JP2021177558A - paste - Google Patents

Abstract

To provide an intercalation paste used for a semiconductor device.SOLUTION: A firing multi-layer stack 1100 includes a substrate 1110, a metal particle layer on at least part of a substrate surface, a modified metal particle layer on at least part of the substrate surface, and a modified intercalation layer 1130 present just above at least a part of the modified metal particle layer. The modified intercalation layer has a solderable surface facing away from the substrate. The modified metal particle layer contains the same metal particles as present in the metal particle layer and at least one substance from the modified intercalation layer.SELECTED DRAWING: Figure 11

Description

Mutual reference of related applications This application is a US provisional patent application No. 62 / 259,636 filed on November 24, 2015, and a US provisional patent application No. 62/318 filed on April 5, 2016, 566, US Provisional Patent Application No. 62/371,236 filed on April 5, 2016, US Provisional Patent Application No. 62/371,236 filed on August 5, 2016, and 2016 The priority of US Provisional Patent Application No. 62 / 423,020 filed on November 16 is claimed, all of which are incorporated herein by reference.
Statement on Government Assistance The present invention was made with Government Assistance under Contract No. IIP-1430721 granted by NSF. Government may have certain rights to the invention.

The present invention relates to an intercalation paste containing noble metal particles, intercalation particles and an organic vehicle.

Intercalation paste can be used to improve the power conversion efficiency of solar cells. The silver-based intercalation paste is fired, subsequently soldered to the tab ribbon, and then printed on an aluminum layer with moderate peel strength. Such pastes are particularly suitable for use in silicon-based solar cells that use an aluminum backside electric field (BSF). Generally, 85-92% of the back surface region of an industrially manufactured single crystal and polycrystalline silicon solar cell silicon wafer is covered with an aluminum particle layer, which forms a back surface electric field to make ohmic contact with silicon. The remaining 5-10% of the silicon surface on the back is covered with a silver back tab layer, which does not generate an electric field and does not make ohmic contact with the silicon wafer. The back tab layer is mainly used for soldering tab ribbons to electrically connect solar cells.

It is estimated that when the silver layer comes into direct contact with the silicon substrate on the back side of the solar cell, the power conversion efficiency of the solar cell decreases by 0.1% to 0.2% in absolute value instead of the silver layer coming into contact with the silicon substrate. NS. Therefore, it is highly desirable that the entire back surface of the solar cell can be covered with an aluminum particle layer, and then the solar cells can be connected to each other using a tab ribbon. In the past, attempts have been made to print the silver paste directly on the top surface of the aluminum particle layer, but during firing at high temperatures in the air, the aluminum and silver layers interdiffuse and the resulting layer surface is oxidized. And loses solderability. Some researchers have attempted to change atmospheric conditions to reduce oxidation. However, the silver paste on the front side works best in an oxidizing atmosphere such as dry air, and after treatment in an inert atmosphere, the overall solar cell efficiency is reduced. Other researchers have attempted to lower the peak firing temperature of the wafer to reduce mutual diffusion, but the silver paste on the front side requires a high peak firing temperature (ie, 650 ° C or higher). The entire silicon nitride will be fired for ohmic contact with the silicon substrate. More recently, researchers have used ultrasonic soldering, which solders a tin alloy directly onto the top surface of aluminum to create a solderable surface. This technique has achieved adequate peel strength (ie, 1-1.5 N / mm), but requires additional equipment and uses large amounts of tin, which increases costs. In addition, the use of ultrasonic soldering on brittle materials such as aluminum and silicon wafers can increase wafer breakage and reduce processing yields.

There is a need to develop a printable paste that can modify the material properties of the underlying metal particle layer during firing. For example, a precious metal-containing paste that is printed directly on aluminum and fired using standard solar cell processing conditions may be able to improve solar cell efficiency. This paste should be able to reduce Ag / Al interdiffusion in order to remain solderable to the tab ribbon. The paste should be screen printable and act as a drop-in replacement, eliminating the need for additional equipment costs and allowing it to be immediately incorporated into existing production lines.

The above aspects and other aspects will be readily appreciated by those skilled in the art from the following description of exemplary embodiments by perusing them in conjunction with the accompanying drawings. The figure is not drawn on the street at a constant scale. The drawings are exemplary only and are not intended to limit the invention.
It is the schematic sectional drawing of the multilayer stack before firing by one Embodiment of this invention. It is the schematic sectional drawing of the fired multi-layer stack according to one Embodiment of this invention. It is a schematic cross-sectional view of the fired multilayer stack in which the intercalation layer is phase-separated. FIG. 5 is a schematic cross-sectional view of a fired multilayer stack in which an intercalation layer is phase-separated into two sublayers. FIG. 5 is a schematic cross-sectional view of a part of the fired multilayer stack shown in FIG. 2 according to an embodiment of the present invention. FIG. 5 is a scanning electron microscope (SEM) cross-sectional image of a co-fired multilayer stack according to an embodiment of the present invention. 9 is a scanning electron micrograph (SEM) cross-sectional image of a co-fired multilayer stack with a silver-bismuth frit layer. A scanning electron microscope (SEM) cross-sectional image (in SE2 mode) of an aluminum particle layer on a silicon substrate. FIG. 8 is a scanning electron microscope (SEM) cross-sectional image (in InLens mode) of an aluminum particle layer on a silicon substrate shown in FIG. A scanning electron microscope (SEM) cross-sectional image (in InLens mode) of a portion of a silicon solar cell containing a multi-layer stack after co-fired. FIG. 10 is a scanning electron microscope (SEM) cross-sectional image (in SE2 mode) of a portion of a silicon solar cell including a co-fired multilayer stack shown in FIG. It is an energy dispersive X-ray (EDX) spectrum from an aluminum particle layer and a modified aluminum particle layer according to one Embodiment of this invention. It is an EDX spectrum of the surface of the back tab layer including the silver-bismuth intercalation layer according to one embodiment of the present invention. It is an X-ray diffraction pattern from a multilayer film stack co-fired on the back tab layer of a silicon solar cell. FIG. 5 is a schematic cross-sectional view of a multilayer film stack including a dielectric layer before firing according to an embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of a fired multilayer film stack including a dielectric layer according to an embodiment of the present invention. It is a plane optical micrograph of a co-fired multilayer film stack in which buckling occurred. A screen design (not drawn to scale) that can be used during the deposition of wet metal particle layers according to one embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a thickened dry metal particle layer deposited using the screen of FIG. 18 according to an embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a thickened modified metal particle layer deposited using the screen of FIG. 18 and then co-fired according to an embodiment of the present invention. It is a top view optical micrograph of a multilayer stack after simultaneous firing shown in FIG. 20. It is a cross-sectional SEM image of a part of a thick fired multilayer stack. 6 is a cross-sectional SEM image showing a part of an aluminum particle film on a silicon substrate having a flat thickness. A surface topology scan of a thick fired multi-layer stack. This is a surface topology scan of the calcined aluminum particle layer. It is the schematic which shows the front surface (or irradiation surface) of a silicon solar cell. It is the schematic which shows the rear surface of a silicon solar cell. FIG. 5 is a schematic cross-sectional view of a solar cell module including a fired multilayer stack according to an embodiment of the present invention. FIG. 5 is a scanning electron micrograph (SEM) cross-sectional view of the back of a solar cell including a fired multilayer stack and a soldered tab ribbon according to an embodiment of the present invention. It is a transmission line measurement plot of the conventional silver back tab layer on silicon. A transmission line measurement plot of a silver-bismuth intercalation layer on an aluminum particle layer that can be used as a back tab layer on silicon.

The calcined multilayer stack is disclosed. In one embodiment of the invention, the stack comprises a substrate, a metal particle layer on at least a portion of the substrate surface, a modified metal particle layer on at least a portion of the substrate surface, and at least a portion of the modified metal particle layer. Includes a modified intercalation layer located directly above. The modified intercalation layer has a solderable surface facing away from the substrate. The modified metal particle layer contains the same metal particles that are present in the metal particle layer and at least one substance from the modified intercalation layer. The modified intercalation layer is composed of precious metals, antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium. , Manganese, molybdenum, niobium, phosphorus, potassium, rhenium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, combinations thereof, alloys thereof, oxides thereof, composites thereof. Includes materials and materials selected from the group consisting of other combinations. In one composition arrangement, the modified intercalation layer is composed of precious metals and bismuth, boron, indium, lead, silicon, tellurium, tin, vanadium, zinc, combinations thereof, and alloys thereof, oxides thereof, and Includes materials selected from the group consisting of these other combinations.

In one embodiment of the invention, the modified intercalation layer has two phases, a noble metal phase and an intercalation phase. More than 50% of the solderable surface of the modified intercalation layer can contain the noble metal phase. The modified metal particle layer can include the metal particles described above and at least one material from the intercalation phase. Intercalation phases include antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, magnesium, manganese, molybdenum, niobium, phosphorus, From potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, their combinations, and their alloys, their oxides, their composites, and other combinations thereof. Contains at least one material selected from the group. The noble metal phase comprises at least one material selected from the group consisting of gold, silver, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof.

In another embodiment of the invention, the modified intercalation layer is intercalated with two sublayers, i.e., an intercalation sublayer located directly above at least a portion of the modified metal particle layer. It has a noble metal sublayer existing immediately above at least a part of the sublayer. The solderable surface of the modified intercalation layer includes a noble metal sublayer. The modified metal particle layer can include the metal particles described above and at least one material from the intercalation sublayer. Possible materials for the intercalation sublayer are the same as described above for the intercalation phase. Possible materials for the noble metal sublayer are the same as described above for the noble metal phase.

In another embodiment of the invention, the fired multilayer stack has a modified aluminum particle layer as its modified metal particle layer. It consists of two sublayers, a bismuth-rich sublayer directly above the modified aluminum particle layer and a silver-rich sublayer directly above the bismuth-rich sublayer. Have. The solderable surface of the modified intercalation layer contains a silver-rich sublayer. The modified aluminum particles include aluminum particles and can also contain at least one material selected from the group consisting of aluminum oxide, bismuth and bismuth oxide.

In one configuration, there is at least one dielectric layer directly above at least a portion of the substrate surface. The dielectric layer comprises at least one material selected from the group consisting of silicon, aluminum, germanium, hafnium, gallium, and oxides, nitrides, composites thereof, and combinations thereof. In another configuration, the aluminum oxide dielectric layer is present directly above at least a portion of the substrate surface, and the silicon nitride dielectric layer is directly above the aluminum oxide dielectric layer.

In one configuration, there is a solid (eg, eutectic) compound layer directly above the surface of the substrate. The solid compound layer comprises one or more metals selected from the group consisting of aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium and silicon, oxygen, carbon, germanium, gallium, arsenic, nitrogen, indium and phosphorus. Includes one or more materials selected from the group consisting of.

A portion of the substrate adjacent to the substrate surface can be doped with at least one material selected from the group consisting of aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, steel and combinations thereof.

In one embodiment of the invention, some of the fired multilayer stacks have a variable thickness. The calcined multilayer stack can have an average height of peaks and valleys greater than 12 μm.
At least 70% by weight of the solderable surface in the modified intercalation layer is selected from the group consisting of silver, gold, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof. Can include materials to be soldered.

The substrate can include at least one material selected from the group consisting of silicon, silicon dioxide, silicon carbide, aluminum oxide, sapphire, germanium, gallium arsenide, gallium nitride, and indium phosphide. Alternatively, the substrate can include materials selected from the group consisting of aluminum, copper, iron, nickel, titanium, steel, zinc, and alloys, composites, and other combinations thereof. The metal particle layer may include a material selected from the group consisting of aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, steel and alloys thereof, composites thereof, and other combinations thereof. can. Noble metals can include materials selected from the group consisting of silver, gold, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof.

The metal particle layer can have a thickness between 0.5 μm and 100 μm and / or a porosity between 1 and 50%. The modified intercalation layer can have a thickness of 0.5 μm to 10 μm. The multi-layer stack after firing can have a contact resistance of 0-5 m ohms as determined by transmission line measurements.

A tab ribbon may be present just above at least a portion of the solderable surface of the modified intercalation layer. In one configuration, the peel strength between the tab ribbon and the modified intercalation layer is greater than 1 N / mm.

In another embodiment of the invention, the fired multilayer stack comprises a substrate, a metal particle layer on at least a portion of the substrate, a modified metal particle layer on at least a portion of the substrate, and modified metal particles. It has a modified intercalation layer located directly above at least a part of the layer. The modified intercalation layer exists in two sublayers, that is, an intercalation sublayer that exists directly above at least a part of the modified metal particle layer, and an intercalation sublayer that exists directly above at least a part of the intercalation sublayer. It has a noble metal sublayer. The modified metal particle layer comprises metal particles and at least one material from the intercalation sublayer. Possible materials for the intercalation sublayer are as described above.

In another embodiment of the invention, the fired multilayer stack comprises a silicon substrate, an aluminum particle layer on at least a portion of the substrate, a modified aluminum particle layer on at least a portion of the substrate, and directly above the modified aluminum particle layer. Has a modified intercalation layer present in. The modified intercalation layer is rich in two sublayers, a bismuth-rich sublayer located directly above the modified aluminum particle layer and a silver-rich sublayer located directly above the bismuth-rich sublayer. It has a sublayer. The modified aluminum particle layer comprises at least one material selected from the group consisting of aluminum, aluminum oxide, bismuth, and bismuth oxide.

In one embodiment of the present invention, the solar cell is a silicon substrate, at least one front dielectric layer existing directly above at least a part of the front surface of the silicon substrate, and a plurality of solar cells existing on a part of the surface of the silicon substrate. A fine grid line, at least one front busbar layer in electrical contact with at least one of the plurality of fine grid lines, an aluminum particle layer existing on at least a part of the back surface of the silicon substrate, and a silicon substrate. It has a back tab layer that exists on a part of the back. The back tab layer includes a modified aluminum particle layer existing on a part of the back surface of the silicon substrate and a modified intercalation layer existing just above a part of the modified aluminum particle layer. The modified intercalation layer has a solderable surface facing away from the silicon substrate. The modified aluminum particle layer comprises aluminum particles and at least one material from the modified intercalation layer. Possible materials for the modified intercalation layer are as described above. The aluminum particle layer can have a thickness between 1 μm and 50 μm and / or a porosity between 3 and 20%. The thickness of the back tab layer may be 1 μm to 50 μm. The silicon substrate may be a single crystal silicon wafer having either a p-type group or an n-type group. The silicon substrate may be a polycrystalline silicon wafer having either a p-type group or an n-type group.

In one embodiment of the invention, the modified intercalation layer comprises two phases, a noble metal phase and an intercalation phase. More than 50% of the solderable surface may be composed of the noble metal phase. The modified aluminum particle layer contains aluminum particles and at least one material from the intercalation phase. Possible materials for forming the intercalation phase are as described above. Possible materials for the noble metal phase are also as described above.

In another embodiment of the invention, the modified intercalation layer is two sublayers, i.e., an intercalation sublayer located directly above at least a portion of the modified metal particle layer, and an intercalation layer. Includes a noble metal sublayer that resides directly above at least a portion of the curation sublayer. The solderable surface contains a noble metal sublayer. The modified aluminum particle layer comprises aluminum particles and at least one material from the intercalation sublayer. Possible materials for forming the intercalation sublayer are as described above. Possible materials for the noble metal sublayer are also as described above.

In another embodiment of the invention, the modified intercalation layer is directly above the two sublayers, namely the bismuth-rich sublayer located directly above the modified aluminum particle layer and the bismuth-rich sublayer. Contains the existing silver-rich sublayer. The modified aluminum particle layer further comprises at least one material selected from the group consisting of aluminum oxide, bismuth and bismuth oxide. In one configuration, the modified aluminum particle layer further comprises bismuth and / or bismuth oxide, and the weight ratio of bismuth to bismuth and aluminum (Bi :( Bi + Al)) is the aluminum particle layer in the modified aluminum particle layer. At least 20% higher than that in. The bismuth-rich sublayer can have a thickness of 0.01 μm to 5 μm, or 0.25 μm to 5 μm.

In one configuration, at least one back dielectric layer is present directly above at least a portion of the back surface of the silicon substrate. The back dielectric layer comprises silicon, aluminum, germanium, hafnium, gallium, and one or more of their oxides, nitrides, composites, and combinations thereof. The back dielectric layer can include silicon nitride. In another configuration, the aluminum oxide back dielectric layer is present directly above at least a portion of the back surface of the silicon substrate, and the silicon nitride back dielectric layer is directly above the aluminum oxide back dielectric layer. In one configuration, there is an aluminum-silicon eutectic layer solidified directly on the silicon substrate. In one configuration, a portion of the silicon substrate adjacent to the back surface of the silicon substrate further contains a backside electric field, which is p-type doped into 10 ¹⁷ to 10 ^{20 atoms per cm 3.}

In one embodiment of the invention, a portion of the back tab layer has a variable thickness and can have an average height from peak to valley greater than 12 μm.
A tab ribbon may be present just above at least a portion of the solderable surface of the modified intercalation layer. The solderable surface may be rich in silver. The solderable surface can contain at least 75% by weight of silver. A tab ribbon soldered to a silver-rich solderable surface can have a peel strength greater than 1 N / mm.

A portion of the modified aluminum particle layer can have a variable thickness. A portion of the modified aluminum particle layer can have a peak-to-valley average height greater than 12 μm. The contact resistance between the back tab layer and the aluminum particle layer can be 0-5 m ohms as determined by transmission line measurements.

In another embodiment of the invention, the solar cell comprises a silicon substrate, at least one front dielectric layer located directly above at least a portion of the front surface of the silicon substrate, and at least one of a plurality of fine grid lines and electricity. It has at least one front busbar layer in contact with the silicon substrate, an aluminum particle layer existing on at least a part of the back surface of the silicon substrate, and a back tab layer existing on a part of the back surface of the silicon substrate. .. The back tab layer has a solderable surface. The back tab layer is rich in bismuth, a modified aluminum particle layer existing on at least a part of the back surface of the silicon substrate, a bismuth-rich sublayer existing just above at least a part of the modified aluminum particle layer, and a bismuth-rich sublayer. Includes a silver-rich sublayer located directly above at least a portion of the sublayer. The modified aluminum particle layer comprises aluminum particles and at least one material selected from the group consisting of aluminum oxide, bismuth and bismuth oxide.

In another embodiment of the invention, the solar cell module comprises a front sheet, a front encapsulation layer present on the back surface of the front sheet, and a first silicon solar cell and a second silicon sun on the front encapsulation layer. Has a battery. Each silicon solar cell can be any of the silicon solar cells described herein. The solar cell module is also present on the back sheet and the back of the back sheet, with a first tab ribbon that makes electrical contact with both the front busbar layer of the first silicon solar cell and the back tab layer of the second silicon solar cell. Includes a first battery interconnect with a back sealing layer. The first portion of the back encapsulation layer is in contact with the first silicon solar cell and the second solar cell, and the second portion of the back encapsulation layer is in contact with the front encapsulation layer.

The first battery interconnect can also include a junction box that contacts the back sheet. The junction box can include at least one bypass diode. These may be at least one busbar ribbon that connects to the first tab ribbon.

In one embodiment of the invention, the paste is disclosed. The paste contains 10% to 70% by weight of noble metal particles, at least 10% by weight of intercalation particles and organic vehicle. The intercalation particles include one or more selected from the group consisting of low temperature base metal particles, crystalline metal oxide particles, and glass frit particles. The weight ratio of the intercalation particles to the noble metal particles may be at least 1: 5.

