cells together, another solar cell is immediately placed on top of the adhesive. The entire module is then heated to cure the adhesive and form a shingle.

[0068] FIG. 1G shows a diagram depicting a conducting polymeric matrix for an example embodiment of a conducting conjugated polymer ICA material 170 in accordance with the present technology. The diagram illustrates the cross-linking of conjugated polymeric strands, as described herein, that impart bulk conduction to render an intrinsically conductive adhesive material. As illustrated by the diagram of FIG. 1G, the exemplary ICA material 170 includes chains of entangled conductive polymers. The conductive polymers may comprise a 7t-conjugated polymer 171 and polyelectrolytes 172 along its backbone. The conductive polymers can be modified to form block co-polymers to impart additional functionalities to the ICA, such as mechanical toughness through constitutional substitutions in the polymer chain (e.g., Block-6) and / or by functionalization of the polymer side chains. To further manipulate mechanical properties of the ICA, crosslinking additives 175 can be introduced (e.g., GOPS). Other additives such as high boiling point solvents, adhesion promoters, or dopants can be introduced into the free volume 177 of the polymer.

[0069] One aim of the disclosed technology is to use a conducting polymer matrix as an adhesive binder for shingled solar cells in order to reduce the use of silver as an electronic filler.

[0070] An example method for fabricating an ICA comprising a 7t-conjugated material and a conducting polymer matrix, in accordance with the present technology, is disclosed. The method can include chemically modifying a base form of a PEDOT:PSS polymer by blending one or more additives to increase bulk conductivity; and further modifying the material by adding polar small molecules as secondary dopants to further increase bulk conductivity. In some embodiments, the one or more additives are metal-free. In some embodiments, additional additive(s) are added to improve mechanical robustness of the engineered material, such as GOPS to stabilize the modified PEDOT:PSS polymer. The method can furth include imparting bulk conduction to the ICA through cross-linking of conjugated polymeric strands to form the conducting polymer matrix. Using the disclosed method, an ICA can fabricated despite PEDOT:PSS not being designed for use as a conductive adhesive.

[0071] The conductivity of PEDOUPSS is typically low, and thus additives can be blended in order to increase the bulk conductivity of PEDOT:PSS. Polar small molecules (e.g., DMSO, EG,glycerol) may be used as secondary dopants for increasing the bulk conductivity without inclusion of metal filler. In addition to improving the mechanical robustness, GOPS may also used to stabilize the PEDOT:PSS film (i.e., under continuous thermal or electrical cycling) and reduce moisture ingress (e.g., swelling). To improve the dispensability of the material and reduce spreading (for a consistent adhesive dispense line) before use, water may be removed from PEDOT:PSS using a rotary evaporator to achieve a desired viscosity (e.g., ~10 Pa-s). In some example embodiments, dispensability of the material can be modified by adding a solvent to the material, removing a solvent from the material, or exchanging a solvent of the material. Some preliminary investigations suggested that, in some disclosed adhesives, the ideal loading of DMSO, EG, and glycerol is 8 vol %, 8 vol%, and 5 vol%, respectively.

[0072] In some other example adhesives, a custom-synthesized PEDOT:PSS copolymer (PEDOT:PSSl-b-PPEGMEA6) was used for the adhesive matrix since it was hypothesized that the soft, stretchable PPEGMEA block would increase the viscoelastic adhesion of the material. However, it was found that Block-6 showed significantly higher resistivities compared to PEDOT:PSS when blended with polar additives and cast in a solid film, suggesting weaker secondary doping effects.Example Implementations

[0073] The following description describes some example implementations of some embodiments of the disclosed conducting conjugated polymer ICA materials, devices, systems, and methods, e g., using various electronic and mechanical techniques to characterize the ICA materials.

[0074] In one example study, shingled solar modules were formed by gluing together Sunpreme 4Busbar Silicon Cells using different formulations of the disclosed ICA materials comprising modified PEDOT:PSS. These formulations were compared to different commercially available formulations of conventional silver-based electrically conductive adhesives (ECAs). Shingled modules were subjected to thermal cycling tests from -40 °C to 85 °C as an accelerated degradation test. At 50-cycle intervals throughout the degradation test, the performance of shingled modules was characterized using IV measurements, reverse-current overload (RCO) tests, and three-point bend tests. For RCO tests, samples were subjected to a constant current of 4 A, 6 A, 8 A, and 10 A for 120 s, with an I-V curve taken immediately after each step. To isolate the effect of the ICA composition on the resistive losses, the series resistance (RS) was extractedfrom each I-V curve using the integration of the I-V curve as described elsewhere. To further characterize the mechanical behavior of PEDOT:PSS as an adhesive lap joint (particularly in comparison to commercial ECAs), tensile tests and lap joint shear tests were performed. Finally, to further understand the degradation behavior of PEDOT:PSS, three different degradation tests were performed on blade coated films (to mimic common shear deposition techniques used to deposit polymer films for commercial processes). These PEDOT:PSS films were subjected to 65% RH at 25 °C, 65% RH at 65 °C, and 100% RH (a water bath) at 65 °C.

[0075] In the description that follows, two example studies performed using adhesives based on the disclosed technology are described.

[0076] FIGS. 2A-2D show example data, related to characterization and degradation of PEDOT:PSS-based formulations, obtained in an example study. In the example study, optimizing the composition of PEDOT-based formulations for use as a conductive adhesive involved exploration of two different PEDOT-based matrices, the use of a silane-based crosslinker (GOPS), and the addition of polar small molecules and multi-walled carbon nanotubes (MWCNT) as silver- free additives. FIG. 2A shows the chemical library and schematic morphology of PEDOT:PSS- based films explored in the example study. The two PEDOT-based matrices compared were a commercial formulation of PEDOT:PSS and a copolymer with a poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMEA) block attached in a 6: 1 ratio relative to PSS (Block-6), the copolymersynthesized in accordance with disclosed techniques.

[0077] FIG. 2B shows viscosity data, obtained in the example study, of PEDOT:PSS relative to solid mass in a dispersion. To reduce the spreading behavior of PEDOT:PSS (as PEDOT:PSS is ~1.3 solid wt% dispersed in water) and control the dispense line of the adhesive, a rotary evaporator was used to first reduce the amount of water and increase the viscosity. An appropriate viscosity was determined to be roughly -10 Pa-s, which corresponded to -3.5 solid wt%. Further concentration past -5 wt% resulted in gelling, which is possibly favorable for printing techniques, but unfavorable for syringe deposition as used here. As such, concentrated solutions of PEDOT:PSS and Block-6 were doped with common organic additives in order to investigate the achievable electronic properties of solid films deposited by shear deposition.

[0078] FIG. 2C shows resistivity data of PEDOT:PSS, PEDOT:PSS / MWCNT, and Block-6 films relative to small molecule dopant (8 vol% DMSO, 8 vol% EG, 5 vol% glycerol, 1 vol% GOPS, 1 wt% MWCNT) added. Three silver-based ECAs are also shown for comparison. Theuse of Block-6 for the adhesive matrix was initially explored because it was hypothesized that the soft, stretchable PPEGMEA block would increase the viscoelastic adhesion of the material. However, it was found that Block-6 showed significantly higher resistivities compared to PEDOT:PSS when blended with polar additives and cast in a solid film, suggesting weaker secondary doping effects. This observation is in agreement with the understanding of the secondary doping mechanism, where the increase in conductivity for PEDOT:PSS is in part attributed phase segregation which results in the formation of larger PEDOT domains. The attachment of the PPEGMEA block to PSS likely weakens this morphological change. While the PPEGMEA chains likely contribute to the ionic conductivity, the copolymer also has a significantly increased proportion of electrically insulating material, resulting in this increased bulk resistivity. Likewise, although the addition of MWCNT decreased the resistivity compared to pristine PEDOT:PSS, the addition of polar dopants rendered the inclusion of MWCNT redundant (as the resistivities of doped PEDOT:PSS were lower than that of doped PEDOT :PSS / MWCNT). Additionally, it was observed that crosslinking any doped PEDOT-based film with 1 vol% GOPS resulted in resistivities comparable to their non-crosslinked counterparts, in agreement with work performed elsewhere. Preliminary design of experiment (DOE) investigations suggested that the ideal loading of DMSO, EG, and glycerol for the concentrated solutions were 8 vol%, 8 vol%, and 5 vol%, respectively. In comparison to the PEDOT-based formulations, lower resistivities were observed for films of all three silver-based EC As (CA-183, ECA-561-147-2, and ECA-5802), with values of around 8* 10‘5Q-cm (compared to PEDOT:PSS / DMSO, with a resistivity of around 5* 10'4Q-cm).

[0079] In the example study, GOPS was used as the crosslinker to stabilize the morphology of the PEDOT:PSS film, create a crosslinked network within the film for increasing energy dissipation, and increase the adhesion at the cell / ECA interface. Likewise, crosslinking with GOPS reduced the ingress of moisture (which could lead to swelling, as well as moisture-assisted delamination and decohesion). To quantify the effect of heat and humidity on PEDOT:PSS films, moisture and thermal accelerated degradation tests were conducted in three types of environments: 25 °C and 65% relative humidity (RH), 65 °C and 65% RH, and a 65 °C water bath (100% RH). FIG. 2D shows normalized conductivity of PEDOT:PSS films under ISOS-D-3 (65 °C, 65% relative humidity) degradation conditions. Little change was observed for films placed in (essentially) atmospheric conditions. Under ISOS-D-3 degradation conditions, onlyPEDOT / glycerol and PEDOT / glycerol / GOPS outperformed CA-183 as a commercial EGA standard in terms of relative conductivity. However, the absolute conductivity of CA-183 was still greater than all PEDOT-based films, even after 20 days. A similar trend was observed for the 65 °C water bath. Only crosslinked films were compared because non-crosslinked films immediately delaminated from the glass substrate when submerged in water. Qualitatively, microscope images taken periodically throughout the 65 / 65 tests showed moisture-driven delamination (wrinkling) and decohesion (crack formation). Partial swelling and discoloration of the crosslinked films under the same conditions was also observed from optical microscopy, suggesting degradation at the surface of the film.

[0080] Notably, for both 65 / 65 (temperature / RH) and 65 / 100 tests, a combination of heat and moisture likely resulted in morphological rearrangement of the solid film, resulting in domains measuring significantly higher sheet resistances. Other studies suggest that the morphology of PEDOT:PSS can suffer from temperature and moisture-driven degradation mechanisms. Previous work suggests that PSS chains preferably reorient towards solution under the presence of temperature and moisture, as loosely-bound polymer chains experience partial dissolution in water. This hypothesis agrees with the relative conductivity measurements, shown in FIG. 2D, taken for films held under 65 / 65 and 65 / 100 degradation conditions. In addition, others have previously observed instability of electrical conductivity due to thermal ageing resulting in the shrinking of conductive domains, which supports the general decrease in conductivity relative to thermal ageing, as well as qualitative observations from four-point probe measurements (suggesting an increasing number of regions of the film with higher sheet resistances relative to time of degradation). However, in ambient conditions (e.g., 25 / 65), contact angle measurements suggest that PEDOT chains preferentially reorient towards the air interface, which agrees with findings showing little change in relative conductivity for all PEDOT:PSS films, even over 30 days. Even for crosslinked samples, when submerged over 20 days in a water bath at 65 °C, films from later timepoints were typically than their pristine counterparts.

