Nano-silver powder for conductive paste, conductive paste, preparation method and application thereof

Abstract

The application provides a kind of nano silver powder for conductive paste, conductive paste and its preparation method and application, the nano silver powder is spherical or spheroidal structure, the D10 particle size of nano silver powder is 100nm-150nm, the D50 particle size is 180nm-220nm, the D90 particle size is 400nm-500nm, and the D100 particle size is less than 600nm.Based on the nano silver powder of the application, the problem of weak bonding force between the solder strip and the grid line in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to a photovoltaic cell, and in particular to a nano silver powder for a conductive paste, the conductive paste, and a preparation method and application thereof. Background Art

[0002] HJT cells, with their simplified manufacturing process and high theoretical conversion efficiency, are one of the future mainstream technologies for crystalline silicon cells. However, due to fluctuations in the international price of silver, a precious metal with global reserves, HJT paste costs remain high. According to current data, the silver paste consumption for PERC cells is 9mg / W, for TOPCon cells it is 12mg / W, and for HJT cells it exceeds 15mg / W. This high silver paste consumption directly impacts cell costs and economic benefits, limiting the industrialization of HJT cells. To reduce silver consumption and improve cell efficiency, Zero Bus Bar (OBB) technology has emerged. OBB technology aims to achieve higher photoelectric conversion efficiency by eliminating the busbars on the front of the cell, reducing the light-shielding area. This technology not only optimizes silver paste usage but also places new demands on paste performance. In traditional cell module manufacturing, the busbars provide a direct path for current collection, while OBB technology relies on a direct connection between the secondary grid (fine gridbars) and the solder ribbon to transmit current. Therefore, the bonding strength between the solder ribbon, the secondary grid and the solar cell has a decisive influence on the overall efficiency and reliability of the module.

[0003] Since traditional sub-grid pastes only serve to collect photogenerated carriers, the system design usually only considers printability, electrical properties and shading area. Therefore, the existing technology focuses on the electrical properties of the conductive paste and the adhesion between the conductive paste and the solar cell, while ignoring the adhesion between the grid line and the soldering ribbon. At the same time, the existing technology often uses flaky silver powder with larger particle size to increase the line contact and surface contact between the powders to reduce the volume resistivity of the conductive paste, thereby improving the photoelectric conversion efficiency of the conductive paste. Therefore, when traditional sub-grid conductive pastes are applied to 0BB technology, there is often a weak bonding force between the soldering ribbon and the grid line, and the soldering ribbon is easy to fall off, which leads to problems such as high CTM loss of the component, reduced yield, and poor reliability. Summary of the Invention

[0004] The main purpose of the present invention is to provide a nano silver powder for conductive paste, conductive paste and its preparation method and application, so as to solve the problem of weak bonding between soldering strips and grid lines in the prior art.

[0005] To achieve the above-mentioned object, according to one aspect of the present invention, a nano silver powder for a conductive paste is provided, wherein the nano silver powder has a spherical or quasi-spherical structure, a D10 particle size of the nano silver powder is 100 nm to 150 nm, a D50 particle size is 180 nm to 220 nm, a D90 particle size is 400 nm to 500 nm, and a D100 particle size is less than 600 nm.

[0006] Furthermore, the melting temperature of the nano silver powder is 165°C to 170°C.

[0007] Furthermore, the specific surface area of ​​the nano silver powder is 2.4 m 2 / g~3.0m 2 / g.

[0008] According to another aspect of the present invention, a conductive paste is provided, comprising the above-mentioned nano silver powder for conductive paste, submicron silver powder, high wettability organic carrier, and low wettability organic carrier; the weight ratio of the nano silver powder, submicron silver powder, high wettability organic carrier, and low wettability organic carrier is (5-25): (55.5-89.5): (2.75-5.25): (2.75-5.25).

[0009] Furthermore, the viscosity of the conductive paste is 300 Pa·s to 450 Pa·s.

[0010] Furthermore, the fineness of the conductive paste is 2.5 μm to 4.5 μm.

[0011] Furthermore, the D10 particle size of the submicron silver powder is 100 nm to 120 nm, and the D50 particle size is 700 nm to 900 nm.

[0012] Furthermore, the conductive paste also includes micron-sized silver powder, the weight ratio of micron-sized silver powder to submicron-sized silver powder is (12-16): (56-60), the D10 particle size of the mixed silver powder of submicron-sized silver powder and micron-sized silver powder is 700nm-900nm, the D50 particle size is 2μm-3μm, and the D100 particle size is 6μm-8μm.

