Multi-metal paste for solar cells, electrode metallization method and solar cell

Abstract

The present invention provides a multi-metal paste for a solar cell, an electrode metallization method and a solar cell. The paste includes metal powder, glass powder and an organic carrier; the metal powder includes a first additive phase and a second additive phase; the first additive phase is selected from any at least one of silver powder, gold powder, platinum powder, iridium powder, silver-coated copper powder, and tin-coated copper powder; the second additive phase is selected from any at least one of tungsten powder, molybdenum powder, tungsten alloy powder, and molybdenum alloy powder; the glass powder is selected from any at least one of lead-based glass powder and lead-boron-based glass powder. With the assistance of the glass powder, after the paste is metallized and exposed to light, the Seebeck effect occurs between the mutually contacting metal powders, generating a microscopic electric field. This microscopic electric field can help carriers cross the grain boundaries and preferentially transport in the metal powders with low resistivity, thereby significantly reducing carrier loss, increasing the open-circuit voltage and short-circuit current, and achieving the effect of improving the photoelectric conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular, to a multi-metal paste for solar cells, an electrode metallization method, and a solar cell. Background Art

[0002] For existing electrode pastes for solar cells, silver pastes using silver powder are mostly used at high temperatures, and silver-coated copper pastes are mostly used at low temperatures. Although silver pastes have excellent electrical conductivity and antioxidant properties, the high sintering temperature can cause damage to the cell wafers, and the electrode metallization is carried out by means of instant high temperature in a belt furnace. Therefore, micron or sub-micron silver powder is mostly used in the electrode paste to meet the sintering requirements, and the large number of silver powder grain boundaries existing in the grid lines after metallization limit the further improvement of the conversion efficiency of solar cells due to the loss of carriers. Summary of the Invention

[0003] Aiming at the defects in the prior art, the purpose of the present invention is to provide a multi-metal paste for solar cells, an electrode metallization method, and a solar cell.

[0004] According to the first aspect of the present application, a multi-metal paste for solar cells is provided, which includes metal powder, glass powder, and an organic carrier;

[0005] The metal powder includes a first additive phase and a second additive phase; the first additive phase is selected from any at least one of silver powder, gold powder, platinum powder, iridium powder, silver-coated copper powder, and tin-coated copper powder; the second additive phase is selected from any at least one of tungsten powder, molybdenum powder, tungsten alloy powder, and molybdenum alloy powder;

[0006] The glass powder is selected from any at least one of lead-based glass powder and lead-boron-based glass powder.

[0007] For the multi-metal paste for solar cells provided by this technical solution, since lead-based or lead-boron-based glass powder is used, the activity of lead is greater than that of copper, silver, and other precious metals. Therefore, during sintering, the lead-containing glass will dissolve the metal into the glass body during the heating process and flow and spread to the gaps between the metal powders. When the temperature drops, the metal in the glass will precipitate simultaneously and grow on the surface of the powders, filling the metal components in the powder gaps and interfaces to form a dense contact, resulting in the Seebeck effect occurring between the mutually contacting metal powders after illumination, generating a microscopic electric field. The microscopic electric field can help carriers cross the grain boundaries, accelerate the movement of carriers, thereby reducing the recombination rate of carriers at the interface and improving Isc (i.e., short-circuit current) and Uoc (i.e., open-circuit voltage).

[0008] Preferably, the metal powder further includes a third additive phase, and the third additive phase is silicon powder.

[0009] Preferably, the first additive phase is any at least one of silver powder and silver-coated copper powder.

[0010] In this technical solution, the inventors found that when the additive phase contains silver powder and / or silver-coated copper powder and silicon powder is added thereto, the added silicon powder can form a silver-silicon alloy with silver in the silver powder and silver-coated copper powder. Compared with pure metals, the Seebeck coefficient of the silver-silicon alloy is larger.

[0011] Preferably, the glass powder is a Bi-containing glass powder.

