Method for improving wettability of conductive silver paste for crystalline silicon solar cell and application thereof

Abstract

The invention discloses a method for improving wettability of conductive silver paste for a crystalline silicon solar cell and application of the method, and belongs to the technical field of conductive silver paste. According to the conductive silver paste, organic solvents in different proportions are subjected to volatility testing at the temperature of 60-220 DEG C, the proportion of the organic solvents with layered volatilization is selected, a contact angle instrument is used for testing the contact angle, and the wettability of the conductive silver paste is analyzed. The conductive silver paste provided by the invention comprises the following components in percentage by mass: 75-90% of silver powder; 2-8% of glass powder; 8-17% of an organic carrier; the organic solvent is a mixed organic solvent composed of texanol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate and dibutyl phthalate according to the mass ratio of 3: 4: 2: 1; the crystalline silicon solar cell is a TOPCon silicon wafer. In the high-temperature sintering process of the organic carrier, uniform distribution of the slurry during high-temperature sintering can be well met through layered volatilization, and the proper wettability can meet the requirements of different types of slurry and step-by-step printing slurry of a battery piece.

Description

Technical Field

[0001] This invention relates to the field of conductive silver paste technology for crystalline silicon solar cells, and more particularly to a method for improving the wettability of conductive silver paste for crystalline silicon solar cells and its application. Background Technology In recent years, the development and utilization of renewable energy has received increasing attention. Renewable energy sources mainly include solar energy, hydrogen energy, wind energy, geothermal energy, bioenergy, and tidal energy, but only solar energy can guarantee humanity's energy needs. Solar energy has advantages such as being clean, inexpensive, efficient, abundant in reserves, and not limited by geographical conditions. Therefore, the development of the solar energy industry has received high attention. Photovoltaic power generation technology is an important component of solar photovoltaic utilization technology, and solar cells that utilize the photovoltaic effect to generate electricity are the most efficient method. Crystalline silicon solar cells are solar cells that convert solar energy into electrical energy using the photovoltaic effect of semiconductor silicon. Among existing technologies, crystalline silicon solar cells have high photoelectric conversion efficiency and are the most widely used solar cells.

[0002] Electrode paste is one of the main components of solar cells. Since silver is the metal with the best electrical conductivity, it is very suitable as the conductive phase in electrode paste. Conductive silver paste is one of the factors affecting the photoelectric performance of the cell, and the organic carrier plays a very important role in this process. In actual production, the organic solvent in the organic carrier needs to have a suitable viscosity and gradual volatility; the composition and ratio of the organic carrier affect the wettability of the paste. Therefore, it is essential to find a conductive silver paste with suitable wettability and rheological properties. Summary of the Invention

[0003] To address the problems of poor wettability and rheological properties of conductive silver paste during screen printing and uneven pore distribution in the surface silver film after high-temperature sintering, this invention aims to provide a conductive silver paste for monocrystalline silicon solar cells, which improves the wettability and rheological properties of the conductive silver paste for crystalline silicon solar cells using organic solvents.

[0004] The conductive silver paste of this invention comprises silver powder, glass powder, and an organic carrier. The organic carrier is composed of an organic solvent, a binder, a thixotropic agent, a surfactant, and a coupling agent. The organic solvent is a mixed solvent composed of dodecyl alcohol ester (boiling point 256°C), diethylene glycol butyl ether (boiling point 230°C), diethylene glycol butyl ether acetate (boiling point 246°C), and dibutyl phthalate (boiling point 340°C), wherein the mass ratio of dodecyl alcohol ester, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibutyl phthalate is 3:4:2:1. The organic solvent can adjust the evaporation rate and wettability of the organic carrier. A single solvent system cannot achieve gradient evaporation, so multiple organic solvents are selected to prepare the organic carrier, so that the organic carrier evaporates uniformly in each temperature range. The organic solvent can also adjust the storage stability of the conductive silver paste.

[0005] Preferably, the binder of the present invention is one or a mixture of ethyl cellulose, acrylic resin, polyisobutylene, nitrocellulose, and phenolic resin; more preferably, it is ethyl cellulose STD10. The binder is a solid powder at room temperature, typically a polymeric substance, in a network or chain-like form, containing strong polar groups. The binder is soluble in organic solvents, increasing the viscosity of the electrode paste and giving it a viscosity suitable for screen printing, thus facilitating screen printing.