[0013] Furthermore, the high wettability organic carrier includes a dispersant, a first organic solvent and a low molecular weight resin; the dispersant is selected from one or more of 9-octadecene amide, fatty acids with a carbon number of 6-12, phosphates, and polyurethanes; the first organic solvent is selected from one or more of diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol monoethyl ether, and diethylene glycol-2-ethylhexyl ether; the low molecular weight resin is selected from one or more of hydrogenated bisphenol A diglycidyl ether, tetrahydrophthalic acid diglycidyl ester, and bisphenol A modified epoxy resin.

[0014] Furthermore, the low-wetting organic carrier includes a thickener, a second organic solvent and a high molecular weight resin; the thickener is selected from one or two of tert-butylphenol formaldehyde, modified rosin, and organic silane compounds; the second organic solvent is selected from one or two of diethylhexyl maleate, diethylene glycol butyl ether acetate, and diethylene glycol ethyl ether acetate; the high molecular weight resin is selected from one or two of polyester resin, modified solid acrylate, and aliphatic solvent-based HDI trimer.

[0015] Preferably, the weight ratio of the dispersant, the first organic solvent, and the low molecular weight resin is (0.10-0.60):(0.95-2.05):(1.70-2.60).

[0016] Preferably, the weight ratio of the thickener, the second organic solvent, and the high molecular weight resin is (0.10-0.60):(0.95-2.05):(1.70-2.60).

[0017] According to another aspect of the present invention, there is provided a method for preparing the conductive paste as described above, comprising the following steps:

[0018] Step S1, dispersing nano silver powder in a high wettability organic carrier to obtain a pre-dispersed mixture;

[0019] Step S2: dispersing the pre-dispersed mixture and submicron silver powder in a low-wetting organic carrier to obtain a conductive paste.

[0020] Furthermore, in step S1, the nano silver powder and the high wettability organic carrier are first stirred and mixed until no dry powder is observed by naked eyes, and then a three-roll mill is used for the first mixing to obtain a pre-dispersed mixture.

[0021] Furthermore, in step S1, the pre-dispersed mixture, submicron silver powder and low wettability organic carrier are mixed until no dry powder is observed by naked eye, then centrifuged and stirred, and after standing, mixed for the second time using a three-roll mill to obtain a conductive paste.

[0022] Preferably, the first mixing time is 20 min to 40 min.

[0023] Preferably, the rotation speed of the centrifugal stirring is 420 r / min to 1000 r / min, and the time is 2 min to 5 min.

[0024] Preferably, the standing time is 20 min to 40 min.

[0025] Preferably, the second mixing time is 20 min to 40 min.

[0026] According to another aspect of the present invention, an electrode is provided, comprising a sub-grid, wherein the sub-grid is prepared by using the conductive paste as described above.

[0027] According to yet another aspect of the present invention, a solar cell is provided. The solar cell comprises the above electrode.

[0028] The technical solution of the present invention utilizes spherical nano-silver powder with a specific particle size distribution, which has a small particle size, a large specific surface area, and high activity. Sintering and micro-melting can occur at relatively low temperatures. Micro-melting of the nano-silver powder surface under thermal action increases direct contact between the silver powders, forming a more effective conductive network. Furthermore, the use of a specific particle size distribution (D10 of 100nm to 150nm, D50 of 180nm to 220nm, D90 of 400nm to 500nm, and D100 less than 600nm) can increase the direct contact points between the silver powders during the curing process, forming more conductive pathways, which helps reduce resistance, improve the conductivity of the electrode, reduce losses during power transmission, and enhance the photovoltaic conversion efficiency of the battery. Furthermore, the micro-melting surface of the highly active spherical nano-silver powder easily contacts and forms an alloy with the similarly micro-melting solder strip, thereby enhancing the bonding strength between the solder strip and the auxiliary grid, improving the yield rate of photovoltaic modules, and extending the battery life.

[0029] The conductive paste prepared by the nano silver powder of the present invention can improve the bonding strength between the auxiliary grid and the welding strip, reduce the bulk resistivity of the electrode, improve the yield rate of the photovoltaic module, extend the service life of the battery, and ultimately achieve the goal of reducing battery cost and improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0031] Figure 1 The SEM photograph of the nano-silver powder in Example 1 during low-temperature sintering and micro-melting is shown. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] As described in the background technology, the existing technology has the problem of weak bonding between the soldering ribbon and the grid line. In order to solve the above problem, according to one aspect of the present invention, a nano silver powder for a conductive paste is provided. The nano silver powder has a spherical or quasi-spherical structure, and the D10 particle size of the nano silver powder is 100nm to 150nm, the D50 particle size is 180nm to 220nm, the D90 particle size is 400nm to 500nm, and the D100 particle size is less than 600nm.