The noble metal particles can include at least one material selected from the group consisting of gold, silver, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof. The noble metal particles can have a D50 between 100 nm and 50 μm and a specific surface area of ^{0.4 to 7.0 m 2 / g.} Some of the noble metal particles can have shapes such as spherical, flaky, and / or elongated. The noble metal particles can exhibit a monomodal particle size distribution or a multimodal particle size distribution. In one configuration, the noble metal particles are silver and have a D50 of 300 nm to ^2.5 μm and a specific surface area of 1.0 to 3.0 m 2 / g.

The intercalation particles can have a D50 of 100 nm to 50 μm and a specific surface area of ^{0.1 to 6.0 m 2 / g.} Some of the intercalation particles can have shapes such as spherical, flake, and / or elongated. Intercalation particles can exhibit a monomodal or multimodal particle size distribution.

The low temperature base metal particles can include materials selected from the group consisting of bismuth, tin, tellurium, antimony, lead, and alloys thereof, composites thereof, and other combinations thereof. In one configuration, the cold base metal particles contain bismuth and have a D50 of 1.5-4.0 μm and a specific surface area of ^{1.0-2.0 m 2 / g.}

In one embodiment of the invention, at least some of the cold base metal particles are silver, nickel, nickel-boron, tin, tellurium, antimony, lead, molybdenum, titanium, and alloys thereof, composites thereof, and their composites. It has bismuth score particles surrounded by a single shell containing materials selected from the group consisting of other combinations. In another embodiment, at least some of the cold base metal particles are bismuth score particles enclosed by a single shell containing a material selected from the group consisting of silicon oxide, magnesium oxide, boron oxide, and any combination thereof. Has.

Crystalline metal oxide particles consist of oxygen and bismuth, tin, tellurium, antimony, lead, vanadium, chromium, molybdenum, boron, manganese, cobalt and their alloys, their composites and other combinations thereof. It may contain a metal selected from.

Glass frit particles include antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, fluorine, gallium, germanium, hafnium, indium, iodine, iron, lantern, lead, lithium, magnesium, manganese. , Molybdenum, niobium, potassium, renium, selenium, silicon, sodium, strontium, tellurium, tin, vanadium, zinc, zirconium, their alloys, their oxides, their composites, and other combinations thereof. It may contain a metal selected from.

The paste can have a solid content of 30% to 80% by weight. The intercalation particles can make up at least 15% by weight of the paste. In one configuration, the paste comprises 45% by weight Ag particles, 30% by weight bismuth particles, and 25% by weight organic vehicle. In another configuration, the paste comprises 30% by weight of Ag particles, 20% by weight of bismuth particles, and 50% by weight of organic vehicle. The paste can have a viscosity of 10,000-200,000 cP at 25 ° C. at a shear rate of 4 seconds- ^1.

In one embodiment of the present invention, a co-fired method for forming a firing multilayer stack is described. The methods include a) applying a wet metal particle layer to at least a portion of the surface of the substrate, b) drying the wet metal particle layer to form a dry metal particle layer, and c) drying the metal. A step of directly applying a wet intercalation layer to at least a part of the particle layer to form a multi-layer stack, d) a step of drying the multi-layer stack, and e) simultaneous firing of the multi-layer stack to form a fired multi-layer stack. Including steps to do.
Another embodiment of the invention describes a successive method of forming a fired multilayer stack. This method involves a) applying a wet metal particle layer to at least a portion of the surface of the substrate, b) drying the wet metal particle layer to form a dry metal particle layer, and c) drying the metal. A step of firing the particle layer to form a metal particle layer, d) a step of directly applying a wet intercalation layer directly on at least a part of the metal particle layer to form a multi-layer stack, and e) a multi-layer stack. It includes a step of drying and a step of f) firing the multi-layer stack to form a calcined multi-layer stack.

In one configuration, in both co-fired and successive methods, the wet intercalation layer has 10% to 70% by weight of noble metal particles, at least 10% by weight of intercalation particles, and an organic vehicle. The intercalation particles may include one or more selected from the group consisting of low temperature base metal particles, crystalline metal oxide particles, and glass frit particles. The wet metal particle layer is a metal composed of a material selected from the group including aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, steel and alloys thereof, composite materials thereof, and other combinations thereof. Can contain particles.

In one configuration, there are additional steps prior to step a) for both the co-fired and successive methods. An additional step involves depositing at least one dielectric layer on at least a portion of the surface of the substrate. In this configuration, step a) involves applying the wet metal particle layer directly to at least a portion of the dielectric layer.

In both the co-fired and sequential methods, each coating step can include a method selected from the group consisting of screen printing, gravure printing, spray coating, slot coating, 3D printing and inkjet printing. In one configuration, step a) involves screen printing through a patterned screen to produce a layer of wet metal particles with varying thickness.

For both co-fired and successive methods, steps b) and d) may involve drying at a temperature below 500 ° C. for 1 second to 90 minutes, or at a temperature of 150 ° C. to 300 ° C. for 1 second to 60 minutes. .. Step e) may involve rapid heating to a temperature above 600 ° C. in the air for 0.5 seconds to 60 minutes, or rapid heating to a temperature above 700 ° C. for 0.5 seconds to 3 seconds in the air.

In one configuration, for both the co-fired and successive methods, the additional step f) involves soldering the tab ribbon to a portion of the firing multilayer stack.
Low temperature base metal particles, crystalline metal oxide particles, glass frit particles, and metal particle layers are described in detail above.

In another embodiment of the invention, the method of manufacturing a solar cell includes a) preparing a silicon wafer, b) applying a wet aluminum particle layer to at least a portion of the back surface of the silicon wafer, and c). The steps of drying the wet aluminum particle layer to form the aluminum particle layer, d) applying the wet intercalation layer directly to at least a part of the aluminum particle layer to form a multi-layer stack, and e) the multi-layer stack. A step of drying, f) a step of applying a plurality of fine grid lines and at least one front busbar layer on the front surface of the silicon wafer, and g) a structure of drying the plurality of fine grid lines and at least one front busbar layer. It includes a step of forming a body and h) a step of simultaneously firing a structure to form a silicon solar cell.

The wet intercalation layer has been described above.
In one configuration, there are additional steps between steps a) and b). An additional step involves depositing at least one dielectric layer on at least a portion of the back surface of a silicon wafer. In this configuration, step b) involves applying the wet aluminum particle layer directly to at least a portion of the dielectric layer.

Each coating step can include a method selected from the group consisting of screen printing, gravure printing, spray coating, slot coating, 3D printing and inkjet printing. In one configuration, step b) involves screen printing through a patterned screen to produce a layer of wet aluminum particles with varying thickness.

For both the co-fired and successive methods, steps e) and g) require drying at a temperature below 500 ° C. for 1 second to 90 minutes, or at a temperature of 150 ° C. to 300 ° C. for 1 second to 60 minutes. Can accompany. Step h) is to rapidly heat to a temperature higher than 600 ° C. in the air for 0.5 seconds to 60 minutes, or to a temperature higher than 700 ° C. for 0.5 seconds to 3 seconds in the air. Can be accompanied by.
Cold base metal particles, crystalline metal oxide particles, and glass frit particles have been described in detail above.

A preferred embodiment is shown in the light of the calcined intercalation paste on the metal particle layer. However, one of ordinary skill in the art will make good electrical contact with semiconductor or conductive materials where the materials and methods disclosed herein are important for good adhesion, high performance and low cost. It will be easily understood that it has applications in many desirable situations.

All publications referred to herein are hereby incorporated by reference in their entirety for all purposes, as if fully described herein.
The present specification discloses the composition and use of an intercalation paste comprising noble metal particles and intercalated particles, which is printed on a metal particle layer and fired into a multi-layer stack after firing. After that, the characteristics of the metal particle layer can be changed. In one embodiment of the invention, an intercalation paste is used to provide a solderable surface on a metal particle layer that is not itself solderable. The intercalation paste can also be used to improve adhesion within the calcined multilayer stack or to alter the interaction of the metal particle layer with the underlying substrate. Intercalation pastes are widely applicable in many applications, including transistors, light emitting diodes, and integrated circuits, but most of the examples disclosed below focus on solar cells.
Definitions and Methods The scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) (collectively referred to as SEM / EDX) used herein are Zeiss equipped with a Bruker XFlash (R) 6 | 60 detector. Gemini Ultra-55 analytical field was performed using a radiation scanning electron microscope. Details of the operating conditions are described for each analysis. A cross-sectional SEM image of the fired multilayer stack was prepared by ion milling. A thin epoxy layer was applied to the top surface of the calcined multilayer stack and dried for at least 30 minutes. The sample was then transferred to an EOL IB-03010CP ion mill and run at 5 kV and 120 uA for 8 hours to remove 80 microns from the edge of the sample. The ground sample was stored in a nitrogen glove box prior to SEM / EDX operation.

The term "drying" refers to a heat treatment at 500 ° C. or lower, or below 400 ° C., or below 300 ° C. for a time between 1 second and 90 minutes or any range of time included therein. The paste typically produces a "wet" layer when applied to the substrate by screen printing or another deposition method. The wet layer can be dried to reduce or remove volatile organic species such as solvents and produce a "dry" layer.

The term "baking" refers to heating at temperatures above 500 ° C., above 600 ° C. or above 700 ° C. for 1 second to 60 minutes or any range of time included therein. The term "fired layer" refers to a fired dry layer.

The term "multilayer stack" is used herein to describe a substrate having two or more layers of different materials on it. A "fired multi-layer stack" is a multi-layer stack in which the layer is dried and fired. There are several ways to fire such a multi-layer stack. The term "co-fired" is used to describe the treatment of multilayer laminates that are fired only once. For example, during the manufacture of silicon solar cells, a layer of aluminum particle paste is first applied to the substrate and dried. Then, a rear tab paste layer is applied to a part of the dried aluminum particle layer and dried to obtain a dried aluminum particle layer and a dried back tab layer. In co-fired, both dry layers are fired in one step at the same time. The term "sequential firing" is used to describe the treatment of multi-layer laminates that are fired multiple times. In the sequential treatment, the metal particle paste is applied onto the substrate, dried and then fired. The intercalation paste is applied to a part of a dried and fired metal particle paste (referred to as a metal particle layer). The entire multilayer stack is then dried and fired a second time. The embodiment of the present invention that describes the multi-layer stack or structure after co-fired is also suitable for the multi-layer stack or structure after sequential firing.

The term "intercalation" is used herein to describe penetration into a porous material. In the embodiments described herein, the term "intercalation" refers to the penetration of the material into the adjacent porous dry metal particle layer by the intercalation particles in the intercalation layer during the firing process. Shown, which results in an intercalation particle material that covers at least a portion of the metal particles (partially or completely). The term "modified metal particle layer" is used herein to describe a calcined metal particle layer infiltrated with material from intercalation particles.

In describing the relationship between adjacent layers, the preposition "on" is used to mean that the layers may or may not be in direct physical contact with each other. For example, the presence of a layer on a substrate means that the layer is directly adjacent to, indirectly above, or adjacent to the substrate. The fact that a particular layer is indirectly present on or adjacent to a substrate may mean that there may be one or more additional layers between the particular layer and the substrate. It does not have to be. In describing the relationship between adjacent layers, the preposition "immediately above" is used herein to mean that the layers are in direct physical contact with each other. For example, the fact that the layer exists directly above the substrate means that the layer is formed directly adjacent to the substrate.

When the metal particle layer mainly consists of metal A particles, it can be referred to as a "metal A particle layer". For example, when the metal particle layer is mainly composed of aluminum particles, it can be called an aluminum particle layer. When the modified metal particle layer is mainly composed of metal A particles, it can be referred to as a "metal A modified particle layer". For example, when the modified metal particle layer contains aluminum particles as a main component, it can be called a modified aluminum particle layer.

The term "solderable surface" is well known in the art. "Solderable surface" refers to a surface that can be soldered to the soldering ribbon. Those skilled in the art are familiar with the concept of solderable surfaces. Examples of materials that produce solderable surfaces include tin, cadmium, gold, silver, palladium, rhodium, copper, zinc, lead, nickel, their alloys, their combinations, their composites and their mixtures. Included, but not limited to. In one embodiment, if at least 70% by weight of the surface is made of materials such as silver, gold, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations, the surface is solderable. be.

The particles described herein can exhibit a variety of shapes, sizes, specific surface areas, and oxygen contents. The particles may be spherical, needle-like, horny, dendritic, fibrous, flaky, granular, irregular, and nodular, as defined in ISO3252. It should be understood that the term "spherical" is commonly used herein to refer to a sphere and can include spheroids, granules, nodules, and sometimes irregular shapes. The term "flakes" refers to flakes, sometimes horns, fibrous, and irregular shapes. The term "elongated" means needle-like, sometimes horny, dendritic, fibrous, and irregular shapes as defined by ISO3252: 1999. Particle shape, morphology, particle size and particle size distribution often depend on synthetic techniques. A group of particles can include a combination of particles of different shapes and particle sizes.

Spherical or elongated particles are generally described by their D50, specific surface area and particle size distribution. The D50 value is defined as a value in which half of the particle population has a diameter less than or equal to the value and half of the particle population has a diameter greater than or equal to the value. Measurement of particle size distribution is generally performed by Horiba.
This is done using a laser diffraction type particle size distribution measuring device such as LA-950. For example, spherical particles are dispersed in a solvent in which they are well separated, and the scattering of transmitted light correlates directly with the particle size distribution from minimum to maximum dimensions. A common approach to representing laser diffraction results is to report a D50 value based on volume distribution. The statistical distribution of particle size can also be measured using a laser diffraction type particle size distribution measuring device. Noble metal particles generally have a single-peak or multi-peak particle size distribution. In the single peak distribution, the particle size is monodisperse and D50 is at the center of the single distribution. The multi-peak particle size distribution has two or more modes (or peaks) in the particle size distribution. The multi-peak particle size distribution can increase the tap density of the powder, which will generally result in a higher green film density.

In some embodiments of the invention, the particles may have the flakes or elongated shapes defined above. The flakes can have a diameter of 1 μm to 100 μm or a diameter of 1 μm to 15 μm and a thickness of 100 nm to 500 nm. The elongated shape can have a diameter of 200 nm to 1000 nm and a length of more than 1 μm. In another embodiment of the present invention, the shape of the particles is not limited, and any particle shape can be used as long as the maximum size thereof is 50 μm, 5 μm, or 1 μm or less.

The specific surface area of the particles can be measured using the BET (Brunauer-Emmett-Teller) method according to DIN ISO 9277, 2003-05. The specific surface areas of the particles disclosed herein, in particular silver and bismuth particles, are measured by the following test methods. That is, the BET measurement is performed using a TriStar 3000 (manufactured by Micromerics Instrument Corporation) that operates based on the physical adsorption analysis technique. Sample preparation involves degassing to remove adsorbed molecules. Nitrogen is the analytical gas and helium is used to measure the void volume of the sample tube. Powder engineering provides silica alumina for use as a reference material, along with preparation procedures and test conditions. The measurement is initiated by adding a reference material of known mass to the sample tube and attaching the sample tube to the BET device manifold. The thermally stable dosing manifold, sample tube, and dedicated tube for measuring _{saturation pressure (P 0) are exhausted.} When sufficient vacuum is achieved, the manifold is filled with helium (non-absorbable gas) and the sample port is opened to measure the warm free space of the sample at room temperature. The sample tube containing the reference substance is immersed in liquid nitrogen, cooled to about 77K, and the free space analysis is performed again. The saturation pressure of the adsorbent is _{measured using a P 0} tube, followed by injecting nitrogen into the manifold at a pressure above atmospheric pressure. The pressure and temperature of the nitrogen are recorded, then the sample port is opened to adsorb the nitrogen to the sample. After a while, the port is closed so that the adsorption reaches equilibrium. The adsorbed amount is the amount obtained by subtracting the residual nitrogen in the sample tube from the amount of nitrogen taken out from the manifold. Using measurement points along the adsorption isotherm, the specific area for the reference material ^{is calculated at m 2} / g, but this procedure is repeated for any sample of interest, such as the particles described herein. Is.

The particles described herein have significant thermal properties, ie, melting points and / or softening points, both of which depend on the crystallinity of the material. The melting point of the particles can be measured by differential scanning calorimetry using a DSC 2500 differential scanning calorimeter manufactured by TA Instruments and the method described in ASTM E794-06 (2012). The melting point of the crystalline material can also be measured using a heating step and X-ray diffraction. When the crystalline material is heated above its melting point, the diffraction peaks begin to disappear. The softening point is the temperature at which the amorphous or glassy particles begin to soften. The softening point of the glass particles can be measured using an expansion meter. The softening point can also be obtained by the fiber elongation method described in ASTM C338-57.
Materials for Making Calcined Multilayer Stacks In one embodiment of the invention, the substrate, metal particle paste, and intercalation paste form a calcined multilayer stack. The substrate may be a solid material, a flat material, or a rigid material.
In one embodiment, the substrate comprises at least one material selected from the group consisting of silicon, silicon dioxide, silicon carbide, aluminum oxide, sapphire, germanium, gallium arsenide, gallium nitride and indium phosphide. Such substrates are commonly used for depositing layers that make up transistors, light emitting diodes, integrated circuits and photovoltaic cells. The substrate may be electronically conductive and / or flexible. In another embodiment, the substrate is at least one selected from the group consisting of aluminum, copper, iron, nickel, titanium, steel, zinc, and alloys thereof, composites thereof, and other combinations thereof. Including material.

In one embodiment of the invention, the metal particle paste comprises metal particles and an organic vehicle. In one configuration, the metal particle paste also comprises an inorganic binder such as glass frit. In one configuration, a common commercially available metal particle paste is used. Aluminum-containing metal pastes commonly used in silicon solar cells are sold by Luxing Technology (eg, RX8252H1), Single crystal (eg, EFX-39), and GigaSolar Materials (eg, M7). The metal particles can include at least one of aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, or alloys thereof, composites thereof, or other combinations thereof. In various configurations, the metal particles have a D50 of 100 nm to 100 μm, 500 nm to 50 μm, 500 nm to 20 μm, or any range included herein. The metal particles may have a spherical, elongated or flake shape and may have a monomodal or multimodal particle size distribution. The glass frit may be contained in a small amount (ie, less than 5% by weight) of the metal particle paste. In one embodiment, the metal particle paste comprises 70% to 80% by weight of aluminum particles, less than 2% by weight of glass frit, and an organic vehicle.