[0081] In all such cases, degradation mechanisms seemed to be heavily moisture-driven, with other literature suggesting that gentle heating alone (i.e., up to 80 °C) shows highly similar ageing behavior (at least, in terms of conductivity) relative to room temperature, and possibly slightly favorable increases in electrical conductivity due improvements to film crystallinity and carrier mobility. While moisture can be a concern for solar modules employing polymer (e.g., EVA) backsheets and encapsulants, moisture ingress is of little concern for glass-glass modules. As such, it was assumed that a PEDOT-based ECA would experience little moisture-driven degradation if employed in encapsulated modules. Likewise, with operating temperatures typically between 10 °C and 85 °C, it was hypothesized that thermal ageing would not be a significant concern for proof- of-concept devices.

[0082] To compare the adhesive functionality of the different EC As investigated in the example study, lap shear, three-point bend, and tensile tests were performed. FIGS. 3A-3F show example data comparing the mechanical properties of PEDOT-based electrically conductive adhesives in the example study to silver-based adhesives.

[0083] Lap shear tests unveil significant differences in the adhesive performance of PEDOT- based adhesives in comparison to commercial, silver-based ECA standards. Others have previously described mechanical figures of merit necessary for interconnected j oints for shingled solar modules.

[0084] FIGS. 3A-3C show exemplary figures of merit for shingled interconnections. Analysis performed by others suggests that the ratio G / zstr (shear modulus to the adhesive strength), is a crucial parameter that should be minimized to reduce mechanical failure, where the shear modulus should be minimized and the adhesive strength should be maximized (FIG. 3A). In the example study presently described, it was found that the calculated G / zstr values differ by several orders of magnitude from ideal parameters, likely as an artifact of the sample preparation method. However, trends within the data show that PEDOT-based formulations have higher G / zstr values, with that of PEDOT:PSS roughly one magnitude greater. Replacing PEDOT:PSS with Block-6 reduces this mechanical figure of merit, but it still remains higher than silver-based ECAs. However, crosslinking both PEDOT:PSS and Block-6 with GOPS reduces the G / zstr. As a comparison for what polymer materials are able to achieve if rationally designed, a commercial polyurethane (PU) is included in FIGS. 3A-3C as a reference for conventional (i.e., non-conjugated) polymer materials, which show the lowest calculated G / zstr value. FIG. 3B shows that the shear moduli extracted from lap shear testing showed relatively similar values between PEDOT:PSS, PEDOT:PSS / GOPS, and the three commercial ECAs, while Block-6, Block-6 / GOPS, and PU showed lower moduli. However, the most significant differences in G / zstr were contributed by the measured adhesive strengths. This is illustrated in FIG. 3C which shows shear strength, as calculated from respective parameters extracted from lap shear tests. Commercial ECAs (and PU)all had strengths approximately one magnitude greater than PEDOT:PSS and Block-6, despite crosslinking with GOPS slightly increasing the strength. This is relatively unsurprising, as PEDOT:PSS is not designed to be an adhesive material, and likely has poor viscoelastic adhesion at the silver / PEDOT:PSS interface. Crosslinking with GOPS increases the cohesive strength of the material by creating a crosslinked network between PSS chains, but this remains insufficient for appropriate adhesive functionality. The differences in failure mechanisms are stark when lap shear tests are performed using silicon cells as the substrates instead of silver coated glass. FIG. 3D shows stress-strain curves of lap shear tests performed with silicon solar cell substrates. CA- 183 is clearly overengineered for its purpose, as fracture first occurs cohesively within the silicon cell. In contrast, mixed failure occurs for the PEDOT:PSS / GOPS interconnect, suggesting that debonding occurs both at the PEDOT :PSS / silicon interface as well as within the PEDOT :PSS film. Similar fracture behavior was observed for three-point bend tests performed using silicon solar cell substrates, where failure occurs cohesively within the solar cell for CA-183 and both cohesively and adhesively within the adhesive joint for PEDOT-based EC As.

[0085] To further elucidate differences between adhesive performance (i.e., energy dissipation), tensile tests were conducted to compare cohesive fracture between materials. FIG. 3E shows some example results from tensile tests of ECAs investigated in the example study. Significant differences between the stress-strain characteristics were observed. Specifically, PEDOT:PSS and PEDOT :PSS / GOPS showed brittle behavior but high tensile strength, while Block-6 showed the opposite. Neither seem to be ideal for energy dissipation, as in the first case, low ductility suggests little possible flow of the polymer chains (although crosslinking with GOPS improving PEDOT:PSS in this regard), and thus few dissipation mechanisms by chain flow and rearrangement. In contrast, Block-6 has low strength and extremely high extensibility, suggesting material that flows too easily. However, in both the case of PEDOT:PSS / GOPS and Block-6, the toughness of the material was greater than all conductive adhesives measured. Such observation suggests that the primary contribution to the high adhesive strength of the silver-based ECAs is the energy dissipation at the interface of the substrate and adhesive, rather than energy dissipation within the bulk of the material.

[0086] Three-point bend tests were also performed on shingled silicon modules that were subjected to increasing amounts of thermal degradation by cycling from -40 °C to 85 °C. FIG. 3F shows maximum load before fracture as extracted from three-point bend tests for different ECAs,relative to accelerated degradation from thermal cycling. It was hypothesized that the temperature cycling would weaken the adhesion of PEDOT-based EC As due to temperature-driven degradation of the film morphology. Likewise, it was hypothesized that inclusion of GOPS as a crosslinker would impede morphological reorganization and phase segregation under thermal stresses. For DMSO and glycerol formulations, crosslinked samples failure under greater loads than their noncrosslinked counterparts (with crosslinked and non-crosslinked EG formulations showing similar performance). However, all formulations generally showed a decrease in the load at failure relative to an increase in thermal ageing.

[0087] Shingled modules were also fabricated in the example study. To fabricate shingled modules, Sunpreme silicon heterojunction (SHJ) cells were laser cut into smaller panels, which were then glued together using PEDOT-based and silver-based (commercial) EC As.

[0088] FIGS. 4A-4E show example photovoltaic characteristics of shingled solar cells under accelerated degradation. FIG. 4A shows example photographs of silicon solar cells shingled with CA-183 (left) and PEDOT-based (middle and right) EC As.

[0089] FIG. 4B shows representative I-V curves of pristine shingled solar cells. FIG. 4C shows the fdl factor of pristine cells shingled with PEDOT-based ECAs in comparison to a silverbased ECA standard (CA-183). From the I-V curves, it was observed that CA-183 modules typically showed the highest fdl factor (the primary metric of interest) as well as the most consistent performance in comparison to the PEDOT-based ECAs. Crosslinked PEDOT formulations typically showed slightly lower fdl factors than their non-crosslinked counterparts, with the exception of PEDOT / EG and PEDOT / EG / GOPS. It has been previously observed that crosslinking PEDOT:PSS fdms resulted in an increase in contact resistivity, which possibly explains this decrease in performance.

[0090] Average fdl factors between PEDOT-based formulations and CA-183 differed less than 8% on average. To compare the effects of PEDOT-based ECAs to CA-183 over longer time lengths, accelerated degradation tests were performed on shingled modules by temperature cycling. Three shingled modules of each formulation were thermally cycled (TC) from -40 °C to 85 °C repeatedly over 200 cycles (TC-200), with I-V curves taken every 50 cycles to track degradation. FIG. 4D shows the fdl factor of shingled cells after being subjected to 200 cycles of thermal cycling (TC-200) from -40 °C to 85 °C. Three samples were individually tracked for each formulation throughout the TC-200 test, with champion samples shown in FIG. 4D. While non-crosslinked samples started off with higher fill factors, their crosslinked counterparts showed far greater stability to thermal stresses.

[0091] Finally, accelerated electrical degradation was incorporated into ageing tests by performing reverse current overload (RCO) tests on individual shingled modules throughout the TC200 test. Here, modules were subjected to 4A, 6A, 8A, and 10A of current (120 s each interval) during every 50 thermal cycles (including TC-0). FIG. 4E shows the fill factor of shingled cells after subjected to a reverse current overload test at each 50-cycle time point. One sample was individually tracked for each formulation.

[0092] In the example study discussed above, PEDOT:PSS was repurposed as a conductive adhesive for shingling solar cells for high-efficiency modules by increasing the solids concentration, and thus the viscosity. In order to increase the electrical conductivity of PEDOT:PSS, the concentrated solutions were doped with organic polar molecules (DMSO, EG, and glycerol), which removes the need for any conductive filler. Finally, the deposited adhesive was stabilized by using GOPS to form a crosslinked PSS network within the polymer film. It was shown that solar cells shingled with PEDOT-based ECAs have similar fill factors to solar cells shingled with commercial silver-based ECAs, despite PEDOT :PSS not designed for this particular application. While commercial ECAs show greater stability when subjected to thermal and thermal / electrical stresses, crosslinking with GOPS offers some resistance to the morphological degradation mechanisms induced.

[0093] While PEDOT:PSS has a low electrical conductivity on its own, recent advancements in polymer synthesis have suggested that polymers can be developed to have high intrinsic conductivities. Likewise, a significant body of literature has been dedicated to synthetically modifying the mechanical properties of conjugated polymers, as well as the adhesive properties of non-conjugated polymers. These areas of research can likely guide the rational design and synthetic modification of conducting polymer adhesives. Future work on intrinsically conductive adhesives for shingling solar modules would likely benefit from the removal of moisture, better doping methods, and reducing the acidity of the solution (in the case of PEDOT PSS). Indeed, other PEDOT-based formulations have already replaced PSS with different counterions, and water with other solvents, e.g., toluene. While the PEDOT-based films in the example study were crosslinked with GOPS, further exploration of synthetic methods to stabilize the polymeric adhesive would be beneficial. Use of crosslinkers could also increase the interfacial adhesion atthe substrate by forming covalent bonds at the surface. Stability is a particular concern for PEDOT:PSS due to the nature of the polyelectrolyte complex that promotes and allows for significant morphological reorientation. While moisture-driven degradation and decohesion mechanisms are likely not a significant factor if employed in glass-glass modules, the electrostatic interactions holding the PEDOT and PSS chains together possibly increases the likelihood of fracture nucleation, decreasing the maximum possible adhesive strength and bending load. Simple approaches that might improve the adhesive behavior (and cohesive strength) of a conducting polymer adhesive could possibly involve blending with common non-conductive polymers that are already commonly used for adhesive applications (e.g., epoxy, polyurethanes).

[0094] Results of the example study demonstrate a new application for conjugated polymers and motivate the rational design of intrinsically conductive adhesives. One benefit of using conducting polymer adhesives for shingling solar cells, among others, is the complete removal of silver from the conductive adhesive interconnect and the majority of silver required for metallization. Calculations suggest that a transition to shingled solar modules with silver-free EC As could reduce silver consumption considerably, such that the disclosed adhesives are accelerated to >2040 on the silver learning curve. As such, the disclosed techniques offer a realistic avenue towards drastically reducing the silver consumption required to scale up solar PV to capacities capable of sustainably decarbonizing the electrical grid by 2050.