[0034] In the technical solution of the present invention, spherical nano-silver powder with a specific particle size distribution is used. It has a small particle size, a large specific surface area, and high activity (high activity refers to low-temperature sintering characteristics, that is, the spherical nano-silver powder easily melts on the powder surface under relatively low heating conditions, flows to the surface of other particles, and forms direct contact between metal particles during the solidification process). Sintering micro-melting can occur at relatively low temperatures. The micro-melting of the nano-silver powder surface under the action of heat can increase direct contact between silver powders, forming a more effective conductive network. In addition, the use of a specific particle size distribution (D10 is 100nm-150nm, D50 is 180nm-220nm, D90 is 400nm-500nm, and D100 is less than 600nm) can increase the direct contact points between silver powders during the solidification process, forming more conductive paths, which is beneficial for reducing resistance, improving the conductivity of the electrode, reducing losses during power transmission, and improving the photoelectric conversion efficiency of the battery. Furthermore, the slightly melted surface of the highly active spherical nano-silver powder easily contacts the similarly slightly melted solder strip and forms an alloy, thereby enhancing the bonding strength between the solder strip and the auxiliary grid, improving the yield rate of photovoltaic modules, and extending the battery life.

[0035] In some embodiments, the melting temperature of the nano-silver powder is 165°C to 170°C.

[0036] In the technical solution of the embodiment of the present invention, the melting temperature of the nano-silver powder is closely related to the size, specific surface area, and surface state of the nano-silver powder. At the above melting temperature (165°C to 170°C), the specific surface area of ​​the nano-silver powder, the proportion of small-sized particles, and the proportion of surface atoms of small-sized particles are relatively high. The surface atoms of the nano-silver powder are more active and easily interact with other substances or other particles of the nano-silver powder, and softening and sintering can occur at lower temperatures. Therefore, the nano-silver powder has high activity and can begin to micro-melt at relatively low temperatures, thereby promoting surface flow and contact between the silver powder particles. When the conductive paste solidifies, the micro-melting of the silver powder particles enables them to flow and contact with each other during the solidification process, which is conducive to forming a denser and continuous metal network, thereby reducing the volume resistivity of the electrode and improving efficiency. In addition, the micro-melting characteristics of the highly active nano-silver powder make it easier to form an alloy contact with the surface of the solder strip at the welding temperature, significantly enhancing the bonding strength between the solder strip and the auxiliary grid, reducing the mechanical stress of the component during the welding process, thereby reducing the problems of solder joint breakage and insufficient solder strip tension, and helping to increase the service life of the component. Furthermore, the use of nano silver powder with the above-mentioned low-temperature sintering characteristics helps to reduce the temperature requirements during the battery sintering process, reduce energy consumption, and avoid damage to the battery.

[0037] In some embodiments, the specific surface area of ​​the nano silver powder is 2.4 m 2 / g~3.0m 2 / g.

[0038] In the technical solution of the embodiments of the present invention, within the above-mentioned specific surface area range, the nano-silver powder can more tightly bond with the resin in the conductive paste, facilitating stable dispersion of the nano-silver powder in the conductive paste and forming a thinner resin coating around the nano-silver powder, thereby improving the paste's dispersibility and printing performance. Furthermore, during the curing process, the resin melts, allowing the nano-silver powder particles to directly contact each other, forming a conductive path. Due to the nano-silver powder's high specific surface area, under the same conditions, the resin layer covering each particle is thinner, facilitating faster resin melting during curing. This allows the nano-silver powder particles to melt and sinter at lower temperatures, forming a more direct metallic contact. This reduces the volume resistivity of the cured electrode and improves the bonding strength between the soldering ribbon and the grid lines. Furthermore, the high specific surface area of ​​the silver powder exhibits improved solderability. During soldering, the micro-melting of the silver powder surface facilitates the formation of intermetallic compounds with the soldering ribbon. This alloying contact significantly strengthens the bonding strength between the soldering ribbon and the secondary grid lines. Furthermore, the thinner resin layer allows the silver powder particles to react more quickly under infrared heating, reducing soldering time and improving production efficiency.

[0039] According to another aspect of the present invention, a conductive paste is provided, comprising the above-mentioned submicron silver powder for conductive paste, a high wettability organic carrier, and a low wettability organic carrier; the weight ratio of the nano silver powder, the submicron silver powder, the high wettability organic carrier, and the low wettability organic carrier is (5-25): (55.5-89.5): (2.75-5.25): (2.75-5.25).

[0040] In the technical solution of the embodiment of the present invention, a high-wetting organic carrier and a low-wetting organic carrier are used to encapsulate and disperse the nano silver powder, so that a conductive paste with high dispersibility and stability can be obtained, and a conductive paste with good printing performance can be obtained. In addition, the conductive paste is prepared using the spherical nano silver powder with the above-mentioned specific particle size distribution. The electrode formed after curing has a lower volume resistivity, and the electrode can more effectively collect and transmit current, reduce power loss, and thus improve the photoelectric conversion efficiency of the battery. In the process of manufacturing the 0BB component, the bonding force between the soldering tape and the auxiliary grid can be significantly enhanced, the loss of the component CTM (current transfer measurement) is reduced, and the reliability and yield rate of the component are improved. Therefore, the conductive paste prepared using the nano silver powder of the present invention has excellent printability and dispersibility, can improve production efficiency and storage stability, improve the yield rate of the component and extend the service life of the battery.

