WO2023018838A1

WO2023018838A1 - Systems and methods for cavitation of core shell particles

Info

Publication number: WO2023018838A1
Application number: PCT/US2022/040004
Authority: WO
Inventors: Dana Lynn HANKEY; Marshall Campion TIBBETTS; Joseph Capobianco; Christopher Davey
Original assignee: Applied Cavitation, Inc.
Priority date: 2021-08-11
Filing date: 2022-08-10
Publication date: 2023-02-16

Abstract

Provided is a paste for solar cell manufacturing. The paste can include a binder. The paste can include core-shell particles entrained in the binder at a predetermined density. The core-shell particles can include a metal core enclosed by a shell. Provided in another embodiment is a process for manufacturing a paste for solar material. The process can include forcing core-shell particles that include a core enclosed by a shell into a hydrodynamic cavitation chamber. The process can include applying a cavitation dispersion process to the core-shell particles to make the paste. Provided in another embodiment is a method of manufacturing paste for solar material. The method can include forcing core-shell particles that include a metal core enclosed by a shell into a hydrodynamic cavitation chamber. The method can include applying a cavitation dispersion process to the core-shell particles to make the paste.

Description

SYSTEMS AND METHODS FOR CAVITATION OF CORE SHELL PARTICLES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Appl. No. 63/232,046 filed on August 11, 2021 which is incorporated herein by reference in its entirety for any and all purposes.

BACKGROUND

[0002] Conventional processes such as three-roll milling, bead milling, rotor stator mixing, and high shear overhead mixing can damage a core-shell particle. These conventional processes utilize macro mixing techniques where the objects acting on the material to mix it are significantly larger than the core-shell particles. These objects then come into physical contact to force the particles to de-agglomerate. However, the objects can exert a crushing force or a high shear force that changes a morphology of particles. For example, the forces applied on the core-shell particles by large objects can cause damage to the shells of the core-shell particles and/or change their structure.

SUMMARY

[0003] In view of the foregoing, the Inventors have recognized and appreciated the advantages of an improved paste for solar cell manufacturing, and the processes and methods of achieving the improved paste.

[0004] Accordingly, provided is an improved paste for solar cell manufacturing. The improved paste can include a binder. The improved paste can include core-shell particles entrained in the binder at a predetermined density. The core-shell particles can include a metal core enclosed by a shell.

[0005] In some embodiments, the core-shell particles entrained in the binder can have a conductivity of 0.5 micro ohms per centimeter squared to 1.5 micro ohms per centimeter squared. In some embodiments, the core-shell particles have a weight % loading between 35% and 95% and a volume % between 30% and 64% of the improved paste. In some embodiments, the core-shell particles include a core comprising copper, ceramic, alumina, silica, carbon, electrically conductive ceramics, antimony tin oxide, indium tin oxide, alumina doped zinc oxide, or electrically conductive polymers, the core enclosed by the shell that includes silver, gold, palladium, platinum, or nickel. In some embodiments, the core-shell particles are arranged in concentric spheres. In some embodiments, the core-shell particles include flake core-shell particles including the metal core enclosed by the shell. In some embodiments, the core-shell particles include multiple metal cores enclosed by multiple concentric shells.

[0006] Provided in another embodiment is a process for manufacturing an improved paste for solar material. The process can include forcing core-shell particles that include a core enclosed by a shell into a hydrodynamic cavitation chamber. The process can include applying, within the hydrodynamic cavitation chamber, a cavitation dispersion process to the core-shell particles to make the improved paste.

[0007] In some embodiments, the improved paste includes core-shell particles entrained in a binder. The improved paste can have a weight consisting of between 35% and 95% of the coreshell particles and a volume consisting of 32% to 64% of the core-shell particles. In some embodiments, the process includes forcing a solvent that includes core-shell particles into the hydrodynamic cavitation chamber. The solvent can have a predetermined viscosity between 0.1 centipoise and 1000 centipoise. In some embodiments, the process includes forcing the coreshell particles into the hydrodynamic cavitation chamber by an air-driven piston, air, hydraulics, or a mechanical force. In some embodiments, the improved paste has a first conductivity. In some embodiments, the process includes heating the improved paste to a predetermined temperature. The heated improved paste can have a second conductivity lower than the first conductivity. In some embodiments, the core-shell particles include a copper core enclosed by a shell that includes silver, gold, palladium, platinum, or nickel. In some embodiments, the coreshell particles are arranged in concentric geometries. In some embodiments, the core-shell particles are flake core-shell particles that include the metal core enclosed by a flake silver shell. In some embodiments, the core-shell particles include multiple metal cores enclosed by multiple concentric shells. In some embodiments, the core-shell particles are sized such that the shell encloses a hollow region that encloses the metal core.

[0008] Provided in another embodiment is a method of manufacturing improved paste for solar material. The method can include forcing, by an air-driven piston, hydraulics, or a mechanical force, core-shell particles include a metal core enclosed by a shell into a hydrodynamic cavitation chamber. The method can include applying, within the hydrodynamic cavitation chamber, a cavitation dispersion process to the core-shell particles to make the improved paste.

[0009] In some embodiments, the method can include heating the core-shell particles to a temperature between 25 °C and 100 °C. In some embodiments, the method can include pressurizing the core-shell particles to a pressure between 0 and 45,000 psi. In some embodiments, the method can include acquiring a short circuit current and open circuit voltage of the improved paste. In some embodiments, the method can include reapplying the cavitation dispersion process to the improved paste until the short circuit current and the open circuit voltage each satisfy a respective predetermine threshold.

[0010] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly used herein that also can appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE FIGURES

[0011] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein can be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features.

[0012] The accompanying drawings are not intended to be drawn to scale. In the drawings, like reference characters generally refer to like features (i.e., functionally similar and/or structurally similar elements). Like reference numbers and designations in the various drawings indicate like elements. For purposes of clarity, not every component can be labeled in every drawing. In the drawings:

[0013] FIG. l is a view of the cavitation machine for applying the cavitation dispersion process, according to some embodiments; [0014] FIG. 2 is a cross-sectional view of the cavitation machine for applying the cavitation dispersion process, according to some embodiments;

[0015] FIG. 3 is a view of the cavitation machine that includes thermal control for applying the cavitation dispersion process, according to some embodiments;

[0016] FIG. 4 is a view of the cavitation machine that includes a feedback loop for applying the cavitation dispersion process, according to some embodiments;

[0017] FIG. 5 is a flow diagram of an embodiment of a method for manufacturing the improved paste for solar material using any of the embodiments of the cavitation machine described in FIGs. 1-4; and

[0018] FIG. 6 is a view of core-shell particles prior to the cavitation dispersion process and after the cavitation dispersion process.

DETAILED DESCRIPTION

[0019] Following below are more detailed descriptions of various concepts related to, and embodiments of, improved paste for solar material. It should be appreciated that various concepts introduced above and discussed in greater detail below can be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0020] For purposes of reading the description of the various embodiments below, the following descriptions of the sections of the specification and their respective contents can be helpful:

[0021] Section A describes an overview of cavitation which can be useful for practicing embodiments described herein;

[0022] Section B describes an overview of cavitation equipment which can be useful for practicing embodiments described herein; and

[0023] Section C describes an improved paste for solar material according to embodiments of the present disclosure. A. Cavitation

[0024] Cavitation can refer to the formation of vapor cavities in a liquid (e.g., small liquid- free zones such as “bubbles” or “voids”) that are formed as a result of forces acting upon the liquid. Cavitation can occur when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low. When subjected to higher pressure, the voids can implode and can generate an intense shockwave. Depending on the application, any suitable mode of cavitation can be used in the methods and systems provided herein. For example, the cavitation dispersion process in can involve, or be, hydrodynamic cavitation.