[0095] In another example study, PEDOT:PSS was employed as a silver-free, intrinsically conductive adhesive (ICA) to create an interconnect between solar cells. In the disclosed approach, silver-based ECAs were replaced with a conductive polymer as the shingled interconnection, removing the need for silver filler entirely. As will be explained in further detail below, even with the removal of silver filler, similar fill factor and overall power conversion efficiency was achieved with shingled interconnects. Furthermore, employing a conducting polymer as the ICA additionally opens a myriad of opportunities for tuning the electronic, mechanical, and adhesive properties for designing next-generation electronic interconnects.

[0096] In contrast to modules with soldered ribbons, shingled solar modules are glued together with an electrically conductive adhesive (EC A), where the electronic filler is typically silver.

[0097] In the example study, ICA formulations were optimized by incorporating a silane-based crosslinker ((3-glycidyloxypropyl)trimethoxysilane, GOPS), polar small molecules, and multiwalled carbon nanotubes (MWCNT) into PEDOTPSS (1.3 solid wt%).

[0098] To control the dispense line of the adhesive for syringe deposition, an appropriate viscosity was found to be roughly -10 Pa-s at 3.5 solid wt% (FIG. 2B). Further concentration past -5 wt% resulted in gelling, which is possibly favorable for printing. Concentrated PEDOT:PSS was then doped with polar additives and deposited by shear deposition to investigate the electronic properties of the resulting fdms using 4-point probe measurements.

[0099] FIGS. 5A and 5B show, respectively, example resistivity and conductivity data of adhesives based on the disclosed technology. FIG. 5A shows resistivity data of PEDOT:PSS and PEDOT:PSS / multi-walled carbon nanotube (MWCNT) fdms with additives (8 vol% DMSO, 8 vol% EG, 5 vol% glycerol, 1 vol% GOPS). Three silver-based ECAs are shown for comparison. While adding MWCNT increased the conductivity of pristine PEDOT :PSS, polar dopants rendered the inclusion of electronic fdler redundant. It was observed that crosslinking any doped PEDOT- based film with GOPS resulted in resistivities comparable to their non-crosslinked counterparts, in agreement with previous work. Favorable PEDOT :PSS-based formulations had resistivities of ~5x 10‘4Q-cm, modestly higher relative to three commercial silver-based ECAs at ~8* 10’5Q-cm. FIG. 5B shows conductivity data of PEDOT:PSS and CA-183 films relative to temperature normalized to the conductivity at 25 °C. The conductivity of PEDOT:PSS-based films remained relatively constant within a temperature range relevant to the typical operating conditions of solar cells (20-65 °C).

[0100] In the example study, shingled cells were fabricated from Sunpreme silicon heterojunction (SHJ) solar cells using PEDOT:PSS-based ICAs and silver-based ECAs as shown in FIG. 4A. All interconnected cells described here were unlaminated and unencapsulated. Lamination and encapsulation itself can change both the mechanical and electrical properties of the adhesive joints.

[0101] Cells shingled with PEDOT :PSS-based ICAs had fill factors lower than but comparable to those shingled with commercial CA-183.

[0102] FIGS. 6A-6E show example results obtained in a study performed in accordance with the disclosed embodiments. FIG. 6A shows example I-V curves of pristine interconnected cells. FIG. 6B shows example fill factors of pristine cells shingled with PEDOT:PSS-based ICAs (n = 7-10) in comparison to a silver-based ECA (CA-183) (n = 13), where the “x” denotes the champion device. Error bars are reported as standard deviation. The champion devices were very similar to the 83% FF of CA-183, with the glycerol-based and DMSO-based ICAs achieving -82% FF.Because of the greater variability in the manual processing of the novel ICAs, these champion results exemplify what may be achievable by each ICA composition. The slightly lower champion fill factors can likely be attributed to an increase in resistive losses, as well as the increased contact resistance for PEDOT:PSS-based ICAs (~10‘2Q-cm2) compared to silver-based EC As (~10‘3Q- cm2). Likewise, crosslinked PEDOT:PSS formulations typically showed slightly lower FFs than their non-crosslinked counterparts, which can again possibly be explained by a further increase in contact resistance (-IO'1Q-cm2). Nevertheless, champion cross-linked ICAs incorporating DMSO / GOPS and EG / GOPS achieve >80% FF in these experiments. Overall, across the various formulations tested, the average FF of ICA-shingled cells was slightly lower than CA-183 (~5%). The reasonably close performance of these proof-of-principle ICAs to CA-183 is put into context considering that PEDOT:PSS is not optimized for such application, as well as the absence of years of process engineering conducted for optimizing the fabrication process relative to the commercial ECA.

[0103] In the example study, accelerated degradation of silver-free conductive adhesives was investigated. Given the competitive performance of the ICAs, an examination of the durability of the ICAs relative to commercial ECAs in accelerated stress tests of the material and in shingled cell formats was performed. In damp heat testing at 65°C and 65% RH (ISOS-D-3, as is used for emerging solar cell technologies), the introduction of crosslinking by the addition of GOPS reduced, but did not fully mitigate, the impact of moisture ingress on both the electrical conductivity and microstructure (e.g., swelling, delamination, and moisture-driven decohesion). The degradation induced by heat and moisture is attributed to morphological rearrangement within the PEDOT:PSS film, in good agreement with prior literature. Given that heating at ambient humidity did not strongly affect conductivity (FIG. 5B) at typical operating temperatures for solar cells (15-65 °C), electrical degradation in PEDOT:PSS films appears to be primarily moisture- driven. PEDOT:PSS-based ICAs would likely benefit from edge-sealed, glass-glass PV packages that are used for thin film PV and are increasingly common for bifacial silicon modules, in which exposure to moisture is excluded.

[0104] Cells interconnected with ICA formulations and control ECAs were subjected to accelerated degradation tests by thermal cycling from 85°C to -40°C following the IEC standard test. FIG. 6C shows normalized fill factor data of shingled cells after being subjected to 200 thermal cycles (TC-200) from - 40 °C to 85 °C. Three samples were individually tracked for eachformulation throughout the TC-200 test, with champion samples shown in FIG. 6C. While thermal cycle tests are typically performed on encapsulated strings, this initial durability test was used to investigate the effect of temperature cycling on the adhesive itself. All crosslinked ICAs showed comparable performance to CA-183 in terms of relative FF, albeit with more variability in photovoltaic performance. In contrast, PEDOT:PSS / EG and PEDOT:PSS / DMSO showed significant degradation after 50 cycles. These data suggest that crosslinking preserves the electronically favorable morphology, with electronic degradation for non-crosslinked ICAs attributed to morphological rearrangement. PEDOT:PSS / glycerol showed comparable performance to crosslinked ICAs, while also having an increased FF. This stability can possibly be attributed to residual glycerol remaining in the film due to its high boiling point (290 °C, compared to 189 °C for DMSO and 197 °C for EG), preserving the favorable electronic morphology induced by secondary doping at relevant temperatures.

[0105] Electrical degradation was then incorporated into thermal ageing tests by subjecting shingled cells to reverse current overload (RCO) tests. FIG. 6D shows normalized fill factor data of shingled cells after subjected to a reverse current overload test at each 50-cycle time point. One sample was individually tracked for each formulation. MostPEDOT:PSS-based ICAs still showed comparable stability under RCO loads as commercial CA-183, with slightly greater degradation but remaining within 10% of their original FFs. Strikingly, PEDOT :PSS / EG / GOPS outperformed CA-183. The accelerated degradation observed was especially transparent for PEDOT:PSS / EG, which showed a -15% relative decrease in FF from thermal cycling but a -55% decrease when RCO was incorporated.

[0106] Finally, three-point bend (3PB) tests were performed on shingled cells that were subjected to temperature cycling. FIG. 6E shows maximum load before fracture data as extracted from three-point bend tests (n = 2-4) relative to thermal cycling. It was hypothesized that thermal stresses would weaken the adhesion of PEDOT:PSS-based ICAs due to temperature-driven rearrangement of the film morphology, and that this morphological reorganization could be impeded by crosslinking. Typically, crosslinked ICAs withstood greater loads than their noncrosslinked counterparts, suggesting some adhesive benefit to crosslinking. However, both noncrosslinked and crosslinked ICAs generally showed a decrease in maximum load relative to increased thermal degradation, while CA-183 remained relatively stable. Most striking was the difference in failure mechanisms. While cells shingled with CA-183 failed cohesively (within asilicon cell), cells shingled with PEDOT:PSS-based ICAs failed adhesively (within the adhesive lap joint). The failure modes observed from 3PB tests suggest that the primary weakness of PEDOT:PSS-based ICAs is the adhesive functionality.

[0107] To understand differences in mechanical performance between PEDOT :PSS-based and silver-based conductive adhesives, lap shear and tensile tests were performed.

[0108] FIGS. 7A-7F show example mechanical properties of PEDOT:PSS-based and silverbased conductive adhesives. Previous work suggests that the ratio of shear modulus to adhesive strength (G rstr1) is an important figure of merit (FOM) for shingled interconnections. FIG. 7A shows example figure of merit data for shingled interconnections. To reduce the likelihood of mechanical failure, the shear modulus should be minimized and adhesive strength maximized, as suggested by the data of FIG. 7A. The G rstr1values extracted from lap shear tests differed significantly from ideal parameters, stemming from an overestimation of the shear strain due to the testing method. However, qualitative trends showed that PEDOT:PSS had the highest G rstr1values, roughly one magnitude greater than silver-based EC As. Crosslinking offered a modest reduction in G rstr'1, but these FOMs were still not comparable to silver-based EC As.

[0109] As a comparison for what is achievable using polymeric materials, a commercial polyurethane (PU) (which had the lowest calculated G rstr1) was included in FIG. 7A reference. FIG. 7B shows example shear modulus data as calculated from the respective parameters extracted from lap shear tests. FIG. 7C shows example shear strength data as calculated from the respective parameters extracted from lap shear tests. The primary differences in G rstr'1values were due to the adhesive strengths, which differed significantly in comparison to the shear moduli (FIGS. 7B- 7C). This difference is relatively unsurprising, as PEDOT:PSS is used here as an ersatz adhesive. Crosslinking with GOPS increased the cohesive strength by creating a crosslinked network between PSS chains, but poor adhesion at the interface remained an avenue for delamination. These differences in failure mechanisms were stark when shear tests were performed using silicon cells as substrates. FIG. 7D shows example stress-strain curves of lap shear test performed with silicon solar cell substrates in the example study. Similarly to 3PB tests, fracture of the module occurred cohesively for CA-183, while PEDOT:PSS / GOPS experienced mixed failure, suggesting debonding occurring at both the PEDOT:PSS / silicon interface as well as within the adhesive joint (FIG. 7D).

[0110] Tensile tests were performed to compare cohesive behavior, and thus elucidatedifferences in energy dissipation. FIG. 7E shows example stress-strain curves of ECAs investigated in the example study, as measured using tensile tests. FIG. 7F shows example toughness data of ECAs investigated in the example study, as extracted from stress-strain curves. PEDOT :PSS and PEDOT :PSS / GOPS were brittle with high tensile strengths, suggesting little flow of the polymer chains and few energy dissipation mechanisms by plastic rearrangement. However, PEDOT:PSS / GOPS had a greater toughness than all silver-based ECAs measured (FIG. 7F). Similarly, PU showed the greatest toughness of all materials, yet a lower adhesive strength than all silver-based ECAs. These observations suggest that the primary contribution to the high adhesive strength of the silver-based ECAs is the energy dissipation at the interface (substrate / adhesive), rather than dissipation within the bulk material. Given the relevant electronic performance and early durability results of the ICAs, future work to increase the adhesion of the ICA could benefit from using the many levers of polymer design (e g., synthetic modification, addition of tackifiers or crosslinkers, polymer blending). Increasing the adhesion of ICAs while maintaining the favorable electronic performance may enable drop-in replacements for silverbased commercial conductive adhesives.