[0041] In some embodiments, the viscosity of the conductive paste is 300 Pa·s to 450 Pa·s.

[0042] In the technical solution of the embodiment of the present invention, limiting the viscosity of the conductive paste to the above range can improve the efficiency and printing quality of the printing process, while reducing the battery manufacturing cost and enhancing the photoelectric conversion efficiency and service life of the battery.

[0043] In some embodiments, the conductive paste has a fineness of 2.5 μm to 4.5 μm.

[0044] In the technical solution of the embodiment of the present invention, the fineness of the conductive paste is limited to the above-mentioned range, which can optimize the printing performance of the paste, especially in narrow-opening screen printing, ensuring the accuracy, continuity and uniformity of printing, while reducing the volume resistivity of the paste, improving the photoelectric conversion efficiency and enhancing the welding performance.

[0045] Micron-grade silver powder refers to silver powder particles with a particle size between 0.1 micron and 1 micron. In some embodiments, submicron-grade silver powder has a D10 particle size of 100nm to 120nm and a D50 particle size of 700nm to 900nm. The use of micron-grade and nano-grade silver powder in conductive pastes facilitates the formation of a denser three-dimensional stacking structure. The larger micron-grade silver powder helps reduce tunneling resistance and improve gate line conductivity, while the smaller submicron-grade silver powder helps better fill the velvet surface of the silicon wafer, thereby reducing contact resistance.

[0046] In some embodiments, the conductive paste further comprises micron-sized silver powder, wherein the weight ratio of the micron-sized silver powder to the submicron-sized silver powder is (12-16):(56-60), and the mixed silver powder of the submicron-sized silver powder and the micron-sized silver powder has a D10 particle size of 700nm-900nm, a D50 particle size of 2μm-3μm, and a D100 particle size of 6μm-8μm. Micron-sized silver powder refers to silver powder particles with a particle size between 1 μm and 1000 μm. The conductive paste is compounded using micron-sized silver powder, submicron-sized silver powder, and nano-sized silver powder to facilitate the formation of a denser grid line structure, thereby reducing the use of silver powder and thus reducing costs while reducing grid line resistance. Preferably, the micron-sized silver powder and the submicron-sized silver powder are spherical or quasi-spherical structures, respectively.

[0047] Highly wettable components have low surface tension and good wetting properties, significantly improving the dispersibility of metal powders and reducing the viscosity of the slurry. In some embodiments, the high-wetting organic vehicle comprises a dispersant, a first organic solvent, and a low molecular weight resin; the dispersant is selected from one or more of 9-octadecene amide, fatty acids with 6-12 carbon atoms, phosphates, and polyurethanes; the first organic solvent is selected from one or more of diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol monoethyl ether, and diethylene glycol-2-ethylhexyl ether; and the low molecular weight resin is selected from one or more of hydrogenated bisphenol A diglycidyl ether, tetrahydrophthalic acid bisglycidyl ester, and bisphenol A modified epoxy resins.

[0048] In the technical solution of the embodiment of the present invention, the use of the above-mentioned high-wettability organic carrier is conducive to obtaining a highly dispersible conductive paste, thereby improving the printing performance of the conductive paste and the bonding strength between the soldering strip and the gate line.

[0049] In order to improve the dispersibility and printing performance of the conductive paste, in one embodiment, the weight ratio of the dispersant, the first organic solvent and the low molecular weight resin is (0.10-0.60): (0.95-2.05): (1.70-2.60).

[0050] The low-wetting component primarily regulates the viscosity and stability of the slurry, helping to control the printing thickness of the slurry, preventing excessive flow or diffusion of the metal powder during printing, achieving a better print appearance, and improving the stability of the slurry during long-term storage. In some embodiments, the low-wetting organic carrier includes a thickener, a second organic solvent, and a high molecular weight resin; the thickener is selected from one or two of tert-butylphenol formaldehyde, modified rosin, and an organosilane compound; the second organic solvent is selected from one or two of diethylhexyl maleate, diethylene glycol butyl ether acetate, and diethylene glycol ethyl ether acetate; and the high molecular weight resin is selected from one or two of a polyester resin, a modified solid acrylate, and an aliphatic solvent-based HDI trimer.

[0051] In the technical solution of the embodiment of the present invention, the use of the low-wettability organic carrier is conducive to obtaining a highly dispersible and highly stable conductive paste, thereby improving the storage stability and printability of the conductive paste.