In one embodiment of the invention, the intercalation paste comprises precious metal particles, intercalation particles and an organic vehicle. The term "solid content" may be used in conjunction with a paste to describe the amount or proportion of noble metal and intercalation particle solids in the paste. The pastes described herein also include organic vehicles, but are not necessarily specified.
Intercalation Particle Components In one embodiment of the invention, the noble metal particles described herein are gold, silver, platinum, palladium, and rhodium, and alloys thereof, composites thereof, or other combinations thereof. Contains at least one material selected from the group consisting of. In one embodiment, the noble metal particles make up 10% to 70% by weight of the paste. In various embodiments, the noble metal particles have a D50 between about 100 nm and 50 μm, between 300 nm and 10 μm, between 300 nm and 5 μm, or in any range included herein. In various embodiments, the noble metal particles have a specific surface area in the range of ^{about 0.4 to 7.0 m 2} / g or about 1 to 5 m ^{2 / g or any range contained herein.} Noble metals can have an oxygen content of up to 2% by weight, but oxygen may be mixed uniformly throughout the particles, or oxygen exists as an oxide shell with a thickness of up to 500 nm. May be good. The noble metal particles have a spherical, elongated, or flake shape and can have a monomodal or multimodal particle size distribution. Silver particles are commonly used in metallized pastes in the solar industry. In an exemplary embodiment, at least some noble metal particles are silver with a D50 of 300 nm-2.5 μm and a specific surface area of ^{1-3 m 2 / g.}

The term "intercalation particles" deforms when heated and, when constructed adjacent to a porous layer of other metal particles, at least partially intercalates with the porous metal particle layer and is affected by heat. It is used to describe particles that can be phase separated from other metal particles. In various configurations, the intercalation particles have a D50 between 50 nm and 50 μm, between 50 nm and 10 μm, between 300 nm and 5 μm, or in any range included herein. In one embodiment, the intercalation particles have a D50 of 300 nm to 3 μm. In various embodiments, the intercalation particles are in the range of about 0.1 to ⁶ m 2 / g, about 0.5 to ³ m 2 / g or about 0.5 to ⁴ m 2 / g, or any contained herein. Has a range of specific surface areas. According to one embodiment, the intercalation particles are flaky and have a specific surface area of ^{about 1.0-3.0 m 2 / g.} The intercalation particles may have a spherical, elongated or flake shape and may have a monomodal or multimodal particle size distribution.

Three groups of particles that can be used as intercalation particles include low temperature base metal particles (LTBM), crystalline metal oxide particles, and glass frit particles. In some configurations, the intercalation particles consist only of either cold base metal particles, or crystalline metal oxide particles, or glass frit particles. In another configuration, the intercalation particles are a mixture of particles from two or more of these. It is desirable that the components of the intercalation particles have low solubility with the components in the adjacent metal particle layer and are not alloyed.

In one embodiment, the intercalation particles are cold base metal particles. The term "low temperature base metal particles" (LTBM) as used herein describes particles consisting only of, or essentially consisting of, any base metal or metal alloy having a low melting point, i.e., a melting point below 450 ° C. Used for. In some formulations, LTBM also contains up to 2% by weight oxygen, which may be mixed uniformly throughout the particles, or in an oxide shell in which oxygen has a thickness of up to 500 nm. It can be present and coats or partially coats the particles. In some configurations, the melting point of LTMB is even lower, such as less than 350 ° C or less than 300 ° C. In one embodiment of the invention, the LTBM is conditioned solely from, or essentially from, bismuth, tin, tellurium, antimony, lead, or alloys thereof, composites thereof, or other combinations thereof. In one embodiment, the intercalation particles contain only bismuth and have a D50 of 1.5-4 μm and a specific surface area of ^{1-2 m 2 / g.}

In another embodiment, the LTBM intercalation particles are bismuth score particles surrounded by a metal or metal oxide shell. In another embodiment, the LTBM intercalation particles consist of silver, nickel, nickel alloys such as nickel boron, tin, tellurium, antimony, lead, molybdenum, titanium, composites thereof and / or other combinations thereof. A bismascore particle surrounded by a single shell. In another embodiment, the LTBM intercalation particles are bismuth score particles surrounded by a single shell, which is an oxide of silicon, an oxide of magnesium, an oxide of boron, or any combination thereof. Each of these shells can have a thickness in the range of 0.5 nm to 1 μm, or 0.5 nm to 200 nm, or any range included herein.

In another embodiment, the intercalation particles are crystalline metal oxide particles. A metal oxide is a compound having at least one oxygen atom (an anion having an oxidation state of -2) and at least one metal atom. Many metal oxides contain multiple metal atoms, all of which may contain the same metal or various metals. A wide range of metal to oxygen atom ratios is possible, as will be appreciated by those skilled in the art. If the metal oxides form a regular periodic structure, they are crystalline. Such crystalline metal oxides are characteristic of these crystal structures and can diffract X-ray radiation with peak patterns of varying intensities. In one embodiment, the crystalline metal oxide particles are, exclusively or essentially, bismuth, tin, tellurium, antimony, lead, vanadium, chromium, molybdenum, boron, manganese, cobalt, and alloys thereof, these. It consists of at least one oxide of a composite material or other combination thereof.

For structures disclosed herein and described in more detail below, when crystalline metal oxide particles are heated, significant interdiffusion is greater than the temperature that can occur within the structure between metal particles of different composition. The particles are useful if they begin to melt at low temperatures (ie, _{if they reach the melting point (TM)).} When the sample is heated above its melting point, the diffraction peak disappears and then disappears. Therefore, the melting point of the crystalline material in the mixed layer can be measured by using the sample heating stage and X-ray diffraction. In some exemplary embodiments, boron oxide _{(III) (B 2 O 3} T M = 450 ℃), vanadium oxide _{(V) (V 2 O 5} T M = 690 ℃), tellurium oxide (IV) ( TeO ₂ T _M = 733oC), and bismuth oxide _{(III) (Bi 2 O 3} T M = 817oC) is deformed during the baking process, and intercalated into the adjacent porous metal particle layer, modified metal A particle layer can be formed. In an exemplary embodiment, the intercalation particles are ^{crystalline bismuth oxide with a D50 of 50 nm to 2} μm and a specific surface area of 1 to 5 m 2 / g. In another embodiment, the crystalline metal oxide particles also contain a small amount (ie, less than 10% by weight) of one or more additive components capable of adjusting the melting point of the particles. Such additives include silicon, germanium, lithium, sodium, potassium, cesium, magnesium, calcium, strontium, barium, zirconium, hafnium, vanadium, niobium, chromium, molybdenum, manganese, renium, iron, cobalt, zinc, Includes, but is not limited to, cadmium, gallium, sulfur, selenium, fluorine, chlorine, bromine, iodine, lanthanum, and cerium.

In another embodiment, the intercalation particles are glass frit particles. In one embodiment, the glass frit particles are exclusively or essentially with oxygen, silicon, boron, germanium, lithium, sodium, potassium, cesium, magnesium, calcium, strontium, barium, zirconium, hafnium, vanadium, niobium. , Chromium, molybdenum, manganese, renium, iron, cobalt, zinc, cadmium, gallium, indium, carbon, tin, lead, nitrogen, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, tellurium, fluorine, chlorine, bromine, iodine Consists of at least one component consisting of, lanthanum, cerium, oxygen, and alloys thereof, composites thereof, and other combinations thereof. In order to effectively deform during firing, it is useful if the glass frit has a softening point of less than 900 ° C or less than 800 ° C. In an exemplary embodiment, the intercalation particles are ^{bismuth glass silicate frit particles with a D50 of 50 nm to 2} μm and a specific surface area of 1 to 5 m 2 / g.

The term "organic vehicle" refers to a mixture or solution of organic chemicals or compounds that assists in the dissolution, dispersion and / or suspension of solid components in a paste. Many different organic vehicle mixtures can be used for the intercalation pastes described herein. Such organic vehicles may or may not contain thixotropes, stabilizers, emulsifiers, thickeners, plasticizers, surfactants and / or other common additives.

The components of organic vehicles are well known to those of skill in the art. The main components of the organic vehicle include one or more binders and one or more solvents. The binder may be a polymeric or monomeric organic compound, a "resin", or a mixture of the two. Polymer binders can have different molecular weights and different polydispersity indices. Polymer binders can include a combination of two different monomer units known as copolymers, in which the monomer units can be present alone or alternately in large blocks (block copolymers). Polysaccharides include commonly used polymeric binders, but not limited to, alkyl celluloses and alkyl derivatives such as methyl cellulose, ethyl cellulose, propyl cellulose, butyl cellulose, ethyl hydroxyethyl cellulose, derivatives and mixtures thereof. included. Other polymer binders include, but are not limited to, polyester, polyethylene, polypropylene, polycarbonate, polyurethane, polyacrylate (including polymethacrylate and polymethacrylate), polyvinyl (polyvinyl chloride, polyvinylpyrrolidone, polyvinylbutyral, etc.). Examples include polyvinyl acetate), polyamides, polyglycols (including polyethylene glycols), phenolic resins, polyterpenes, derivatives thereof and combinations thereof. The organic vehicle binder can contain 1-30% by weight of the binder.

Solvents are organic species that are usually removed from the paste during treatment by thermal means such as vaporization. Generally, the solvents that can be used in the pastes described herein include polar, non-polar, protic, aprotic, aromatic, non-aromatic, chlorinated and non-chlorinated solvents. Not limited to these. Examples of solvents that can be used in the pastes described herein are alcohols, dialcohols (including glycols), polyhydric alcohols (including glycerol), mono- and polyethers, mono- and poly-. Includes esters, alcohol ethers, alcohol esters, mono- and di-substituted adipate esters, mono- and poly-acetates, ether acetates, glycol acetates, glycol ethers (ethylene glycol monobutyl ethers, diethylene glycol monobutyl ethers, and triethylene glycol monobutyl ethers). ), Glycol ether acetate (including ethylene glycol monobutyl ether acetate), linear or branched saturated and unsaturated alkyl chains (including butane, pentane, hexane, octane and decane), terpen (alpha-, beta-, gamma-, And 4-terpineol), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (also known as texanol®), 2- (2-ethoxyethoxy) ethanol ( Examples include, but are not limited to, carbitols (also known as registered trademarks), derivatives thereof, combinations thereof, and mixtures thereof.

In one configuration, the organic vehicle contains 70-100% by weight of solvent. The proportions and composition of binders, solvents and optional additives achieve the desired dispersion or suspension of paste particles, the desired carbon content, and / or the desired rheological properties, as will be appreciated by those skilled in the art. Can be adjusted to. For example, paste rheology can be modified by adding a thixotrope such as Thixatur Max ™ (Tixatrol Max). In another embodiment, the carbon content of the organic vehicle can be increased or decreased by modifying the binder and thixotrope to take into account the peak calcination temperature, calcination profile, and airflow generated during thermal annealing. can. A small amount of additive may be included. Examples of such additives include, but are not limited to, thixotropic agents and surfactants. Such additives are well known in the art and the effective amount of such ingredients can be determined by routine experimentation to maximize the efficiency and reliability of the device. In one embodiment of the invention, the metallized paste is at a shear rate of 10,000-200,000 cP at ^{25 ° C. and 4-1 seconds-1 as measured using a temperature controlled Brookfield RVDV-II + Pro viscometer.} Has adhesiveness.
Intercalation Particle Blending Composition An exemplary composition range of the intercalation paste is shown in Table I according to some embodiments of the present invention. In various embodiments, the intercalation paste has a solid content of 30% to 80% by weight, the noble metal particles make up 10% to 70% by weight of the intercalation paste, and the intercalation particles It constitutes at least 10% by weight, 15% by weight, 20% by weight, 25% by weight, 30% by weight, or 40% by weight of the intercalation paste, and the ratio of the intercalation particles to the noble metal particles is at least 1: 1. It is 5. In an exemplary embodiment, the noble metal particle content is 50% by weight and the intercalation particles make up at least 10% by weight of the intercalation paste. In various embodiments, the ratio of intercalation particles to noble metal particles in the intercalation paste is at least 1: 5, or 2: 5, or 3: 5, or 1: 1, or 5: 2 by weight. Is.

In one embodiment of the invention, for solar cell applications, the intercalation paste is composed of 20-50% by weight of noble metal particles (ie, intercalation paste range II in Table I), LTBM, crystalline metal oxidation. It contains 10-35% by weight of intercalation particles, which can include objects, glass frit, or combinations thereof. In one embodiment, the intercalation particles are metallic bismuth particles. Intercalation paste A (Table I) contains 50% by weight silver particles, 12.5% by weight bismuth particles, and 37.5% by weight organic vehicle, and the ratio of intercalation particles to noble metal particles ( Weight ratio) is 1: 4. Intercalation paste C (Table I) contains 45% by weight silver particles, 30% by weight bismuth particles, and 25% by weight organic vehicle, with an intercalation particle to noble metal particle ratio of 1: 1.5. (Weight). If the intercalation paste contains silver and bismuth particles, the notation Ag: Bi is used.

In another embodiment, the intercalation particles are glass frit particles. Intercalation paste B (Table I) contains 45% by weight silver particles, 30% by weight bismuth-based glass frit particles, and 25% by weight organic vehicle, with intercalation particles to noble metal particles 1: 1. It becomes 5 (weight ratio). In another embodiment, the intercalation particles are a mixture of LTBM, crystalline metal oxide particles, and glass frit particles. Intercalation paste D (Table I) may contain 30% by weight silver particles, 15% by weight metal bismuth particles, 5% by weight high lead-containing glass frit particles and 50% by weight organic vehicle. The composition of the intercalation paste can be adjusted to achieve the desired bulk resistance, contact resistance, layer thickness, and / or peel strength for the particular metal layer.

In another embodiment of the invention, the method of forming the intercalation paste involves the step of providing the noble metal particles, the step of providing the intercalation particles, and the mixing of the noble metal particles and the intercalation particles in an organic vehicle. Including steps to do. In one configuration, intercalation particles are added to the organic vehicle, mixed with a planetary mixer (eg, Thinky AR-100), then precious metal particles (and additional organic vehicles as needed) are added, and , Mix with a planetary mixer. The intercalation paste can be ground by using, for example, a three-roll kneader (eg, Exact 50I), but this is not necessary. In one configuration, the intercalation paste contains 10-70% by weight of noble metal particles and more than 10% by weight of intercalation particles.
Method for Forming a Calcined Multilayer Stack In one embodiment of the invention, the calcined multilayer stack comprises a substrate in which at least one metal particle layer and at least one intercalation layer are present. In one embodiment, the calcined multilayer stack applies a metal particle layer to the surface of the substrate, dries the metal particle layer, applies the intercalation layer directly to a part of the dried metal, and dries the intercalation layer. It is then formed by using a co-fired process that involves the steps of co-firing the multilayer stack. In another embodiment, the fired multi-layer stack coats the surface of the substrate with a metal particle layer, dries the metal particle layer, fires the metal particle layer, dries the intercalation layer, and then fires the multi-layer stack. Formed by using a sequential process involving steps, in one embodiment, during firing, a portion of the intercalation layer penetrates the metal particle layer, thereby converting the metal particle layer into a modified metal particle layer. In some embodiments, each coating step comprises a method independently selected from the group consisting of screen printing, gravure printing, spray coating, slot coating, 3D printing and inkjet printing. In one embodiment, the metal particle paste is screen-printed on a part of the substrate to apply the metal particle layer, and the intercalation paste is screen-printed on a part of the dry metal particle layer to apply the intercalation layer. In one embodiment, a portion of the substrate surface is covered by at least one dielectric layer and a metal particle layer is applied to the portion of the dielectric layer.
Morphology of a multi-layer stack that has been dried and fired FIG. 1 is a schematic cross-sectional view showing a multi-layer stack 100 that has not been co-fired according to an embodiment of the present invention. The dried metal particle layer 120 exists directly above a part of the substrate 110. As described above, the intercalation layer 130 composed of the intercalation particles and the noble metal particles exists directly above a part of the dry metal particle layer 120. In various embodiments of the invention, the intercalation layer 130 has an average thickness of 0.25 μm to 50 μm, 1 μm to 25 μm, 1 μm to 10 μm, or any range included herein. In one embodiment of the invention, the intercalation layer 130 includes noble metal particles, intercalation particles, and any organic binder (which may remain in the intercalation layer 130 after drying). Prior to co-fired, the noble metal particles and the intercalation particles can be uniformly distributed within the intercalation layer 130. In one configuration, the noble metal particles and the intercalation particles do not deform after drying (and before firing) and retain their original size and shape.

In one embodiment of the invention, the dry metal particle layer 120 is porous and is aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium and alloys thereof, composites thereof, and other combinations thereof. Includes at least one of. In one configuration, prior to co-fired, the dry metal particle layer 120 may or may not contain metal particles and may or may not contain an organic binder and may or may not contain non-metal particles such as glass frit. .. Metal particles generally do not deform after drying (and before firing) and retain their original size and shape.

During firing, the intercalation particles from the intercalation layer 130 intercalate with a portion of the dry metal particle layer 120 adjacent to the intercalation layer 130 (shown below in FIG. 1). For the purposes of the present disclosure, the portion of the dry metal particle layer 120 adjacent to the intercalation layer 130 and infiltrated with the intercalation particle material is referred to as a "modified metal particle layer". The rest of the dry metal particle layer 120, which is not adjacent to the intercalation layer after firing and is not penetrated by the intercalation particle material or is intercalated only in trace amounts, is the object of the present disclosure. In the above, it is referred to as a "metal particle layer". In one configuration, the particles in the dry metal particle layer 120 are sintered or melted during firing so that the metal particle layer has a different morphology and a lower degree of porosity than the dry metal particle layer 120. Can be done. Fluctuations that occur during firing and the firing multi-layer stack structure will be described in more detail below.

FIG. 2 is a schematic cross-sectional view showing a fired multilayer stack 200 (structure 100 in FIG. 1 after firing) according to an embodiment of the present invention. The fired multilayer stack 200 includes a modified (by firing) metal particle layer 222 adjacent to at least a portion of the substrate 210 and a modified (by firing) intercalation layer 230 adjacent to the modified metal particle layer 222. .. During calcination, at least some of the noble metal particles and the intercalated particles in the intercalation layer (shown at 130 in FIG. 1 before calcination) form phases that are phase-separated from each other. The noble metal particles can be sintered or melted to change the morphology of the modified intercalation layer 230 and reduce porosity. As at least a portion of the noble metal particles (which can be sintered or melted) moves towards the solderable surface 230S of the modified intercalation layer 230, at least a portion of the intercalation particles melts and is adjacent. It flows into the modified metal particle layer 222, that is, intercalates. The modified metal particle layer 222 contains metal particles. The material from the intercalation particles in the intercalation layer (before firing is shown as 130 in FIG. 1) permeates the metal particles, and one of the dry metal particle layers (before firing is shown as 120 in FIG. 1). The modified metal particle layer 222 is formed by changing the material properties of the parts. The material from the intercalation particles can bind loosely connected metal particles in the modified metal particle layer 222, or coat metal particles that are already in contact with each other in the modified metal particle layer 222. can.

In some configurations, there is also a metal particle region 220 infiltrated with a small or trace amount of intercalation particle material. In one configuration, the metal particle layer 220, which is not in direct contact with the modified intercalation layer 230, does not contain components from the intercalation particles in such a high concentration. In some configurations, the metal particle layer 220 and the modified metal particle layer 222 form a compound (s) with the substrate 210 during co-fired or dope the substrate 210 (not shown). FIG. 2 shows a sharp boundary between the metal particle layer region 220 and the modified metal particle layer 222, but it should be understood that the boundary is generally not sharp. In some configurations, the boundary is determined by the degree of lateral diffusion of the modified intercalation layer 230 material into the metal particle layer 220 that occurs during co-fired.

In some embodiments of the present invention, the material in the modified intercalation layer 230 of FIG. 2 is phase separated into a phase containing the material from the intercalation particles and a phase containing the noble metal. FIG. 3 shows a fired multilayer stack 390 (equivalent to the structure 200 of FIG. 2), which is a schematic cross-sectional view in which the intercalation layer 330 is phase-separated. The fired multilayer stack 390 (only in the region 350) includes a modified (by firing) metal particle layer 322 in the region 350 between a portion of the substrate 300 and the modified (by firing) intercalation layer 330. The metal particle layer 320 containing the metal particles 392 exists on the substrate 300 adjacent to the multilayer stack region 350.

