Nano silver powder for conductive paste, conductive paste and preparation method and application of nano silver powder

Abstract

The invention provides nano silver powder for conductive paste, the conductive paste and a preparation method and application of the nano silver powder, the nano silver powder is of a spherical or sphere-like structure, the D10 particle size of the nano silver powder ranges from 100 nm to 150 nm, the D50 particle size of the nano silver powder ranges from 180 nm to 220 nm, the D90 particle size of the nano silver powder ranges from 400 nm to 500 nm, and the D100 particle size of the nano silver powder is smaller than 600 nm. Based on the nano silver powder, the problem of weak binding force between a welding strip and a grid line in the prior art is solved.

Description

Technical Field

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

[0002] HJT cells have fewer manufacturing process steps and higher theoretical conversion efficiency, and are one of the future mainstream crystalline silicon cell technology directions. However, due to the fluctuations in the international silver price of the global reserve level of precious metals, the cost of HJT paste is still at a high level. According to current data, the silver paste consumption of PERC cells is 9mg / W, that of TOPCon cells is 12mg / W, and that of HJT cells exceeds 15mg / W. The high consumption of silver paste is directly related to the cost and economic benefits of the cells, limiting the industrial development of HJT cells. In order to reduce silver consumption and improve cell efficiency, 0BB (Zero Bus Bar) technology came into being. 0BB technology aims to achieve higher photoelectric conversion efficiency by eliminating the main busbar on the front of the cell and reducing the shading area. This technology not only optimizes the amount of silver paste used, but also puts forward new requirements for the performance of the paste. In traditional battery module manufacturing, the presence of the main busbar provides a direct path for current collection, while 0BB technology relies on the direct connection between the secondary grid (thin gridbar) and the welding ribbon to complete the current transmission. Therefore, the bonding strength between the solder strip, the secondary grid and the solar cell has a decisive influence on the overall efficiency and reliability of the module.

[0003] Traditional sub-grid paste, because it only plays the role of collecting photogenerated carriers, usually only considers printability, electrical properties and shading area in system design. Therefore, the existing technology focuses on the electrical properties of the conductive paste and the adhesion between the conductive paste and the battery cell, and ignores the adhesion between the grid line and the soldering strip. 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 powder to reduce the volume resistivity of the conductive paste, thereby improving the photoelectric conversion efficiency of the conductive paste. Therefore, when the traditional sub-grid conductive paste is applied to 0BB technology, there is often a weak bonding force between the soldering strip and the grid line, and the soldering strip is easy to fall off, which leads to problems such as high CTM loss of components, 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 a preparation method and application thereof, so as to solve the problem of weak bonding force between soldering strips and grid lines in the prior art.

[0005] In order to achieve the above-mentioned object, according to one aspect of the present invention, a nano silver powder for conductive paste is provided, the nano silver powder is spherical or quasi-spherical structure, the D10 particle size of the 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.

[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, submicron silver powder, high wettability organic carrier and low wettability organic carrier for conductive paste; 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 100nm to 120nm, and the D50 particle size is 700nm to 900nm.

[0012] Furthermore, the conductive paste also includes micron-sized silver powder, the weight ratio of the micron-sized silver powder to the submicron-sized silver powder is (12-16): (56-60), the D10 particle size of the mixed silver powder of the submicron-sized silver powder and the 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-butyl phenolic 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; 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 above conductive paste, 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, and then centrifugally stirred and mixed, and after standing, three-roll mill mixing is used for the second time 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 scheme of the present invention is applied, and the spherical nano silver powder with a specific particle size distribution is used, which has a small particle size, a large specific surface area and high activity, and can be sintered and micro-melted at a relatively low temperature. The micro-melting of the surface of the nano silver powder under the action of heat can increase the direct contact between the silver powders and form 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 the silver powders during the curing process, forming more conductive paths, which is conducive to reducing resistance, improving the conductivity of the electrode, reducing the loss during power transmission, and improving the photoelectric conversion efficiency of the battery. Furthermore, the micro-melting surface of the highly active spherical nano silver powder is easy to contact with the same micro-melting welding strip and form an alloy, thereby improving the bonding force between the welding strip and the auxiliary grid, improving the yield rate of the photovoltaic module, and extending the battery life.