[0052] In order to improve the printability of the conductive paste, improve the accuracy of grid line printing, and reduce the problems of virtual printing or broken lines, in one embodiment, the weight ratio of the thickener, the second organic solvent, and the high molecular weight resin is (0.10~0.60): (0.95~2.05): (1.70~2.60).

[0053] According to another aspect of the present invention, there is provided a method for preparing the conductive paste as described above, comprising the following steps:

[0054] Step S1, dispersing nano silver powder in a high wettability organic carrier to obtain a pre-dispersed mixture;

[0055] Step S2: dispersing the pre-dispersed mixture and submicron silver powder in a low-wetting organic carrier to obtain a conductive paste.

[0056] In the technical solution of the present invention, the nano-silver powder is first dispersed in a high-wetness organic carrier and then dispersed in a low-wetness organic carrier (i.e., graded feeding dispersion is adopted). This can fully wet the surface of the spherical nano-silver powder, improve its dispersibility in the slurry, reduce the viscosity and fineness of the slurry, and improve its printability, especially the printability on a narrow-opening screen.

[0057] In some embodiments, in step S1, the nano-silver powder and the high-wetness organic carrier are first stirred and mixed until no dry powder is observed with the naked eye, and then a three-roll mill is used for the first mixing to obtain a pre-dispersed mixture; preferably, in order to fully disperse the nano-silver powder in the high-wetness organic carrier and improve process efficiency, the first mixing time is 20 min to 40 min.

[0058] In some embodiments, in step S1, the pre-dispersed mixture, submicron silver powder and low-wetness organic carrier are mixed until no dry powder is observed with the naked eye, and then centrifuged and stirred. After standing, a three-roll machine is used for mixing for the second time to obtain a conductive slurry; centrifugal stirring takes a short time and has a high degree of dispersion, and can reduce the extrusion of the metal powder by the three-roll process, thereby causing deformation. Standing allows the organic carrier and the metal powder to have sufficient contact time to better infiltrate the powder; the preferred centrifugal stirring speed is 420r / min~1000r / min, and the time is 2min~5min; the preferred standing time is 20min~40min; in order to fully disperse the nano silver powder in the low-wetness organic carrier and improve the process efficiency, the preferred second mixing time is.

[0059] According to another aspect of the present invention, an electrode is provided, comprising a sub-grid, wherein the sub-grid is prepared by using the conductive paste as described above.

[0060] In the technical solution of the present invention, the above-mentioned conductive slurry is used to prepare the electrode sub-grid, which can improve the conductivity of the electrode, reduce the energy loss during current transmission, and improve the electrical performance of the battery component; in addition, the grid line prepared by the slurry of the present invention can obtain higher solder joint stability during welding, reduce the CTM loss of the HJT battery component, improve the yield and reliability of the photovoltaic component, and extend the service life of the battery.

[0061] According to another aspect of the present invention, a solar cell is provided, comprising the above-mentioned electrode. The solar cell according to the present invention has high photoelectric conversion efficiency, high yield rate of photovoltaic modules and long service life.

[0062] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0063] Example 1

[0064] A conductive paste comprising nano silver powder for conductive paste, a mixture of submicron silver powder and micron silver powder, a high-wetness organic carrier, and a low-wetness organic carrier; the weight ratio of the nano silver powder, submicron silver powder, micron silver powder, high-wetness organic carrier, and low-wetness organic carrier is 20:58:14:4:4;

[0065] The nano silver powder is spherical, with a D10 particle size of 120 nm, a D50 particle size of 180 nm, a D90 particle size of 420 nm, and a D100 particle size of 510 nm.

[0066] The micron-sized silver powder and submicron-sized silver powder are spherical in structure respectively. The mixed silver powder of submicron-sized silver powder and micron-sized silver powder has a D10 particle size of 800 nm, a D50 particle size of 3 μm, and a D100 particle size of 7 μm.

[0067] The high-wetting organic carrier includes a surfactant 9-octadecene amide, a first organic solvent diethylene glycol diethyl ether, and a low-molecular-weight resin hydrogenated bisphenol A diglycidyl ether, and the weight ratio of the surfactant 9-octadecene amide, the first organic solvent diethylene glycol diethyl ether, and the low-molecular-weight resin hydrogenated bisphenol A diglycidyl ether is 0.3:1.5:2.2;

[0068] The low-wetting organic carrier includes a thickener, tert-butylphenol formaldehyde, a second organic solvent, diethylhexyl maleate, and a high molecular weight resin, polyester resin, and the weight ratio of the thickener, tert-butylphenol formaldehyde, the second organic solvent, diethylhexyl maleate, and the high molecular weight resin, polyester resin L480, is 0.3:1.5:2.2;

[0069] The preparation steps of conductive paste are as follows:

[0070] Step 1: First, the nano silver powder and the high wettability organic carrier are manually stirred and mixed until no dry powder is observed by naked eye, and then mixed using a three-roll mill for 30 minutes to obtain a pre-dispersed mixture;

[0071] Step 2: First, add the pre-dispersed mixture, submicron silver powder and micron silver powder into the low-wetting organic carrier and stir manually until no dry powder is observed with the naked eye, then centrifuge and stir for 2 minutes at a speed of 420r / min to mix, let it stand for 30 minutes after mixing, and after standing, use a three-roll mill to mix for 30 minutes to obtain a conductive slurry.