[0025] The cavitation dispersion process can refer to vaporization, bubble generation, and bubble implosion which occurs in a flowing liquid as a result of a decrease and subsequent increase in pressure. Hydrodynamic cavitation can be produced by passing a liquid through a constricted channel at a specific velocity or by mechanical rotation of an object through a liquid. In the case of the constricted channel and based on the specific (or unique) geometry of the system, the combination of pressure and kinetic energy can create the hydrodynamic cavitation cavern downstream of the local constriction generating high energy cavitation bubbles.

[0026] Orifices or a Venturi can be used for generating cavitation. A Venturi can be used because of its smooth converging and diverging sections, such that that it can generate a higher velocity at the throat for a given pressure drop across it. On the other hand, an orifice can accommodate a greater number of holes (larger perimeter of holes) in a given cross sectional area of the pipe. Both options are possible.

[0027] Some of the pre-existing cavitation systems utilize opposing waterjets to create the pressure needed for cavitation to occur while others create the pressure and resulting vacuum by having hydraulic pumps driving and oscillating plungers which draw the low viscosity materials in and then push the low viscosity material through the specific point where cavitation occurs. However, none of these pre-existing systems is equipped to handle a raw material that has a viscosity larger than that of a fluid, to disperse the constituents, or to attain the desired particle size distribution through de-agglomeration. B. Cavitation Equipment

[0028] Depending on the application, any suitable equipment capable of carrying out cavitation or emulsification can be used. Provided is a cavitation machine that can include a first feed tube adapted to contain a raw material, which has a first viscosity and is to be supplied into a hydrodynamic cavitation chamber that is downstream and separate from the apparatus. The cavitation machine can include an air-driven piston configured to create a condition having a first pressure and a first temperature sufficiently high to reduce the first viscosity to a second viscosity which is sufficiently low for the raw material to be pushed into an orifice of the hydrodynamic cavitation chamber to undergo a hydrodynamic cavitation dispersion process to de-agglomerate core-shell particles without changing their morphology.

[0029] Referring now to FIG. 1 and in brief overview, shown is a view of the cavitation machine 105 for applying the cavitation dispersion process, according to some embodiments. The cavitation machine 105 can include an inlet 110, an outlet 115, a feed tube 120, raw material 125, a piston 130, air valve 135, and an airline 140.

[0030] Still referring to FIG. 1 and in further detail, the cavitation machine 105 can be a commercially available or custom-designed. The inlet 110 provided herein and attached to the cavitation machine 105 can be configured to feed the raw material 125 into the cavitation machine 105. The cavitation machine 105 provided herein can fabricate the raw material 125. The raw material 125 can include core-shell particles, glass, organic material, inorganic materials, or any other material described herein.

[0031] The cavitation machine 105 can include the feed tube 120, the raw material 125 inside the feed tube 120, and the piston 130 that pushes the material down the feed tube 120, forcing it into the inlet 110 of the cavitation machine 105. The cavitation machine can also include the air valve 135 on the back end of the feed tube 120, which air valve 135 controls the flow of compressed air into the feed tube 120. The cavitation machine can include an airline 140, which feeds compressed air into the air valve 135 and into the feed tube 120 from a source of compressed air.

[0032] The cavitation machine 105 can include any suitable components, depending on the application. For example, the cavitation machine 105 can include two hydraulic pumps which are utilized to push the paste through a very small orifice, into a very small vacuum chamber, and out another very small orifice that creates a specific desired back pressure. In some embodiments, this combination of small orifices with a vacuum chamber in the middle is where the hydrodynamic cavitation occurs.

[0033] Now referring to FIG. 2 and in brief overview, shown is a cross-sectional view of the cavitation machine for applying the cavitation dispersion process, according to some embodiments. The cavitation machine 105 can include a cavitation chamber 205, a heat exchanger 210, an oscillating plunger 215, a ball check 220, a hydraulic reservoir 225, a motor 230, a nitrogen bag 240, and a pump 245.

[0034] Still referring to FIG. 2 and in further detail, the cavitation machine 105 can include a hydraulic reservoir 225, a motor 230, which runs a pump 245, to pump the hydraulic oil up to an intensifier 235, which drives the oscillating plunger 215 that pushes the material through the cavitation chamber 205, while the ball check 220 closes to allow the material to be forced through the cavitation chamber 205, where the orifices are housed and the cavitation takes place. As the intensifier 235 pushes the oscillating plunger 215 forward, hydraulic oil in the front of the intensifier 235 is pushed against a nitrogen bag 240. After the oscillating plunger 215 is all the way forward, a positioning sensor stops the pump 245 from driving the intensifier 235, and the pressure accumulates against the nitrogen bag 240, causing the oscillating plunger 215 to be pushed back to its starting position. The material that undergoes cavitation can flow from the cavitation chamber 205 to the heat exchanger 210 and into the outlet 115.

[0035] Depending on the application, the setups, including the number of feed tubes, can be varied. In some embodiments, a small single feed tube containing the medium to high viscosity raw material can be used for small batches that can be tested after each pass through the cavitation machine. The cavitation dispersion process can generate a lot of heat while cavitating the raw material 125. In some embodiments, a thermal control can control the temperature of the product material as it exits the cavitation machine 105 so that the material can exit the cavitation dispersion process at an appropriate and stable temperature. The temperature is preferably below a thermal degradation temperature of the product material. The thermal degradation temperature is a function of the material properties of the constituents of the material. For example, downstream from the cavitation chamber, some embodiments of the cavitation machine described herein can include a thermal control, which includes at least one of a heat exchanger, a thermocouple, and a cooling fluid reservoir configured to supply the fluid to cool the product material discharged from the hydrodynamic cavitation chamber. The thermal control can be configured to control the second temperature to be below a thermal degradation temperature of the raw material.

[0036] Now referring to FIG. 3 and in brief overview, shown is a view of the cavitation machine 105 that includes thermal control for applying the cavitation dispersion process, according to some embodiments. The cavitation machine 105 can include a heat exchanger 305, a thermocouple 310, a water valve 315, inlet water tubing 320, outlet water tubing 325, and a chilled water source 330.

[0037] Still referring to FIG. 3 and in further detail, the cavitation machine 105 can include the heat exchanger 305 inline directly after the material exits the cavitation dispersion process. The heat exchanger 305 can be followed (downstream) by a thermocouple 310, which is configured to read the temperature of the material after the material has passed the heat exchanger 305. Chilled water can be applied to the heat exchanger using at least a water valve 315, which allows water to flow from a chilled water source 330 to the heat exchanger 305 via the inlet water tubing 320 through the heat exchanger 305, then out of the heat exchanger 305 and back to the return water connection of the chilled water via the outlet water tubing 325.

[0038] The flow of the water can be controlled manually or automatically, such as by a software program. In some embodiments, a predetermined temperature can be inputted into a software program that, when executed, causes at least one processor to execute the thermal control. In another embodiment, the feedback from the thermocouple can enable the software to adjust the water valve 315 such that the temperature of the material exiting the thermal control is within a desired range. In some embodiments, the raw material 125 undergoes cavitation in a single discrete pass and delivered to a second tube via the outlet 115. The tubes are then interchanged and the cavitation dispersion process can be repeated for as many passes as needed to achieve the desired product material properties.

[0039] Now referring to FIG. 4 and in brief overview, shown is a view of the cavitation machine 105 that includes a feedback loop for applying the cavitation dispersion process, according to some embodiments. The cavitation machine 105 can include feed tube 405, two- way valves 410A and 41 OB (generally referred to as two-way valves 410), a three-way valve 415, a pressure transducer 420, and an air valve 425.