[0111] In the example study discussed above, PEDOT:PSS was employed as an intrinsically conductive adhesive (ICA) for shingling solar cells for high-efficiency shingled modules. Doping concentrated solutions of PEDOT:PSS with DMSO, EG, or glycerol increased the electrical conductivity, removing the need for any Ag filler. To stabilize the morphology and increase the cohesive strength, a crosslinked PSS network was formed within the deposited adhesive using GOPS. Solar cells shingled with PEDOT :PSS-based ICAs had the same Voc and Jsc, and achieved champion fill factors -82%, only -1% absolute lower than cells interconnected with silver-based ECAs. Crosslinking proved to be effective in preserving the favorable electronic morphology against thermal cycling, with crosslinked ICAs showing comparable stability to commercial silverbased ECAs. PEDOT:PSS / glycerol also showed comparable stability, likely due to residual dopant remaining in the adhesive due to the high boiling point of glycerol. Critically, replacing silver-based ECAs with ICAs significantly reduces the silver demanded by the solar module. The results indicate a new application for conjugated polymers for solar PV and motivate the rational design of intrinsically conductive adhesives.

[0112] FIG. 8 shows a flow diagram of an example method 800 of producing an intrinsically conductive adhesive (ICA) for interconnecting solar modules. At operation 802, the method 800comprises acquiring a material comprising an insulating epoxy matrix. At operation 804, the method 800 comprises synthesizing the ICA by replacing the insulating epoxy matrix with a conducting polymer matrix free of electronic filler material. At operation 806, the method 800 comprises obtaining (e.g., modifying) one or more formulations of the ICA by incorporating at least one of a crosslinker, polar dopants, adhesion promoters, or carbon nanotubes into the ICA. Examples of adhesion promoters that can be incorporated in the ICA formulation(s) can include silane compounds. Examples of polar dopants that can be incorporated in the ICA formulation(s) can include dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol. Examples of crosslinkers that can be incorporated in the ICA formulation(s) can include a silane-based compound or (3-glycidyloxypropyl)trimethoxysilane (GOPS).

[0113] FIG. 9 shows an example embodiment of a solar assembly system 900, in accordance with the present technology. The solar assembly system 900 includes a plurality of solar modules 902 configured to receive solar radiation and convert the solar radiation to electrical power. The solar assembly system 900 includes an intrinsically conductive adhesive (ICA) material 910 coupled to and interconnecting the plurality of solar modules 902 such that the plurality of solar modules 902 are in thermal and electrical communication with each other. In one example implementation, each of the solar modules in the plurality of solar modules 902 includes a positive and negative electrical contact. The ICA material 910 can be used to connect, for example, the positive contact of a first solar module to the negative contact of a second solar module such that the electrical power (e g., voltage) accumulated by the first solar module and the second solar module may be added together. This process can be repeated for each of the solar modules in the plurality of solar modules 902. In some implementations, a conductive wire can be used to transfer the electrical power from the plurality of solar modules 902 to one or more additional modules or devices (e.g., an inverter). In some implementations, each solar module in the plurality of solar modules 902 may be electrically connected to an inverter. The plurality of solar modules 902 may correspond to a plurality of solar cells in some implementations.

[0114] Example embodiments of the ICA material 910 can include any of the example embodiments described above or below, where some examples of the ICA material 910 include a ^-conjugated material having a conducting polymer matrix. The solar assembly system 900 can be configured on a base surface 950. In some implementations, the base surface 950 can include a roof of a building or other structure. In some embodiments, the solar assembly system 900 can(optionally) include one or more electrical connector(s) 980 (e g., wire(s), cable(s), and the like) to conduct electrical energy from the ICA material 910 to an electronic device 990, such as a charge controller electrically connected with a battery and / or inverter.

[0115] Some example implementations of the ICA material 910 for interconnecting solar modules 902 can include a attaching the ICA material 910 to ribbon wires on solar modules 902 (not shown in FIG. 9). For example, some solar modules use attached ribbon wires from the front side of one cell to the backside of the next without soldering (which heats the cell and can cause irreversible damage and at a minimum causes substantial residual stresses that can lead to early mechanical failure of contacts and lower power outputs). Using the disclosed ICA materials, the exemplary ICA material 910 can be put down with the ribbon to be put on top of the ICA.

[0116] FIG. 10 shows a diagram comparing a conventional silver-based conductive adhesive material with an example embodiment of an ICA material in accordance with the present technology. The conventional silver based material, shown on the left side of the diagram, depicts Ag particles that provide conductive pathways for electric conductivity, in which the silver particles are contained within an epoxy matrix. In contrast, the exemplary ICA material, shown on the right side of the diagram, depicts a conducting polymeric matrix having a cross-linking of conjugated polymeric strands that impart bulk conduction to render an intrinsically conductive adhesive material.

[0117] FIG. 11 shows an example plot of the annual percentage of silver used for solar PV relative to annual available supply. Open circles show the projected consumption of silver according to a 30% annual growth rate in solar capacity until 2030. This projection assumes that the current rate of silver consumption remains unchanged, and that the annual supply of silver remains constant to the supply available in 2023.

[0118] Table 1 shows projected total solar PV capacity necessary to reach net-zero emissions goals by 2050.Table 1.Projected Solar PVYearCapacity [TW]2023 1.39462024 3.20762025 3.7515

[0119] FIG. 12A shows example viscosities of disclosed PEDOT :PSS solutions. The viscosity of PEDOT PSS solutions can be increased by removing water using a rotary evaporator, thus increasing the concentration of solids. FIG. 12B shows example viscosity data of a disclosed, concentrated PEDOT:PSS (—10 Pa-s) solution relative to silver-based ECA solutions as measuredusing a rheometer. FIG. 12C shows example shear modulus data of the concentrated PEDOT:PSS (~10 Pa-s) solution relative to silver-based ECA solutions as measured using a rheometer.

[0120] FIGS. 13A-13C show photographs of example PEDOT-based films which were deposited by shear deposition and investigated in an example study performed in accordance with disclosed embodiments.

[0121] In some disclosed ICA materials, GOPS was used to create a crosslinked PSS network within the solid film to stabilize the solid morphology, increase energy dissipation, and increase the adhesion at the substrate / ICA interface. An additional benefit of crosslinking with GOPS was the reduction of the ingress of moisture (which results in swelling, delamination, and moisture- assisted decohesion) as was determined in an example study.

[0122] FIGS. 14A-14F show some example results obtained in the study. FIG. 14A shows the water intake of CA-183, PEDOT:PSS and PEDOT:PSS / GOPS (crosslinked) films relative to a storage environment after 24 h. FIG. 14B shows the relative conductivity of PEDOT:PSS films relative to CA-183 films as stored in a 25 °C, 65% relative humidity environmental chamber for 30 days. FIG. 14C shows the relative conductivity of PEDOTPSS films compared to CA-183 films as stored in a 65 °C, 65% relative humidity environmental chamber for 20 days. FIG. 14D shows the thickness of PEDOTPSS films compared to CA-183 films as stored in a 65 °C, 65% relative humidity environmental chamber for 20 days. FIG. 14E shows the relative conductivity of crosslinked PEDOTPSS films relative to CA-183 as stored in a 65 °C water bath for 20 days. FIG. 14F shows the thickness of crosslinked PEDOTPSS films relative to CA-183 as stored in a 65 °C water bath for 20 days. No non-crosslinked films are shown due to delamination from the glass substrate when submerged in water.

[0123] Little electrical degradation was observed in PEDOTPSS films placed in atmospheric conditions, 25 °C / 65% relative humidity (RH) (FIG. 14B). However, increasing the temperature to 65 °C accelerated moisture-driven degradation, leading to wrinkling (swelling) and crack formation in non-crosslinked films, as well as degradation at the surface of crosslinked films. Under 65 / 65 (°C / %RH) degradation conditions, only PEDOTPSS / glycerol andPEDOTPSS / glycerol / GOPS outperformed CA-183 in terms of relative conductivity, but the absolute conductivity of CA-183 remained greater than all PEDOTPSS films (FIG. 14C). A similar trend was observed for the crosslinked films in 65 / 100 conditions (FIG. 14E). Literature suggests that the degradation induced by heat and moisture is attributed to morphologicalrearrangement within the PEDOT:PSS film. Other thermal ageing experiments suggest that PEDOT:PSS experiences little electrical degradation at mildly elevated temperatures (65 °C). As degradation seems to be primarily moisture-driven at typical operating temperatures (15-75 °C), the findings indicate that PEDOT:PSS-based ICAs would need to be employed in glass-glass modules to reduce the ingress of moisture. Although water ingress is still possible from the sides of glass-glass modules, others have described strategies for reducing the effects of moisture diffusion on encapsulated devices (e.g., edge seal materials, incorporation of desiccants).

[0124] For both 65 / 65 (temperature / RH) and 65 / 100 tests, a combination of heat and moisture likely results in morphological rearrangement of the solid film, resulting in domains measuring significantly higher resistances (and difficulty obtaining consistent sheet resistance measurements). Other studies elucidate a number of ways by which the morphology of PEDOT:PSS can suffer from temperature and moisture-driven degradation mechanisms. Some studies have observed instability of electrical conductivity in doped PEDOT:PSS, while other studies suggested thermal ageing could detrimentally affect conductivity due to the shrinking of conductive domains. However, others have found that gentle heating alone (i.e., up to 80 °C) yields ageing behavior similar to that of room temperature, suggesting that moisture likely plays a much bigger role in morphological degradation. Work performed elsewhere suggests that PSS chains preferably reorient towards solution under the presence of temperature and moisture, as loosely-bound polymer chains experience partial dissolution in water.

[0125] FIG. 15 show a diagram of an example fabrication scheme for shingled solar cells in accordance with disclosed embodiments. In an example study disclosed herein, silicon cells were first laser cut (red) at each busbar (silver) to form smaller shingles. Conductive adhesive was applied on the edge of one shingle, before a second shingle was placed on top. The cells were then annealed to bond. Silver fingers, which run perpendicular to the busbars, are not shown in FIG. 15.

[0126] In an example study, the photovoltaic properties of shingled cells using ICAs based on the disclosed technology were investigated.

[0127] FIGS. 16A and 16B show images of example ribbons that can be used to form part of shingled solar cells based on the disclosed embodiments. FIG. 16A shows an image of two example ribbons were soldered onto the shingled cells. FIG. 16B shows an image of the two example ribbons of FIG. 16A connected by alligator clips to a source meter used to measure currentas a function of applied voltage in the example study.

[0128] FIG. 17 shows a representative I-V curve of a full Sunpreme SHJ wafer obtained in an example study performed in accordance with disclosed embodiments. The photovoltaic properties were as follows: Isc = 8.77 A, Jsc = 35.97 mA / cm2, Voc = 0.7266 V, FF = 75.28%, PCE = 19.63%.