[0072] Example 2

[0073] The only difference from Example 1 is that the D10 particle size of the nano silver powder is 100 nm, the D50 particle size is 180 nm, the D90 particle size is 400 nm, and the D100 particle size is 450 nm.

[0074] Example 3

[0075] The only difference from Example 1 is that the D10 particle size of the nano silver powder is 150 nm, the D50 particle size is 220 nm, the D90 particle size is 500 nm, and the D100 particle size is 580 nm.

[0076] Example 4

[0077] A nano silver powder for conductive paste, which differs from Example 1 only in the preparation steps of the conductive paste. The specific preparation steps are as follows:

[0078] The mixed silver powder of nano silver powder, submicron silver powder and micron silver powder, high wettability organic carrier and low wettability organic carrier were manually stirred and mixed until no dry powder was observed with the naked eye, and then centrifuged and stirred for 2 minutes at a speed of 420 r / min for mixing. After mixing, the mixture was allowed to stand for 30 minutes. After standing, a three-roll mill was used to mix for 30 minutes to obtain a conductive paste.

[0079] Comparative Example 1

[0080] The only difference from Example 1 is that the particle size of the nano silver powder D10 is 1200 nm, the particle size of D50 is 1590 nm, the particle size of D90 is 2270 nm, and the particle size of D100 is 4530 nm.

[0081] Comparative Example 2

[0082] The only difference between this embodiment and Comparative Example 1 is that the preparation steps of the conductive paste are different. The specific preparation steps are as follows:

[0083] The mixed silver powder of nano silver powder, submicron silver powder and micron silver powder, high wettability organic carrier and low wettability organic carrier were manually stirred and mixed until no dry powder was observed with the naked eye, and then centrifuged and stirred for 2 minutes at a speed of 420 r / min for mixing. After mixing, the mixture was allowed to stand for 30 minutes. After standing, a three-roll mill was used to mix for 30 minutes to obtain a conductive paste.

[0084] Comparative Example 3

[0085] The only difference from Example 1 is that the D10 particle size of the nano silver powder is 220 nm, the D50 particle size is 460 nm, the D90 particle size is 1000 nm, and the D100 particle size is 2180 nm.

[0086] Comparative Example 4

[0087] The only difference between this embodiment and Comparative Example 3 is that the preparation steps of the conductive paste are different. The specific preparation steps are as follows:

[0088] The mixed silver powder of nano silver powder, submicron silver powder and micron silver powder, high wettability organic carrier and low wettability organic carrier were manually stirred and mixed until no dry powder was observed with the naked eye, and then centrifuged and stirred for 2 minutes at a speed of 420 r / min for mixing. After mixing, the mixture was allowed to stand for 30 minutes. After standing, a three-roll mill was used to mix for 30 minutes to obtain a conductive paste.

[0089] Comparative Example 5

[0090] The only difference from Example 1 is that the D10 particle size of the nano silver powder is 70 nm, the D50 particle size is 110 nm, the D90 particle size is 190 nm, and the D100 particle size is 240 nm.

[0091] Comparative Example 6

[0092] The only difference between this embodiment and Comparative Example 5 is that the preparation steps of the conductive paste are different. The specific preparation steps are as follows:

[0093] The mixed silver powder of nano silver powder, submicron silver powder and micron silver powder, high wettability organic carrier and low wettability organic carrier were manually stirred and mixed until no dry powder was observed with the naked eye, and then centrifuged and stirred for 2 minutes at a speed of 420 r / min for mixing. After mixing, the mixture was allowed to stand for 30 minutes. After standing, a three-roll mill was used to mix for 30 minutes to obtain a conductive paste.

[0094] Performance Testing

[0095] 1. The D10 particle size, D50 particle size, D90 particle size and D100 particle size of the nano silver powder were measured using a laser particle size analyzer. The particle size test results of the nano silver powder in the embodiment and the comparative example are shown in Table 1.

[0096] 2. The specific surface area of ​​the nano-silver powder was tested by the nitrogen adsorption BET test method. The test results of the specific surface area (SSA) of the nano-silver powder in the examples and comparative examples are shown in Table 1.