[0029] The conductive paste prepared by the nano silver powder of the present invention can improve the bonding force 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 battery life, and ultimately achieve the goal of reducing battery cost and improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the 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 in the embodiments of the present 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, there is a problem of weak bonding between the soldering strip and the grid line in the prior art. 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 is a spherical or quasi-spherical structure. 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, which has small particle size, large specific surface area and high activity (high activity means low temperature sintering characteristics, that is, spherical nano silver powder is easy to melt on the powder surface under low heating conditions, flow to the surface of other particles, and form direct contact between metal particles during the solidification process). Sintering micro melting can occur at a relatively low temperature. Micro melting on the surface of nano silver powder under the action of heat can increase the direct contact between silver powders and form a more effective conductive network. In addition, the use of a specific particle size distribution (D10 is 100nm to 150nm, D50 is 180nm to 220nm, D90 is 400nm to 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 conducive to reducing resistance, improving the conductivity of the electrode, reducing the loss during power transmission, and improving the photoelectric conversion efficiency of the battery. Furthermore, the micro-molten surface of the highly active spherical nano-silver powder is easy to contact with the similarly micro-molten solder strip and form an alloy, thereby enhancing the bonding strength between the solder strip and the secondary grid, improving the yield rate of photovoltaic modules, and extending the service life of the battery.

[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, surface state, etc. 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 easy to react with other substances or other particles of the nano silver powder. Softening and sintering can occur at a lower temperature. Therefore, the nano silver powder has high activity and can start micro melting at a relatively low temperature, thereby promoting the surface flow and contact between the silver powder particles. When the conductive paste is solidified, the micro melting of the silver powder particles enables them to flow and contact 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 welding strip at the welding temperature, significantly enhancing the bonding force between the welding 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 welding strip tension, which is conducive to improving 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 embodiment of the present invention, within the above-mentioned specific surface area range, the nano silver powder can be more closely combined with the resin in the conductive paste, which is conducive to the stable dispersion of the nano silver powder in the conductive paste and the formation of a thinner resin coating layer on the nano silver powder, thereby improving the dispersibility and printing performance of the conductive paste. At the same time, during the curing process, the resin melts so that the nano silver powder particles are in direct contact to form a conductive path. Since the nano silver powder has a high specific surface area, under the same conditions, the thickness of the resin layer covering the surface of each particle is thinner, which is conducive to faster melting of the resin during curing, so that the nano silver powder particles can be melted and sintered at a lower temperature, forming a more direct metal contact, thereby reducing the volume resistivity of the electrode after curing and improving the bonding force between the welding strip and the grid line. In addition, the above-mentioned silver powder with a high specific surface area has better welding performance. During the welding process, the micro melting of the silver powder surface is easy to form an intermetallic compound with the welding strip, and this alloy contact greatly enhances the bonding force between the welding strip and the auxiliary grid. At the same time, the thinner resin layer allows the silver powder particles to react faster under infrared heating conditions, reducing the time required for welding and improving production efficiency.

[0039] According to another aspect of the present invention, a conductive paste is provided, comprising the submicron silver powder, high wettability organic carrier and low wettability organic carrier for conductive paste as described above; the weight ratio of 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).

[0040] In the technical scheme of the embodiment of the present invention, the nano silver powder is wrapped and dispersed by a high wettability organic carrier and a low wettability organic carrier, and 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 by using the spherical nano silver powder with the above-mentioned specific particle size distribution, and the electrode formed after curing has a lower volume resistivity, and the electrode can collect and transmit current more effectively, 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 welding strip and the auxiliary grid can be significantly enhanced, the loss of the component CTM (current transfer measurement) can be reduced, and the reliability and yield rate of the component can be improved. Therefore, the conductive paste prepared by 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 within 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 fineness of the conductive paste is 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 within the above range, which can optimize the printing performance of the paste, especially in narrow opening screen printing, to ensure the printing accuracy, continuity and uniformity, 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, the D10 particle size of submicron-grade silver powder is 100nm-120nm, and the D50 particle size is 700nm-900nm. The conductive paste is conducive to forming a more compact three-dimensional stacking structure by using micron-grade silver powder and nano silver powder. Among them, the micron-grade silver powder with a larger particle size is conducive to reducing the tunneling resistance and improving the conductivity of the gate line, and the submicron-grade silver powder with a smaller particle size is conducive to better filling the velvet surface of the silicon wafer, thereby reducing the contact resistance.