[0012] The metal activity series is ranked from strongest to weakest as: K, Ca, Na, Mg, Al, Zn, Fe, Sn, Pb, (H), Cu, Hg, Ag, Pt, Au. Both Pb and Bi are common elements in the glass design for photovoltaic applications, and both can achieve good contact effects. Among them, due to its stronger reaction activity and better contact effect, Pb has always been a difficult-to-replace element. In existing electrode pastes, the conductive phase is generally silver. Pb glass powder will react with silver at the beginning stage of the electrode metallization process to form silver oxide. However, since the activity of Pb is stronger than that of Ag, Ag will re-precipitate as a single substance in the later stage of the reaction and become the conductive component in the electrode. However, the inventors found that when the conductive phase contains easily oxidized base metals such as copper-coated tin, the base metals (such as Sn) will also be replaced by lead to form oxides in the early stage of the reaction. However, because the activity of Sn is stronger than that of Pb, it will not re-precipitate as a single metal in the later stage of the reaction but will always remain in the form of oxides, which reduces the proportion of the conductive component in the electrode and increases the proportion of the non-conductive phase, which is not conducive to the fill factor and conversion efficiency. After using the Bi-containing glass powder, Bi elements replace part of the Pb elements, which can not only ensure the contact effect of the electrode paste but also reduce the oxidation of base metals such as Sn. Therefore, pastes containing highly active metals such as copper-coated tin have better effects with Bi-containing glass powder (it should be noted that Bi cannot completely replace Pb because using relatively weakly active elements requires a higher sintering temperature, which will damage the battery chips. Therefore, a sufficient amount of Pb is required to ensure the Ohmic contact of the electrode under instantaneous high temperature. If Bi elements are used completely, a higher sintering temperature will be required, which is not conducive to the final conversion efficiency of the battery chips. Therefore, the lead glass powder system containing Bi is the best choice after comprehensively considering the reaction activity, oxidation degree, and sintering temperature).

[0013] Preferably, the tungsten alloy powder is selected from any at least one of tungsten-molybdenum alloy powder, niobium-tungsten alloy powder, tungsten-cobalt alloy powder, tungsten-nickel alloy powder, and tungsten-titanium alloy powder; the molybdenum alloy powder is selected from any at least one of titanium-molybdenum alloy powder, molybdenum-rhenium alloy powder, and hafnium-molybdenum alloy powder.

[0014] Preferably, the tungsten alloy powder is tungsten-molybdenum alloy powder, and the molybdenum alloy powder is titanium-molybdenum alloy powder.

[0015] Preferably, by mass percentage, the composition of the metal powder is: 60% - 99% of the first additive phase and 1% - 40% of the second additive phase.

[0016] In this technical solution, the inventor found through many experiments that for the multi-metal conductive paste in this application, on the one hand, due to the use of lead-based or lead-boron-based glass powder, the activity of lead is greater than that of copper, silver, and other precious metals. Therefore, during sintering, the lead-containing glass will dissolve the metal into the vitreous body during the heating process and flow and spread into the gaps between metal powders. When cooling, the metal in the glass will precipitate simultaneously and grow on the surface of the powders, filling the metal components in the powder gaps and interfaces to form dense contacts, resulting in the Seebeck effect occurring between the mutually contacting metal powders after illumination, generating a microscopic electric field. The microscopic electric field can help carriers cross the grain boundaries, accelerate the movement of carriers, thereby reducing the recombination rate of carriers at the interface and improving Isc and Uoc. On the other hand, due to the addition of tungsten, molybdenum metals or their alloys, which have poor conductivity, the line resistance increases, thereby reducing FF (i.e., the fill factor), causing a negative effect. Therefore, the amount of increase in Eta (i.e., the conversion efficiency) depends on these positive and negative effects. The inventor found that when the amount of the second additive phase is controlled within the range of 1% - 40%, the improvement effect of Eta is more ideal. At the same time, the addition of tungsten powder can reduce the amount of silver used, achieving the effect of cost reduction and efficiency improvement.

[0017] Preferably, by mass percentage, the composition of the metal powder is: 60% - 99% of the first additive phase, 1% - 40% of the second additive phase, and 0.01% - 20% of the third additive phase.

[0018] Preferably, by mass percentage, the composition of the paste is: 45% - 95% of the metal powder, 0.1% - 10% of the glass powder, and 5% - 55% of the organic carrier.