[0040] Still referring to FIG. 4 and in further detail, this embodiment can allow or facilitate multiple cavitation passes. The feedback loop, which can be further downstream from the thermal control, can include a second feed tube; a plurality of two-way valves and three-way valves configured to resupply the product material back into the hydrodynamic cavitation chamber to repeat the hydrodynamic cavitation dispersion process; and a pressure transducer. This embodiment can be suitable for a larger-scale production than the smaller (e.g., R&D) embodiment described above. One benefit of the feedback loop described herein is mitigation (such as complete elimination) of exposure to contamination (e.g., air).

[0041] In addition to the thermal control as shown in FIG. 3, the cavitation machine 105 as shown in FIG. 4 can include two tubes of similar size that are set up with air driven pistons. In some embodiments, the size of the tubes can be a factor to determine the batch size, although there is no limit as to the amount of the raw material 125 that can be cavitated by the cavitation machine 105 described herein. The automation that can be applied to the cavitation machine 105 as described in FIG. 3 can similarly be applied to the cavitation machine 105 described in FIG. 4. For example, the automation can use valves to control the direction of the raw material 125 as it goes into and out of the cavitation machine 105.

[0042] The two-way valves 410 can control the direction of the raw material 125 when it is being pushed into the cavitation machine 105, as well as the direction the raw material 125 travels after it exits the heat exchanger 305. The cavitation machine 105 can include the three- way valve 415, which is desirably in sync with the two-way valves 410 for the material to travel into the cavitation machine 105. In some embodiments, when the material in feed tube 120 is forced down the tube by the piston 130, the two-way valve 410 must be closed so that the material travels past that valve and to the three-way valve 415. When the material is in feed tube 120, the three-way valve 415 allows the material to travel from feed tube 120 into the cavitation machine 105. [0043] After cavitation takes place, the material travels through the thermal control and out of the heat exchanger 305, and past the thermocouple 310. At this point, the material can flow through the two-way valve 410B and into feed tube 405, pushing the air-driven piston down the tube towards the back of the tube where the air valve 425 supplies air to the piston in tube 405. While moving the material from feed tube 405, the air valve 425 is open so that air can be pushed out of tube 405 as it fills with material and the piston 130 is forced towards the back of tube 405. When feed tube 120 is empty, the piston 130 inside hits the front of feed tube 120, and there is no more pressure on the material being forced into the machine.

[0044] The pressure transducer 420, which can be located near the inlet of the machine by the three-way valve, can transmit this drop in pressure to software, which then causes at least one processor to switch the two-way valves and three-way valves so that the material can travel from tube 405 back through cavitation machine 105 and back into feed tube 120. Once the valves have switched (e.g., valve 410B is closed, valve 410A is open, and valve 415 is switched) so that material travels from tube 405 into cavitation machine 105, the air valve 425 can automatically turn on and force the piston 130 and the material down tube 405 and back to feed tube 120.

[0045] An operator or user can choose the number of times the material can pass through the cavitation machine 105, thereby repeating the cavitation or cooling (by the thermal control). In some embodiments, after the pre-determined number of passes is achieved, the cavitation machine 105, as well as the air driving the valves and pistons, can automatically shut off. This safety feature can release the air pressure once the current cycle is completed. In some embodiments, the cavitation machine 105 described herein allow samples of the material to be taken at any time to determine if the desired results have been achieved after a certain number of passes at the desired operating pressure(s) and temperature(s).

[0046] In some embodiments, the cavitation machine 105 provided herein can control the temperature of the material by at least one of software and several thermocouples used to determine the temperature of the material at any point during the cavitation dispersion process and actuate a water valve, which controls the flow of chilled water to the heat exchanger put inline directly after the cavitation takes place. In some embodiments, the material is cooled after cavitation to reduce the temperature to a range that is suitable for the material being cavitated so that it remains stable and ready for the next cycle or pass. Without this temperature control, the material in at least some embodiments can retain too much heat and can gain even more heat energy though each pass, resulting in damaging some of its constituents. When the material is cavitated with set parameters for pressure and temperature, which can be determined for each material through trial and errors and/or parametric studies, the consistency of the product from lot to lot can be superior to any other pre-existing process for preparing medium to high viscosity inks, pastes, slurries or dispersions of Nano-particles.

C. Cavitation of Core-Shell Particles

[0047] Core-shell particles can be adopted and utilized for biomedical, pharmaceutical, catalysis, electronics, optical properties, a solar cell, an electronic device, an optoelectronic device, a printed sensor, transparent conductive coatings (e.g., at least one of carbon nanotubes, graphene, and indium tin oxide), advanced ceramics, a biosensor, an actuator, an energy harvesting device, a hybrid circuit, a sonar, a radar, a touch screen, a 3D printing device, and a thermal management material. Core-shell particles can also be used in silver-filled polymer inks for organic solar cell applications, touch screen applications, or any other application that utilizes fine line printing and high electrical conductivity.

[0048] Core-shell particles can include a non-porous core in the center and a porous layer outside of the core. Core-shell particles can be synthesized in a wide range of configurations. Some exemplary configurations are concentric spheres or non-spherical shapes such as hexagonal core-shell particles. Core-shell particles can also be synthesized to contain multiple cores, multiple concentric shells, or hollow shells. Core-shell particles can include moveable cores within shells that contain “empty space.” Nanoparticles can fill interstitial spaces within the formulation. The nanoparticles can be core-shell particles or silver particles. The core can include organic or inorganic materials. The shells can include organic or inorganic materials. The core-shell particles can include an inorganic core and an inorganic shell, an organic core and an inorganic shell, an inorganic core and an organic shell, and an organic core and an organic shell. Core-shell materials can be prepared with shells that passivate the core. In these applications, the shell can be used to preserve core materials that would otherwise decompose or undergo irreversible chemical reactions that render them ineffective for their intended purpose. [0049] Dispersing the core-shell particles can improve performance metrics of the core-shell particles, such as their conductivity. However, conventional mixing and dispersion methods of core-shell particles can have adverse effects on the function of the core-shell material.

[0050] Core-shell particles can reduce manufacturing costs. In catalyst materials, the core can be hollow or include inert or less costly materials, whereas the shell can include the catalytic properties. However, the catalytic ability of the resultant material can be adversely affected if the shell of the material is disrupted during or post manufacturing. In solar applications, copper can have the prerequisite conductivity for inclusion in a photovoltaic (PV) conductive paste. Since the cost of copper can be less than silver, utilizing silver-shell and copper-core particles can lower the cost of the PV conductive paste by reducing the amount of silver in the paste. The silver shell can prevent the copper from oxidizing by isolating it from the air during sintering. However, conventional mixing and dispersion methods of conductive particles, which can also include glass in its organic vehicle, can damage the Ag shell of the core-shell particle. For example, when PV conductive paste is printed onto a wafer and goes through a firing profile to burn off the organic vehicle, some of the glass particles mixed with the conductive particles (e.g., silver) can melt, dissolve the conductive phase, and penetrate the anti -reflective coating on the wafer (silicon nitride) to make contact with the emitter layer. If the shell (e.g., silver) of a coreshell particle is damaged, the core (e.g., copper) gets exposed, which can disrupt passivation or containment of the core to create electrical problems (e.g., conductivity, changes to short circuit current (ISC) and the open circuit voltage (VOC) for the PV cell, etc.).

[0051] In another example, core-shell particles can be engineered with shells to enhance dispersion and solubility within a specific medium. Disrupting the surface coating can reduce the ability for homogeneous suspensions to be prepared and reduce the stability or shelf life of prepared suspensions.