The modified intercalation layer 330 includes two phases, a noble metal phase 335 and an intercalation phase 333, and has a solderable surface 335S. Most (at least 50% or more) of the solderable surface is composed of the precious metal phase 335. In some configurations, the noble metal phase 335 and the intercalation phase 333 are not completely phase separated during firing, so there are also some intercalation phases 333 on the solderable surface 335S. The modified metal particle layer 322 contains metal particles 392 and a portion of the material from the intercalation phase 333. An interface 322I exists between the modified intercalation region 330 and the adjacent metal particles 392 in the modified metal particle layer 322. Interface 322I may not be smooth and depends not only on the firing conditions but also on the size and shape of the metal particles 392. In an embodiment in which any glass frit is included in the dry metal particle layer (120 in FIG. 1) prior to firing, the modified metal particle layer 322 and the metal particle layer 320 constitute a layer of less than 3% by weight. A small amount of glass frit (not shown) can also be included.

In another embodiment, the material in the modified intercalation layer 230 of FIG. 2 is phase separated to form a layered structure. FIG. 4 is a schematic cross-sectional view showing a fired multilayer stack 400 (corresponding to the structure 200 of FIG. 2) including an intercalation layer having two sublayers. The fired multilayer stack 400 (only within region 450) includes a modified (by firing) metal particle layer 422 in the region 450 between a portion of the substrate 410 and the modified (by firing) intercalation layer 430. The metal particle layer 420 includes metal particles 402 present on the substrate 410 adjacent to the multilayer stack region 450.

The modified intercalation layer 430 has two sublayers, that is, an intercalation layer 433 existing directly above the modified metal particle layer 422 and a noble metal sublayer 435 existing directly above the modified intercalation layer 433. And include. The precious metal sublayer 435 has a solderable surface 435S. The modified metal particle layer 422 contains metal particles 402 and some material 403 from the intercalation sublayer 433. An interface 4221 exists between the modified intercalation layer 430 (or the modified intercalation layer 433) and the uppermost metal particles 402 of the modified metal particle layer 422. In an embodiment in which any glass frit is included in the dry metal particle layer (120 in FIG. 1) prior to firing, the modified metal particle layer 422 and the metal particle layer 420 constitute a layer of less than 3% by weight. A small amount of glass frit (not shown) can also be included.

These multiple layers were identified using cross-sectional SEM imaging and the thickness of the layers in the multi-layer stack was measured. The average layer thickness of the layers in the fired multilayer stack was obtained by averaging at least 10 thickness measurements, each separated by at least 10 μm over the entire cross-sectional image. In various embodiments of the invention, the metal particle layer (such as 220 in FIG. 2) is 0.5 μm to 100 μm, 1 μm to 50 μm, 2 μm to 40 μm, 20 μm to 30 μm, or an average in any range included herein. Has a thickness. These metal particle layers on the substrate are generally smooth and have minimum and maximum layer thicknesses within 20% of the average metal particle layer thickness over a 1 x 1 mm region. In addition to the cross-sectional SEM, layer thickness and variation over the described areas can be accurately measured using an Olympus LEXT 4000 3D laser measuring microscope and / or a profile meter such as the Veeco Tektake 150.

In an exemplary embodiment, the metal particle layer (such as 220 in FIG. 2) is made of sintered aluminum particles and has an average thickness of 25 μm. The porosity of the metal particle layer can be measured in the range of 0.01 kPa to 2 MPa using a mercury porosimeter such as the CE equipment Pascal 140 (low pressure) or Pascal 440 (high pressure). The calcined metal particle layer can have a porosity of 1% to 50%, 2% to 30%, 3% to 20%, or any range contained herein. A calcined metal particle layer made of aluminum particles and used for solar cell applications can have a porosity between 10% and 18%.

The thicknesses of the intercalation sublayer and the noble metal sublayer, such as those schematically shown as 433 and 435 in FIG. 4, were measured in an actual multilayer stack using a cross-sectional SEM / EDX. The sublayers were distinguished by SEM due to the difference in contrast between the intercalation and the noble metal phase. EDX mapping was used to locate the interface shown in 4321 of FIG. In various embodiments, the noble metal sublayer has a thickness of 0.5 μm to 10 μm, 0.5 μm to 5 μm, 1 μm to 4 μm, or within any range. In various embodiments, the intercalation sublayer has a thickness of 0.01 μm to 5 μm, 0.25 μm to 5 μm, 0.5 μm to 2 μm, or within any range.

In one embodiment of the invention, the modified intercalation layer comprises two phases, namely a noble metal phase and an intercalation phase. This structure is shown in detail in FIG. Normally, the intercalation phase cannot be soldered, so it is useful if the solderable surface 230S mainly contains a noble metal phase that guarantees solderability. In various configurations, the solderable surface comprises greater than 50%, greater than 60%, or greater than 70% noble metal phase. In one configuration, the solderable surface of the modified intercalation layer mainly contains noble metals. Plan view EDX was used to measure the concentration of components on the surface of the modified intercalation layer. Using the above device, SEM / EDX was performed at an acceleration voltage of 10 kV, a sample working distance of 7 mm, and a magnification of 500 times. In various embodiments, at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, or at least 98% by weight of the outer surface 230S of the modified intercalation layer 230 is one or more gold. , Silver, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof. The firing conditions, the type and particle size of the intercalation particles and the noble metal particles all affect the degree of phase separation in the modified intercalation layer morphology.

The modified metal particle layer (shown as 222 in FIG. 2) contains a much higher concentration of intercalation particle material than the metal particle layer (shown as 220 in FIG. 2). Using a comparison of the modified metal particle layer and the EDX spectra taken from the cross section of the modified metal particle layer in the actual multilayer stack, the concentration of the material from the modified intercalation layer intercalated to the modified metal particle layer was measured. can do. Using the SEM / EDX device operated at 20 kV at a sample working distance of 7 mm, the metal from the intercalation particles (eg, bismuth) to the total metal (eg, bismuth and aluminum) in the cross-sectional sample of the modified metal particle layer. The ratio of was measured. The weight ratio (intercalation metal to total metal) is called the IM: M ratio. Baseline EDX analysis was performed in the region of the metal particle layer at least 500 μm away from the modified metal particle layer to ensure reproducible measurements. A second EDX spectrum was collected from the modified metal particle layer and the spectra were compared. In measuring the IM: M ratio, only the peaks of the metal components were considered (ie, the peaks from carbon, sulfur and oxygen were ignored). In analyzing this ratio, precious metals and metal components from the substrate were excluded to prevent unreliable results. In one exemplary embodiment, if the dry metal particle layer (shown as 120 in FIG. 1) contains aluminum particles and the intercalation layer 130 contains bismuth particles and silver particles, then the metal particle layer (ie, calcined). Later) contained more than 98% by weight aluminum with about 1% by weight bismuth and a 1:99 Bi: (Al + Bi) (IM: M) ratio. Other intercalation metal components make up a modified metal particle layer of less than 0.25 wt%, but are not considered in the calculation of the IM: M ratio. In various other embodiments, the IM: M ratio is 1: 10 ⁶ , 1: 1000, 1: 100, 1:50, 1:25 or 1:10.

The base material may have a certain surface roughness, and the interface with them may also be rough. FIG. 5 is a schematic cross-sectional view showing a portion of such a substrate 510, a modified metal particle layer 522, and a modified intercalation layer 530 according to an embodiment of the present invention. There is a non-planar interface 501B between the substrate 510 and the modified metal particle layer 522. A non-planar interface 522B exists between the modified metal particle layer 522 and the modified intercalation layer 530. Line 502 shows the deepest penetration of substrate 510 into the modified metal particle layer 522. Line 504 shows the deepest penetration of the modified intercalation layer 530 into the modified metal particle layer 522. The region of the modified metal particle layer 522 between the wire 502 and the wire 504 can be referred to as the sampling region 522A. In identifying the IM: M ratio in the modified metal particle layer 522, it may be useful to limit such analysis to the sampling region 522A so that the results are not false due to interfacial roughness.

In an exemplary embodiment, the IM: M ratio in the modified metal particle layer is 20% higher, 50% higher, 100% than in the metal particle layer (at least 500 μm away from the modified metal particle layer). High, 200% high, 500% high, or even 1000% high. In one exemplary embodiment, an intercalation layer containing bismuth particles is present on the aluminum particle layer and the modified metal particle layer (analyzed in a sampling region such as the example shown as 522A in FIG. 5) is 4 It contains% by weight bismuth and 96% by weight aluminum and has a Bi: (Al + Bi) (or IM: M) ratio of 1:25. The Bi: (Al + Bi) ratio in the modified metal particle layer is 400% higher than in the metal particle layer.

When the intercalation layer contains a crystalline metal oxide and / or a glass frit containing two or more metals, the intercalation metal components are quantified by EDX and totaled to determine the IM: M ratio. For example, if the glass frit contains both bismuth and lead, the ratio is defined as (Bi + Pb) :( Bi + Pb + Al).

In various embodiments, the calcined multilayer stack also comprises a solid compound layer formed from the interaction between the metal particles in the dry metal particle layer and the substrate during calcining. The solid compound layer can include, but is not limited to, alloys, eutectics, composites thereof, mixtures thereof, or combinations thereof. In one configuration, the modified metal particle layer and the substrate form a solid compound region (s) at their interface. The solid compound region may include one or more alloys. The solid compound region (s) may be continuous (layered) or semi-continuous. Depending on the composition of the substrate and the metal particle layer, the alloys or other compounds formed are aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, silicon, oxygen, carbon, germanium, gallium, arsenic, indium. And one or more of phosphorus can be included. For example, aluminum and silicon can form eutectics above 660 ° C., which when cooled results in a solid aluminum-silicon (Al-Si) eutectic layer at the silicon interface. In one exemplary embodiment, the solid compound layer is a solid Al—Si eutectic layer formed on a portion of a silicon substrate. The formation and morphology of solid Al—Si eutectic layers is well known in silicon solar cells. In another embodiment, the substrate is doped with at least one of aluminium, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, and alloys thereof, composites thereof, and other combinations thereof. NS. In one embodiment, aluminum is the p-type dopant in silicon and during firing, aluminum from the aluminum particle layer adjacent to the substrate provides more aluminum dopant and advanced p-type doping into the silicon substrate. Form a region. This is known as the backside electric field.

Depending on atmospheric conditions, the intercalation particles may undergo a multiphase transition as they melt and intercalate into the modified metal particle layer in the calcined multilayer stack. Depending on the modified metal particle layer and the material in the substrate, the intercalation particles can form crystalline compounds upon intercalation with the modified metal particle layer. Such crystalline compounds improve aggregation between metal particles in the modified metal particle layer, prevent mutual diffusion of certain components, and / or reduce electrical contact resistance between the metal layers in the calcined multilayer stack. can do. In one embodiment, the modified intercalation layer and the modified metal particle layer are crystals consisting of bismuth and at least one of oxygen, silicon and silver and alloys thereof, composites thereof, and other combinations thereof. Including children.

In one embodiment of the invention, the noble metal phase comprises at least one material selected from the group consisting of gold, silver, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof. include. In one configuration, the noble metal phase consists essentially of one or more of these materials. If one of these materials makes up the majority of the noble metal phase, the noble metal phase is described as rich in that material. For example, when the noble metal phase, the noble metal layer or the noble metal sublayer mainly contains silver, it can be referred to as a silver-rich region, a silver-rich layer, or a silver-rich sublayer, respectively.

The intercalation phase contains components from the intercalation particles and from components from the external environment (eg, oxygen) and the noble metal particles of the adjacent metal particle layer, and further incorporated nearby groups during firing. It may also contain small amounts of ingredients from the wood. A wide range of component sequences can be present in the intercalation phase, depending on whether cold base metals, crystalline metal oxides and / or glass frits are used as intercalation particles. In one embodiment (when the intercalation particles are only cold base metals), the intercalation phase is bismuth, boron, tin, tellurium, antimony, lead, oxygen, and alloys thereof, composites thereof, and Includes at least one material selected from the group consisting of these other combinations. In another embodiment (when the intercalation particles are only crystalline metal oxides), the intercalation phases are bismuth, tin, tellurium, antimony, lead, vanadium chromium, molybdenum, boron, manganese, cobalt, and. Includes at least one material selected from the group consisting of these alloys, these composites, and oxides of other combinations thereof. In another embodiment (when the intercalated particles are exclusively glass frit), the intercalation phase is oxygen and the following components: silicon, boron, germanium, lithium, sodium, potassium, cesium, gallium, calcium. , Strontium, barium, zirconium, hafnium, vanadium, niobium, chromium, molybdenum, manganese, renium, iron, cobalt, zinc, cadmium, gallium, indium, carbon, tin, lead, nitrogen, phosphorus, arsenic, antimony, bismuth, sulfur , Serene, tellurium, fluorine, chlorine, bromine, iodine, lanthanum, cerium, and alloys thereof, composites thereof, and at least one component of these other combinations. If one of these materials occupies most of the intercalation region, the intercalation region is described as rich in that material. For example, when the intercalation region, the intercalation layer or the intercalation sublayer mainly contains bismuth, they can be referred to as a bismuth-rich region, a bismuth-rich layer, or a bismuth-rich sublayer, respectively.
Examples and Applications of Post-Sinter Multilayer Stacks Metal particle layers predominantly containing aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum and titanium are combined with mildly activated (RMA) flux and tin solder after calcination. Cannot be soldered. However, in solar cells and other devices, it is highly desirable to solder the ribbon in order to make an electrical connection with a metal particle layer such as an aluminum particle layer. As disclosed herein, the intercalation pastes of the present invention containing noble metals such as silver and gold are used on metal particle layers and fired in the air to produce highly solderable surfaces. be able to. This is another attempt to increase the solderability of the metal particle layer by adding a noble metal, as the noble metal usually interdiffuses with the metal particle layer (eg, aluminum) when fired in a multi-layer stack. As a result, the solderable surface contains almost no precious metals, which is in contrast to other attempts at poor soldering. For example, firing a layer of commercially available silver-containing rear tab paste containing less than 10% by weight of glass frit on an aluminum particle layer does not yield a solderable surface. The resulting silver-alumina surface is not solderable because such layers undergo significant silver-aluminum interdiffusion during the firing step.

The etching layers disclosed herein are 1) blocking the diffusion of noble metals and providing a solderable surface, 2) mechanically strengthening the metal particle layer, and 3) underneath the metal particle layer. It can be used to modify the material properties of the metal particle layer with the purpose of assisting the etching of the layer. In one embodiment of the invention, a multilayer stack using an intercalation paste containing noble metal particles made of silver and intercalation particles made of bismuth metal or bismuth-based glass frit, and an adjacent metal particle layer containing aluminum particles. Formed. The fired multilayer stack screen-prints aluminum paste (commonly used for solar cell applications) on bare silicon wafers, dries the sample at 250 ° C. for 30 seconds, and intercalates paste onto a portion of the dried aluminum particle layer. Is screen-printed, the sample is heated at 250 ° C. for 30 seconds, and the sample is co-fired using a spike firing profile with a peak temperature of 700 ° C. to 820 ° C. and a ramp-up and cooling rate above 10 ° C./sec. It was formed. All drying and firing steps were performed using a Despatch CDF7210 furnace commonly used in the manufacture of silicon solar cells.

SEM / EDS analysis was used to identify the component composition of various regions in the calcined multilayer stack in the polished cross section and to study the intercalation process. SEM / EDX was performed using the device described above with two different operating modes. SEM micrograph is SE
Imaged with a Zeiss Gemini Ultra-55 analytical field emission SEM using two modes called 2 and Inlens. The SE2 mode was operated at 5-10 kV, a working distance of 5-7 mm using an SE2 secondary electron detector, and a scanning cycle time of 10 seconds. In order to maximize the contrast between the intercalation region and the Al particles, the brightness and contrast were varied between 0-50% and 0-60%, respectively. The Inlens mode was operated at 1 to 3 kV, a working distance of 3 to 7 mm using an InLens secondary electron detector, and a scanning cycle time of 10 seconds. In order to image the BSF in the Inlens mode, the brightness was set to 0% and the contrast was set to about 40%.

In one embodiment of the invention, the intercalation particles containing 10-15% by weight of the intercalation particles block the mutual diffusion between the noble metal (ie, silver) and the metal particles (ie, aluminum). The intercalation paste A (shown in Table I) contains 12.5% by weight of bismuth particles and 50% by weight of Ag, and the weight ratio of the intercalation particles to the noble metal particles is 1: 4. A fired multi-layer stack was made as described above. A calcined multilayer stack SEM was performed using the above apparatus in SE2 mode with an acceleration voltage of 5 kV, a working distance of 7 mm, and a magnification of 4000 times.

FIG. 6 is a cross-sectional image of a scanning electron microscope of a co-fired multilayer stack. The modified intercalation layer 630 is directly above the modified metal particle layer 622. The modified intercalation layer 630 includes a bismuth-rich (intercalation phase) sublayer 632 containing bismuth oxide and a silver (precious metal) -rich sublayer 634. The modified metal particle layer 622 contains aluminum particles 621 and an intercalation phase material 623 extending from the bismuth-rich sublayer 632. The intercalation region 632 is located just above the aluminum particles 621, at least near the interface region 631. The intercalation sublayer 632 appears to prevent mutual diffusion of silver from the modified intercalation layer 630 and aluminum from the modified metal particle layer 622 during the co-fired process. FIG. 6 is an example of the hierarchical structure described in FIG. 4 above. The noble metal sublayer 634 provides a highly solderable surface (away from the modified metal particle layer 622). The intercalation phase material 623 does not penetrate deep into the modified metal particle layer 622. The modified metal particle layer 622 mainly contains aluminum particles that are weakly sintered at the same time, and has low mechanical strength after co-fired. Not enough bismuth to penetrate deep into the metal particle layer 622, the intercalation sublayer 632 can stress the modified metal particle layer 622, which can mechanically weaken the co-fired multilayer stack. be. The peel strength of the multilayer stack after such co-fired is less than 0.4 N / mm (Newton / millimeter) with the main fracture mechanism between Al particles. Current solar industry standards require a peel strength of greater than 1 N / mm to be considered commercially feasible.