[0019] According to the second aspect of the present application, a method for metallizing a solar cell electrode is provided, including the following steps:

[0020] Screen-print the multi-metal paste for solar cells described in any one of the above on the surface of the solar cell wafer, dry it, and sinter it in air at 500 - 750 °C to obtain a sintered cell wafer.

[0021] Preferably, it further includes the following step: subject the obtained sintered cell wafer to laser enhanced sintering and apply a reverse deflection voltage simultaneously to complete the metallization of the solar cell wafer.

[0022] In this technical solution, the laser enhanced sintering process is added. Laser enhanced sintering maximally retains the original passivation layer and avoids the carrier recombination caused by the direct contact between the metal and the silicon substrate, improving Uoc, thereby enhancing Eta.

[0023] According to the third aspect of the present application, a solar cell is provided, which is prepared by using the solar cell electrode metallization method described in any one of the above.

[0024] Preferably, the solar cell is a solar cell with a P region on the front and an N region on the back, or an N region on the front and a P region on the back, or a BC back-contact solar cell with a P region on the back and an N region on the back.

[0025] Compared with the prior art, the present invention has the following beneficial effects: [[ID=⑧]]

[0026] The multi-metal paste for solar cells provided by the present invention, with the assistance of specially selected glass powder, after metallization, due to the different thermal conductivities between different metal powders, the Seebeck effect will occur in the metal powders in contact with each other under illumination, generating a microscopic electric field. This microscopic electric field can help carriers cross the grain boundaries and preferentially transport in the metal powders with low resistivity, thereby significantly reducing carrier loss, increasing the open-circuit voltage and short-circuit current, and achieving the effect of improving the photoelectric conversion efficiency. Moreover, in the present invention, the second additive phase contained in the metal powder is selected from tungsten powder, molybdenum powder, tungsten alloy powder, molybdenum alloy powder, etc. The addition of these powders can reduce the amount of silver used, thereby also achieving the effect of cost reduction and efficiency improvement. Detailed Embodiments

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application.

[0028] The following detailed description of the embodiments of the present application is not intended to limit the scope of the present application claimed, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0029] Examples and Comparative Examples

[0030] Example 1

[0031] Example 1 provides a multi-metal paste for solar cells, and its preparation steps are as follows:

[0032] S1. First, put 3 g of C-type glass powder and 7 g of organic carrier into the wide-mouth bottle of a planetary mixer, stir evenly with a spatula, and mix for 3 min at a rotation speed of 800 rpm with the planetary mixer. Then grind 4 times with a three-roll grinder, and test that its grinding fineness is less than 5 μm to obtain a uniformly mixed glass powder solution.

[0033] S2. Add 90 g of metal powder to the glass powder solution obtained in step S1, and stir evenly with a spatula; then mix with a planetary mixer at a speed of 800 rpm for 3 min to obtain a sample slurry.

[0034] Among them, the composition of the metal powder is 80 wt% silver powder and 20 wt% tungsten powder; the C-type glass powder is made by mixing 80 wt% PbO, 1 wt% SiO2 and 19 wt% B2O3, quenching and grinding; the organic carrier is a mixture of ethyl cellulose, butyl carbitol acetate and alcohol ester-12 mixed in a mass ratio of 1.5:2.7:2.7.

[0035] S3. Grind the sample slurry obtained in S2 with a three-roll grinder 5 times, test that its grinding fineness is less than 10 μm, and the Brookfield viscosity is between 300-350 Pa·s to prepare a multi-metal conductive paste for front P-region metallization.

[0036] Example 2

[0037] Example 2 provides a multi-metal paste for solar cells, which is only different from Example 1 in that: by mass percentage, the composition of the metal powder is 99 wt% silver powder and 1 wt% tungsten powder.

[0038] Example 3

[0039] Example 3 provides a multi-metal paste for solar cells, which is only different from Example 1 in that: by mass percentage, the composition of the metal powder is 60 wt% silver powder and 40 wt% tungsten powder.