[0097] 3. Place the nano-silver powder in an oven and heat it at 200°C for 20 minutes. After cooling, observe the morphology using a scanning electron microscope to determine whether the tested nano-silver powder exhibits low-temperature sintering micro-melting. The low-temperature sintering micro-melting performance test results of the nano-silver powder in the Examples and Comparative Examples are shown in Table 1. Figure 1 This is an SEM photograph of the nano-silver powder in Example 1 during low-temperature sintering and micro-melting. It can be seen that the powder surface is melting and flowing to the surfaces of other particles, such as adjacent nano-silver powder, submicron silver powder and micron silver powder, forming direct contact between the metal particles.

[0098] 4. The viscosity of the conductive paste was tested by a rotational viscometer. The viscosity of the conductive paste in the embodiment and the comparative example is shown in Table 1.

[0099] 5. The fineness of the conductive paste was tested using a fineness plate. The fineness of the conductive pastes in the examples and comparative examples is shown in Table 1.

[0100] 6. Electrical performance test and photoelectric performance test, the steps are as follows:

[0101] (1) Preparation of cell simulation samples: The conductive paste was printed on the front and back sides of the blue film (Huasheng heterojunction 182H blue film) by screen printing, and then cured at 200°C for 15 minutes to obtain a cell simulation sample with a metallization layer.

[0102] (2) Volume Resistivity: The volume resistivity of the metallization layer on the surface of the cell simulated sample was measured using a four-point probe resistivity tester. The volume resistivity test results of the metallization layer on the surface of the cell simulated sample prepared with the conductive paste in the Examples and Comparative Examples are shown in Table 1.

[0103] (3) IV curve test: Use a solar cell tester to perform IV curve test on the cell simulation sample. The test is conducted under standard test conditions, namely AM 1.5G (standard spectrum of solar simulator), 100mW / cm 2 The photoelectric conversion efficiency of the cell simulation samples prepared with the conductive pastes in the examples and comparative examples is shown in Table 1.

[0104] 7. Adhesion test: Conductive paste is screen-printed on the front side of the blue film (Huasheng heterojunction 182H blue film) to print the auxiliary grid. The printing performance is shown in Table 1 (wherein, excellent printing performance means that the printed pattern is clear and complete, without broken grids; good printing performance means that the printed pattern is clear, with a broken grid rate of less than 10%; poor printing performance means that the printed pattern is incomplete, with a broken grid rate of more than 50%). After heating the soldering iron to 300°C, use the soldering iron to solder the tinned copper soldering strip soaked in PV112B flux to the grid line of the auxiliary grid. Use a Tobo tensile tester to test the tensile force. The tensile test results are shown in Table 1. Among them, the tensile force refers to the adhesion formed between the soldering strip and the surface of the auxiliary grid. The magnitude of the tensile force affects the physical series / parallel connection performance of the final component composed of solar cells.

[0105] Table 1

[0106]

[0107]

[0108] As shown in Table 1, the conductive pastes prepared in Examples 1 to 4 using spherical nano-silver powder with a specific particle size distribution exhibit low-temperature sintering properties. The electrode layers (i.e., metallization layers) of the batteries prepared using the conductive pastes containing the spherical nano-silver powder exhibit low volume resistivity, and the cells exhibit high photoelectric conversion efficiency. Furthermore, the conductive pastes prepared in Examples 1 to 4 using the spherical nano-silver powder with a specific particle size distribution exhibit viscosities ranging from 301 Pa·s to 445 Pa·s, and fineness ranging from 3.0 μm to 4.0 μm. The conductive pastes exhibit excellent ink flowability, and the printed patterns are clear and complete, exhibiting excellent printability and meeting the requirements of narrow-aperture screen printing.

[0109] Compared with Examples 1 to 4, the D10 particle size, D50 particle size, D90 particle size and D100 particle size of the silver powder in Comparative Examples 1 and 3 are significantly increased, and the specific surface area and the viscosity of the conductive paste are significantly reduced. The silver powder particle size used in Comparative Examples 1 and 3 is too large, resulting in increased fineness of the obtained paste and decreased printing performance. The volume resistivity of the electrode layer in Comparative Examples 1 and 3 is significantly increased, and the photoelectric conversion efficiency of the battery cell is significantly reduced.

[0110] Compared with Example 1, the D10 particle size, D50 particle size, D90 particle size and D100 particle size of the nano silver powder in Comparative Example 5 are significantly reduced, and the specific surface area is significantly increased. Since the particle size of the nano silver powder in Comparative Example 5 is too low and the specific surface area is too high, the viscosity of the conductive paste is significantly increased, and the particles are easily agglomerated, resulting in an increase in fineness. The printing performance of the conductive paste is reduced, the volume resistivity of the electrode layer is increased, and the photoelectric conversion efficiency of the cell is reduced.