[0129] FIG. 18 shows exemplary series resistance data extracted from I-V curves obtained in an example study performed in accordance with disclosed embodiments. The error bars denote standard deviation (n = 7). Series resistance of champion devices is denoted with gold “x” markers.

[0130] FIGS. 19A-19B shows microscope images of example PEDOT:PSS films obtained in an example study performed in accordance with the disclosed embodiments. FIG. 19A shows microscope images of representative PEDOT:PSS films after deposition, which were obtained in an example study performed in accordance with disclosed embodiments. FIG. 19B shows microscope images of the representative PEDOT:PSS films of FIG. 19A after 30 days at 25 °C, 65% relative humidity conditions.

[0131] FIG. 20 shows microscope images of example embodiments of PEDOT:PSS films stored in 65 °C / 65% relative humidity and 65 °C water bath conditions after 3 days.

[0132] FIG. 21 shows images of example embodiments of PEDOT:PSS films stored in 65 °C / 65% relative humidity conditions after 3 days.

[0133] FIG. 22 shows image of example embodiments of PEDOT:PSS films stored in 65 °C / 65% relative humidity and 65 °C water bath conditions after 11 days.

[0134] FIG. 23 shows microscope images of example embodiments of PEDOT:PSS films stored in 65 °C / 65% relative humidity and 65 °C water bath conditions after 15 days.

[0135] FIG. 24 shows microscope images of example embodiments of PEDOT:PSS films stored in 65 °C / 65% relative humidity and 65 °C water bath conditions after 20 days.

[0136] FIG. 25A shows photographs of example embodiments of PEDOTPSS films after 30 days of storage in 25 °C / 65% relative humidity. FIG. 25B shows photographs of example embodiments of PEDOT:PSS films after 20 days of storage in 65 °C / 65% relative humidity. FIG. 25C shows photographs of example embodiments of PEDOTPSS films after 20 days of storage in a 65 °C water bath. Portions of the films were removed due to contact with a printed holder.

[0137] FIG. 26 shows photographs of example embodiments of PEDOTPSS films after 20 days of storage in 65 °C / 65% relative humidity.

[0138] FIG. 27 shows photographs depicting water-assisted delamination of non-crosslinkedPEDOT:PSS films based on the disclosed technology.

[0139] FIG. 28A shows a comparison of example fill factors for champion devices, obtained in an example study, which were subjected to TC-200 degradation tests. FIG. 28B shows a comparison of example fill factors for the champion devices after being subjected to TC-200 degradation tests with reverse current overload (RCO) tests performed every 50 cycles (FIG. 28B).

[0140] Table 2 shows fill factor data, expressed in percentage, of example embodiments of shingled cells based on the disclosed technology. The shingled cells were tracked through TC-200 degradation conditions in an example study. Different samples are tracked by sample number in Table 2.Table 2: Example fill factor data of disclosed shingled cells

[0141] Table 3 shows open circuit voltage (Voc) data, expressed in units of Volts, of example embodiments of shingled cells based on the disclosed technology. The shingled cells were tracked through TC-200 degradation conditions in an example study. Different samples are tracked by sample number in Table 3.Table 3: Example open circuit voltage data of disclosed shingled cells

[0142] Table 4 shows short circuit current (Isc [A], Jsc [mA / cm2]) data of example embodiments of shingled cells which were tracked in an example study. Asterisks in Table 4 indicate that the difference in short circuit current for the identified samples is attributed simply to a difference in the overlap width of the shingled cells.Table 4: Example short circuit data of disclosed shingled cells

[0143] Table 5 shows example power conversion efficiency (PCE) data of example embodiments of shingled cells which were tracked through TC-200 degradation conditions in an example study. Different samples are identified by sample number in Table 5.Table 5: Example power conversion efficiency data of disclosed shingled cells

[0144] Table 6 shows fill data of example embodiments of shingled cells (one sample per ECA formulation) which were tracked through TC-200 degradation conditions in an example study. Reverse current was applied at each 50-cycle interval. I-V curves were taken after each applied current (4A, 6A, 8A, 10A). In Table 6, a single asterisk is used to indicate I-V curves which were mistakenly overwritten for the 4A, 6A, and 8A current steps during the TC-0 and TC-50 measurements. A double asterisk in Table 6 is used to indicate bond failure.Table 6: Example fill data of disclosed shingled cells

[0145] In an example embodiment of an ICA material, a formulation of poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with 1.3 wt% solid material dispersed in water was selected as a polymer matrix for the ICA.

[0146] For a PEDOT-based dispersion with a solid concentration of ~1.3 wt%, experimental results showed that the viscosity was comparable to that of water (0.001 Pa-s). However, when dispensed from a needle gauge, this solution would spread on the substrate, which is unfavorable for forming an adhesive line. Thus, to properly dispense an adhesive line of accurate width, the viscosity of the polymer solution was increased. Solvent was removed from each dispersion using a rotary evaporator (rotovap) such that the viscosity of the final solution was -10 Pa-s. The viscosity of the solution was checked using as a function of shear rate on a Discovery Hybrid Rheometer (HR) 30 (TA Instruments) with 40 mm stainless steel parallel plates.

[0147] To incorporate multi-walled carbon nanotubes (MWCNT) into the PEDOT:PSS matrix, carbon nanotube powder was weighed out in a scintillation vial. Then, concentrated PEDOT :PSS PH1000 solution was added to the MWCNT in the desired ratio. After mixing briefly by hand, the PEDOT:PSS / MWCNT solution was sonicated in a bath sonicator for 30 min, followed by probe sonication for 2 h (40% amplitude, 5 s on 5 s off pulse sonication) in a water bath to prevent local heating.

[0148] Secondary dopants were added to PEDOT:PSS in order to increase the conductivity of the solid film. Dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol were mixed into each concentrated polymer solution at the desired ratio before being dispensed. Experimental results suggested that the ideal loadings of DMSO, EG, and glycerol were 8 vol%, 8 vol%, and 5 vol%, respectively. (3-glycidyloxypropyl)trimethoxysilane (GOPS) was also incorporated as a crosslinker for the PEDOT-based matrices by simply blending at the desired ratio, which was keptat 1 vol% for the instant ICA material presently disclosed.

[0149] In an example study, the conductive polymer-based matrices were compared to commercial ECAs for shingled silicon cells. All commercial ECAs used in the study were composed of silver particles dispersed in a polymer matrix. CA-183 and ECA 147-561-2 was dispersed in epoxy matrices, while ECA 5802 was dispersed in a polydimethylsiloxane (PDMS) elastomeric matrix. All ECAs were stored in a -20 °C freezer. To defrost before use, all ECAs were left at room temperature for 1 hour.

[0150] Example Substrate Preparation. Square glass substrates (25 mm x 25 mm xl.l mm, Biotain Crystal Company), microscope glass substrates (76.2 mm x 25.4 mm x 1.1 mm, Fisherbrand), or silicon substrates (diced into 10 mm x 10 mm or 25 x 25 mm, 525 pm thickness, WaferPro C04002 N / PH (100) 1 - 5 Q cm) were cleaned by sonication in Alconox and water, deionized (DI) water, acetone, and isopropyl alcohol (IP A) for 10 min each in a bath sonicator. Before use, substrates were dried using compressed air and plasma treated in air (10 min, -400 mTorr) to increase the wettability of the substrate. Before cleaning, microscope glass substrates were diced in half (38.1 mm x 25.4 mm x l. l mm) using a diamond-tipped substrate cutter for lap joint shear samples. After cleaning and plasma treatment, 100 nm of silver was deposited on one side of these shear test substrates (25 mm x 25.4 mm) by thermal evaporation (AJA Orion PVD system, 1 A s'1), such that the silver was deposited all the way to the edge of the substrate. These samples were held in a physical vapor deposition (PVD) chamber using a custom laser-cut aluminum holder and mask. Silver substrates were placed under vacuum (e g., in the antechamber of a glove box) until use.

[0151] In some disclosed embodiments, shingled solar cells are formed using disclosed ICAs. In one example implementation of forming shingled solar cells, PEDOT:PSS (PH1000) was prepared by adding 1000 pL of concentrated solution (-10 Pa-s) into a glass vial along with an appropriate amount of DMSO (80 pL), EG (80 pL), or glycerol (50 pL). If crosslinker was included, then GOPS (10 pL) was added as well before the solution was mixed well to combine. Silicon solar cells (Sunpreme 4Busbar Silicon Cells, Type BM156NZ, M2 wafer size, 22.0 - 23.0% single-cell efficiency) were purchased and used as received. Full silicon wafers were laser- scribed and cleaved to 156.75 mm x 39 mm. To form a shingled string (i.e., 2 interconnected cells), a syringe and needle (TE Needle 22 GA 1 / 2” angled) was used to dispense a line of adhesive -1 mm from one edge of the cell, across the length of the cell, by hand. The amount of adhesivetypically totaled ~60 mg. Immediately afterwards, another cut cell was placed on top of the bottom cell such that the overlap was between 5 mm - 10 mm. Shingles were cured at 150 °C for 15 min on a hot plate to dry. After curing, two SnPb 60 / 40 ribbons (Luvata, 310 mm x 1 mm x 0.1 mm) were soldered on the top and bottom of the shingled cells (one top, one bottom). Alligator clips were attached to these ribbons in order to connect the shingled cells to the source meter used to measure the current as a function of applied voltage.

[0152] FIGS. 29A shows a photograph of three-point bend tests performed on the example shingled cells described above. FIG. 29B shows a photograph after a three-point bend test was performed on example cells shingled with CA-183, where fracture occurs cohesively within the cell. FIG. 29C shows photographs of example cells shingled with PEDOT-based EC As after three- point bend tests, showing fracture at the adhesive joint. FIG. 29D shows maximum load before failure for all example PEDOTPSS samples as extracted from three-point bend tests, relative to accelerated degradation from thermal cycling. FIG. 29E shows representative force-displacement curves of exemplary PEDOT:PSS / DMSO, PEDOT:PSS / DMSO / GOPS (crosslinked), and CA- 183, as well as the fracture behavior observed during three-point bend tests.

[0153] An electronic characterization of the shingled cells was conducted in an example study. To measure the photovoltaic behavior of shingled solar cells, IV curves for sample shingled cells were obtained using a solar simulator (Stinton, FMT-500, xenon light source, AM 1.5). The sample was first placed, with the positive side exposed, on a piece of glass backing with a dark, opaque backsheet taped behind. This sample was taped down using a high temperature silicon adhesive polyester (PET) tape, with the tape applied where the ribbons begin to protrude from the sample. This sample was clamped down facing the solar simulator light source and attached to leads on both the positive (top ribbon) and negative (bottom ribbon) sides. Finally, an IV curve was collected by turning on the light source and performing a voltage sweep at standard temperature (room temperature, ~25 °C) and pressure using a multi-flash system (pulse length to 50% is roughly ~3 s). Only forward scans were taken due to negligible hysteresis for the Sunpreme silicon heterojunction cells used in this study. The solar simulator was calibrated using an ISFH SunPower silicon cell before each set of measurements. Photovoltaic parameters (short-circuit current, open-circuit voltage, fill factor, and power conversion efficiency) were analyzed and extracted from the resulting IV curve using MultiFlash vl.5 software (Sinton Instruments). The cell area was assumed to be 54.86 cm2for all cells (as determined from the average area of onepreliminary batch of fabricated modules). Shingled cells were placed in an oven (Espec Corp, ESX-4CA) and cycled from -40 °C to 85 °C for 200 cycles (TC-200). At every 50-cycle interval, tracked samples were pulled out for IV measurements. To perform reverse-current overload (RCO) tests, shingled cells were subjected to 4A, 6A, 8A, and 10A of current using a DC power supply. For each current step, the shingled cells were held at that current for 120 s before an IV test was performed, in sequential (increasing) current order.