[0006] Preferably, the thixotropic agent of the present invention is one or a mixture of hydrogenated castor oil, polyamide wax, fumed silica, and organobentonite; more preferably, it is polyamide wax and hydrogenated castor oil. The thixotropic agent can increase the thixotropy of the electrode paste. Good thixotropy ensures that the printed front electrode silver grid lines are both fine and high, while maintaining a small light-shielding area and a large cross-sectional area of ​​the grid lines, resulting in low line resistance.

[0007] Preferably, the surfactant described in this invention is one or a mixture of triethanolamine, lecithin, xylene, and Span 85; more preferably, it is Span 85 and lecithin. The surfactant reduces the surface tension at the interface between the organic carrier and the silver powder, allowing the organic carrier to fully wet the surface of the silver powder. The addition of the surfactant enables the silver powder particles to be uniformly and stably dispersed in the organic carrier; this is a result of the electrostatic steric hindrance effect generated by the dispersion action of the surfactant.

[0008] Preferably, the coupling agent of the present invention is one or a mixture of various types of silane coupling agents KH570, KH560, and KH550; more preferably, it is silane coupling agent KH570. The coupling agent can reduce the spacing between silver powder particles and increase the thixotropy of the organic carrier, improve the adhesion strength between the organic carrier and the silver powder and glass powder particles, form silver grid lines with high silver powder density, and enable the silver powder particles and silicon wafer to make full contact.

[0009] The method for preparing conductive silver paste for solar cells according to the present invention specifically includes the following steps: (1) The specific preparation process of the organic carrier is as follows: weigh the organic solvent, binder, thixotropic agent, surfactant and coupling agent according to the mass percentage content; wherein, the organic solvent is 78~85%, the binder is 8~12%, the thixotropic agent is 1~3%, the surfactant is 2~5%, and the coupling agent is 1~4%. First, place the organic solvent in a beaker and heat it at 70~120℃ with a magnetic stirrer. Then, add the weighed binder, thixotropic agent, surfactant and coupling agent in sequence. Stir magnetically at 450rpm for 30~90min to obtain the organic carrier.

[0010] (2) Preparation of conductive silver paste: Weigh 75~90wt% silver powder, 2~8wt% glass powder and 8~17wt% organic carrier, mix them evenly in an agate mortar, and grind them with a three-roll mill until the fineness is less than 5μm to obtain conductive silver paste.

[0011] The method for preparing the conductive silver paste described in this invention is a conventional method. Glass powder and silver powder are weighed in the required proportions and mixed evenly, as glass powder and silver powder are easier to grind evenly in powder form, and soft agglomerated lumps of silver powder can also be well dispersed. Next, an organic carrier is weighed and slowly added to a mortar and mixed evenly with the solid powder until it completely wets the solid powder to obtain the conductive silver paste. The preparation of the silver powder and glass powder can refer to existing conductive silver paste preparation processes, and will not be specifically described here.

[0012] During use, the conductive silver paste can be rolled to obtain a suitable fineness according to actual needs. The specific method is as follows: use a three-roll mill to roll the initial mixed silver paste 3 to 5 times until the gap between the front and rear of the three-roll mill is adjusted to 3-5μm. Take out a portion of the rolled paste for fineness testing. When the fineness is less than 5μm, a conductive silver paste with suitable fineness is obtained. If the fineness is greater than 5μm, it can be rolled 1 to 2 more times to ensure that the powder in the paste is completely dispersed.

[0013] Another objective of this invention is to provide the application of conductive silver paste with good wettability for crystalline silicon solar cells in the screen printing fabrication of solar cells. The prepared conductive silver paste is screen printed onto Topcon solar cells and then held at 200°C~300°C for 20~30 minutes in an electrically heated drying oven. After cooling, it is placed in a muffle furnace for high-temperature sintering to obtain crystalline silicon solar cells.

[0014] The beneficial effects of this invention are: The conductive silver paste of this invention effectively controls the viscosity and wettability of the organic carrier by changing the proportion of organic solvent in the organic carrier, significantly improving the rheological properties of the paste and ensuring stable printability during the manufacturing process of crystalline silicon solar cells. The organic solvent evaporates in stages at high temperatures, resulting in more complete printability of the conductive silver paste, improved viscosity and leveling properties, and smooth and uniform pores formed after sintering.