[0111] By comparing Example 1 with Example 4, Comparative Example 1 with Comparative Example 2, Comparative Example 3 with Comparative Example 4, and Comparative Example 5 with Comparative Example 6, it can be seen that the use of graded feeding dispersion can effectively reduce the viscosity of each conductive paste and increase the fineness of the conductive paste, especially significantly reducing the viscosity and fineness of the conductive paste containing nano-silver powder with smaller particle size.

[0112] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a conductive paste, characterized in that: The conductive paste comprises nano silver powder, submicron silver powder, a high wettability organic carrier, and a low wettability organic carrier; the weight ratio of the nano silver powder, the submicron silver powder, the high wettability organic carrier, and the low wettability organic carrier is (5-25): (55.5-89.5): (2.75-5.25): (2.75-5.25); The nano silver powder has a spherical or quasi-spherical structure, a D10 particle size of 100 nm to 150 nm, a D50 particle size of 180 nm to 220 nm, a D90 particle size of 400 nm to 500 nm, and a D100 particle size of less than 600 nm. The submicron silver powder has a D10 particle size of 100 nm to 120 nm and a D50 particle size of 700 nm to 900 nm; The high wettability organic carrier comprises a dispersant, a first organic solvent and a low molecular weight resin; the low molecular weight resin is selected from one or more of hydrogenated bisphenol A diglycidyl ether, tetrahydrophthalic acid diglycidyl ester and bisphenol A modified epoxy resin; The low-wetting organic carrier includes a thickener, a second organic solvent and a high molecular weight resin; the high molecular weight resin is selected from one or two of polyester resin, modified solid acrylate, and aliphatic solvent-based HDI trimer; The preparation method of the conductive paste comprises the following steps: Step S1, dispersing nano silver powder in a high wettability organic carrier to obtain a pre-dispersed mixture; Step S2: dispersing the pre-dispersed mixture and submicron silver powder in a low-wetting organic carrier to obtain the conductive paste.

2. The method for preparing the conductive paste according to claim 1, wherein: The melting temperature of the nano silver powder is 165° C. to 170° C.

3. The method for preparing the conductive paste according to claim 1, wherein: The specific surface area of ​​the nano silver powder is 2.4 m 2 / g~3.0m 2 / g.

4. The method for preparing the conductive paste according to claim 1, wherein: The viscosity of the conductive paste is 300 Pa∙s to 450 Pa∙s; and / or, The conductive paste has a fineness of 2.5µm to 4.5µm; and / or, The conductive paste also includes micron-sized silver powder, and the weight ratio of the micron-sized silver powder to the submicron-sized silver powder is (12-16): (56-60). The mixed silver powder of the submicron-sized silver powder and the micron-sized silver powder has a D10 particle size of 700 nm to 900 nm, a D50 particle size of 2 μm to 3 μm, and a D100 particle size of 6 μm to 8 μm.

5. The method for preparing the conductive paste according to claim 1, wherein: The dispersant is selected from one or more of 9-octadeceneamide, fatty acids with a carbon number of 6-12, phosphates, and polyurethanes; the first organic solvent is selected from one or more of diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol monoethyl ether, and diethylene glycol-2-ethylhexyl ether; and / or, The thickener is selected from one or two of tert-butylphenolic acid, modified rosin, and organic silane compounds; the second organic solvent is selected from one or two of diethylhexyl maleate, diethylene glycol butyl ether acetate, and diethylene glycol ethyl ether acetate.

6. The method for preparing the conductive paste according to claim 5, wherein: The weight ratio of the dispersant, the first organic solvent and the low molecular weight resin is (0.10-0.60): (0.95-2.05): (1.70-2.60).

7. The method for preparing the conductive paste according to claim 5, wherein: The weight ratio of the thickener, the second organic solvent, and the high molecular weight resin is (0.10-0.60): (0.95-2.05): (1.70-2.60).

8. The method for preparing the conductive paste according to claim 1, wherein: In the step S1, the nano silver powder and the high wettability organic carrier are first stirred and mixed until no dry powder is observed by naked eye, and then a three-roll mill is used for the first mixing to obtain the pre-dispersed mixture; and / or, In the step S1, the pre-dispersed mixture, submicron silver powder and low-wetness organic carrier are mixed until no dry powder is observed by naked eye, and then centrifuged and stirred. After standing, they are mixed for the second time using a three-roll mill to obtain the conductive paste.

9. The method for preparing the conductive paste according to claim 8, wherein: The first mixing time is 20min~40min; The centrifugal stirring speed is 420r / min~1000r / min, and the time is 2min~5min; The standing time is 20 min to 40 min; The second mixing time is 20 min to 40 min.

10. A conductive paste, characterized in that: The conductive paste is prepared by the preparation method of any one of claims 1 to 9.

11. An electrode comprising a secondary grid, characterized in that: The auxiliary grid is prepared using the conductive paste according to claim 10.

12. A solar cell, characterized in that: The solar cell comprises the electrode according to claim 11.

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