[0052] In another example, core-shell particles can be prepared with shells that contain chemically reactive functional groups on their surface. In biomedical applications, these functional groups can be used to covalently attach oligonucleotides, proteins, or carbohydrates. However, the disruption of the coating can impact biomedical device performance. For example, in diagnostic applications, disruptions can lead to false negative or false positive responses. [0053] In another example, composite applications can include fillers coated with chemically reactive groups to crosslink with materials in the matrix. However, in composite applications, disrupting the shell can affect the number of functional groups present. Disruptions to the stoichiometry can affect the ability of the material to affectively cure. Disruption can also adversely affect device properties such as mechanical strength, electrical conductivity, or thermal conductivity.

[0054] Many applications that utilize core-shell particles also depend on a particular weight or volume ratio between the core and the shell. For example, multicore and banded materials have unique ratios between the core and the shell. In biomedical applications, the ratio can be used to control the release of a drug, or ensure that a host is isolated from a core. Disrupting the ratio can lead to uncontrolled elution rates of drugs, or lead to exposure of toxic components that would then trigger immune responses. In semiconductor materials, the ratio of the core and the shell can be selected for a specific efficiency (e.g., electrical, bandwidth, etc.). Disrupting the ratio in semiconductor materials can affect optoelectronic performance of displays or absorption/emission patterns for bio-imaging.

[0055] In another example, core-shell particles can be designed with specific magnetic properties. Therefore, if the ratio between the core and the shell is modified, the resulting magnetic or paramagnetic performance of the materials can be adversely affected. These disruptions can cause issues with immunomagnetic separation and/or delivery. For example, immunomagnetic applications can use core-shell particles that include multiple magnetic particles within a polymeric shell. The materials can be paramagnetic materials that enable the particles to disperse and not aggregate throughout a formulation. Upon the exposure to a magnetic field, the particles can be attracted or collected to facilitate separation or delivery. If the core-shell structure and thus the magnetic field is affected, then the particles might not be effectively recovered or delivered to their target.

[0056] A cavitation dispersion process, such as but not limited to the embodiments discussed in reference to FIGs. 1-4, of core-shell particles can de-agglom erate them without changing their morphology. The cavitation dispersion process can utilize the implosion of vacuum bubbles to exert force on the core-shell particles to cause them to de-agglomerate and mix with other constituents. The vacuum bubbles that form and implode during the cavitation can be on the size scale of the particles (in the micron size range). Therefore, the implosion of the vacuum bubbles can release forces that are sufficient for dispersing core-shell particles without damaging the structure of the core-shell particle or altering their morphology. Accordingly, the cavitation dispersion process avoids utilizing macro-objects that expose the particles to damaging physical forces, such as the crushing or striking of the particles that is common in conventional mixing techniques.

[0057] In solar applications, a cavitation dispersion process can de-agglomerate PV conductive paste that contains silver-coated copper conductive particles that were screen-printed onto a PV wafer. After the cavitation dispersion process was applied, reliability tests performed have indicated that the silver shells are intact and the copper cores are not exposed. For example, the reliability tests of the conductive pastes can be based on microscopy or performance (e.g., electrical properties, conductivity, etc.) of the PV cell.

[0058] Provided is an improved paste for solar cell manufacturing. The improved paste can include a binder. The binder can be any material or substance that holds or draws other materials together to form a cohesive whole mechanically, chemically, by adhesion or cohesion. The binders can be liquid or dough-like substances that harden by a chemical or physical process and bind fibers, filler powder and other particles added into it. For example, binders can include glue, adhesive and thickening agents.

[0059] The improved paste can include core-shell particles entrained in the binder at a predetermined density. The core-shell particles entrained in the binder can have a non-uniform density. The core-shell particles can include a variety of combinations of core materials and shell materials. For example, the cores can include ceramic, metal, or polymers. The shells can include polymers, ceramic, or metal. Table 1 includes core-shell combinations:

Table 1 - Core-Shell Combinations:

[0060] The shells can be a coating that encloses the cores. A thickness of the shell can be uniform. More specific combinations of core-shell particles can include a metal core enclosed by a silver shell. The core can include copper, ceramic, alumina, silica, palladium rhodium, iridium, carbon materials, electrically conductive ceramics (e.g., antimony tin oxide, indium tin oxide, alumina doped zinc oxide, etc.), electrically conductive polymer (e.g., PANNI and PEDOT-PSS), or any other electrically conducive material. The shell enclosing the core can include silver, gold, palladium, platinum, nickel, a ceramic (ITO, etc.), carbon, or conductive polymer (PANI, PEDOT-PSS). The shells can serve a role of passivation without affecting the conductivity of a cured or sintered film. The conductivity of the improved paste can be suitable for solar applications. In some embodiments, the core-shell particles entrained in the binder can have a conductivity of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10 micro ohms per centimeter squared. Surface resistivity can be important for thin layers of paste in which conductivity is measured in two dimensions. Bulk resistance can be important for thick layers of films or paste in which conductivity is a factor in three dimensions.

[0061] Ceramic shells can passivate metallic cores. Formation or densification of the ceramic shell materials can be completed with a heat treatment. Preservation of the shell can facilitate it fulfilling its purpose (e.g., passivation). For example, core-shell quantum dots can include a shell that surrounds their quantum dot core to improve stability and photoluminescence efficiency. However, cores such as cadmium sulfide can adversely affect the performance of the material if exposed and thus should remain enclosed.

[0062] Polymer shells can protect cores. For example, polymer thick film applications can encapsulate cores such as a curative in a two-part thermoset. The shell can prevent the curative from crosslinking while mixing and maximizing printing pot life and shelf life. However, heat can melt the shell such that the curative core is exposed.

[0063] Cores can improve conductivity of the core-shell particle. For example, a cermetsolar cell can include conductive gridlines with low bulk and surface resistance. Cores can satisfy surface resistance with inert, stable, and lower cost materials such as a polymer or ceramic. For example, polymer thick film applications such as ESD, or thin film applications such as thin film or organic solar cells, can utilize polymer or ceramic cores. In some embodiments, the core is 30, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, or 64% of the volume of the improved paste. The core can be 10, 20, 30, 40, 50, 60, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, or 95% of the total weight of the improved paste.

[0064] The weight and volume can relate to the molecular formulation of the improved paste. In some embodiments, the core-shell particles are between 35% and 95% of the weight of the improved paste. In some embodiments, the core-shell particles are between 30% and 64% of the volume of the improved paste. Improved pastes that include glass of a lower density can have a lower weight percentage of the core-shell particles to maintain a desired volume. For example, improved pastes with silica cores can have up to 64% of its volume and 95% of its weight be silica. In another example, improved pastes with silver cores can have up to 55% of its volume and 92% of its weight be silver.

[0065] In some embodiments, the core-shell particles can be a solvent-based slurry. The core-shell particles entrained in the binder can have any viscosity. For example, the viscosity can be 0.1, 1; 5; 10; 20; 40; 60; 80; 100; 150; 200; 250; 300; 350; 400; 500; 600; 700; 800; 900;

1,000; 5,000; 10,000; 25,000; 50,000; 75,000; 100,000; or 250,000 centipoise. There is no upper limit or lower limit for the viscosity.

[0066] In some embodiments, the core-shell particles are arranged in concentric spheres. In some embodiments, the core-shell particles include flake core-shell particles including the metal core enclosed by the shell. In some embodiments, multiple shells can enclose one core. In some embodiments, the core-shell particles include multiple metal cores enclosed by multiple concentric shells. For example, the multiple concentric shells can be multiple concentric silver shells, multiple concentric nickel shells, or a combination of the two. The shells can be a passivating layer that does not adversely affect the electrical, thermal, or magnetic characteristics of the improved paste. The particles can have any geometry, shape, or sizes. For example, the particles can be a sphere, a sheet, a flake, a frit, an ellipsoid, or an irregular shape. The particle can be any size. The term “size” referred to herein can refer to the diameter, radium, length, width, height, etc., depending on the context and geometry of the particle. In some embodiments, when the term “size” is used to describe a plurality of particles, the size can refer to an average size of the plurality.