[0015] The organic carrier prepared by the organic solvent with good wettability used in this invention can fully mix the organic carrier, silver powder and glass powder particles in the conductive silver paste, improve the compatibility of each component, improve the problems of poor stability, printing line breakage and unevenness of traditional silver paste, ensure that the paste is evenly covered during screen printing, form a complete conductive line, and ensure the stable conductivity of the prepared battery. Attached Figure Description

[0016] Figure 1 These are contact angle test diagrams of the organic solvents in Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention on silicon wafers, glass powder, and silver powder.

[0017] Figure 2 This is the surface silver film morphology of the crystalline silicon solar cell Sc1 under a SEM electron microscope in Embodiment 1 of the present invention.

[0018] Figure 3 This is the surface silver film morphology of the crystalline silicon solar cell Sc2 under a SEM electron microscope in Comparative Example 1 of the present invention.

[0019] Figure 4 This is the surface silver film morphology of the crystalline silicon solar cell Sc3 under a SEM electron microscope in Comparative Example 2 of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0021] Example 1 The conductive silver paste described in this embodiment includes silver powder, glass powder, and an organic carrier; the organic carrier is composed of an organic solvent, a binder, a thixotropic agent, a surfactant, and a coupling agent; the organic solvent is a mixed solvent composed of dodecyl alcohol ester, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibutyl phthalate in a mass ratio of 3:4:2:1; the preparation of the conductive silver paste and the sintering of the crystalline silicon solar cell specifically include the following steps: (1) Preparation of organic carriers: Weigh out 8 wt% ethyl cellulose STD10, 82 wt% organic solvent (dodecyl alcohol ester: diethylene glycol butyl ether: diethylene glycol butyl ether acetate: dibutyl phthalate in a mass ratio of 3:4:2:1), 2 wt% Span 85, 2 wt% lecithin, 3 wt% silane coupling agent, 1.5 wt% polyamide wax, and 1.5 wt% hydrogenated castor oil. First, place the weighed organic solvent in a beaker and heat it at 70°C with a magnetic stirrer. Then, add the weighed binder, thixotropic agent, surfactant, and coupling agent in sequence, and stir magnetically at 450 rpm for 50 min to obtain the organic carrier.

[0022] (2) Preparation of conductive silver paste: Weigh 88wt% silver powder, 2wt% glass powder, and 10wt% organic carrier prepared in step (1), mix them evenly in an agate mortar, and grind them with a three-roll mill until the fineness is less than 5μm to obtain the prepared conductive silver paste S1.

[0023] (3) Sintering of crystalline silicon solar cells: The prepared conductive silver paste S1 was screen-printed onto the solar cell in a 15mm × 15mm rectangular silver electrode pattern, and then held at 200℃ for 20 minutes in an electrically heated drying oven. After cooling, it was placed in a muffle furnace at 800℃ and held for 1 minute to obtain a crystalline silicon solar cell named Sc1.

[0024] Example 2 The conductive silver paste described in this embodiment includes silver powder, glass powder, and an organic carrier; the organic carrier is composed of an organic solvent, a binder, a thixotropic agent, a surfactant, and a coupling agent; the organic solvent is a mixed solvent composed of dodecyl alcohol ester, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibutyl phthalate in a mass ratio of 3:4:2:1; the preparation of the conductive silver paste and the sintering of the crystalline silicon solar cell specifically include the following steps: (1) Preparation of organic carriers: Weigh out 12 wt% ethyl cellulose STD10, 78 wt% organic solvent (dodecyl alcohol ester: diethylene glycol butyl ether: diethylene glycol butyl ether acetate: dibutyl phthalate in a mass ratio of 3:4:2:1), 2.5 wt% Span 85, 2.5 wt% lecithin, 4 wt% silane coupling agent, 0.5 wt% polyamide wax, and 0.5 wt% hydrogenated castor oil. First, place the weighed organic solvent in a beaker and heat it at 90°C with a magnetic stirrer. Then, add the weighed binder, thixotropic agent, surfactant, and coupling agent in sequence, and stir magnetically at 450 rpm for 90 min to obtain the organic carrier.

[0025] (2) Preparation of conductive silver paste: Weigh 75wt% silver powder, 8wt% glass powder, and 17wt% organic carrier prepared in step (1). Mix them evenly in an agate mortar and grind them with a three-roll mill until the fineness is less than 5μm to obtain the prepared conductive silver paste S2.