Intercalation paste B (shown in Table I) uses glass frit as the intercalation particles to achieve a solderable surface. The intercalation paste B contains 30% by weight of bismuth-based glass frit (intercalated) particles and 45% by weight of Ag, and the weight ratio of the noble metal particles to the intercalation particles is 1: 1.5. The glass frit mainly contains bismuth, has a glass transition temperature of 387 ° C, and a softening point of 419 ° C. A calcined multilayer stack SEM was performed using the above apparatus in SE2 mode with an acceleration voltage of 5 kV, a working distance of 7 mm, and a magnification of 4000 times. FIG. 7 is a cross-sectional view of a scanning electron microscope of such a co-fired multilayer stack according to an embodiment of the present invention. The modified metal particle layer 722 contains aluminum particles 730. Since the bismuth-based glass frit does not completely phase-separate from the Ag particles during simultaneous firing, it has two phases, namely the noble metal phase 721 and a bismuth-based intercalation phase 740 similar to that shown in FIG. 3 above. A modified intercalation layer 750 is obtained. The surface 750S on the modified intercalation layer 750 contains more than 50% noble metal phase 721. The surface 750S is a flux commonly used in the solar battery industry (eg, Kester 952S, K).
It can be soldered by ester 951 and Alpha NR205). The peel strength of the entire calcined multilayer stack is less than 0.5 N / mm, which may be due to the relatively low penetration of the bismuth intercalation phase 740 into the modified aluminum particle layer 722. In general, the morphology of the modified intercalation layer can be modified by varying the composition of the intercalation particles and their content in the intercalation layer.
Intercalation paste that blocks the interdiffusion of components to reinforce the underlying metal particle layer. Illustrates two paste formulations designed in, but the fired layer lacks adequate mechanical strength when soldered. Intercalation paste C (shown in Table I) contains 30% by weight bismuth particles and 45% by weight silver particles (ie, Ag: Bi intercalation paste), and the weight ratio of the intercalation particles to the noble metal particles. Is 1: 1.5. The increased content of intercalation particles in the paste increases the concentration of intercalation material in the modified metal particle layer, resulting in a mechanically stronger calcined multilayer stack. This intercalation paste C was used as a drop-in substitute for a commercially available silver rear tab paste during the manufacture of BSF polycrystalline p-type solar cells. The intercalation paste C can also be referred to as silver (Ag-on-Al) on aluminum, rear tabs, floating rear tabs, or tab-invation paste. Using a series of evaluation tools for the obtained calcined multilayer stack, the IM: M (intercalation metal: metal) ratio and the noble metal surface coverage were evaluated, and whether crystals were formed in the intercalation region. I decided whether or not.

The effect of the intercalation layer on the metal particle layer is best demonstrated by first showing the morphology of the aluminum particle layer fired on a silicon substrate in the absence of the intercalation layer. FIG. 8 shows the aluminum particle layer 822 thus fired on the silicon substrate 810 taken from the region of the silicon solar cell not including the intercalation layer taken with a scanning electron microscope (SEM) in SE2 mode. It is a cross-sectional image. The fired aluminum particle layer 822 is about 20 μm thick and contains aluminum particles 821 and a small amount of inorganic binder (ie, glass frit) 840. An InLens mode scanning electron micrograph of the same aluminum particle layer is shown in FIG. In the InLens mode, in addition to the backside electric field region 970 and the solidified aluminum-silicon (Al-Si) eutectic layer 980, the aluminum particle layer 922, the aluminum particles 921 and the silicon substrate 910 can be clearly seen.

The effect of the intercalation layer on forming the modified metal particle layer after co-fired can be understood by referring to FIG. FIG. 10 is an InLensSEM cross-sectional image of the same silicon solar cell used in the image shown in FIG. 8, taken from a region containing a co-fired multilayer stack made with intercalation paste C (shown in Table I). It is a thing. The co-fired multilayer stack 1000 includes a modified intercalation layer 1030, a modified aluminum particle layer 1022, a solidified Al—Si eutectic layer 1080, an aluminum-doped back surface electric field (BSF) region 1070, and a silicon substrate 1010. In an exemplary embodiment, BSF in the silicon substrate is doped p-type between 1 cm ³ per ^{1017 20} atoms.

The SE2 mode scanning electron micrograph of the co-fired multilayer stack of FIG. 10 is shown in FIG. While the InLens mode clearly shows the BSF region, the SE2 mode is the preferred mode for imaging bismuth (intercalation phase) in the modified aluminum particle layer. The co-fired multilayer stack 1100 includes a modified intercalation layer 1130, a modified aluminum particle layer 1122, and a silicon substrate 1110. Silver sublayer 1134 and bismuth intercalation sublayer 1132 in modified intercalation layer 1130
Can also be visually observed. The BSF region and the solidified Al—Si eutectic layer are not clearly visible in this image. The modified aluminum particle layer 1122 contains a large amount of bismuth intercalation material 1103 intercalated around the aluminum particles 1102 during simultaneous firing. In some cases, the contrast between bismuth and silver may not be strong enough to clearly distinguish between its sublayer and the degree of bismuth intercalation into the aluminum particle layer. In such cases, SEM / EDX can be used to create a cross-sectional component map to completely identify the placement of silver and bismuth in the co-fired multilayer stack.

The amount of intercalation metal (ie, bismuth) in the modified aluminum particle layer by intercalation should be compared with the modified aluminum particle layer region and the EDX spectrum obtained from the aluminum particle layer region in the same cross-sectional sample. Can be identified by. This is most effective when the regions are separated from each other by 1 μm or more. This comparison method has been described above as an IM: M or Bi: (Bi + Al) ratio. Such an analysis can be useful in determining whether the intercalation paste has been used in the manufacture of solar cells. The metallized layer of a solar cell generally consists of a narrow subset of metals containing aluminum, silver, bismuth, lead, and zinc. In commercially available solar cells, the aluminum particle layer contains almost only aluminum.

In one embodiment, the intercalation particles in the intercalation paste C contain only bismuth, and the metal particles in the metal particle layer are mostly aluminum. Comparing the bismuth to bismuth + aluminum ratio (Bi: (Bi + Al)) in the aluminum particle layer (ie, having no interaction with the intercalation paste) and the modified aluminum particle layer is an intercalation paste. Is a useful criterion in determining whether or not is incorporated into a solar cell. The EDX spectrum of these two layers was measured at an acceleration voltage of 20 kV and a working distance of 7 mm for about 3 minutes using the above device. The EDX spectrum of the calcined aluminum particle layer 822 of FIG. 8 was collected from the region 898. The EDX spectrum of the modified aluminum particle layer 1122 of FIG. 11 was collected from region 1199. Component quantification was performed on these spectra using Bruker Quantax Esprit 2.0 software for automatic component identification, background removal, and peak fitting. The EDX spectrum is shown in FIG. The peak areas of aluminum and bismuth metal were quantified from the EDX spectrum of FIG. 12 for the two layers, and the weight% was calculated. It is summarized in Table II below. No significant amounts could be identified for other metals in this EDX spectrum. As shown in Table II, a 1: 244 Bi: (Bi + Al) weight% ratio was obtained from the EDX spectrum of the aluminum particle layer shown in FIG. 12A, and about 1 from the spectrum of the modified aluminum particle layer shown in FIG. 12B. A Bi: (Bi + Al) weight% ratio of 4: 4 is obtained. The Bi: (Bi + Al) weight% ratio of the modified aluminum particle layer 1122 is about 62 times higher than that of the calcined aluminum particle layer 822 that is not in contact with the Ag: Bi intercalation layer. In various embodiments, the Bi: (Bi + Al) ratio in the fired multilayer stack produced is at least 20%, or at least 50%, or at least twice, or at least in the modified aluminum particle layer than in the aluminum particle layer. 5 times, or at least 10 times or at least 50 times higher.

The plan view EDX can be used to measure the component concentration on the surface of the back tab layer in a silicon solar cell. In the plan view, EDX explored the surface to a depth of about 4 μm or less, which is an effective technique for determining the degree of mutual diffusion of multi-layer stacks after co-fired, and the high concentration of precious metals means that the concentration of precious metals is high. Less interdiffusion means less noble metal concentration means more interdiffusion. FIG. 13 is a plan view EDX spectrum taken from the surface of the back tab layer including the Ag: Bi intercalation layer according to the embodiment of the present invention. The EDX spectrum was collected using an SEM operated at an acceleration voltage of 10 kV, a working distance of 7 mm, and a magnification of 500 times. The major peaks of 3.5 keV to 4 keV and the smaller peaks at 0.3 keV are all identified as silver. The remaining small peaks in the spectrum are as follows: 0.3 keV carbon (enclosed by small silver peaks), 0.52 keV oxygen, 1.48 keV aluminum, and 2.4 keV. Identified as bismuth. Component quantification was performed automatically using Bruker Quantax Esprit 2.0 software, background was subtracted, component peaks were identified, and then the peak intensities of X-ray energies were adapted. The normalized weight percent of each component is shown in Table III below. The silver coverage over the entire surface of the back tab layer is 96.3 weight percent (wt%).

The intercalation layer containing silver and bismuth can form some unique crystalline phases when calcined on a dry aluminum-based metal particle layer. XRD distinguishes between calcined multilayer stacks using bismuth particles in the intercalation layer and calcined multilayer stacks using conventional silver-based tabbed pastes with less than 10% by weight glass frit as an inorganic binder. Can be used for. XRD was performed using a Bruker ZXS D8 Discover GADDS X-ray diffractometer equipped with a VANTEC-500 area detector and a cobalt X-ray source operating at 35 kV and 40 mA. The XRD pattern of the multi-layer stack fired on the back tab layer of the silicon solar cell is shown in FIG. Diffractograms were measured using the cobalt Kα wavelength in two 25 ° frames combined for a 25-80 ° overall window at 2θ. Each frame was measured for 30 minutes under X-ray irradiation. No background subtraction was performed on the two diffraction patterns of FIG. The pattern was normalized to 1 for the maximum peak and 0.01 background was added to the data and plotted in Log.

The XRD diffraction pattern indicates that the calcined multilayer stack formed by the Ag: Bi intercalation layer or the back tab layer in the solar cell has a pattern different from that formed without bismuth. .. The XRD pattern A is from a co-fired multilayer stack on the back tab layer in a silicon solar cell. This co-fired multilayer stack was formed with intercalation particles containing about 45% by weight silver, 30% by weight Bi, and 25% by weight organic vehicle (for paste C in Table I above). It contained a modified intercalation layer. Peak 1410 is identified as silver and peak 1420 is a microcrystal of _{bismuth oxide (Bi 2} O _3). The XRD pattern B is from a co-fired multilayer stack on the back tab layer in a silicon solar cell formed using a commercially available rear tab paste containing less than 10% by weight of glass frit as an intercalation layer on the aluminum particle layer. It is a thing. The multi-layer stack after this co-fired is dark in color, showing significant silver-aluminum interdiffusion. Peak 1450 is identified as a silicon-aluminum eutectic phase. The peak 1460 is identified as a silver-aluminum alloy phase (ie, Ag2Al). Silver peak 1410 is observed in pattern A with the bismuth oxide compound and not in pattern B where silver is observed only as part of the silver-aluminum alloy 1450. This is further evidence that bismuth prevents mutual diffusion in calcined multilayer stacks. In one embodiment, the back tab layer of the silicon solar cell is at least one such as bismuth microcrystals and silicon, silver, and oxides thereof, alloys thereof, composites thereof, or other combinations thereof. Contains other ingredients. In another embodiment, the back tab layer comprises bismuth oxide microcrystals. In another embodiment, the intercalation region undergoes a multiphase transformation during calcination.
The intercalation layer can be etched through the dielectric layer during firing In some device applications, the dielectric layer is placed before the metal layer is deposited to passivate the substrate surface and improve electronic properties. It is deposited on the surface of the substrate. The dielectric layer can also prevent interspecific interdiffusion between the substrate and the adjacent metal particle layer. In some cases, it is highly desirable to etch the dielectric layer to form a compound between the substrate and the metal particle layer for the purpose of improving electrical conduction between the substrate and the metal particle layer. Glass frits containing bismuth and lead are known to penetrate various dielectric layers (eg, silicon nitride) during co-fired silicon solar cells. In an exemplary embodiment, the intercalation paste D is about 30% by weight silver, 20% by weight intercalation particles (15% by weight metal bismuth particles, 5% by weight high lead-containing glass frit) and 50. Contains% by weight organic vehicle. Such an intercalation paste can be particularly useful when the etching penetrates the dielectric layer.

FIG. 15 shows a schematic cross-sectional view of a multilayer stack 1500 including a substrate 1510 coated with at least one dielectric layer 1513 prior to firing according to an embodiment of the present invention. The dry metal particle layer 1520 is present on a portion of the dielectric layer 1513. As described above, the intercalation layer 1530 is composed of intercalation particles and noble metal particles, and is located on a part of the dry metal particle layer 1520. Prior to firing, the noble metal particles and the intercalation particles can be uniformly distributed in the intercalation layer 1530. The dielectric layer contains at least one of silicon, aluminum, germanium, hafnium, gallium, oxides thereof, nitrides thereof, composites thereof, and combinations thereof. In one configuration, the dielectric layer 1513 is a silicon nitride layer having a thickness of 75 nm. In another embodiment, there is a second dielectric layer (not shown) between the dielectric layer 1513 and the substrate 1510. In one configuration, the second dielectric layer is a 10 nm-thick alumina layer that exists directly above the substrate 1510, and the dielectric layer 1513 is a 75 nm-thick silicon nitride layer that exists directly above the alumina layer. .. The dry metal particle layer 1520 is formed by depositing a metal particle paste on the dielectric layer 1513 and then drying it. In one configuration, the dry metal particle layer 1520 is 20 μm thick and contains aluminum particles. An intercalation layer 1530 containing intercalation particles such as glass frit containing lead or bismuth is deposited and dried on the dry metal particle layer 1520 so as to cover at least a part of the dry metal particle layer 1520. ..

FIG. 16 is a schematic cross-sectional view showing a fired multilayer stack 1600 (structure 1500 in FIG. 15 after firing) according to an embodiment of the present invention. During the co-fired, at least some of the intercalation particles (including the glass frit described with reference to FIG. 15) in the modified intercalation layer 1630 began to melt and flow into the modified metal particle layer 1622. Intercalate. In one configuration, the material from the glass frit particles in the modified interaction layer 1630 penetrates into the metal particles in the modified metal particle layer 1622 and is etched into the dielectric layer 1613 (1513 before firing). It allows certain metals from the modified metal particle layer 1622 to chemically and electrically interact with the substrate 1610 to form one or more new compounds 1614. Other intercalation particles from the modified intercalation layer 1630 (eg, bismuth particles) can also intercalate into the modified metal particle layer 1622 to provide a structural support. In one configuration, the noble metal particles and at least some of the intercalation particles in the modified intercalation layer 1630 form phases that are phase-separated from each other, as described in more detail with reference to FIG. In some configurations, there is also a metal particle region 1620 (on the dielectric layer 1613), in which only trace or trace amounts of intercalation particle material permeate. In an exemplary embodiment, the intercalated particles are bismuth particles and glass frit particles, and the metal particles are aluminum.
Intercalation layers that introduce layer thickness variation in the metal particle layer to reduce buckling can cause stress in the underlying modified metal particle layer during firing, which causes buckling or wrinkling. This can lead to inadequate strength and electrical communication between layers. For example, the intercalation layer may have a different coefficient of thermal expansion than the adjacent modified metal particle layer, causing the layer to expand or contract differently during firing. Another source of stress in the adjacent modified metal particle layer can be the intercalation of the intercalation particle material that melts between the metal particles. Such stresses can cause buckling or wrinkling in the modified metal particle layer and / or the modified intercalation layer. Buckling or wrinkles can be categorized as significant, periodic or aperiodic deviations in layer thickness. In many cases, this results in delamination between the layers. For example, before the intercalation layer on the dry metal particle layer is fired, the initial thickness of the stack containing the intercalation layer and the dried metal particle layer is about the same everywhere. After co-fired, the thickness of the fired multilayer stack containing the modified intercalation layer and the modified metal particle layer can be as much as three times the initial thickness in some regions.

FIG. 17 is a plan view optical micrograph of a co-fired multilayer stack in which buckling has occurred. The modified intercalation layer 1730 can be seen. The modified intercalation layer 1730 is buckled and some peak regions 1712 are shown in FIG. The adjacent metal particle layer 1720 is not buckled and remains smooth or substantially flat. Even if the intercalation layer 1730 buckles, the mechanical integrity of the multi-layer stack after co-fired remains robust at peel strengths greater than 1 N / mm. However, buckling can make good and strong contact difficult when soldering the modified intercalation layer 1730 and the tab ribbon (not shown) together. The buckled surface of the modified intercalation layer 1730 can cause incomplete solder wetting over the range of the intercalation layer 1730, reducing peel strength and solder bonding reliability. It may be effective to reduce or eliminate buckling of the multilayer stack after co-fired to ensure soldering to the tab ribbon.

The thickness change can be incorporated into the calcined multilayer stack to significantly reduce layer buckling and / or wrinkles. If one or more layers have varying thickness, a non-planar interface may occur between such layers. The variable thickness reading is the non-planar interface between the layers in the fired multilayer film stack. The thickening involves patterning a portion of the first layer, followed by printing the second layer directly on the patterned portion of the first layer to create a non-planar interface between the two layers. It can be created by creating it. In one configuration, one layer will have varying thickness as a result of being printed using a patterned screen. After firing, the thickness of the individual layers can be reduced, but firing does not result in layers of varying thickness. Various thicknesses of this layer can be measured and quantified using both cross-section SEM and surface topology techniques before and after firing. In various embodiments, if a layer has a thickness variation of at least 20% greater or at least 20% less than the average thickness of the layer measured within 1 x 1 mm, then the phase may be described as having a variation. can.

FIG. 18 is a screen according to an embodiment of the present invention that can be used while depositing a metal particle paste to achieve thickening on a dry metal particle layer. The screen 1800 has an open mesh 1810 and some pattern regions 1820. The pattern region 1820 includes a confined region 1821 and an open region 1822. When the screen 1800 is used during printing of the wet metal particle layer, the paste flows through the openings 1822 and the opening mesh 1810 is blocked by the enclosed area 1821, varying the thickness of the deposited wet metal particle layer. .. In one embodiment, the wet metal particle layer is then dried to form a thickened dry metal particle layer and the intercalation paste is deposited directly on the thickened dry metal particle layer.

There are several factors that can affect the thickness of the dry metal particle layer, such as the number of meshes, wire diameter and shape, wire angle to frame, emulsion thickness and screen design. The mesh size and wire diameter determine the smallest printable pattern shape and opening. The thickness variation of the dry metal particle layer is also affected by the rheology of the metal particle paste, which affects the collapse of the layer. The paste can be designed with high viscosity and thixotropy to precisely control where it deposits on the substrate. It is also possible to change the magnitude of the thickness variation of the metal particle layer by adjusting the emulsion thickness of the screen. The screen can also be designed to ensure that the thickness of the fluctuating layer is continuously deposited on the surface of the substrate, either overall or only in specific areas. In an exemplary embodiment, the metal particle paste is printed using a 230-mesh screen with an emulsion thickness of 5 μm. In one configuration, the pattern 1820 has a series of 100 μm × 3 mm opening regions 1822 adjacent to a 100 μm × 3 mm enclosed region 1821. There are no restrictions on the type, periodicity (or lack thereof), or size of the pattern. Many patterns can result in thickening and the patterns can be adjusted for various printing conditions and paste formulations.

FIG. 19 is a schematic cross-sectional view showing a thickened dry metal particle layer deposited on a substrate 1910 using the screen 1800 of FIG. 18 according to an embodiment of the present invention. The dry metal particle layer 1920 outside the region 1825 was formed by depositing the metal particle paste through the open mesh region 1810 of the screen 1800 and then drying the metal particle paste. The thickened dry metal particle layer 1922 within the region 1925 is deposited through the masked region 1820 of the screen 1800 and has a variable thickness. The intercalation paste was then printed directly onto the thickened dry metal particle layer 1922 within the region 1925 and dried to form the intercalation layer 1930.