[0067] The core-shell particles can also include different materials. For example, the coreshell particles can be a blend of conductive and conductive coated particles. In some embodiments, the core-shell particles can include an electrically conductive material, at least one type of glass, at least one organic solvent, and/or at least one polymer material. In some embodiments, the electrically conductive material can be silver. Any of the constituent particles can have any of the particle sizes as described above.

[0068] Depending on the constituents of the core-shell particles, core-shell particles can have a variety of particle sizes because each of the constituents can have a different particle size from the others. In some embodiments, some of the constituents have similar or the same sizes. For example, the glass and the electrically conductive material can have similar or the same sizes. In some embodiments, all of the constituents have different sizes. In some embodiments, the coreshell particles can include at least two (e.g., 2, 3, 4, 5, 6, 7, 8, or more) average particle size distributions.

[0069] Electrically conductive core-shell particles can include any suitable material that is electrically conductive, depending on the application. For example, it can include a metal, an alloy, a semiconductor, and/or a carbon-based material that is electrically conductive. In some embodiments, the electrically conductive material includes at least one of silver, palladium, palladium rhodium, iridium, gold, platinum, nickel, copper, ruthenium, or an alloy thereof. A formulation thereof is also possible. In another embodiment, the electrically conductive material includes at least one of carbon black, graphene, carbon nanotubes, and graphite (e.g., carbon allotropes). [0070] The improved paste can include any type of suitable glass, depending on the application. The glass can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10% of the improved paste. The improved paste can include one type of glass. For example, the improved paste can include 1, 2, 3, 4, 5, 6, 7, 8, or more types of glass (e.g., lead or borosilicate). In some embodiments, the improved paste includes at least two types of glass. In some embodiments, a weight ratio of the first type of glass and the second type of glass in the improved paste is 8: 1. Other ratios, such as 10: 1, 15: 1, 20: 1, etc., are also possible, depending on the application.

[0071] The glass can include silicate such as a borosilicate. The borosilicate glass can be a lead-containing borosilicate glass. Table 2 includes example glass with lead monoxide for combining with core-shell particles to manufacture the improved paste:

Table 2 - Glass with Lead Monoxide

[0072] The borosilicate glass can be lead-free. The lead-free glass can be a bismuth- containing borosilicate glass. Table 3 includes examples of lead-free bismuth-containing borosilicate glass for combining with core-shell particles to manufacture the improved paste:

Table 3 - Lead-Free Bismuth-Containing Borosilicate Glass

[0073] Table 4 includes examples of lead-free glass for combining with core-shell particles o manufacture the improved paste:

Table 4 - Lead-Free Glass

[0074] At the minimal flow temperature, the glass can have minimal inter-granular glass transfer. At the ideal flow temperature, the glass can exhibit low viscosity and improved substrate wetting. The flow temperatures are for pure glass after 10 minutes at the specified temperature. The flow characteristics can change based on additives and glass ratios.

[0075] The glass can be a tellurium-containing borosilicate glass. Table 5 includes examples of glass with tellurium for combining with core-shell particles to manufacture the improved paste:

Table 5 - Tellurium-Containing Borosilicate Glass

[0076] The glass can have any suitable material properties, depending on the application.

For example, the glass can have a softening temperature between 200 °C and 800 °C, between 350 °C and 480 °C, between 400 °C and 460 °C, between 410 °C and 450 C, between 420 °C and 440 °C, etc. Other softening temperature values are also possible, depending on the material.

[0077] The glass can have a glass transition temperature between 200 °C and 800 C, between 250 °C and 450 °C, between 300 °C and 400 °C, between 320 °C and 385 °C, between 340 °C and 370 °C, between 350 °C and 360 °C, etc. Other glass transition temperature values are also possible, depending on the material. For example, a first glass type can have a first transition temperature and a second glass type can have a second transition temperature. The second transition temperature can be higher than the first transition temperature.

[0078] The improved paste can include any type of suitable organic solvent, depending on the application. The organic solvent can include at least one of an alcohol, an aliphatic, an aromatic, a ketone, ethyl acetates, and an ester. The alcohol can include a monoterpene alcohol or an alcohol ester. In some embodiments, the organic solvent can include at least one of ester alcohol and alpha terpineol. The ester alcohol can be, for example, TEXANOL.

[0079] The polymer material can include any type of suitable polymer material, depending on the application. The polymer material can include at least one of a resin, a thixotropic agent, a lubricant, a plasticizer, and a wax. The resin can include ethyl cellulose. The thixotropic agent can include modified castor oil derivative. The lubricant or plasticizer can include olefin copolymers, poly-alkyl methacrylates, styrene polymers, etc.

[0080] In some embodiments, the improved paste includes (i) 0.5 to 6.0 wt.% and 2 to 5% by volume of glass; (ii) 80 to 90 wt.% of core-shell particles (e.g., copper core and silver shell); (iii) 10.8 to 16.4 wt.% of an organic solvent; and (iv) 1.2 to 1.6 wt.% of a polymer material.

[0081] In some embodiments, the improved paste includes (i) 0.5 to 6.0 wt.% of glass; (ii) 65 to 77 wt.% of core-shell particles (e.g., copper core and silver shell); (iii) 18 to 29 wt.% of an organic solvent; and (iv) 2 to 5 wt.% of a polymer material. [0082] In some instances, non-electrically conductive material can be included with the coreshell particles. In some instances, the core-shell particles can also include incidental, inevitable impurities. The organic solvent and/or polymer material can be of any suitable content of the core-shell particles, depending on the application. For example, the product material can include 8-10 wt. % of at least one of (i) at least one organic solvent and (ii) at least one polymer material. Other wt. % values are also possible. The content can change as a result of the cavitation dispersion process. For example, the cavitation dispersion process can melt or remove the impurities from the core-shell particles.

[0083] Now referring to FIG. 5 and in brief overview, shown is a schematic flowchart illustrating in some embodiments a method 500 for manufacturing an improved paste for solar material using any of the embodiments of the cavitation machine described in FIGs. 1-4. As shown in FIG. 5, formulation that includes at least the core-shell particles can be forced into a hydrodynamic cavitation chamber (505). A cavitation dispersion process can be applied to the formulation to make the improved paste (510). The improved paste can undergo reliability tests after cavitation (515).

[0084] Still referring to FIG. 5 and in further detail, the formulation can be forced into a hydrodynamic cavitation chamber (505). In some embodiments, the formulation can include core-shell particles entrained in a binder. In some embodiments, a solvent that includes the coreshell particles is forced into the hydrodynamic cavitation chamber. The solvent can have a predetermined viscosity between 0.1 centipoise and 1000 centipoise. In some embodiments, the core-shell particles include a copper core enclosed by a shell that includes silver, gold, palladium, palladium rhodium, iridium, platinum, or nickel. In some embodiments, the coreshell particles are arranged in concentric geometries. In some embodiments, the core-shell particles include flake core-shell particles that include the metal core enclosed by a flake silver shell. In some embodiments, multiple shells can enclose one core. In some embodiments, the core-shell particles can include multiple metal cores enclosed by multiple concentric shells. For example, the multiple concentric shells can be multiple concentric silver shells, multiple concentric nickel shells, or a combination of the two. The shells can be a passivating layer that does not adversely affect the electrical, thermal, or magnetic characteristics of the improved paste. In some embodiments, the core-shell particles are sized such that the shell encloses a hollow region that encloses the metal core. [0085] The formulation can be loaded into an engineered cavitation feed tube, which is attached to the cavitation machine (e.g., cavitation machine 105). In some embodiments, the formulation is forced into the hydrodynamic cavitation chamber by an air-driven piston, air, hydraulics, or a mechanical force. A piston in the feed tube is then driven down the feed tube (pneumatically in this example) to push or force the formulation into the cavitation machine.