[0046] In some embodiments, the conductive paste further comprises micron-grade silver powder, the weight ratio of micron-grade silver powder to submicron-grade silver powder is (12-16): (56-60), the D10 particle size of the mixed silver powder of submicron-grade silver powder and micron-grade silver powder is 700nm-900nm, the D50 particle size is 2μm-3μm, and the D100 particle size is 6μm-8μm. Micron-grade silver powder refers to silver powder particles with a particle size between 1 μm and 1000 μm. The conductive paste is compounded with micron-grade silver powder, submicron-grade silver powder and nano-grade silver powder, which is conducive to forming a denser grid line structure, and the use of silver powder can be reduced to reduce costs under the premise of reducing grid line resistance; preferably, the micron-grade silver powder and submicron-grade silver powder are spherical structures or quasi-spherical structures, respectively.

[0047] The high wetting component has low surface tension and good wetting properties, which can significantly improve the dispersibility of metal powder and reduce the viscosity of the slurry. In some embodiments, the high wetting 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, phosphate esters, 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.

[0048] In the technical solution of the embodiment of the present invention, the use of the above-mentioned high-wetness organic carrier is conducive to obtaining a highly dispersible conductive paste, improving the printing performance of the conductive paste and the bonding force 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 mainly plays the role of adjusting the viscosity and stability of the slurry, helps to control the printing thickness of the slurry, helps to prevent excessive flow or diffusion of metal powder during printing, obtains a better printing appearance, and improves the stability of the slurry in 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-butyl phenolic 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; the high molecular weight resin is selected from one or two of polyester resin, modified solid acrylate, and aliphatic solvent-based HDI trimer.

[0051] In the technical solution of the embodiment of the present invention, the use of the low-wetting organic carrier is conducive to obtaining a highly dispersible and highly stable conductive paste, and 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 problem 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 above conductive paste, 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 wettability organic carrier and then dispersed in a low wettability organic carrier (i.e., graded feeding dispersion is adopted), which 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 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 a pre-dispersed mixture; preferably, in order to fully disperse the nano silver powder in the high wettability organic carrier and improve the process efficiency, the first mixing time is 20min to 40min.

[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 by naked eye, and then centrifugally stirred and mixed. After standing, a three-roller 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 and thus cause deformation. Standing allows the organic carrier and the metal powder to have sufficient contact time and better infiltrate the powder; preferably, the speed of centrifugal stirring is 420r / min~1000r / min, and the time is 2min~5min; preferably, the 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 second mixing time is preferably.

[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 using 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, the solar cell comprising the above electrode. The solar cell based on the present invention has high photoelectric conversion efficiency, photovoltaic module yield and service life.

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

[0063] Example 1

[0064] A conductive paste, comprising nano silver powder for conductive paste, mixed silver powder of submicron silver powder and micron silver powder, high wettability organic carrier, and low wettability organic carrier; the weight ratio of the nano silver powder, submicron silver powder, micron silver powder, high wettability organic carrier, and low wettability 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 the submicron-sized silver powder are spherical structures respectively, and the mixed silver powder of the submicron-sized silver powder and the micron-sized silver powder has a D10 particle size of 800nm, a D50 particle size of 3μm, and a D100 particle size of 7μm;

[0067] The high wettability 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 the conductive paste are as follows:

[0070] Step 1: first manually stir and mix the nano silver powder and the high wettability organic carrier until no dry powder is observed by naked eyes, and then use a three-roll mill to mix for 30 minutes to obtain a pre-dispersed mixture;

[0071] Step 2: first add the pre-dispersed mixture, submicron silver powder and mixed silver powder of micron silver powder into a 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 420 r / min to mix, let 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 between the embodiment 1 and the embodiment 1 is that the particle size of the nano silver powder D10 is 100 nm, the particle size of the nano silver powder D50 is 180 nm, the particle size of the nano silver powder D90 is 400 nm, and the particle size of the nano silver powder D100 is 450 nm.

[0074] Example 3

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

[0076] Example 4

[0077] A nano silver powder for conductive paste, which is different from Example 1 only in that the preparation steps of the conductive paste are different. 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 420r / 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 slurry.

[0079] Comparative Example 1

[0080] The only difference between it and 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 it 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 420r / 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 slurry.

[0084] Comparative Example 3

[0085] The only difference between the embodiment 1 and the embodiment 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 it 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 420r / 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 slurry.

[0089] Comparative Example 5

[0090] The only difference between the embodiment 1 and the embodiment 1 is that the particle size D10 of the nano silver powder is 70 nm, the particle size D50 is 110 nm, the particle size D90 is 190 nm, and the particle size D100 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 420r / 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 slurry.