[0154] The series resistance of each I-V curve was calculated using the area under the curve, such thatwhere A is the area under the curve, AB is the Boltzmann constant (1.3806488 x 10’23J / K), Zis the temperature (here, assumed to be 25 °C), and q is the electronic charge (1.602 x 10’19C).

[0155] A mechanical characterization of the shingled cells was also conducted in the example study. Three-point bend (flexural) tests were conducted on shingled cells (FIG. 26) using an Instron 3366 with a three-point bend fixture. The radius of curvature of the three-point bend fixture was approximately 5 mm. The speed of compression was set to be 2 mm / min.

[0156] Electronic Characterization of Conducting Polymer-Based Formulations. To evaluate the conductivity and resistivity of solid films resulting from the disclosed polymeric conductive adhesives, 4-point probe measurements were performed. To mimic the shingle deposition process, in which the adhesive material is sheared across a stencil to form an adhesive line, a Zehntner ZAA2300 blade coater was used to deposit films for conductivity measurements. After plasma treatment of 25 mm square glass substrates, approximately 150 pL of material was deposited on one edge of the substrate. With the applicator height set to 1.3 pm (i.e., 200 pm above the substrate height) and speed set to 62.5 mm s’1, films were fabricated by solution sheared deposition. Immediately after deposition, films were put on a hot plate set at 150 °C for ~20 min to anneal. To cool, films were transferred to the ceramic surface of another hot plate at room temperature for ~5 min. Finally, films were placed in the antechamber of a glove box under vacuum overnight to remove any residual solvent. The next day, the sheet resistance of each film was measured using a four-point probe in 5 spots across the film (and corrected using a geometric correction factor according to the dimensions of the substrate and spacing of the probe tips). To convert sheet resistance to conductivity and resistivity, the thickness of the film was measured across 5 spots byscoring the film and performing profilometry measurements using a Dektak XT. The error associated with these four-point measurements was determined by error propagation (i.e., considering both the variation in sheet resistance measurements as well as the variations in thickness).

[0157] To evaluate the temperature-dependent conductivity, blade-coated films were deposited as described above. These films were placed on a hot plate set to 25 °C, 45 °C, and 65 °C to equilibrate for 5 min at each step before 4-point probe measurements were conducted. One film was used for each condition such that after the 25 °C measurement, the same film was annealed at 45 °C, and onwards. To measure the conductivity of these films at 5 °C and -15 °C, these films were placed in a refrigerator and a freezer, respectively, for 30 min. Finally, to convert the measured sheet resistances to conductivity, the thicknesses of these films were measured using a Dektak XT profilometer.

[0158] Mechanical Characterization of Conducting Polymer-Based Formulations. Tensile tests, lap joint shear tests, and 3-point bend tests were performed in order to evaluate the mechanical properties of commercial adhesives and disclosed embodiments of conducting polymer-based electronic adhesives.

[0159] For tensile tests, conductive polymer-based formulations were drop cast (~1 mL) into an inversed dogbone mold milled from a block of Teflon (length = 1.3 cm, center width = 0.7 cm, depth = 1 cm). The mold containing PEDOT-based solution was gently heated at 60 °C overnight to dry the films. The dried films were carefully removed from the mold using tweezers, and any excess edges of non-uniform height were carefully trimmed off using scissors. Commercial EC As were deposited by blade coating a thin and uniform film of adhesive on top of a PTFE film with an adhesive backing (McMaster-Carr) using a commercial Zehntner ZAA2300 blade coater. The adhesive film was then cured in an oven at 150-160 °C for ~20 min until dry. The ECA film was then carefully peeled off the PTFE substrate. A 3D-printed dogbone mold was used to trace dogbone geometries on the thin ECA film, which were then cut out using scissors. Before testing, the thickness of the dogbone specimens were measured using a digital micrometer (REXBETI, 0.001 mm resolution). To perform the tensile tests, dogbone samples were placed in 3D-printed or purchased grips (Mark-10, G1003) attached to a 10 N force gauge (Mark-10, M5-2) on a linear actuator (Mark- 10, ESM303). These samples were elongated at a strain rate of 1 mm min’1until fracture. Load-travel data were converted to stress-strain data using the geometries of eachdogbone.

[0160] For lap joint shear tests, a small amount of adhesive was applied to one edge of a silver- coated substrate before another substrate was glued on top. For conducting polymer-based formulations, a plastic 1 mb syringe (Henke-Ject) was used to dispense the adhesive line. For commercial EC As, a slim, rounded wooden craft stick was used to carefully draw a thin adhesive line across the edge of the bottom silver-coated substrate before the top substrate was applied. When the top substrate was applied, a microscope slide was placed underneath the free edge of the top substrate in order to keep the top substrate level. Conducting polymer-based samples had an overlap of approximately 6-10 mm, while commercial EC A samples had an overlap of approximately 2-4 mm. These samples were cured in the oven at -150 °C for 15 min and left under vacuum overnight before testing. Prior to testing, the length of the substrate overlap was measured and recorded using a caliper, and the thickness was measured using a micrometer by first measuring the thickness of the lap joint, and then subtracting by the thickness of each substrate. To perform the lap joint shear tests, samples were loaded vertically onto the Mark-10 linear actuator (ESM303) with wedge grips (G1061-3, rubber jaw faces) holding both ends attached to a 100 N force gauge (for conducting polymer samples) or 2.5 kN force gauge (for commercial ECA samples). The samples were pulled apart in a shearing setup with the actuator moving upwards at a rate of 1.3 mm min'1(ASTM D1002 standards). The adhesive strength was calculated by dividing the maximum load by the surface area of each lap joint, and the energy dissipated was calculated by dividing the work (the area under the force-displacement curve) by the surface area of each lap joint. The travel was converted to the shear strain by dividing by the thickness of the lap joint. To compare the lap shear behavior of adhesive lap joints for glass / silver substrates to their tested use case (i.e., shingling silicon solar cells), a Sunpreme cell was laser scribed and diced into 38 mm x 20 mm x 175substrates. An adhesive lap joint was formed as described above using these silicon solar cell pieces and the shear behavior of these samples was evaluated using the same lap joint shear tests.

[0161] To understand how the electronic properties of disclosed PEDOT:PSS fdms change over time in comparison to CA-183, three different degradation conditions were tested in an example study. First, PEDOT:PSS and CA-183 fdms were subjected to 65% relative humidity (RH) at 25 °C. Second, fdms were subjected to 65% RH at 65 °C. Finally, fdms were submerged in water at 65 °C. For each of these degradation tests, fdms were prepared by solution shearing(blade coating) as described above. As 4-point probe measurements can puncture the soft PEDOT:PSS fdms, nine fdms were fabricated in each sample set, such that for each time point of a degradation condition, a new film is measured using a 4-point probe (sheet resistance) and profilometer (thickness). Films at each degradation timepoint were measured using the 4-point probe after being dried in a vacuum chamber (to remove residual moisture) overnight. For films that were only subjected to 65% RH, 4-point probe measurements were performed both before and after drying in the vacuum chamber. Optical microscopy images were taken on representative samples throughout each degradation test using a Leica DM2700M microscope (bright field, 10- 20* magnification, bottom light source). To approximate the moisture absorbed by ECA films under different environmental conditions, four sets of films of PEDOT:PSS, PEDOT:PSS / GOPS, and CA-183 were blade coated on 25 mm x 25 mm silicon substrates with an applicator height of 650 pm. These films were then all dried in a vacuum chamber (glove box antechamber, -100 in Hg) overnight to remove residual moisture. Following this, one set of films were placed in each of the following environments: a vacuum chamber, a 25 °C and 65% RH chamber, a 65 °C and 65% RH chamber, and a 65 °C water bath (100% RH). Afterwards, each film was dried in a vacuum oven (85 °C, -30 kPa) overnight. Each sample was weighed using a Mettler Toledo XPE205 balance (0.01 mg resolution) before film deposition (to get the mass of the bare Si substrate), after drying in vacuum, after being subjected to each degradation condition for 24 h, and after being dried in the oven. These measurements were used to estimate the mass of the deposited film and the moisture absorbed by each film under 24 h of each degradation condition.

[0162] FIG. 30A shows example images obtained from lap joint shear tests which were performed with glass / silver substrates (left) and laser cut silicon cells (middle, right). FIG. 30B shows example shear stress-strain curves from lap joint tests performed with glass / silver substrates. The right plot in FIG. 30B provides a detailed view of the PEDOT-based material behavior. FIG. 30C shows an optical microscope image of example cells shingled with PEDOT:PSS / GOPS, showing the thickness of the lap joint to be approximately 64 pm.

[0163] Table 7 shows the dimensions of the example lap joint shear samples. All samples included a lap joint formed between two substrates where silver was evaporated on top. The structure of these samples was deposited to be glass / Ag (100 nm) / ECA / Ag (100 nm) / glass. The width of all samples in Table 7 was assumed to be the width of the substrate, 25.4 mm.Table 7: Dimensions of example lap shear joints

[0164] Table 8 shows dimensions of example ECA samples used for tensile tests. The thickness, length, and width describe the rectangular region of the dogbone geometry.Table 8: Dimensions of example ECA samples

[0165] FIG. 31 A shows example stress-strain curves from tensile tests ofPEDOT:PSS blended with different additives in an example study. FIG. 3 IB shows example elastic modulus data from tensile tests of PEDOT PSS blended with different additives in the example study. FIG. 31C shows example tensile strength data from tensile tests of PEDOT:PSS blended with different additives in the example study. FIG. 3 ID shows example linear elasticity data from tensile tests ofPEDOT:PSS blended with different additives in the example study. FIG. 3 IE shows example toughness data from tensile tests of PEDOT:PSS blended with different additives in the example study. FIG. 3 IE shows example fracture strain data from tensile tests of PEDOT:PSS blended with different additives in the example study.

[0166] The use of Block-6 for the adhesive matrix of disclosed ICA materials was explored in an example study. It was hypothesized that the soft, stretchable PPEGMEA block would increase the viscoelastic adhesion of the material. However, experimental results demonstrated that Block- 6 showed significantly higher resistivities compared to PEDOT:PSS when blended with polar additives and cast in a solid film, suggesting weaker secondary doping effects (FIGS. 31A-31F).

[0167] This observation is in agreement with understandings of the secondary doping mechanism, where the increase in conductivity for PEDOT:PSS is in part attributed phase segregation which results in the formation of larger PEDOT domains. The attachment of the PPEGMEA block to PSS likely weakens this morphological change. While the PPEGMEA chains likely contribute to the ionic conductivity, the copolymer also has a significantly increased proportion of electrically insulating material, resulting in this increased bulk resistivity.