[0086] A cavitation dispersion process can be applied within the hydrodynamic cavitation chamber to formulation that includes the core-shell particles to make the improved paste (510). The cavitation dispersion process can de-agglomerate the core-shell particles without changing their morphology. For example, the cavitation dispersion process can de-agglomerate the coreshell particles without damaging the shells and/or exposing the cores of the core-shell particles. In another example, the cavitation dispersion process can homogenously disperse solid fillers in the suspension of core-shell particles. By de-agglomerating the core-shell particles without changing their morphology, the cavitation dispersion process can enable the manufacture of the improved pasted as described herein.

[0087] The cavitation dispersion process can be applied to the whole formulation of the materials described herein. For example, the cavitation dispersion process can be applied to a formulation that includes core-shell particles, glass, an organic solvent, and a polymer. Applying the cavitation dispersion process to the whole formulation can be efficient (e.g., use less time or power) and result in an improved pasted (e.g., higher conductivity).

[0088] The cavitation dispersion process can be applied separately to each material in a formulation. For example, it can be difficult to cavitate some pre-mixed formulation of materials (e.g., high viscosity of the formulation). Therefore, cavitation dispersion process can be separately applied to individual materials such that the viscosity of each of the materials can be lowered and the materials themselves de-agglomerated. The cavitated materials can then be mixed into the improved paste. The cavitation dispersion process can be applied to the formulation of cavitated materials.

[0089] In one example, the cavitation dispersion process can be applied separately to the glass and the core-shell particles. After the glass and the core-shell particles undergo cavitation, they can be mixed into the formulation. Additional materials, such as a polymer binder, can be added to the formulation. The cavitation dispersion process can also be applied to the formulation. [0090] The cavitation dispersion process can be separately applied to a plurality of materials. For example, the cavitation dispersion process can be applied to a first material, such as the coreshell particles. The cavitated first material can be stored in a first container. The cavitation dispersion process can be applied to a second material, such as glass. The second material can be stored in a second container. The cavitation dispersion process can be applied to each material multiple times. For example, each material can undergo multiple passes (e.g., 2, 3, 4, or 5) in the cavitation machine. Each material can undergo a unique number of passes in the cavitation machine. The cavitation dispersion process can be applied to the materials until they reach a predetermined chemical or physical characteristic. For example, the cavitation dispersion process can be applied to the materials until their viscosity is lower than a predetermined threshold, or they are de-agglomerated. The cavitated materials can mixed. For example, the cavitated first material and the cavitated second material can be mixed into a formulation. The cavitation dispersion process can be applied to the formulation. For example, cavitation dispersion process can be applied to a formulation that includes the first material and the second material.

[0091] The materials can be separately added to the formulation of cavitated materials. For example, the first material can be pushed down a feed tube into the cavitation machine. The cavitation dispersion process can be applied to the first material such that the first material is passed through the cavitation machine and returned to the feed tube via a feedback tube. The second material can be pushed down the feed tube into the cavitation machine. The cavitation dispersion process can be applied to both the first material, which underwent a pass within the cavitation machine, and the added second material. The first and second material can undergo one or more passes in the cavitation machine. For example, the cavitation dispersion process can be applied to the formulation such that it undergoes 1, 2, 3, 4, or 5 passes in the cavitation machine before additional materials are added. The cavitation dispersion process can be applied to the formulation until it has a predetermined chemical or physical characteristic. For example, the cavitation dispersion process can be applied to the formulation until its viscosity is lower than a predetermined threshold, or it is de-agglomerated. Additional materials can be added to the formulation. More than one material can be added at any given time. For example, cavitation dispersion process can be applied to a formulation that includes the first and second material, a third and fourth material can be added, and then the cavitation dispersion process can be applied to a formulation of the third material, the fourth material, and the cavitated formulation of the cavitated first material and the cavitated second material.

[0092] The materials can be separately forced into the cavitation machine for cavitation as a formulation. For example, the first material can be pushed down a first feed tube into the cavitation machine, and the second material can be pushed down a second feed tube into the cavitation machine. Additional materials can be added via additional feed tubes. The cavitation dispersion process can be applied to all the materials as they are separately forced into the cavitation machine. Additional materials can be added at any time, such as after the previous materials undergo a predetermined amount of passes within the cavitation machine.

[0093] The formulation can be forced into the cavitation machine to undergo the cavitation dispersion process. The driving-through-piston or a heat blanket can heat the formulation. The formulation can go through the cavitation dispersion process and the temperature thereof increases due at least in part to thermal energy generated by high pressures. In some embodiments, the cavitation machine can heat the formulation to a temperature between 25 °C and 100 °C. In some embodiments, the temperature can be between 20 °C and 100 °C, between 25 °C and 80 °C, between 30 °C and 60 °C, between 35 °C and 50 °C, between 40 °C and 50 °C, etc. Other values are also possible, depending on the application. In some embodiments, the cavitation machine can pressurize the formulation to a pressure between 0 and 45,000 psi. In some embodiments, the pressure can be between 100 psi and 100,000 psi, between 500 psi and 80,000 psi, between 1,000 psi and 50,000 psi, between 2.000 psi and 10,000 psi, between 3,000 psi and 5,000 psi, etc. Other values are also possible, depending on the application.

[0094] The formulation then go into a heat exchanger after exiting the cavitation dispersion process to cool to a predetermined temperature (or temperature range), during which a thermocouple measures the temperatures downstream and/or upstream from the heat exchanger. A software program can receive feedback from the thermocouple located downstream from the heat exchanger and actuates a water valve that controls the flow of chilled water to the heat exchanger. When the improved paste exits the heat exchanger, it is at the desired predetermined temperature at least as a result of the thermal control.

[0095] In some embodiments, the cavitation machine described herein applies the cavitation dispersion process multiple times to the formulation. As the formulation is pushed down a feed tube, it passes a closed two-way valve and travels through an open three-way valve, past a pressure transducer and thermocouple and into the cavitation machine. After the formulation is forced into the cavitation machine, the formulation passes through the cavitation dispersion process. After the cavitated formulation flows out of the heat exchanger, it passes through the open two-way valve connecting to feed tube and into feed tube, pushing the piston in feed tube towards the back of the tube. When feed tube is empty and the formulation has completed one pass, the piston that forces the formulation then hits the front of the feed tube and stops; at this time the pressure of the formulation going through the three-way valve drops. A pressure transducer mounted to the three-way valve reads the pressure drop as a result of the feed tube being empty — when the software receives this feedback, it switches the two-way valves, three- way valve, and product air valves that control the air pushing the piston in the feed tube. After the software switches the valves and air supply, the formulation begins to feed back into the cavitation machine from feed tube, past a closed two-way valve and through the three-way valve to return into the machine. The software allows a user to enter the number of passes and set the temperature; after this information has been entered into the software, the machine can run the set number of passes automatically at a consistent temperature.

[0096] Depending at least on the equipment involved, the manufacturing of the improved paste for solar material can include a number of additional steps. For example, the improved paste can be cooled using a thermal control, including, for example, at least a feedback temperature control. In another example, the formulation can be pressurized by using at least an air-driven piston, hydraulics, or a mechanical force. In another example, forcing the formulation into the cavitation chamber (through the small orifice) can generate a lot of heat. The elevated temperature as a result of the addition of this heat can be controlled subsequently through the thermal control as described above.

[0097] Reliability tests can be performed to assess the improved paste (515). The reliability tests can determine whether the improved paste is de-agglomerated without damage to the coreshell morphology of the core-shell particles of the formulation. Visual observation can be carried out by a naked eye, an optical microscope, or an electron microscope. For example, the improved paste can be assessed or analyzed using microscopy with compositional characterization devices. The analysis can be based on EDS/WDS, Auger, or Raman/FTIR. In some embodiments, the metric used to describe the phenomenon of the particles in the product material maintaining their core-shell structures intact can be the lack of changes in conductivity. In some embodiments, the metric corresponds to solar cell efficiency. The core-shell structures can remain intact for an extended period of time.