FIG. 20 is a schematic cross-sectional view showing the structure of FIG. 19 after co-fired according to an embodiment of the present invention. As described above, in the simultaneous firing, the material from the intercalation layer 1930 (FIG. 19) is intercalated with the thickened dry metal particle layer 1922 (FIG. 19) which is the base thereof, and the thickened metal particles. The layer 1922 can be converted into a modified metal particle layer 2022 with a variable thickness, and the intercalation layer 1930 can be converted into a modified intercalation layer 2030. In one configuration, the modified metal particle layer 2022 has patterned thickness variations including, but not limited to, periodic bumps, ridges, edges and other prominent shapes. The thickness of the modified intercalation layer 1930 is often uniform, and the non-planar interface (due to its thickness) between the modified intercalation layer and the modified metal particle layer is a multi-layer stack. It can be inferred by measuring the variation in the overall thickness of.

FIG. 21 is a plan view optical micrograph of a co-fired multilayer stack in which metal particle paste is printed in various thicknesses (in some areas) using a screen as shown in FIG. The multilayer stack was co-fired directly on the variable thickness region of the metal particle layer, and the modified intercalation layer 2121 adjacent to either side was formed on the upper surface by the substantially flat metal particle layer 2120. The metal particle layer 2120 has a flat top surface. The surface of the modified intercalation layer 2121 is non-planar with a pattern that reflects variations in the thickness of the underlying modified metal particle layer. The surface of the modified intercalation layer 2121 shows no signs of buckling or wrinkles, as is clearly visible in the modified intercalation layer 1730 of FIG. In one embodiment of the invention, some of the co-fired multilayer stacks have a variable thickness.

A useful criterion to explain the variation is to compare the peak and valley thicknesses with the average thickness. Unintended thickness variations can occur in any layer, but such variations are typically less than 20% of the average thickness of the layers. A layer can be considered flat (having a uniform thickness) if the layer thickness varies by less than 20% of the average thickness of the layer. By carefully designing the screen for printing the metal particle paste, thickness variations that are at least 20% greater than or less than at least 20% less than the average thickness of the layers when measured within a 1x1 mm area. It is possible to produce a layer with a thickening.

The thickness change of the calcined multilayer stack can be measured from the SEM image of the polished cross-sectional sample. FIG. 22 is a partial cross-sectional SEM image of the fired multilayer stack 2210 having a variable thickness according to an embodiment of the present invention. Cross-section samples were prepared and imaged using the method described above. The fired multilayer stack 2210 includes a modified intercalation layer 2211, a modified aluminum particle layer 2212, and a silicon substrate 2213. Two interfaces on both sides of the modified aluminum particle layer 2212, that is, the interface 2218 between the silicon substrate 2213 and the modified aluminum particle layer 2212, and the interface between the modified aluminum particle layer 2212 and the modified intercalation layer 2211. 2217 is identified in the image. Interface 2216 is a solderable surface. For comparison, FIG. 23 shows a silicon substrate 2322 having a flat aluminum particle film 2321 without thickness change.

The average thickness of the modified aluminum particle layer 2212 in FIG. 22 is calculated by averaging the thickness measurements. The thickness between the two interfaces 2217 and 2218 in FIG. 22 was measured at regular intervals (eg, 10 microns) throughout the sample. Thickness was also measured at local maxima and local minima. Software such as ImageJ 1.50a can be used to obtain average thickness, minimum thickness and maximum thickness. The peaks and valleys found in a single cross-section sample may not be representative of the entire calcined multi-layer stack. Therefore, it is useful to make such measurements over several cross-section samples to ensure that a large number of peaks and valleys are measured. These are methods known to those of skill in the art.

In the case of the sample shown in FIG. 22, the modified aluminum particle layer 2212 has an average thickness of 11.3 μm, a peak thickness of 18.4 μm, and a valley thickness of 5.2 μm. The peak thickness is 64% larger than the average thickness, and the valley portion is 54% smaller than the average thickness. In various embodiments, the layer with varying thickness has a peak thickness that is at least 20%, at least 30%, at least 40%, or at least 50% greater than the average thickness of the layer. In various embodiments, the layer with varying thickness has a valley thickness that is at least 20%, at least 30%, at least 40%, or at least 50% less than the average thickness of the layer.

When the modified intercalation layer 2211 is continuous and substantially uniform in thickness, the solderable surface 2216 of the modified intercalation layer 2211 is approximately parallel to the interface 2217. In one embodiment of the invention, all measurements described above for the modified aluminum particle layer 2212 are the modified aluminum particle layer 2212 and the modified intercalation layer present between the solderable surface 2216 and the interface 2217. This can be done for a total thickness of 2211. The comparison of the thickness measurements of the two combined layers is a good approximation for the comparison of the thickness measurements for the modified aluminum particle layer 2212 only. In the case of the combined layers of FIG. 22, the peak thickness is 44% larger than the average total thickness of 13.2 μm, and the valley thickness is 43% smaller than the average total thickness. This alternative method may not systematically measure the thickness variation of the fired multilayer stack.

In some applications, it may be desirable that only part of the calcined multilayer stack has variability. For example, the back aluminum particle layer of a silicon solar cell is generally flat. On the back side of such cells, it may be useful to introduce a thickening into the back tab layer portion (including the modified intercalation layer). It is possible to compare the thickness variation of a part of the surrounding aluminum particle layer with the thickness variation of a part of the back tab layer to determine whether the layer with the variation was used on the back side of the solar cell. did it.

Another useful criterion for determining thickness in a fired multilayer film stack is the peak-to-valley average height, which is the difference between the average of the local maximum and the average of the local minimum. .. Surface shape measurement methods such as profileometry, coherent scanning interferometry, and focal variation microscopy are more useful for cross-sectional SEM images because the maximum and minimum within the image are not guaranteed. An example of a profile meter is a Bruker or Veeco Dectake 150 or equivalent. The coherent scanning interferometry can be performed using an Olympus LEXT OLS4000 3D laser measurement microscope. The software associated with these methods can automatically calculate the average peak-to-valley difference.

In an exemplary embodiment, profiles are used to measure peak-to-valley average heights for both calcined multi-layer stacks with different thicknesses and aluminum particle layers with uniform thickness within the same sample. Measurements are used. A 3D topological surface map was created by measuring the surface of a 1 × 1 mm region using a probe with a radius of 12.5 mm using a Veco Tektake 150. FIG. 24 is a 3D surface topology map of the calcined multilayer stack with varying thickness, and FIG. 25 is a 3D surface topology map of (adjacent) aluminum particle layers with uniform thickness. The brightest area in the figure shows the maximum, and the darkest area shows the minimum. FIG. 24 shows the variation in thickness (from -20.2 μm to 15.9 μm), which is expected for calcined multilayer stacks containing modified metal particle layers of varying thickness. FIG. 25 shows the thickness variation (-4.9 μm to 5.5 μm) expected for an aluminum particle layer having a uniform thickness. Using the Veco Vision v4.20 program, the average height from peak to valley was calculated, the maximum and minimum were automatically identified and averaged, and the difference was subtracted. The average height from peak to valley of the fired multilayer stack of FIG. 24 is 35.54 μm, and the aluminum layer of FIG. 25 is 9.51 μm. In various embodiments, the layer has varying thickness if the average height from peak to valley exceeds 10 μm, exceeds 12 μm, or exceeds 15 μm.

In one embodiment of the invention, when the modified intercalation layer of the co-fired thickened multilayer stack as shown in FIG. 20 is soldered to the tab ribbon, the fired multilayer stack having no thickening It will have twice the peel strength. In one configuration, the modified intercalation layer on the surface of such a variable thickness fired multilayer laminate is soldered to a tin-based tab ribbon and is greater than 1.5 N / mm or 2 N / mm. It has a peel strength greater than or greater than 3 N / mm. The thickness variation can be optimized to provide a continuous metal particle layer and backside electric field on the substrate for silicon solar cells. It is possible to optimize the thickness variation so that the contact resistance in such a co-fired variable thickness multilayer stack is equal to or less than the contact resistance of the co-fired multi-layer stack in a nearly flat surface. can. In an exemplary embodiment, when an intercalation paste is used to penetrate and etch through the dielectric layer, the thickness variation in the dry and modified metal particle layers is 20 μm, 10 μm, 5 μm or 2 μm. Includes less than area.

The one or more variable layer thickness layers described above can be used as one or more components of any of the fired multilayer stacks described herein. One or more layers of variable thickness, such as variable thickness dry metal particle layers and modified metal particle layers, can be used in any silicon solar cell to reduce buckling of the back tab layer.
Intercalation Paste as a Replacement in Silicon Solar Cells One embodiment comprises 45% by weight noble metal particles, 30% by weight intercalation particles, and 25% by weight organic vehicle (paste C in Table I above). The intercalation paste can be used as a replacement for forming the back tab layer within the silicon solar cell. The manufacture of pn-junction silicon solar cells is well known in the art. Goodrich et al. (Goodrich et al.) Provide a complete process flow for manufacturing backside electric field silicon solar cells, which are "standard c-Si solar cells". Is called. "Wafer-based Single Crystal Solar Photovoltaic Roadmap: Utilizing Known Technology Improvement Opportunities for Further Reduction of Manufacturing Costs" by Goodrich et al., Solar Energy Materials and Solar Cells (2013) See pages 110-135. This is incorporated herein by reference. In one embodiment, the method of manufacturing a solar cell electrode includes a step of providing a silicon wafer whose front surface is partially covered with at least one dielectric layer, and a step of applying an aluminum particle layer to the back surface of the silicon wafer. , Drying step, apply an intercalation paste (rear tab) layer to a part of the aluminum particle layer, dry the intercalation paste layer, and silicon wafer multiple fine grid lines and at least one front bus bar layer. It involves applying to the dielectric layer on the front surface and drying and co-firing the silicon wafer. Various layers can be applied using methods such as screen printing, gravure printing, spray deposition, slot coating, 3D printing and / or inkjet printing. As an example, an Ekra or Baccini screen printer can be used to deposit an aluminum particle layer, an intercalation paste layer and anterior grid lines and a busbar layer. In another embodiment, the solar cell has at least one dielectric layer covering at least a portion of the back surface of the silicon wafer. In the PERC (Passivation Emitter Rear Cell) architecture, two dielectric layers (ie, alumina and silicon nitride) are applied to the back of the silicon solar cell prior to the application of the aluminum particle layer. Drying of the various layers can be carried out in a belt furnace at a temperature of 150 ° C. to 300 ° C. for 30 seconds to 15 minutes. In one configuration, a Despatch CDF7210 belt furnace is used to dry and co-fire silicon solar cells containing the firing multilayer stacks described herein. In one configuration, co-fired is carried out by heating in air to a temperature of 760 ° C. or higher for 0.5 to 3 seconds using rapid heating technology, which is the general temperature profile of aluminum backside electric field silicon solar cells. be. The temperature profile of the wafer is often calibrated using a DataPaq ™ system with a thermocouple attached to the bare wafer.

FIG. 26 is a schematic view showing the front surface (or irradiation surface) of the silicon solar cell 2600. The silicon solar cell 2600 has a silicon wafer 2610 with at least one dielectric layer (not shown) on which fine grid lines 2620 and front busbar lines 2630 are present. In one embodiment, the front side dielectric layer of a silicon wafer is at least one material selected from the group consisting of silicon, nitrogen, aluminum, oxygen, germanium, hafnium, gallium, composites thereof, and combinations thereof. including. In another embodiment, the dielectric layer on the front side of the silicon wafer is silicon nitride and has a thickness of less than 200 nm. Commercially available front side silver metallized pastes known in the art can be used to form fine grid lines 2620 and front busbar lines 2630. The front side silver layer (ie, fine grid wire 2620 and front busbar wire 2630 made from silver metallized paste) is etched through the dielectric layer during co-fired and comes into direct contact with the silicon wafer 2610. In one embodiment, the silicon wafer 2610 is single crystal and is doped into either n-type or p-type. In another embodiment, the silicon wafer 2610 is polycrystalline and is doped into either n-type or p-type. In an exemplary embodiment, the substrate is a polycrystalline p-type silicon wafer with an n-type emitter.

FIG. 27 is a schematic view showing the back surface of the silicon solar cell 2700. This back surface is covered with an aluminum particle layer 2730 and has a back surface tab layer 2740 distributed on a silicon wafer 2710. In one embodiment, the backside dielectric layer is selected from the group consisting of silicon, nitrogen, aluminum, oxygen, germanium, hafnium, gallium, composites thereof, and combinations thereof on the front surface of the silicon wafer. Contains one material. In another exemplary embodiment, the dielectric layer on the front surface of the silicon wafer is silicon nitride and has a thickness of less than 200 nm. In one embodiment, there is no dielectric layer on the back surface of the silicon wafer. Commercially available aluminum pastes known in the art can be printed on at least 85%, or at least 90% or at least 95%, or at least 97% of the total surface area of the back surface of a silicon wafer before firing, which is complete. It can be described as an Al coating. The average thickness of the aluminum particle layer (after co-fired) 2730 is 20 to 30 μm. In various embodiments, the aluminum particle layer 2730 has a porosity of 3 to 20%, 10 to 18%, or any range included herein. In a conventional BSF (backside electric field) solar cell architecture, the backside tab layer is applied directly to the silicon wafer. However, in order to improve the power conversion efficiency of the solar cell, it may be useful to print the back tab layer on the aluminum particle layer. In one embodiment, the intercalation layer is applied directly onto a portion of the dry aluminum particle layer to form the back tab layer 2740. FIG. 27 shows one possible pattern of the back tab layer 2740. The intercalation layer and the aluminum particle layer beneath it are co-fired to form the fired multilayer stack described herein. In various configurations, the modified intercalation layer (or back tab layer) 2740 has an average thickness of 1 μm to 20 μm, or 2 μm to 10 μm, or 2.5 μm to 8 μm.

The thickened metal (aluminum) particle layer described above can be used on the back side of a silicon solar cell to reduce buckling of the back tab layer and improve adhesion and electrical contact. In one embodiment of the invention, a portion of the back tab layer has a variable thickness. In another embodiment of the invention, some of the modified aluminum particle layers have a variable thickness. In one configuration, the back tab layer present on the surface of such a thickened modified aluminum particle layer is soldered to a tin-based tabling ribbon, over 0.7 N / mm, over 1.5 N / mm. It provides a peel strength of more than 2N or more. This thickness variation can be optimized to provide a continuous metal particle layer and backside electric field on the substrate for silicon solar cells. In another embodiment, in the back tab layer region, a portion of the composite layer (modified aluminum particle layer and back tab layer) in that region is greater than the average thickness of the composite layer measured over an area of 1 × 1 mm. It has a thickness that is at least 20%, 30%, or 40% larger. In another embodiment, in the back tab layer region, a portion of the composite layer (modified aluminum particle layer and back tab layer) in that region is greater than the average thickness of the composite layer measured over an area of 1 × 1 mm. It has a thickness that is at least 20%, 30%, or 40% larger.

In one embodiment of the invention, a solar cell comprising any of the fired multilayer stacks discussed herein can be incorporated into the solar module. As is known to those of skill in the art, there are many possible solar cell designs in which such solar cells are used. It is not intended to limit the number of solar cells in the module. Generally, 60 or 72 solar cells are incorporated into a commercially available module, but more or less can be incorporated depending on the application (ie, consumer electronics, residential, commercial, utility, etc.). Modules typically include a bypass diode (not shown), a junction box (not shown) and a support frame (not shown) that do not come into direct contact with the solar cell. Bypass diodes and junction boxes can also be considered as part of the cell interconnect.

FIG. 28 is a schematic cross-sectional view showing a part of the solar cell module according to the embodiment of the present invention. This solar cell module includes at least one silicon solar cell 2840. The front surface 2840F of the silicon solar cell 2840 is attached to the first tab ribbon 2832 (located in the front-rear direction on the page), on which the front surface sealing layer 2820 and the front surface sheet 2810 are present. The back side 2840B of the silicon solar cell 2840 is attached to the second tab ribbon 2834, on which the back sealing layer 2850 and the back sheet 2860 are present. The tab ribbons 2832, 2834 electricity the adjacent solar cells to the front side of one cell (ie, the front busbar on the front side) and the back side of the adjacent solar cell (ie, the back tab layer on the back side) via a solder connection. Connect. Many solar cells in a solar module can be electrically coupled to each other using tab ribbons as cell interconnects.

Typical cell interconnects include metal tab ribbons soldered to solar cells and metal bus ribbons that connect the tab ribbons. In one embodiment of the invention, the tab ribbon is a metal ribbon with a solder coating. Such solder-coated tab ribbons can have a thickness range of 20 to 1000 μm, 100 to 500 μm, 50 to 300 μm, or any range included herein. The width of the solder-coated tab ribbon can be 0.1 to 10 mm, 0.2 to 1.5 mm, or any range included herein. The length of the tab ribbon depends on the application, design and board dimensions. The thickness of the solder coating can be 0.5 to 100 μm, 10 to 50 μm, or any range of thicknesses included herein. Solder coatings can include tin, lead, silver, bismuth, copper, zinc, antimony, manganese, indium, or alloys thereof, composites thereof, or other combinations thereof. The metal tab ribbon can have a thickness of 1 μm to 1000 μm, 50 to 500 μm, 75 to 200 μm, or any range included herein. The metal tab ribbon can include copper, aluminum, silver, gold, carbon, tungsten, zinc, iron, tin or alloys thereof, composites thereof, or other combinations thereof. The width of the metal tab ribbon can be 0.1 to 10 mm, 0.2 to 1.5 mm, or any range included herein. In one embodiment, the tab ribbon is a copper ribbon with a thickness of 200 μm and a width of 1 mm, and the entire surface is coated with a tin: lead (60: 40% by weight) solder having a thickness of 20 μm.

The front sheet 2810 of FIG. 28 provides some mechanical support to the module and has good optical transmission characteristics over a portion of the solar spectrum designed to be absorbed by the solar cell 2840. The solar module is configured such that the front sheet 2810 faces an illumination source such as sunlight 2860. The front sheet 2810 is generally made of soda-lime glass with a low iron content. The front sealing layer 2820 and the back sealing layer 2850 protect the solar cell 2840 from electrical, chemical and physical stressors during operation. The encapsulant is generally in the form of a polymer sheet. Examples of materials that can be used as encapsulants include ethylene vinyl acetate (EVA), polyethylene-co-methacrylic acid (ionomer), polyvinyl butyral (
PVB), thermoplastic urethane (TPU), poly-α-olefins, polydimethylsiloxane (PDMS), other polysiloxanes (ie, silicones), and combinations thereof, but not limited to these. ..

The backsheet 2860 protects the solar cell 2840 from the back side and may or may not be optically transparent. The solar module is configured such that the backsheet 2860 faces away from a lighting source such as sunlight 2860. The backsheet 2860 may have a multilayer structure composed of three polymer films. DuPont® Tedlar® polyvinyl fluoride (PVF) films are commonly used for backsheets. Fluoropolymers and polyethylene terephthalate (PET) can also be used for backsheets. A glass sheet can also be used as the backsheet, which can help provide structural support to the solar module. Structural support can also be improved with support frames (not shown), which are generally made of aluminum.