[0168] FIG. 32A shows the chemical structure of Block-6. FIG. 32B shows example fill factors of pristine shingled cells using Block-6 / DMSO and Block-6 / EG. FIG. 32C shows example bulk resistivity data of Block-6 in comparison to PEDOT:PSS-based and silver-based conductive adhesives. FIG. 32D shows a comparison of a figure of merit for example shingled interconnections using Block-6 (both crosslinked and non-crosslinked). FIG. 32E shows shear modulus data of example shingled interconnections. FIG. 32F shows shear strength data, as calculated from the respective parameters extracted from lap shear tests, of example shingled interconnections. FIG. 32G shows example stress-strain curves of Block-6, with extracted toughness, in comparison to other materials, as measured using tensile tests.

[0169] Findings of the example study described above suggest that temperature accelerates the moisture-driven morphological rearrangement, resulting in little change of electrical conductivity over 30 days at 25 / 65, but greater degradation at 65 / 65 and 100 / 65. Interestingly, crosslinked fdms under 65 / 65 conditions seemed to degrade faster than in a 65 °C water bath. Microscope images for samples on day 11, 15, and 20 (FIGS. 21-23) and photographs on day 20 (FIGS. 25A-25C) showed significant discoloration on the surface of crosslinked films stored at 65 / 65, but relatively pristine films submerged in a water bath. This degradation also seems to result in decreasedelectronic conductivity, with the exception of PEDOT:PSS / glycerol / GOPS (FIG. ID). Likewise, it was noticed, qualitatively, that four-point probe measurements for crosslinked PEDOT:PSS films stored in 65 / 65 conditions were often inconsistent and highly variable.

[0170] Profilometry measurements showed a significant decrease in thickness for the 100 / 65 films but relatively constant thickness for 65 / 65 films, aside from glycerol / GOPS (FIGS. 14A-F). Together with electrical measurements and microscope images, these data suggest that under 65 / 65 conditions, morphological rearrangement disrupts the electronically favorable PEDOT:PSS morphology. Here, PSS chains are driven to the surface and partially dissolve in a humid environment. However, the majority of these loose chains remain in the film (as the thickness does not change), creating an insulating, PSS-rich layer at the interface. These domains of increased hydrophilicity interact with the moisture in the environment, creating the visible beading effects and discoloration on the film surface. For PEDOT:PSS / glycerol / GOPS and PEDOT:PSS / glycerol, profilometry showed that the thickness of the film decreased over time, suggesting that PSS chains were likely being removed (particularly non-crosslinked polymer chains, in the case of PEDOT :PSS / glycerol / GOPS). This difference resulted in a smaller decrease in electrical conductivity compared to the other PEDOT:PSS films. In contrast, in a water bath, it is possible that non-crosslinked PSS chains were immediately removed by dissolution, preserving the crosslinked morphology. In all such cases, degradation mechanisms seemed to be heavily moisture driven.

[0171] In the following description, an example price comparison between silver-based ECAs and example ICAs based on the disclosed technology is provided. The price of silver-based ECAs is strongly tied to the price of silver itself. It was approximated the price of silver-based ECAs is approximately 20% greater than the price of silver to account for the polymer dispersion, labor, and mixing, with an additional 10% markup. The average price of silver (and also copper) was reported as the spot price of silver (as of August 2023), with the error being calculated from the peak and valley price range in 2023. The price of PEDOT:PSS was reported as the bulk price. The error was calculated by collecting several quotes for 1 kg of PEDOT:PSS and determining the peak and valley prices (as a percentage of the mean price).

[0172] FIG. 33 shows an example plot comparing cost of silver required for busbar and shingled solar cell architectures.

[0173] Data on the total annual supply of silver, total annual demand of silver, average annualprice of silver, and annual demand of silver by solar photovoltaics were taken from World Silver Surveys as published by The Silver Institute. The percentage of silver consumed annually by solar PV is calculated by simply dividing the annual demand of silver by solar PV by the total annual supply of silver. Projections for the consumption of silver required for meeting sustainable energy targets were calculated using a projection for total solar capacity. This projection was calculated by approximating the total installed capacity to 2023 to be 1.3946 TW installed, and assuming 30% growth in total capacity until 2030 to reach 10 TW. Finally, our projection assumed steady state growth from 2030 to 2050 until 75 TW is reached, such that a linear regression is calculated using the installed capacity at 2030 and the target capacity (75 TW) at 2050 (Table 1).

[0174] For the amount of silver required to reach these targets, silver learning curve projections, determined elsewhere, were used. For simplicity, linear rather than logarithmic learning was assumed by calculating the amount of silver used (mg / W) to be the average of the current silver usage (18 mg / W) and the lowest projected silver usage in 2050, assuming a total installed capacity of 75 TW (5 mg / W). As such, the projected silver demand scaled linearly with the total installed capacity. The low and high bounds for the silver consumption projection were determined from the current silver usage (high estimate) and silver learning curve projection at 2050 (low estimate). The amount of silver required for modules shingled with silver-based ECAs and silver-free (all-polymer) ECAs was calculated. For projections of silver consumption using shingled modules, the (unrealistic) assumption that 100% of projected solar capacity installed is shingled was made (i.e., a complete and immediate transition from conventional busbar modules). Again, linear approximations were made for the upper and lower projected limits.

[0175] To determine the amount of silver used in shingled modules, it was assumed that the solar cells would be completely busbar-free. As such, silver would only be used for the fingers. Others have determined that busbar-free cells had approximately 61% less silver than conventional cells with printed silver busbars. As such, it was approximated that removing the busbars in a shingled architecture would reduce the silver used (per module, per Watt, and per cell) by 60%. Because disclosed, all-polymer conductive adhesives completely remove silver from the EC A, this approximation was used to estimate the current silver consumption of passivated emitter and rear contact (PERC) cells (p-type), tunnel oxide passivated contact (TOPCon) cells (n-type) and silicon heterojunction (SHJ) cells (n-type). The silver consumption for conventional busbar PERC (14.4 - 15.7 mg / W), TOPCon (20.4 - 26 mg / W), and SHJ (30.3 - 37.4 mg / W) cells were taken fromcalculations tabulated elsewhere .

[0176] Table 9 shows an example estimation of silver consumption of shingled solar modules using silver-free conductive adhesives.Table 9: Example estimation of silver consumption of shingled solar modules

[0177] The cost of silver per Watt for silver-free shingled modules was determined by multiplying the average mass of silver per Watt used by the spot price of silver (0.00082788 $ / mg, August 2023). The low and high error bounds were calculated from the low and high estimations for silver consumption.

[0178] To determine the amount of silver used in the adhesive joint formed using silver-based EC As, it was assumed that the volume of the ECA used is equivalent to the volume of the shingle overlap formed (i.e., that there are no void spaces). The width of the average overlap was approximated to be 1 mm, and the error to be a 25% deviation in overlap (0.75 mm and 1.25 mm). The use of M2 (-156.75 mm2) cells was assumed, such that the side length was always 156.75 mm. Therefore, it was assumed that the length of the adhesive line was always 156.75 mm. As such, the surface area of the proposed lap joint was calculated to be 156.75 mm2(with the low error bound to be 117.56 mm2and high error bound to be 195.94 mm2). To determine the volume, it was assumed that the thickness of the lap joint formed would be 35 pm ± 15 pm. The lower bound of the error was determined by taking the minimum lap joint thickness and multiplying it by the lowest possible surface area (117.56 mm2x 0.02 mm), while the upper bound of the error was determined by taking the maximum lap joint thickness and multiplying it by the greatest possible surface area (195.94 mm2x 0.05 mm). As such, the mean volume was found to be 156.75 mm2x 0.035 mm = 5.48625 mm3, with lower and upper volumes of 2.35125 mm3and 9.79688 mm3, respectively. To calculate the mass of the lap joint, volume was converted to mass using the density of CA-183, which the technical specification sheet lists at 4 g / cm3. As such, the mass of ECA used for one shingle was determined to be 21.945 mg (with lower and upper bounds of 9.405mg and 39.1875 mg, respectively). Typical solar modules are composed of 60 or 72 cells, where 60-cell modules are typically used for residential solar and 72-cell modules are typically used for commercial solar. Here, the use of 72-cell modules with a surface area of 2 m2in surface area was assumed, such that approximately 5 shingles can be formed per wafer. This calculation yields an approximation of 360 shingles per solar module, which was used as a conversion factor to determine the amount of ECA used per module. It was approximated that the amount of silver contained in a commercial silver-based ECA is between 70-80 wt%, as suggested by other reports. As such, the average silver loading was taken to be 75%, with 70% and 80% as the bounded error. Thus, the average mass of silver used per solar module was approximated as 5.92515 g per module, with lower and upper bounds of 2.337006 g and 11.286 g, respectively. To convert this calculated silver usage to a per Watt basis, we again used data tabulated elsewhere, which states that a PERC module typically yields 440 - 450 W, a TOPCon module typically yields 450 - 460 W, and a SHJ module typically yields 465 - 470 W. Again, the average power generated is used for the average calculation, while the lower and upper bounds are used for the error calculations. The calculated values are provided in the Table 10 below.

[0179] Table 10 shows the estimated silver consumption of silver-based conductive adhesives used as interconnect replacements.Table 10

[0180] To determine the amount the cost of the applied adhesive per Watt, only raw material costs were considered. The price of the silver ECA was approximated at $1000 / kg for the conversion factor. Finally, to determine the total amount of silver used by the entire module (i.e., the adhesive and the deposited fingers), the calculated values in Table 9 were added to the respective values in Table 10.

[0181] Table 1 1 shows the total estimated silver consumption of shingled solar modules using silver-based conductive adhesives.Table 11 : Total estimated silver consumption of shingled solar modules

[0182] In FIG. IB, the silver consumption of shingled modules using silver-free EC As was calculated to be 40% of the silver consumed by busbar modules. Likewise, the projection of silver consumption for shingled modules using silver-based EC As was calculated assuming the type of cell used is only p-type PERC cells (such that the median, low, and high values can be found in Table 11). The confidence intervals were calculated such that the high error assumes no improvement upon the current usage of silver, while the low error assumes immediate improvement to the projected 2050 rate on the silver learning curve. In FIG. IE, similar assumptions are made, such that the silver demand of shingled modules using silver-free ECAs is calculated to be 40% by the current consumption of silver from busbar modules. The projected silver demand for conventional busbar values that are shown for comparison are approximated from the silver learning curve as previously described.Examples

[0183] Embodiments of the disclosed technology support inter alia the following examples.

[0184] Example 1. In some example embodiments, a method of producing an intrinsically conductive adhesive (ICA) for interconnecting solar modules comprises acquiring a material comprising an insulating epoxy matrix; synthesizing the ICA by replacing the insulating epoxy matrix with a conducting polymer matrix free of electronic filler material; and modifying one or more formulations of the ICA by incorporating at least one of a crosslinker, polar dopants, adhesion promoters, or carbon nanotubes into the ICA.

[0185] Example 2. The method of example 1 or any of examples 1-8, wherein the material is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

[0186] Example 3. The method of example 1 or any of examples 1-8, wherein the crosslinker is silane-based or (3-glycidyloxypropyl)trimethoxysilane (GOPS).

[0187] Example 4. The method of example 1 or any of examples 1 -8, wherein the polar dopants include dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol.