[0098] The core-shell particles can be between 35% and 95% of the weight and 30% to 64% of the volume of the formulation. The formulation can include a mixture of core-shell particles and silver particles. The formulation can include nanoparticles to fill interstitial spaces within the formulation. The nanoparticles can be core-shell particles or silver particles. In some embodiments, the improved paste has a conductivity lower than a conductivity of the formulation before cavitation. In some embodiments, a short circuit current and open circuit voltage of the improved paste can be acquired. In some embodiments, the cavitation dispersion process can be reapplied to the improved paste until the short circuit current and the open circuit voltage each satisfy a respective predetermined threshold.

[0099] The viscosity of the improved paste can generally be lower after the cavitation dispersion process than the viscosity before the cavitation dispersion process due at least in part because of subjecting the formulation to the temperatures and the pressures. The viscosity varies with the material and also varies with the pressure and the temperature. For example, the viscosity after cavitation can be 10% to 90% of the viscosity before cavitation, 20% to 80%, 30% to 70%, 40% to 60%, 45% to 55%, etc., of the first viscosity. In some embodiments, the second viscosity is 25% to 50% of the first viscosity.

[0100] The product material as a result of fabrication can be used in a variety of devices. For example, the product material can be disposed onto a substrate to form a pattern on the substrate. The pattern can be, for example, gridlines. The substrate can be a part of a device, such as any of the devices described herein.

[0101] As described above, any part of the method, when used in conjunction with the cavitation machines described herein, can be automated. The automation can be accomplished at least in part using a software program. In some embodiments, the software program is stored on a non-transitory computer-readable medium. The program, when executed, causes at least one processor (such as a computer) to execute any of the methods (or portions thereof) described herein.

[0102] Now referring to FIG. 6, shown is particle dispersion of core-shell particles prior to the cavitation dispersion process and after the cavitation dispersion process. The core-shell particles are agglomerated (605). The core-shell particles undergo the cavitation dispersion process described herein (610), which causes the core-shell particles to be de-agglomerated in (615). The cavitation dispersion process (610) can de-agglomerate the core-shell particles without damaging their core-shell structures such that no visually observable agglomeration of the core-shell particles is observed in the improved paste (615).

Example 1 High Temperatures Crystalline p-type Solar Cells

[0103] Example 1 describes an exemplary formulation for high temperature crystalline p- type solar cells designed to accommodate printing of very fine gridlines (< 50 pm). Pre-existing typical peak firing (processing) temperatures are in the 700 °C-900 °C range. The formulation can include silver powder with a distribution of at least 3 different particle sizes and shapes (ranging from Nano-powders dispersed in a solvent to dry powders commercially available) to maximize the particle packing density to achieve an increased bulk electrical conductivity over industry standard formulations in the fired state after processing. Pre-existing inks can contain one or more glass types or powders with different softening points. The glass can include glass frits with phase separations in the frit, such as PYREX. For example, the glass can include one frit that is a combination of two or more frits.

[0104] The glass can facilitate the transport of silver to the emitter layer and also enhance the densification of the fired film through liquid phase sintering mechanisms. Denser films can have higher bulk electrical conductivities, and the ability to transport silver to the emitter layer of the cell can result in higher efficiencies (e.g., higher conductivity).

[0105] The individual constituents and inks/pastes can be pressurized from 1,000 psi to 30,000 psi. The orifices for controlling the internal pressures, flow rates, particle size limitations, and cavitation levels can range from 0.005 inches to 0.050 inches. Flow rates for the materials in the cavitation machine can depend on and commensurate with the various configurations. Flow rates for small sample volumes were in the 100 ml per minute range while production throughputs approached and even exceeded 20-30 liters per minute. The back pressure created in the cavitation region of the cavitation machine is important and varies depending on valve designs, orifice plate restrictions, and orientation. Temperature control of the feed materials and the material flowing into the cavitation machine can be important and depend on the organic constituent properties. Conditions can vary with respect to the order of the addition of the various materials, respective ink/paste viscosities, cavitation dispersion times, or the percentage of solid materials in the organic medium. Yields can be 100% once the cavitation machine reaches its initial charge volume, which is highly beneficial when applying the cavitation dispersion process to raw material 125 such as precious metals.

[0106] By applying the cavitation dispersion process with the equipment described herein, solar thick film screen printable formulations (front gridline contact) with a thickness of 12-20 pm and width of < 50 microns can fabricated:

Table 6 - Exemplary Ink Formulation

[0107] The cavitation dispersion process can include heating the silver solar front-side paste as described in Table 6 to 38 °C to 48 °C. The pressure range can be 4,500 psi to 45,000 psi. With respect to the orifice sizes of the cavitation machine, three different orifice sizes in sequence were used to create the pressure transitions need to form a vacuum and then cause the vacuum bubbles to implode. A primary orifice, then several secondary orifices, then a final orifice can be used to create back pressure. The primary 0.020" orifice can be used to break up larger agglomerates. After three passes, the orifice can be switched to a primary orifice 0.015", a secondary orifice 0.068", and a final orifice to create back pressure 0.038". The formulation can undergo any number of cavitation passes in the cavitation machine, such as 12 passes (three passes with primary .020", then remaining 9 with primary orifice .015").

[0108] The average silver particle sizes were in the range of <0.1 microns to 3.0 microns. The range for the total particle size distribution was from 0.1 microns to 10 microns. Three different silver powders spherical in nature were used to optimize packing density. The average particle sizes of the three various spherical powders were 0.2 pm, 0.5 pm, and 1.5 pm. The ratio of each on a wt. % basis in the solar formulation in Example 1 can be: 4:2:94 (based on 87% total silver weight in the solar ink formulation). The weight ratios can vary depending on the solar gridline width requirements. The primary larger constituent can be the primary component for silver spheres and can be >80% while the smaller sizes can each range from 0-15 wt. %. [0109] Borosilicate glasses can include silicon-boron-lead-aluminum (that can have a substitute such as bismuth for lead) in the ink or paste formulations described in Example 1. The glass formulation of Example 1 can be 4.5 wt. % and can be based on two different glass formulations that have properties in the ranges specified above. The glass with the higher melting point can have a ratio of 8: 1 for a formulation with two types of glass (e.g., lead and borosilicate). The glass with the lower melting point can cause the liquid phase sintering of the silver particles and uniform etching through the antireflective coating layer to make contact at the emitter layer where the charge carriers reside.

[0110] The organic solvent and polymer constituents can be in the wt. % range shown in Table 6. Solvents are TEXANOL and alpha-terpineol in an 8: 1 ratio, while the polymer constituents can vary based on the gridline geometry requirements. Polymer constituents can include ethyl celluloses, thixotropic agents, plasticizers and waxes. The percentage of organic vehicle (in the ink or paste formulation) that is synthesized from the solvents and various polymers into the single carrier formulation can be in the 8-10 wt. %.

Example 2 - Low Temperature Silver Inks for Solar Cells

[OHl] Silver conductive ink/paste formulations in Example 2 can be developed for solar cell designs, such as the back passivated solar cells. The designs described in Example 2 can utilize cell construction configurations that can increase the long wavelength carrier collection due to improved back side reflectance (BSR) and reduced back surface recombination velocity (BSRV). The low BSRV and high BSR can result in higher solar cell efficiencies (e.g., better conductivity). In contrast to the requirements of typical front silver gridlines on pre-existing solar cells in production, the silver inks described in Example 2 can adhere to back side dielectric after sintering at low temperature (250 °C-450 °C) to give provide high conductivity (e.g., less than 2 micro-ohm-cm) and preserve the passivation property of the back side dielectric.