[0026] (3) Sintering of crystalline silicon solar cells: The prepared conductive silver paste S2 was screen-printed onto the solar cell in a 15mm × 15mm rectangular silver electrode pattern, and then held at 250℃ for 30 minutes in an electrically heated drying oven. After cooling, it was placed in a muffle furnace at 800℃ and held for 1 minute to obtain a crystalline silicon solar cell.

[0027] Example 3 The conductive silver paste described in this embodiment includes silver powder, glass powder, and an organic carrier; the organic carrier is composed of an organic solvent, a binder, a thixotropic agent, a surfactant, and a coupling agent; the organic solvent is a mixed solvent composed of dodecyl alcohol ester, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibutyl phthalate in a mass ratio of 3:4:2:1; the preparation of the conductive silver paste and the sintering of the crystalline silicon solar cell specifically include the following steps: (1) Preparation of organic carriers: Weigh out 10 wt% ethyl cellulose STD10, 85 wt% organic solvent (dodecyl alcohol ester: diethylene glycol butyl ether: diethylene glycol butyl ether acetate: dibutyl phthalate in a mass ratio of 3:4:2:1), 1 wt% Span 85, 1 wt% lecithin, 1 wt% silane coupling agent, 1 wt% polyamide wax, and 1 wt% hydrogenated castor oil. First, place the weighed organic solvent in a beaker and heat it at 120°C with a magnetic stirrer. Then, add the weighed binder, thixotropic agent, surfactant, and coupling agent in sequence, and stir magnetically at 450 rpm for 30 min to obtain the organic carrier.

[0028] (2) Preparation of conductive silver paste: Weigh 90wt% silver powder, 2wt% glass powder, and 8wt% organic carrier prepared in step (1). Mix them evenly in an agate mortar and grind them with a three-roll mill until the fineness is less than 5μm to obtain the prepared conductive silver paste S3.

[0029] (3) Sintering of crystalline silicon solar cells: The prepared conductive silver paste S3 was screen-printed onto the solar cell in a 15mm × 15mm rectangular silver electrode pattern, and then held at 300℃ for 25 minutes in an electrically heated drying oven. After cooling, it was placed in a muffle furnace at 800℃ and held for 1 minute to obtain a crystalline silicon solar cell.

[0030] Comparative Example 1 The preparation of the conductive silver paste and the sintering of the crystalline silicon solar cell described in this comparative example differ from that in Example 1 in the proportion of the organic solvent, and specifically includes the following steps: (1) Preparation of organic carriers: Weigh out 8 wt% ethyl cellulose STD10, 82 wt% organic solvent (dodecyl alcohol ester: diethylene glycol butyl ether: diethylene glycol butyl ether acetate: dibutyl phthalate in a mass ratio of 2:2:3:1), 2 wt% Span 85, 2 wt% lecithin, 3 wt% silane coupling agent, 1.5 wt% polyamide wax, and 1.5 wt% hydrogenated castor oil. First, place the weighed organic solvent in a beaker and heat it at 70°C with a magnetic stirrer. Then, add the weighed binder, thixotropic agent, surfactant, and coupling agent in sequence, and stir magnetically at 450 rpm for 50 min to obtain the organic carrier.

[0031] (2) Preparation of conductive silver paste: Weigh 88wt% silver powder, 2wt% glass powder, and 10wt% organic carrier prepared in step (1), mix them evenly in an agate mortar, and grind them with a three-roll mill until the fineness is less than 5μm to obtain the prepared conductive silver paste S4.

[0032] (3) Sintering of crystalline silicon solar cells: The prepared conductive paste S4 was screen-printed onto the solar cell in a 15mm × 15mm rectangular silver electrode pattern, and then held at 200℃ for 20 minutes in an electrically heated drying oven. After cooling, it was placed in a muffle furnace at 800℃ and held for 1 minute to obtain a crystalline silicon solar cell named Sc2.

[0033] Comparative Example 2 The preparation of the conductive silver paste and the sintering of the crystalline silicon solar cell described in this comparative example differ from that in Example 1 in the proportion of the organic solvent, and specifically includes the following steps: (1) Preparation of organic carriers: Weigh out 8 wt% ethyl cellulose STD10, 82 wt% organic solvent (dodecyl alcohol ester: diethylene glycol butyl ether: diethylene glycol butyl ether acetate: dibutyl phthalate in a mass ratio of 3:3:2:1), 2 wt% Span 85, 2 wt% lecithin, 3 wt% silane coupling agent, 1.5 wt% polyamide wax, and 1.5 wt% hydrogenated castor oil. First, place the weighed organic solvent in a beaker and heat it at 70°C with a magnetic stirrer. Then, add the weighed binder, thixotropic agent, surfactant, and coupling agent in sequence, and stir magnetically at 450 rpm for 50 min to obtain the organic carrier.