In one embodiment of the invention, a method of forming a solar cell module is provided. Solder tabs are applied to individual solar cells, including any of the fired multilayer stacks described herein, either manually or using automatic tabbing or stringing equipment. The individual cells are then electrically connected in series by soldering directly to the tab ribbon. The resulting structure is referred to as the "cell string". A plurality of cell strings are often formed on a front sealing layer attached to a front sheet. These plurality of cell strings are connected to each other using a bus ribbon to form an electric circuit. Bus ribbons are wider than the tab ribbons used for cell strings. When the electrical circuit between all the cell strings is completed, the rear encapsulating material is applied to the back of the connected cell strings and the backsheet is constructed on the back encapsulating material. The assembly is then sealed using a vacuum stacking method and heated to polymerize the encapsulating material (typically less than 200 ° C.). Generally, a frame is mounted around the front seat to provide structural support. Finally, the junction box is connected to the cell interconnect and attached to the solar module. The bypass diode is placed in the junction box or mounted inside the module during the cell interconnection process.

In one embodiment of the invention, the method of forming a solar module is: a) a step of providing at least one solar cell having a front surface and a back surface including a fired multilayer stack, and b) a portion of the tab ribbon on the back tab layer. And the step of soldering to a part of the front bus bar layer to form a cell string, c) optionally soldering a tab ribbon to the bus ribbon to complete the electrical circuit, and d) being applied to the front sheet. The steps of forming a cell string on the front encapsulation layer, e) applying the rear encapsulation layer to the cell string, and attaching the back sheet to the rear encapsulation layer to form a module assembly, and f) the module assembly. Includes a step of laminating and g) a step of electrically connecting and physically attaching the junction box.

It is possible to disassemble the solar module to determine if the fired multi-layer stack described herein is incorporated using the following steps. Remove the backseat and back encapsulant to expose the tabbed back of the solar cell. Apply fast-curing epoxy around the tab ribbon and the back of the solar cell. After the epoxy has cured, remove the cell from the module and use a diamond saw to cut the ribbon / solar tab. The cross section is ground using the ion mill described above and SEM / EDX is performed to determine if the structure is as described in embodiments of the present invention. FIG. 29 is a polished cross-sectional SEM image of the back surface (non-irradiated surface) of the solar cell. This sample was from a solar cell (including a new fired multi-layer stack) built into the solar module and then removed as described above. The image shows a metal tab ribbon 2932 soldered to a fired multilayer stack 2902 and its solder coating 2931. The constituent layers of the fired multilayer stack 2902 are clearly visible. Immediately below the solder coating 2931, there are a modified intercalation layer 2945, a modified metal particle layer 2944, and a silicon substrate 2941. The layers identified in the figure can be more easily identified using EDX.
Architectures of other PV cells Intercalation paste can be used to create a variety of fired multilayer stacks that can be used as metallized layers on the front and back of many different solar cell architectures (basic design concepts). The intercalation paste and fired multi-layer stacks disclosed herein are solar cell architectures including BSF silicon solar cells, passivated emitter and rear contact (PERC) solar cells, and two-sided and comb back contact solar cells. It can be used for, but is not limited to these.

The PERC solar cell architecture improves the BSF solar cell architecture by using a dielectric barrier between the silicon substrate and the back contact to reduce back contact surface recombination. In the PERC cell, a portion of the back surface of the silicon wafer (ie, the non-irradiated surface) is passivated by at least one dielectric layer to reduce current carrier recombination. The novel fired multilayer stacks disclosed herein can be used in PERC solar cells. In one embodiment, the dielectric layer on the back surface of a silicon wafer comprises at least one of silicon, nitrogen, aluminum, oxygen, germanium, hafnium, gallium, composites thereof, or combinations thereof. In another embodiment, the dielectric layer on the back surface of the silicon wafer includes an alumina layer having a thickness of 10 nm on the silicon surface and a silicon nitride layer having a thickness of 75 nm on the alumina layer. Commonly used aluminum pastes designed for PERC cells (eg, single crystal EFX-39, EFX-85) do not penetrate the dielectric layer (s). In order for the aluminum particle layer to chemically interact and make ohmic contact with silicon, some regions of the dielectric layer are removed by laser ablation prior to the deposition of the aluminum particle layer.

PERL (passivation emitter with locally diffused back) and PERT (passivation emitter with fully diffused back) are two variations of the architecture in the PERC cell that further improve the performance of the device. Both of these variations rely on doping the back of the silicon substrate to further suppress recombination at the back contact, which plays a role similar to the back electric field of the BSF cell. In a Perl cell, the back surface of the silicon substrate is doped around the dielectric opening in contact with the rear aluminum layer. Doping is usually achieved by using a boron compound or aluminum from the aluminum particles that make up the back contact and diffusing the dopant through the dielectric openings, similar to the BSF manufacturing process. The PERT cell is a similar PERL, but the entire silicon in contact with the back dielectric layer is doped in addition to the silicon adjacent to the dielectric opening in contact with the back contact.

In one embodiment, an intercalation paste containing intercalation particles that do not penetrate through the dielectric layer (s) and are not etched is used as the back tab layer of the PERC, PERL, or PERT cell. A "non-etched" intercalation paste is used to provide a solderable silver surface and to mechanically reinforce the underlying (modified) aluminum particle layer. The resulting fired multilayer stack comprises a silicon wafer covered with at least one dielectric layer, a modified aluminum particle layer and a modified intercalation layer, and in the case of PERL or PERT, the silicon is only the dielectric opening. Or similarly, the entire dielectric interface is doped. By using a non-etched intercalation paste, etching of the dielectric layer (s) can be further reduced and surface recombination can be reduced. For example, if the busbar paste conventionally used for the back tab layer of the PERC cell is printed directly on the dielectric layer, the dielectric layer is partially etched to increase surface recombination during co-firing.

According to one embodiment of the invention, in cells using a back dielectric layer (ie, PERC, PERL, PERT), the intercalation paste is etched into the modified dielectric layer to create a silicon region in the dielectric opening. Can support the diffusion doping of. An "etched" intercalation paste (eg, Intercalation Paste D in Table I) is used to provide a solderable silver surface, mechanically strengthening the underlying (modified) aluminum particle layer, and a dielectric. Etching the layer to expose the silicon surface to aluminum particles can cause aluminum doping of the exposed silicon. The resulting calcined multilayer stack includes a silicon wafer, a modified aluminum particle layer and a modified intercalation layer. The fired multilayer stack may further include an Al-doped region near the silicon surface (similar to the backside electric field of the BSF cell) and a solid silicon-aluminum eutectic layer at the interface between the silicon wafer and the modified aluminum particle layer. can. Etching the dielectric layer (s) using the intercalation paste has several advantages. First, it is a cheap alternative to laser ablation steps that have proven to be expensive and unreliable in the past. Second, laser ablation can often remove tens to hundreds of microns of silicon substrate material, thus creating large pores between the silicon substrate and the aluminum particle layer during simultaneous wafer firing. May bring. Since the etching intercalation paste does not cause fluctuations on the wafer surface before simultaneous firing, this improves bond formation, reduces pore formation, and improves reproducibility as compared with the case of using laser ablation.

According to one embodiment of the invention, an intercalation paste can be used to provide a solderable surface in a cell architecture that relies on an aluminum particle layer to make ohmic contact with p-type silicon. Examples of this architecture include interlocking back contact solar cells, n-type BSF cell structures and two-sided solar cells. In one embodiment, intercalation paste C (from Table I) is applied to the Al layer on a comb-shaped back electrode solar cell architecture such as a Zebra cell. In the n-type BSF architecture with 20% power conversion efficiency for fully Al-coated cells, the intercalation particles can replace the traditional rear tab Ag paste in direct contact with silicon. Reduces the _Voc of the solar cell. In some n-wafer based solar cell architectures, the intercalation paste can be used on the front surface (ie, the illuminated surface). The intercalation paste can be used in combination with the Al paste in order to reduce the cost of the double-sided solar cell. Currently, double-sided solar cell architectures use Ag paste containing a small amount of aluminum (ie, less than 5% by weight Al) to make ohmic contact with the p-type silicon layer. Current dihedral architectures use nearly twice as much silver as BSF architectures, which can be costly. It is useful to use a pure aluminum paste with a double structure, but Al cannot be soldered. Intercalation pastes containing silver (eg, Paste C in Table I) can be printed on Al pastes in a two-sided design, reducing mechanical stability and soldering while reducing the amount of Ag used. Provides both with an attachable surface.
Material Properties of Calcined Multilayer Stacks and Impact on Silicon Solar Cells Important material properties in calcined multilayer stacks for use in solar cells and other electronic devices include solderability, peel strength, and contact resistance.

Solderability is the ability to form a strong physical bond between two metal surfaces by flowing molten metal solder between the two metal surfaces at a temperature of less than 400 ° C. Soldering of the fired multilayer stack to the modified intercalation layer can be performed after heating to 650 ° C. or higher in the atmosphere. Soldering involves the use of flux, which is any chemical that cleans or etches one or both of the surfaces prior to reflow of the molten solder. A commonly used solder flux for solar cells called RMA (eg, Kester ™ 186) or R (eg, Kester ™ 952) is placed on the tab ribbon and dried at 70 ° C. These fluxes are not effective for etching many metal oxides such _{as alumina (Al 2} O ₃ ) that form on aluminum particles when fired in the air.

The peel strength is an index of solder joint strength and is an index of reliability in the utilization of integrated circuits, light emitting diodes and solar cells. A solder-coated metal ribbon having a width of 0.8 to 20 mm and a thickness of 100 to 300 μm can be dipped in a flux and dried. This can be placed on the modified intercalation layer and soldered at a temperature of 200 ° C. to 400 ° C. using a soldering iron. The peel strength is the force required for peeling by dividing by the width of the soldered ribbon with respect to a given peeling speed at an angle of 180 ° from the soldering direction. The solder joint formed in this soldering process has an average peel strength greater than 1 N / mm at 1 mm / sec (eg, a 2 mm tab ribbon requires a peel force greater than 2 N at 1 mm / sec). The solar cells are electrically connected by a tab ribbon, which is soldered to the front busbar of one cell and the back tab layer of the adjacent cell. In contact with the tab ribbon of a commercially available solar cell, the peel strength is generally 1.5 to 4 N / mm. When using a fired multi-layer stack as the back tab layer, the primary failure mode is near the Al—Si interface, which can be determined using the plan view SEM / EDX. In an exemplary embodiment, the peel strength exceeds 1 N / mm when the silver-rich sublayer (of the modified intercalation layer) is soldered with a tin-based tab ribbon.

Meyer et al. Explain how electrical measurements of a four-point probe are used to measure the resistivity of each metallized layer on a finished solar cell. Meier et al., "Determining components of series resistance from measurements on a finished cell", IEEE (2006) pp. See 21615. The bulk resistance of the metallized layer is directly related to the bulk resistance of the material from which it is made. In one embodiment of the invention, the bulk resistance of pure Ag is 1.5 × 10 ^-8 Ω−m, and the pure Ag metallized layer used in industrial solar batteries is one of the bulk resistance of pure Ag. It has a bulk resistance that is 5 to 5 times higher. Bulk resistance is important for fine grid lines that must carry current over relatively long (ie, 1 cm or more) lengths. If the cells are tabbed within the module, the resistance of the front busbar and the back tab layer is less important.

In most integrated circuit, LED and solar cell architectures, current flows from the metal particle layer through the modified metal particle layer to the modified intercalation layer. For fired multi-layer stacks, the contact resistance between these three layers can play an important role in device performance. The contact resistance between them in a fired multilayer stack can be measured by using transmission line measurement (TLM) (reference: Cu Backside Busbar Tape by Meier et al .: Crystalline. (Eliminating Ag and Enabling Full Al Coverage in Copper Silicon Solar Cells and Modules), IEEE PVSC (2015), p. (2015). This TLM is plotted as the distance between the resistance vs. the electrodes. Specifically, TLM was used to measure 1) the contact resistance between the metal particle layer and the modified metal particle layer, and 2) the contact resistance between the modified metal particle layer and the modified layer. The contact resistance of the fired multilayer stack is the sum of the above contact resistances 1) and 2). The contact resistance of the calcined multilayer stack is half the y-intercept value of the linear fit for resistance vs. distance measurement. The electrical resistance between the busbars was measured using a Keithley 2410 Sourcemeter with a 4-point probe setting where current was applied between -0.5A and + 0.5A and the voltage was measured. In various embodiments, the contact resistance of the calcined multilayer stack is 0-5 m ohms, 0.25-3 m ohms, 0.3-1 m ohms, or any range included herein. The sheet resistance of the metal particle layer is determined by the product of the slope of the wire and the length of the electrode. The contact resistance and the sheet resistance are used to numerically determine the transfer length and the subsequent contact resistivity. Fluctuations in series resistance are determined by dividing the resistivity by the area coverage of the modified intercalation layer. In various embodiments, the variation of the series resistance is less than 0.200Ω-cm ^2, less than 0.100Ω-cm ^2, less than 0.050Ω-cm ^2, less than 0.010Ω-cm ^2, or 0.001 ohm-cm Less than ^2.

The contact resistance between the back tab layer and the aluminum particle layer can affect the series resistance and power conversion efficiency of the solar cell. Such contact resistance can be determined by transmission line measurement. A transmission line plot of a conventional silver back tab layer on silicon with an overlap of 300 μm with the aluminum particle layer is shown in FIG. FIG. 31 shows a transmission line plot of the modified intercalation layer used as the back tab layer on the aluminum particle layer. The y-intercept value of FIG. 31 is 1.11 mm ohm compared to the y-intercept value of 0.88 of FIG. The contact resistance between the back tab (intercalation) layer and the aluminum particle layer is 0.56 m ohms. The contact resistance of the conventional rear tab structure is 0.44 m ohm. In various embodiments, the contact resistance between the back tab (intercalation) layer and the aluminum particle layer is 0-5 m ohms, 0.25-3 m ohms, or 0.3-1 m ohms, or included herein. It is an arbitrary range. The sheet resistance of the aluminum layer is determined by the slope of the line × the length of the electrode, and is about 9 m ohm / square in FIGS. 30 and 31.

TLM is the preferred method for accurately extracting the contact resistance of the fired multi-layer stack (ie, the back tab layer and the aluminum particle layer), measuring the contact resistance of a complete solar cell using the 4-point probe method. Is possible. This method first measures the resistance between the two dorsal tab layers (RA _Ag-to-Ag ) and then moves the probe over the aluminum particle layer (within 1 mm of the dorsal tab layer) to R _{Al. -Get Al} . This contact resistance is identified by subtracting R _{Ag-to-Ag from R Al-to-Al} and dividing by two. This is not as accurate as the TLM measurement, but the measurements from multiple solar cells can be averaged within 0.50 m ohms.

Contact resistance and sheet resistance are used to numerically identify the transfer length and subsequent contact resistivity. In FIG. 31, the transfer length of the multilayer stack after simultaneous firing is 5 mm, and the contact resistance is 2.2 mΩ. Fluctuations in series resistance can be estimated by dividing this number by the area coverage of the intercalation layer. In FIG. 31, the estimated variation of the series resistance is 0.023Ω-cm ² , which is equivalent to the estimated variation of ^{the series resistance of 0.020Ω-cm 2} calculated for the conventional back tab layer measured in FIG. Fluctuations in series resistance produce controlled BSF (backside electric field) silicon solar cells with full Al coverage and no back tab layer, and BSF silicon solar cells with full aluminum coverage and Ag: Bi intercalation layer. It can be measured directly. The series resistance of the cell can be derived via current-voltage curves under various light intensities, and the difference in series resistance can be attributed to the increased contact resistance between the rear tab and the fired aluminum particle layer. can. In various embodiments, the variation of the series resistance in the solar cell is less than 0.200Ω-cm ^2, less than 0.100Ω-cm ^2, less than 0.050Ω-cm ^2, less than 0.010Ω-cm ^2, or 0. It is less than 001Ω-cm ^2.

One advantage of using an intercalation layer on a silicon solar cell is the improvement in _{open circuit voltage (V oc) caused by the continuous backside electric field formation on the silicon wafer.} If both devices have the same Riabasuba surface area, as described herein, the conventional BSF solar cell Ag: By comparing the BSF solar cell containing Bi intercalation paste, directly V _oc gain Can be measured. Conventional BSF silicon solar cells are manufactured by printing a silver-based rear tab paste directly on a silicon wafer and surrounding it with an aluminum particle layer. The intercalation layer (eg, one manufactured using intercalation paste C) can be used in silicon solar cells with perfect aluminum surface coverage. _{The Voc} of both solar cells is measured by a current-voltage test under one solar intensity. For solar cells with a rear tab surface area ^{greater than 5 cm 2} _{, the V oc} is at least 0.5 mV, at least 1 mV, at least 2 mV, or at least when compared to the back tab layer on a traditional silicon architecture using an intercalation layer. It can be increased by 4 mV. Finally, the short circuit current density (J _sc ) and fill factor can also be improved when using an intercalation layer architecture instead of the traditional rear tabb design. Silver does not make ohmic contact with p-type silicon. The silver tab layer located directly above the p-type silicon reduces the current acquisition that can be estimated by making electroluminescence or photoluminescence measurements on a complete or incomplete solar cell. The increase in J _sc can also be measured by directly testing the intercalation architecture and the back tab layer on silicon. Another advantage is the increase in fill factor, which _{can be positively altered by increased Voc} , reduced contact resistance, and / or fluctuations in recombination dynamics on the back of the solar cell.

The invention described herein can be carried out with different devices, materials and devices, and various changes relating to both the device and the operating procedure can be achieved without departing from the scope of the invention itself. I want you to understand.