[0112] These silver inks can include a glass constituent that has low softening and melting points, as well as a low glass transition temperature. These glass powders can soften, melt, and flow in order to provide liquid-phase assisted sintering at temperatures at or below 450 °C, with an optimal maximum below 400 °C. In contrast, silver inks for pre-existing front-side gridlines are can be manufactured with temperatures above 700 °C. [0113] The silver film formed in Example 2 can include characteristics, such as but not limited to: the core-shell particles, glass powders, or flakes can have a fine and narrow particle size distribution to achieve densification and acceptable electrical conductivity at a low cell manufacturing temperature. The silver film can form an acceptable electrical contact to the rear contacts that can be silver, aluminum, silver pads, or vias. The silver film does not penetrate the passivation layer to any extent but must have good adhesion to same. The silver film can be deposited by screen-printing. If the electrical conductivity is high enough, the film thickness is minimized, thus saving significant materials costs. The formulation of the silver screen-printable ink for such designs described in Example 2 is shown in Table 7:

Table 7 - Exemplary Ink Formulation

[0114] The cavitation dispersion process can include heating the silver solar front-side paste to 30 °C to 45 °C. The cavitation dispersion process can include pressurizing the materials to 1,000 psi to 20,000 psi. With respect to the orifice sizes of the cavitation machine, three different orifice sizes in sequence can be used to create pressure transitions needed to form a vacuum and then cause the vacuum bubbles to implode. A primary orifice, then several secondary orifices, then a final orifice can be used to create back pressure. The primary 0.020" orifice can be used to break up larger agglomerates. After 3 passes, it can be switched to primary orifice 0.015", secondary orifices 0.068", and a final orifice 0.038" to create back pressure.

[0115] Borosilicate glasses can include silicon-boron-lead-aluminum (that can have a substitute such as bismuth for lead) in the ink or paste formulations described in Example 2. The glass can have softening points in the range of 330 °C to 350 °C. The glass transition temperature range can be from 250 °C-270 °C. The particle size ranges for the glass and silver flakes and spheres can be the same as described in Example 1.

[0116] All literature and similar material cited in this application, including, but not limited to, patents, patent applications, articles, books, treatises, and web pages, regardless of the format of such literature and similar materials, are expressly incorporated by reference in their entirety. In the event that one or more of the incorporated literature and similar materials differs from or contradicts this application, including but not limited to defined terms, term usage, described techniques, or the like, this application controls.

[0117] While the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.

[0118] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments can be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0119] The above-described embodiments of the invention can be implemented in any of numerous ways. For example, some embodiments can be implemented using hardware, software or a combination thereof. When any aspect of an embodiment is implemented at least in part in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.

[0120] In this respect, various aspects of the invention can be embodied at least in part as a computer readable storage medium (or multiple computer readable storage media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium or non-transitory medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the technology discussed above. The computer-readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present technology as discussed above.

[0121] The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be used to program a computer or other processor to implement various aspects of the present technology as discussed above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of the present technology need not reside on a single computer or processor, but can be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present technology.

[0122] Computer-executable instructions can be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules can be combined or distributed as desired in various embodiments.

[0123] Also, the technology described herein can be embodied as a method, of which at least one example has been provided. The acts performed as part of the method can be ordered in any suitable way. Accordingly, embodiments can be constructed in which acts are performed in an order different than illustrated, which can include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0124] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. [0125] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” Any ranges cited herein are inclusive.

[0126] The terms “substantially” and “about” used throughout this specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.

[0127] The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements can optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising,” can refer, in some embodiments, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0128] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. [0129] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements can optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in some embodiments, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0130] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

[0131] The claims should not be read as limited to the described order or elements unless stated to that effect. It should be understood that various changes in form and detail can be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. All embodiments that come within the spirit and scope of the following claims and equivalents thereto are claimed.

Claims

CLAIMS What is claimed is:

1. An improved paste for solar cell manufacturing comprising: a binder; and core-shell particles entrained in the binder at a predetermined density, the core-shell particles comprising a metal core enclosed by a shell.

2. The improved paste of claim 1, wherein the core-shell particles entrained in the binder have a conductivity of 0.5 micro ohms per centimeter squared to 1.5 micro ohms per centimeter squared.

3. The improved paste of claim 1, wherein the core-shell particles comprise a weight % loading between 35% and 95% and a volume % between 30% and 64% of the improved paste.

4. The improved paste of claim 1, wherein the core-shell particles comprise a core comprising copper, ceramic, alumina, silica, carbon, electrically conductive ceramics, antimony tin oxide, indium tin oxide, alumina doped zinc oxide, or electrically conductive polymers, the core enclosed by the shell comprising silver, gold, palladium, platinum, or nickel.

5. The improved paste of claim 1, wherein the core-shell particles are arranged in concentric spheres.

6. The improved paste of claim 1, wherein the core-shell particles comprise flake core-shell particles comprising the metal core enclosed by the shell.

7. The improved paste of claim 1, wherein the core-shell particles include multiple metal cores enclosed by multiple concentric shells.

8. An improved paste for solar material manufactured using a process of:

36 forcing core-shell particles comprising a core enclosed by a shell into a hydrodynamic cavitation chamber; and applying, within the hydrodynamic cavitation chamber, a cavitation dispersion process to the core-shell particles to make the improved paste.

9. The improved paste of claim 8, wherein the improved paste comprises the core-shell particles entrained in a binder, the improved paste having a weight consisting of between 35% and 95% of the core-shell particles and a volume consisting of 32% to 64% of the core-shell particles.

10. The improved paste of claim 8, wherein forcing the core-shell particles comprises forcing a solvent comprising the core-shell particles into the hydrodynamic cavitation chamber, the solvent having a predetermined viscosity between 0.1 centipoise and 1000 centipoise.

11. The improved paste of claim 8, wherein forcing the core-shell particles comprises forcing the core-shell particles into the hydrodynamic cavitation chamber by an air-driven piston, air, hydraulics, or a mechanical force.

12. The improved paste of claim 8, wherein the improved paste has a first conductivity, and wherein the process includes heating the improved paste to a predetermined temperature, wherein the heated improved paste has a second conductivity lower than the first conductivity.

13. The improved paste of claim 8, wherein the core-shell particles comprise a copper core enclosed by a shell comprising silver, gold, palladium, platinum, or nickel.

14. The improved paste of claim 8, wherein the core-shell particles are arranged in concentric geometries.

15. The improved paste of claim 8, wherein the core-shell particles comprise flake core-shell particles comprising the metal core enclosed by a flake silver shell.

16. The improved paste of claim 8, wherein the core-shell particles include multiple metal cores enclosed by multiple concentric shells.

37

17. The improved paste of claim 8, wherein the core-shell particles are sized such that the shell encloses a hollow region that encloses the metal core.

18. A method of manufacturing improved paste for solar material comprising: forcing, by an air-driven piston, hydraulics, or a mechanical force, core-shell particles comprising a metal core enclosed by a shell into a hydrodynamic cavitation chamber; and applying, within the hydrodynamic cavitation chamber, a cavitation dispersion process to the core-shell particles to make the improved paste.

19. The method of claim 18, wherein applying the cavitation dispersion process further comprises: heating the core-shell particles to a temperature between 25 °C and 100 °C; and pressurizing the core-shell particles to a pressure between 0 and 45,000 psi.

20. The method of claim 18, further comprising: acquiring a short circuit current and open circuit voltage of the improved paste; and reapplying the cavitation dispersion process to the improved paste until the short circuit current and the open circuit voltage each satisfy a respective predetermine threshold.