[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 tested using a laser particle size analyzer. The particle size test results of the nano silver powder in the embodiments and comparative examples 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 embodiments 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 with a scanning electron microscope to determine whether the tested nano silver powder has low temperature sintering micro melting. The low temperature sintering micro melting performance test results of the nano silver powder in the embodiment and the comparative example are shown in Table 1. Figure 1 This is a 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 flows to the surfaces of other particles, such as adjacent nano-silver powder, submicron silver powder and micron silver powder, forming direct contact between metal particles.

[0098] 4. The viscosity of the conductive paste is 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 paste in the embodiments 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 onto 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 tested 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 embodiment and the comparative example 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, i.e. AM 1.5G (standard spectrum of solar simulator), 100mW / cm 2 The photoelectric conversion efficiency of the cell simulation samples prepared by the conductive paste in the embodiment and the comparative example is shown in Table 1.

[0104] 7. Bonding strength test: The conductive paste is screen-printed on the front side of the blue film (Huasheng heterojunction 182H blue film) to print the secondary 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, and the broken grid rate is less than 10%; poor printing performance means that the printed pattern is incomplete, and the broken grid rate is greater than 50%). After heating the electric soldering iron to 300°C, use the electric soldering iron to solder the tinned copper soldering strip soaked in PV112B flux to the grid line of the secondary grid. Use the 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 secondary grid. The magnitude of the tensile force affects the physical series / parallel connection performance of the final component composed of the battery cells.

[0105] Table 1

[0106]

[0107]

[0108] As can be seen from Table 1, in Examples 1 to 4, spherical nano silver powder with a specific particle size distribution is used to prepare the conductive paste. The nano silver powder has low temperature sintering performance, and the electrode layer (i.e., metallization layer) of the battery prepared with the conductive paste containing it has a low volume resistivity, and the battery cell has a high photoelectric conversion efficiency. In addition, in Examples 1 to 4, the conductive paste prepared with spherical nano silver powder with a specific particle size distribution has a viscosity of 301 Pa·s to 445 Pa·s, and the fineness of the conductive paste is 3.0 μm to 4.0 μm. The conductive paste has good ink passing properties, and the printed pattern is clear and complete, has good printability, and can meet the requirements of narrow opening 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 battery 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 improve the fineness of the conductive paste, especially can significantly reduce the viscosity and fineness of the conductive paste containing nano silver powder with smaller particle size.

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A nano silver powder for conductive paste, characterized in that: The nano silver powder is spherical or quasi-spherical in structure, the D10 particle size of the 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.

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

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

4. A conductive paste, characterized in that: The conductive paste comprises the nano silver powder, submicron silver powder, high wettability organic carrier and low wettability organic carrier according to any one of claims 1 to 3; 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)。 5. The conductive paste according to claim 4, characterized in that: The viscosity of the conductive paste is 300 Pa·s to 450 Pa·s; and / or, The conductive paste has a fineness of 2.5 μm to 4.5 μm; and / or, The D10 particle size of the submicron silver powder is 100nm~120nm, and the D50 particle size is 700nm~900nm; and / or the conductive paste also includes micron-sized silver powder, 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.

6. The conductive paste according to claim 4, characterized in that: The high wettability organic carrier 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 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; and / or, 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-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; the high molecular weight resin is selected from one or two of polyester resin, modified solid acrylate, and aliphatic solvent-based HDI trimer; 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)； 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)。 7. The method for preparing the conductive paste according to any one of claims 4 to 6, characterized in that: The steps include: 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.

8. The method for preparing the conductive paste according to claim 7, characterized in that: 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 eyes, 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-wetting organic carrier are mixed until no dry powder is observed by naked eyes, and then centrifuged and stirred, and then allowed to stand and then mixed for the second time using a three-roll mill to obtain the conductive paste; and / or, Preferably, the first mixing time is 20 min to 40 min; Preferably, the speed of the centrifugal stirring is 420r / min to 1000r / min, and the time is 2min to 5min; Preferably, the standing time is 20 min to 40 min; Preferably, the second mixing time is 20 min to 40 min.

9. An electrode, comprising a secondary grid, characterized in that: The secondary grid is prepared by using the conductive paste according to any one of claims 4 to 6.

10. A solar cell, characterized in that: The solar cell comprises the electrode according to claim 9.

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