[0188] Example 5. The method of example 1 or any of examples 1-8, wherein dispensability of the ICA is modified by adding a solvent to the material, removing a solvent from the material, or exchanging a solvent of the material.

[0189] Example 6. The method of example 1 or any of examples 1-8, wherein a conductivity of the ICA is controlled based on a concentration of the polar dopants.

[0190] Example 7. The method of example 1 or any of examples 1-8, wherein the conducting polymer matrix includes a block copolymer, wherein the block copolymer is PEDOT:PSSl-b- PPEGMEA6.

[0191] Example 8. The method of example 1 or any of examples 1-7, wherein incorporating the crosslinker reduces moisture ingress into the ICA or a volume change of the ICA upon exposure to a solvent.

[0192] Example 9. In some example embodiments, an engineered material for constructing solar apparatus comprises a 7t-conjugated material comprising a conducting polymer matrix free of electronic fdler material, wherein the ^-conjugated material includes at least one of a crosslinked network, polar dopants, adhesion promoters, or carbon nanotubes, wherein the engineered material is electrically conductive.

[0193] Example 10. The engineered material of example 9 or any of examples 9-18, wherein the 7t-conjugated material is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

[0194] Example 11. The engineered material of example 10 or any of examples 9-18, wherein the crosslinked network is formed between PSS chains of PEDOT:PSS.

[0195] Example 12. The engineered material of example 9 or any of examples 9-18, wherein the polar dopants and the carbon nanotubes are substantially free of metal, wherein one or more electrical properties of the engineered material are controllable based on the polar dopants or the carbon nanotubes.

[0196] Example 13. The engineered material of example 9 or any of examples 9-18, wherein the polar dopants include dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol.

[0197] Example 14. The engineered material of example 9 or any of examples 9-18, wherein the conducting polymer matrix is made to be adhesive by copolymerization and functionalization of polymer side chains of the conducting polymer matrix.

[0198] Example 15. The engineered material of example 9 or any of examples 9-18, wherein the conducting polymer matrix is formed using a block copolymer.

[0199] Example 16. The engineered material of example 15 or any of examples 9-18, wherein the block copolymer is a block 6 copolymer or poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMEA).

[0200] Example 17. The engineered material of example 9 or any of examples 9-18, wherein the crosslinked network is formed using a silane-based crosslinker.

[0201] Example 18. The engineered material of example 9 or any of examples 9-18, further comprising copolymer blocks attached to the 7r-conjugated material.

[0202] Example 19. In some embodiments, a method includes interconnecting solar modules using any one of the engineered materials of examples 9-18.

[0203] Example 20. In some embodiments, a device includes solar modules interconnected using any one of the engineered materials of examples 9-18.

[0204] Example 21. In some embodiments, a method includes providing an electrical interconnection between electronics devices using any one of the engineered materials of examples 9-18.

[0205] Example 22. In some example embodiments, a solar assembly system includes a plurality of solar modules configured to receive solar radiation and convert the solar radiation to electrical power; and an intrinsically conductive adhesive (ICA) coupled to and interconnecting the plurality of solar modules such that the plurality of solar modules are in thermal and electrical communication with each other, wherein the ICA comprises a ^-conjugated material comprising a conducting polymer matrix.

[0206] Example 23. The system of example 22 or any of examples 22-28, wherein the plurality of solar modules is arranged as roof shingles in the solar assembly system using the ICA, wherein at least a portion of each solar module overlaps with another portion of an adjacent solar module.

[0207] Example 24. The system of example 22 or any of examples 22-28, wherein the solar assembly system is free of silver.

[0208] Example 25. The system of example 22 or any of examples 22-28, wherein the conducting polymer matrix is free of electronic filler material.

[0209] Example 26. The system of example 22 or any of examples 22-28, wherein the n- conjugated material is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

[0210] Example 27. The system of example 22 or any of examples 22-28, wherein the plurality of solar modules includes at least one stretchable interconnection formed using the ICA, wherein the at least one stretchable interconnection enables at least some of the plurality of solar modules to extend and contract by deformation of the stretchable interconnection.

[0211] Example 28. The system of example 22 or any of examples 22-28, wherein the ICA is produced according to any one of the methods of examples 1-8.

[0212] Example 29. In some example embodiments, a method for interconnecting shingled solar modules uses a silver-free adhesive that includes a conducting conjugated polymer to interconnect at least two solar modules.

[0213] Example 30. The method of example 29, wherein the conducting conjugated polymer is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

[0214] Example 31. In some embodiments, an intrinsically conductive adhesive (ICA) material includes a conducting conjugated polymer material having a plurality of cross-linked conjugated polymeric strands that impart bulk electrical conduction to the ICA material, wherein the cross-linked conjugated polymeric strands include a 7t-conjugated polymer having polyelectrolytes along its backbone, and wherein the cross-linked conjugated polymeric strands are configured to form block co-polymers that impart a bulk mechanical toughness to the ICA material.

[0215] Example 32. The ICA material of example 31 or any of examples 31-38, further including one or more cross-linking additive substances that manipulate at least one mechanical property of the ICA.

[0216] Example 33. The ICA material of example 31 or any of examples 31-38, wherein the block co-polymers are formed by constitutional substitutions in the polymer chain using Block-6.

[0217] Example 34. The ICA material of example 31 or any of examples 31-38, wherein the block co-polymers are formed by functionalization of side chains of the conducting conjugated polymer.

[0218] Example 35. The ICA material of example 31 or any of examples 31-38, furtherincluding at least one of a polar dopant, an adhesion promoter, or a carbon nanotube attached to the conducting conjugated polymer.

[0219] Example 36. The ICA material of example 35 or any of examples 31-38, wherein the polar dopant includes at least one of dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol.

[0220] Example 37. The ICA material of example 31 or any of examples 31-38, wherein the ^-conjugated material is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

[0221] Example 38. The ICA material of example 31 or any of examples 31-37, wherein the ICA material is metal free.Conclusion

[0222] Implementations of the subject matter and the functional operations described in this patent document can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing unit” or “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

[0223] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in aportion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0224] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0225] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0226] While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0227] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

[0228] Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.

Claims

CLAIMSWhat is claimed:

1. A method of producing an intrinsically conductive adhesive (ICA) for interconnecting solar modules, comprising: acquiring a polymer material comprising an insulating epoxy matrix; synthesizing the ICA by replacing the insulating epoxy matrix with a conducting polymer matrix free of electronic filler material; and optimizing at least one functional property of the ICA by modifying one or more formulations of the ICA including incorporating one or more of a crosslinker, polar dopants, adhesion promoters, or carbon nanotubes into the ICA.

2. The method of claim 1, wherein the polymer material is poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

3. The method of claim 1, wherein the crosslinker is silane-based or (3- glycidyloxypropyl)trimethoxysilane (GOPS).

4. The method of claim 1, wherein the polar dopants include dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol.

5. The method of claim 1, wherein dispensability of the ICA is modified by adding a solvent to the material, removing a solvent from the material, or exchanging a solvent of the material.

6. The method of claim 1, wherein a conductivity of the ICA is controlled based on a concentration of polar dopants.

7. The method of claim 1, wherein the conducting polymer matrix includes a block copolymer, wherein the block copolymer is PEDOT:PSSl-b-PPEGMEA6.

8. The method of claim 1, wherein incorporating the crosslinker reduces moisture ingress into the ICA or a volume change of the ICA upon exposure to a solvent.

9. An engineered material for constructing solar apparatus, comprising: a 7r-conjugated material comprising a conducting polymer matrix free of electronic fdler material, wherein the ^-conjugated material includes at least one of a crosslinked network, polar dopants, adhesion promoters, or carbon nanotubes, wherein the engineered material is electrically conductive.

10. The engineered material of claim 9, wherein the ^-conjugated material is poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

11. The engineered material of claim 10, wherein the crosslinked network is formed between PSS chains of PEDOT:PSS.

12. The engineered material of claim 9, wherein the polar dopants and the carbon nanotubes are substantially free of metal, wherein one or more electrical properties of the engineered material are controllable based on the polar dopants or the carbon nanotubes.

13. The engineered material of claim 9, wherein the polar dopants include dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol.

14. The engineered material of claim 9, wherein the conducting polymer matrix is made to be adhesive by copolymerization and functionalization of polymer side chains of the conducting polymer matrix.

15. The engineered material of claim 9, wherein the conducting polymer matrix is formed using a block copolymer.

16. The engineered material of claim 15, wherein the block copolymer is a block 6 copolymer or poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMEA).

17. The engineered material of claim 9, wherein the crosslinked network is formed using a silane-based crosslinker.

18. The engineered material of claim 9, further comprising copolymer blocks attached to the 7r-conjugated material.

19. The engineered material of any of claims 9-18, wherein the engineered material is used in a device that comprises solar modules interconnected using the engineered material.

20. The engineered material of any of claims 9-18, wherein the engineered material is used in a method of interconnecting solar modules.

21. The engineered material of any of claims 9-18, wherein the engineered material is used in a method of providing an electrical interconnection between electronic devices.

22. A solar assembly system, comprising: a plurality of solar modules configured to receive solar radiation and convert the solar radiation to electrical power; and an intrinsically conductive adhesive (ICA) coupled to and interconnecting the plurality of solar modules such that the plurality of solar modules are in thermal and electrical communication with each other, wherein the ICA comprises a ^-conjugated material comprising a conducting polymer matrix.

23. The system of claim 22, wherein the plurality of solar modules are arranged as roof shingles in the solar assembly system using the ICA, wherein at least a portion of each solar module overlaps with another portion of an adjacent solar module.

24. The system of claim 22, wherein the solar assembly system is free of silver.

25. The system of claim 22, wherein the conducting polymer matrix is free of electronic filler material.

26. The system of claim 22, wherein the 7t-conjugated material is poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

27. The system of claim 22, wherein the plurality of solar modules includes at least one stretchable interconnection formed using the ICA, wherein the at least one stretchable interconnection enables at least some of the plurality of solar modules to extend and contract by deformation of the stretchable interconnection.

28. The system of claim 22, wherein the ICA is produced according to any one of the methods of claims 1-8.

29. An intrinsically conductive adhesive (ICA) material, comprising: a conducting conjugated polymer material having a plurality of cross-linked conjugated polymeric strands that impart bulk electrical conduction to the ICA material, wherein the crosslinked conjugated polymeric strands include a ^-conjugated polymer having polyelectrolytes along its backbone, and wherein the cross-linked conjugated polymeric strands are configured to form block co-polymers that impart a bulk mechanical toughness to the ICA material.

30. The ICA material of claim 29, further comprising: one or more cross-linking additive substances that manipulate at least one mechanical property of the ICA.

31. The ICA material of claim 29, wherein the block co-polymers are formed by constitutional substitutions in the polymer chain using Block-6.

32. The ICA material of claim 29, wherein the block co-polymers are formed by functionalization of side chains of the conducting conjugated polymer.

33. The ICA material of claim 29, further comprising: at least one of a polar dopant, an adhesion promoter, or a carbon nanotube attached to the conducting conjugated polymer.

34. The ICA material of claim 33, wherein the polar dopant includes at least one of dimethyl sulfoxide (DMSO), ethylene glycol (EG), or glycerol.

35. The ICA material of claim 29, wherein the ^-conjugated material is poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

36. The ICA material of claim 29, wherein the ICA material is metal free.

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