[0034] (2) Preparation of conductive silver paste: Weigh 88wt% silver powder, 2wt% glass powder, and 10wt% organic carrier prepared in step (1). Mix them evenly in an agate mortar and grind them with a three-roll mill until the fineness is less than 5μm to obtain the prepared conductive silver paste S5.

[0035] (3) Sintering of crystalline silicon solar cells: The prepared conductive paste S5 was screen-printed onto the solar cell in a 15mm × 15mm rectangular silver electrode pattern, and then held at 200℃ for 20 minutes in an electrically heated drying oven. After cooling, it was placed in a muffle furnace at 800℃ and held for 1 minute to obtain a crystalline silicon solar cell named Sc3.

[0036] The organic solvents used in Example 1, Comparative Example 1, and Comparative Example 2 were tested using Topcon silicon wafers, glass powder, and silver powder as substrates, respectively. The contact angles of the organic solvents were measured using a contact angle meter. The contact angles are as follows: Figure 1 As shown, the organic solvent in Example 1 exhibits the smallest contact angle and best wettability. The surface morphology of Sc1, Sc2, and Sc3 was observed using SEM electron microscopy. Figure 3 and Figure 4 As shown, the surface morphology of Sc2 and Sc3 exhibits an uneven texture with numerous pores. This is due to the rapid evaporation of a large amount of organic solvent at a single temperature, resulting in the formation of numerous uneven pores on the silver layer surface, thus affecting the smoothness. Figure 2 As shown, the silver film surface of Sc1 has a smooth morphology. The organic solvent in this proportion evaporates in layers at high temperatures, resulting in smooth and uniform pores. Wetting angle testing using a contact angle meter shows that Example 1 exhibits the smallest contact angle, good wettability, and a smooth surface morphology. In summary, good wettability allows for thorough mixing between the organic carrier and the silver and glass powder particles, ensuring uniform coverage of the conductive paste during screen printing and guaranteeing stable conductivity of the prepared battery.

[0037] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for improving the wettability of conductive silver paste for crystalline silicon solar cells, characterized in that, The wettability of conductive silver paste for crystalline silicon solar cells is improved by using an organic solvent. The conductive silver paste includes silver powder, glass powder, and an organic carrier. The organic carrier is composed of an organic solvent, a binder, a thixotropic agent, a surfactant, and a coupling agent. The organic solvent is a mixed solvent composed of dodecyl alcohol ester, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibutyl phthalate, wherein the mass ratio of dodecyl alcohol ester, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, and dibutyl phthalate is 3:4:2:

1.

2. The method for improving the wettability of conductive silver paste for crystalline silicon solar cells according to claim 1, characterized in that, The conductive silver paste has the following mass percentage content of each component: silver powder 75~90%; glass powder 2~8%; organic carrier 8~17%.

3. The method for improving the wettability of conductive silver paste for crystalline silicon solar cells according to claim 1, characterized in that, The organic carrier has the following mass percentage content of each component: organic solvent 78-85%, binder 8-12%, thixotropic agent 1-3%, surfactant 2-5%, and coupling agent 1-4%.

4. The method for improving the wettability of conductive silver paste for crystalline silicon solar cells according to claim 1, characterized in that, The binder is one or a mixture of ethyl cellulose, acrylic resin, polyisobutylene, nitrocellulose, and phenolic resin.

5. The method for improving the wettability of conductive silver paste for crystalline silicon solar cells according to claim 1, characterized in that, The thixotropic agent is one or more of hydrogenated castor oil, polyamide wax, fumed silica, and organobentonite.

6. The method for improving the wettability of conductive silver paste for crystalline silicon solar cells according to claim 1, characterized in that, The surfactant is one or a mixture of triethanolamine, lecithin, xylene, and Span 85.

7. The conductive silver paste for crystalline silicon solar cells according to claim 1, characterized in that, The coupling agent is one or more of the following: KH570, KH560, and KH550.

8. The application of the conductive silver paste for crystalline silicon solar cells according to claims 1 to 7 in the screen printing fabrication of solar cells.

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