Claims (80)

A substrate having a substrate surface and
A metal particle layer existing on at least a part of the surface of the substrate and containing metal particles,
A modified metal particle layer existing on at least a part of the substrate surface,
A fired multilayer stack comprising a modified intercalation layer that is present directly above at least a portion of the modified metal particle layer and has a solderable surface.
The modified metal particle layer comprises the metal particles and at least one material from the modified intercalation layer.
The modified intercalation layer includes precious metals, antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, Magnesium, manganese, molybdenum, niobium, phosphorus, potassium, rhenium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, their combinations, their alloys, their oxides, these A fired multi-layer stack containing a composite material and a material selected from the group consisting of other combinations thereof. The modified intercalation layer is composed of precious metals and bismuth, boron, indium, lead, silicon, tellurium, tin, vanadium, zinc, combinations thereof, alloys thereof, oxides thereof, composite materials thereof, and these. The fired multilayer stack according to claim 1, comprising a material selected from the group consisting of other combinations. The modified intercalation layer contains two phases, a noble metal phase and an intercalation phase.
More than 50% of the solderable surface contains the noble metal phase
The modified metal particle layer comprises the metal particles and at least one material from the intercalation phase.
The intercalation phase is antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium, manganese, molybdenum. , Niobium, phosphorus, potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, combinations thereof, and alloys thereof, oxides thereof, composite materials thereof, and these. The fired multilayer stack according to claim 1, comprising a material selected from the group consisting of other combinations. The modified intercalation layer is an intercalation sublayer existing directly above at least a part of the modified metal particle layer, and a noble metal sublayer existing directly above at least a part of the intercalation sublayer. Includes two sublayers consisting of
The solderable surface contains the precious metal sublayer and contains the noble metal sublayer.
The modified metal particle layer comprises metal particles and at least one material from the intercalation sublayer.
The intercalation sublayers are antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium, manganese, Molybdenum, niobium, phosphorus, potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, combinations thereof, and alloys thereof, oxides thereof, composite materials thereof, and The fired multilayer stack according to claim 1, comprising a material selected from the group consisting of other combinations thereof. The modified metal particle layer contains aluminum particles and is a modified aluminum particle layer.
The modified intercalation layer has two sublayers, one is a bismuth-rich sublayer directly above the modified aluminum particle layer and the other is a silver-rich sublayer immediately above the bismuth-rich sublayer. Including
The solderable surface contains a silver-rich sublayer.
The fired multilayer stack according to claim 1, wherein the modified metal particle layer further comprises at least one material selected from the group consisting of aluminum oxide, bismuth, and bismuth oxide. Further including at least one dielectric layer existing directly above at least a part of the substrate surface, the dielectric layer includes silicon, aluminum, germanium, hafnium, gallium, oxides thereof, nitrides thereof, and the like. The fired multilayer stack according to claim 1, which comprises a composite material of the above, and at least one material selected from the group consisting of combinations thereof. A first dielectric layer existing directly above at least a part of the substrate surface and containing aluminum oxide, and a second dielectric layer immediately above the first dielectric layer and containing silicon nitride. The fired multilayer stack according to claim 1, further comprising. The fired multilayer stack according to claim 1, further comprising a tab ribbon present just above at least a portion of the solderable surface of the modified intercalation layer. The solid compound layer further comprises a solid compound layer existing directly above the surface of the substrate, and the solid compound layer is formed of one or more metals selected from the group consisting of aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, and titanium. The fired multilayer stack according to claim 1, comprising one or more materials selected from the group consisting of silicon, oxygen, carbon, germanium, gallium, arsenic, nitrogen, indium and phosphorus. A portion of the substrate adjacent to the substrate surface is doped with at least one material selected from the group consisting of aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, steel and combinations thereof. The fired multilayer stack according to claim 1. The fired multi-layer stack according to claim 1, wherein a part of the fired multi-layer stack has a variable thickness. The fired multi-layer stack according to claim 1, wherein a part of the fired multi-layer stack has an average height from peak to valley exceeding 12 μm. A group in which at least 70% by weight of the solderable surface of the modified intercalation layer consists of silver, gold, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof. The fired multilayer stack according to claim 1, comprising a material selected from. The first aspect of claim 1, wherein the substrate comprises at least one material selected from the group consisting of silicon, silicon dioxide, silicon carbide, aluminum oxide, sapphire, germanium, gallium arsenide, gallium nitride, and indium phosphide. Baked multi-layer stack. The metal particle layer comprises a material selected from the group consisting of aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, steel and alloys thereof, composites thereof, and other combinations thereof. The fired multilayer stack according to claim 1. The fired multilayer stack according to claim 1, wherein the noble metal comprises a material selected from the group consisting of silver, gold, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof. .. The first aspect of claim 1, wherein the substrate comprises a material selected from the group consisting of aluminum, copper, iron, nickel, titanium, steel, zinc, and alloys thereof, composites thereof, and other combinations thereof. Baked multi-layer stack. The fired multilayer stack according to claim 1, wherein the metal particle layer has a thickness of 0.5 μm to 100 μm. The fired multilayer stack according to claim 1, wherein the metal particle layer has a porosity of 1 to 50%. The fired multilayer stack according to claim 1, wherein the modified intercalation layer has a thickness of 0.5 μm to 10 μm. The fired multilayer stack according to claim 1, wherein the fired multilayer stack has a contact resistance of 0 to 5 m ohms when identified by transmission line measurement. 1 The fired multi-layer stack described in. With the board
A metal particle layer existing on at least a part of the substrate and
A modified metal particle layer present on at least a part of the substrate,
A fired multilayer stack including a modified intercalation layer existing immediately above at least a part of the modified metal particle layer.
The modified intercalation layer includes an intercalation sublayer existing immediately above at least a part of the modified metal particle layer, and a noble metal sublayer existing directly above at least a part of the intercalation sublayer. Including two sublayers of
The modified metal particle layer comprises metal particles and at least one material from the intercalation sublayer.
The intercalation sublayers include antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium, manganese, Molybdenum, niobium, phosphorus, potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, their combinations, their alloys, their oxides, their composites, these A fired multi-layer stack containing materials selected from the group consisting of other combinations. With a silicon substrate
An aluminum particle layer existing on at least a part of the silicon substrate,
A modified aluminum particle layer existing on at least a part of the silicon substrate,
A fired multilayer stack including a modified intercalation layer existing directly above the modified aluminum particle layer.
The modified intercalation layer is a two-layer layer consisting of a bismuth-rich sublayer immediately above the modified aluminum particle layer and a silver-rich sublayer immediately above the bismuth-rich sublayer. Including
The modified aluminum particle layer is a fired multilayer stack containing aluminum particles and at least one material selected from the group consisting of aluminum oxide, bismuth, and bismuth oxide. A silicon substrate with front and back surfaces and
With at least one front dielectric layer existing directly above at least a part of the front surface of the silicon substrate,
A plurality of fine grid lines existing on a part of the front surface of the silicon substrate,
With at least one front busbar layer in electrical contact with at least one of the plurality of fine grid lines,
An aluminum particle layer existing on at least a part of the back surface of the silicon substrate, the aluminum particle layer containing the aluminum particles, and the aluminum particle layer.
A solar cell comprising a back tab layer existing on a portion of the back surface of the silicon substrate.
The back tab layer
A modified aluminum particle layer existing on a part of the back surface of the silicon substrate,
Includes a modified intercalation layer that resides directly above at least a portion of the modified aluminum particle layer and has a solderable surface.
The modified aluminum particle layer comprises the aluminum particles and at least one material from the modified intercalation layer.
The modified intercalation layer includes precious metals, antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, Magnesium, manganese, molybdenum, niobium, phosphorus, potassium, rhenium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, their combinations, their alloys, their oxides, these A solar cell comprising a material selected from the group consisting of composite materials and other combinations thereof. The modified intercalation layer comprises precious metals and bismuth, boron, indium, lead, silicon, tellurium, tin, vanadium, zinc, combinations thereof, and alloys thereof, oxides thereof, composite materials thereof, and composite materials thereof. 25. The solar cell of claim 25, comprising a material selected from the group consisting of other combinations thereof. The modified intercalation layer contains two phases, a noble metal phase and an intercalation phase.
More than 50% of the solderable surface contains the noble metal phase
The modified aluminum particle layer comprises the aluminum particles and at least one material from the intercalation phase.
The intercalation phase is antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium, manganese, molybdenum. , Niobium, phosphorus, potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, combinations thereof, and alloys thereof, oxides thereof, composite materials thereof, and these. 25. The solar cell of claim 25, comprising a material selected from the group consisting of other combinations. The modified intercalation layer is an intercalation sublayer existing directly above at least a part of the modified aluminum particle layer, and a noble metal sublayer existing directly above at least a part of the intercalation sublayer. Including two sublayers of
The solderable surface contains the precious metal sublayer and contains the noble metal sublayer.
The modified aluminum particle layer comprises the aluminum particles and at least one material from the intercalation sublayer.
The intercalation sublayers are antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium, manganese, Molybdenum, niobium, phosphorus, potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, their combinations, their alloys, their oxides, their composites, these 25. The solar cell of claim 25, comprising a material selected from the group consisting of other combinations. The modified intercalation layer is present directly above the modified aluminum particle layer and has two sublayers, a bismuth-rich sublayer and a bismuth-rich sublayer that is directly above the bismuth-rich sublayer and is rich in silver. Including layers
The modified aluminum particle layer further comprises at least one material selected from the group consisting of aluminum oxide, bismuth, and bismuth oxide, and the bismuth-rich sublayer has a thickness of 0.01 μm to 5 μm. Item 25. The solar cell according to Item 25. Claim that the aluminum particle layer further comprises bismuth, and the weight ratio of bismuth to bismuth and aluminum (Bi :( Bi + Al)) is at least 20% higher in the modified aluminum particle layer than in the aluminum particle layer. 29. The solar cell. 25. The solar cell of claim 25, wherein the noble metal comprises a material selected from the group consisting of silver, gold, platinum, palladium, rhodium, and alloys thereof, composites thereof, and other combinations thereof. Further comprising at least one back dielectric layer existing directly above at least a portion of the back of the silicon substrate, the back dielectric layer is silicon, aluminum, germanium, hafnium, gallium, and oxides thereof. 25. The solar cell of claim 25, comprising a material selected from the group consisting of nitrides, composites thereof, and combinations thereof. A first back dielectric layer existing directly above at least a part of the back surface of the silicon substrate and containing aluminum oxide, and a second back dielectric layer existing directly above the first back dielectric layer and containing silicon nitride. 25. The solar cell of claim 25, further comprising a back dielectric layer. The solar cell according to claim 25, further comprising a solid aluminum-silicon eutectic layer existing directly above the silicon substrate. The solar cell according to claim 25, wherein a part of the back tab layer has an average height from a peak to a valley portion exceeding 12 μm. 25. The solar cell of claim 25, further comprising a tab ribbon just above at least a portion of the solderable surface of the modified intercalation layer. 25. The solar cell of claim 25, wherein the solderable surface comprises at least 70% by weight of silver. The solar cell according to claim 25, wherein a part of the modified aluminum particle layer has an average height from a peak to a valley portion exceeding 12 μm. The solar cell according to claim 25, wherein the aluminum particle layer has a thickness of 1 μm to 50 μm. The solar cell according to claim 25, wherein the back tab layer has a thickness of 1 μm to 50 μm. A silicon substrate with front and back surfaces and
With at least one front dielectric layer existing directly above at least a part of the front surface of the silicon substrate,
A plurality of fine grid lines existing on a part of the front surface of the silicon substrate,
With at least one front busbar layer in electrical contact with at least one of the plurality of fine grid lines,
An aluminum particle layer existing on at least a part of the back surface of the silicon substrate and containing aluminum particles,
A back tab layer existing on a part of the back surface of the silicon substrate,
Is a solar cell containing
The back tab layer has a solderable surface and the back tab layer
A modified aluminum particle layer existing on at least a part of the back surface of the silicon substrate,
A bismuth-rich sublayer existing directly above at least a part of the modified aluminum particle layer,
Includes a silver-rich sublayer that is present directly above at least a portion of the bismuth-rich sublayer.
The modified aluminum particle layer is a solar cell containing the aluminum particles and at least one material selected from the group consisting of aluminum oxide, bismuth and bismuth oxide. It ’s a solar cell module,
Front seats with front and back and
A front sealing layer existing on the back surface of the front sheet and
A first silicon solar cell and a second silicon solar cell on the front sealing layer are provided, and each silicon solar cell is
A silicon substrate with front and back surfaces and
With at least one front dielectric layer existing directly above at least a part of the front surface of the silicon substrate,
A plurality of fine grid lines existing on a part of the front surface of the silicon substrate,
With at least one front busbar layer in electrical contact with at least one of the plurality of fine grid lines,
An aluminum particle layer existing on at least a part of the back surface of the silicon substrate and containing aluminum particles.
Includes a back tab layer that resides on a portion of the back of the silicon substrate.
The back tab layer
A modified aluminum particle layer existing on a part of the back surface of the silicon substrate,
Includes a modified intercalation layer that resides directly above at least a portion of the modified aluminum particle layer and has a solderable surface.
The modified intercalation layer includes precious metals, antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, Magnesium, manganese, molybdenum, phosphorus, potassium, rhenium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, combinations thereof, alloys thereof, oxides thereof, composite materials thereof. , And one material selected from the group consisting of other combinations thereof.
The modified aluminum particle layer comprises the aluminum particles and at least one material from the modified intercalation layer.
The solar cell module further includes a first cell interconnect, the first cell interconnect.
A first tab ribbon that is in electrical contact with both the front busbar layer of the first silicon solar cell and the back tab layer of the second silicon solar cell.
A back sheet having a front surface and a back surface, wherein the back surface of the back sheet is exposed to an external environment.
Includes a back sealing layer that resides on the front surface of the back sheet.
Includes a first portion of the back encapsulation layer above the first silicon solar cell and the second solar cell and a second portion of the back encapsulation layer above the front encapsulation layer. Solar cell module. The modified intercalation layer comprises precious metals and bismuth, boron, indium, lead, silicon, tellurium, tin, vanadium, zinc, combinations thereof, and alloys thereof, oxides thereof, composite materials thereof, and composite materials thereof. 42. The solar cell module of claim 42, comprising a material selected from the group consisting of other combinations thereof. The modified intercalation layer contains two phases, a noble metal phase and an intercalation phase.
More than 50% of the solderable surface contains the noble metal phase
The modified aluminum particle layer comprises the aluminum particles and at least one material from the intercalation phase.
The intercalation phase is antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium, manganese, molybdenum. , Niobium, phosphorus, potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, combinations thereof, and alloys thereof, oxides thereof, our composite materials, and 42. The solar cell module of claim 42, comprising a material selected from the group consisting of other combinations thereof. The modified intercalation layer is an intercalation sublayer existing directly above at least a part of the modified intercalation layer and a precious metal sublayer existing directly above at least a part of the intercalation sublayer. Including two sublayers with
The modified aluminum particle layer comprises the aluminum particles and at least one material from the intercalation sublayer.
The intercalation sublayers are antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, gallium, germanium, hafnium, indium, iron, lantern, lead, lithium, magnesium, manganese, Molybdenum, niobium, phosphorus, potassium, renium, selenium, silicon, sodium, strontium, sulfur, tellurium, tin, vanadium, zinc, zirconium, combinations of these, their alloys, their oxides, our composites, 42. The solar cell module of claim 42, comprising a material selected from the group consisting of and other combinations thereof. The modified intercalation layer has two sublayers, one is a bismuth-rich sublayer directly above the modified aluminum particle layer and the other is a silver-rich sublayer directly above the bismuth-rich sublayer. Including layers
42. The solar cell module according to claim 42, wherein the modified aluminum particle layer comprises the aluminum particles and at least one material selected from the group consisting of aluminum oxide, bismuth, and bismuth oxide. 42. The solar cell module of claim 42, wherein the first cell interconnect further comprises a junction box that contacts the back sheet. 42. The solar cell module of claim 42, further comprising at least one busbar ribbon that connects to the first tab ribbon. The front dielectric layer comprises at least one material selected from the group consisting of silicon, aluminum, germanium, hafnium, gallium, and oxides thereof, nitrides thereof, composites thereof, and combinations thereof. 42. The solar cell module according to claim 42. At least one back dielectric layer is further provided directly above the back surface of the silicon substrate, and the back dielectric layer includes silicon, aluminum, germanium, hafnium, gallium, oxides thereof, nitrides thereof, and a composite thereof. 42. The solar cell module of claim 42, comprising materials and at least one material selected from the group consisting of combinations thereof. A first back dielectric layer existing directly above at least a part of the back surface of the silicon substrate and containing aluminum oxide, and a second back dielectric layer existing directly above the first back dielectric layer and containing silicon nitride. 42. The solar cell module according to claim 42, further comprising a back dielectric layer. 42. The solar cell module according to claim 42, further comprising a solid aluminum silicon eutectic layer existing directly above the back surface of the silicon substrate. The modified intercalation layer contains bismuth, and the weight ratio of bismuth to bismuth and aluminum (Bi :( Bi + Al)) is at least 20% higher in the modified aluminum particle layer than in the aluminum particle layer. 42. The solar cell module according to claim 42. 42. The solar cell module according to claim 42, wherein a part of the back tab layer has an average height from a peak to a valley portion exceeding 12 μm. With 10% to 70% by weight of precious metal particles,
With at least 10% by weight intercalation particles,
Including organic vehicles
A paste in which the intercalation particles contain one or more selected from the group consisting of low temperature base metal particles, crystalline metal oxide particles, and glass frit particles. The paste according to claim 55, wherein the weight ratio of the intercalation particles to the noble metal particles is at least 1: 5. The paste according to claim 55, wherein the noble metal particles contain at least one material selected from the group consisting of gold, silver, platinum, palladium, rhodium, and alloys, composites, and other combinations thereof. The paste according to claim 55, wherein the noble metal particles have a D50 of 100 nm to 50 μm. The paste according to claim 55, wherein the noble metal particles have ^{a specific surface area of 0.4 to 7.0 m 2 / g.} The paste according to claim 55, wherein some of the noble metal particles have a shape selected from the group consisting of spherical, flake-shaped, and elongated shapes. The paste according to claim 55, wherein at least one of the noble metal particles and the intercalation particles has a monomodal size distribution. The paste according to claim 55, wherein at least one of the noble metal particles and the intercalation particles has a multi-peak particle size distribution. The paste according to claim 55, wherein at least some of the precious metal particles are silver and have a D50 of 300 nm to ^{2.5 μm and a specific surface area of 1.0 to 3.0 m 2 / g.} The paste according to claim 55, wherein the intercalation particles have a D50 of 100 nm to 50 μm. The paste according to claim 55, wherein the intercalation particles have ^{a specific surface area of 0.1 to 6.0 m 2 / g.} The paste according to claim 55, wherein some of the intercalation particles exhibit a shape selected from the group consisting of a spherical shape, a flake shape, and an elongated shape. The paste according to claim 55, wherein the low temperature base metal particles include a material selected from the group consisting of bismuth, tin, tellurium, antimony, lead, and alloys, composites, and other combinations thereof. The paste according to claim 67, wherein the low temperature base metal particles contain bismuth and have a D50 of 1.5 to 4.0 μm and ^{a specific surface area of 1.0 to 2.0 m 2 / g.} At least some of the cold base metal particles consist of silver, nickel, nickel-boron, tin, tellurium, antimony, lead, molybdenum, titanium, and alloys thereof, composites thereof, and other combinations thereof. The paste of claim 55, comprising bismuth score particles surrounded by a single shell containing the material of choice. 55. A bismuth score particle in which at least some of the cold base metal particles are surrounded by a single shell made of a material selected from the group consisting of silicon oxide, magnesium oxide, boron oxide, and combinations thereof. The paste described in. The crystalline metal oxide particles are derived from oxygen and bismuth, tin, tellurium, antimony, lead, vanadium, chromium, molybdenum, boron, manganese, cobalt, and alloys thereof, composites thereof and other combinations thereof. 55. The paste of claim 55, comprising a metal selected from the group. The glass frit particles are antimony, arsenic, barium, bismuth, boron, cadmium, calcium, cerium, cesium, chromium, cobalt, fluorine, gallium, germanium, hafnium, indium, iodine, iron, lantern, lead, lithium, magnesium, Consists of manganese, molybdenum, niobium, potassium, renium, selenium, silicon, sodium, strontium, tellurium, tin, vanadium, zinc, zirconium, their alloys, their oxides, their composites, and other combinations thereof. The paste of claim 55, comprising a material selected from the group. The paste according to claim 55, wherein the paste has a solid content of 30% to 80% by weight. The paste according to claim 55, wherein the intercalation particles contain at least 15% by weight of the paste. The paste according to claim 55, wherein the paste comprises 45% by weight Ag particles, 30% by weight bismuth particles, and 25% by weight organic vehicle. The paste according to claim 55, wherein the paste comprises 30% by weight Ag particles, 20% by weight bismuth particles, and 50% by weight organic vehicle. The paste according to claim 55, wherein the paste has a viscosity of 10,000 to 200,000 cP at 25 ° C. at a shear rate of ^{4 seconds-1.} With 10% to 70% by weight of silver particles,
With at least 10% by weight bismuth metal particles,
A paste characterized by containing an organic vehicle. With 10% to 70% by weight of silver particles,
With at least 10% by weight crystalline bismuth oxide particles,
A paste characterized by containing an organic vehicle. The paste according to claim 78 or 79, further comprising glass frit particles.

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