[0040] Example 4

[0041] Example 4 provides a multi-metal paste for solar cells, which is only different from Example 1 in that: by mass percentage, the composition of the metal powder is 80 wt% silver powder, 10 wt% molybdenum powder and 10 wt% silicon powder.

[0042] Example 5

[0043] Example 5 provides a multi-metal paste for solar cells, which is only different from Example 1 in that: by mass percentage, the composition of the metal powder is 80 wt% silver powder, 10 wt% tungsten powder and 10 wt% silicon powder.

[0044] Example 6

[0045] Example 6 provides a multi-metal paste for solar cells, which is only different from Example 1 in that: by mass percentage, the composition of the metal powder is 80 wt% silver powder and 20 wt% titanium molybdenum alloy powder.

[0046] Example 7

[0047] Example 7 provides a multi-metal paste for solar cells, which is different from Example 1 only in that: by mass percentage, the composition of the metal powder is 80 wt% silver powder and 20 wt% tungsten-molybdenum alloy powder.

[0048] Example 8

[0049] Example 8 provides a multi-metal paste for solar cells, which is different from Example 1 only in that: by mass percentage, the composition of the metal powder is 40 wt% silver powder, 40 wt% silver-coated copper powder, and 20 wt% tungsten powder.

[0050] Example 9

[0051] Example 9 provides a multi-metal paste for solar cells, which is different from Example 1 in that: by mass percentage, the composition of the metal powder is 40 wt% silver powder, 40 wt% tin-coated copper powder, and 20 wt% tungsten powder.

[0052] Examples 10, 15

[0053] Examples 10, 15 provide a multi-metal paste for solar cells, which is different from Example 9 in that: the glass powder used is Type A glass powder, which is made by mixing 75 wt% PbO, 1 wt% Li2CO3, 0.5 wt% SiO2, 0.5 wt% Al2O3, 11.5 wt% B2O3, and 11.5 wt% Bi2O3 and then quenching and grinding.

[0054] Example 11

[0055] Example 11 provides a multi-metal paste for solar cells, which is different from Example 9 only in that: the glass powder used is Type B glass powder, which is made by mixing 30 wt% PbO, 5 wt% Li2CO3, 10 wt% B2O3, 45 wt% Bi2O3, and 10 wt% ZnO and then quenching and grinding.

[0056] Examples 12, 14

[0057] Examples 12, 14 provide a multi-metal paste for solar cells, which is different from Example 8 only in that: the prepared multi-metal conductive paste is used for backside N-region metallization.

[0058] Example 13

[0059] Example 13 provides a multi-metal paste for solar cells, which is different from Example 12 only in that: the prepared multi-metal conductive paste is used for frontside P-region metallization.

[0060] Example 16

[0061] Example 16 provides a multi-metal paste for solar cells, which is different from Example 11 only in that: the prepared multi-metal conductive paste is used for back N-region metallization.

[0062] Example 17

[0063] Example 17 provides a multi-metal paste for solar cells, which is different from Example 8 only in that: by mass percentage, the metal powder is 90 wt%, the glass powder is 4 wt%, and the organic carrier is 6 wt%; the prepared conductive paste is used for the P-region and N-region on the back of the BC cell.

[0064] Comparative Example 1

[0065] Comparative Example 1 provides a multi-metal paste for solar cells, which is different from Example 1 only in that: all the metal powders are silver powders.

[0066] Comparative Example 2

[0067] Comparative Example 2 provides a multi-metal paste for solar cells, which is different from Comparative Example 1 only in that: the prepared conductive paste is used for back N-region metallization.

[0068] Comparative Example 3

[0069] Comparative Example 3 provides a multi-metal paste for solar cells, which is different from Example 17 in that: all the metal powders are silver powders.

[0070] The formulations and applications of the multi-metal pastes provided in the above examples and comparative examples are shown in Table 1 below:

[0071] Table 1

[0072]

[0073] In the above examples and comparative examples, the formulations of A-type, B-type, and C-type glass powders are shown in Table 2 below:

[0074] Table 2

[0075]

[0076] Experimental group and control group

[0077] Experimental Group 1

[0078] Experimental Group 1 provides an electrode metallization method and a solar cell, and its preparation steps are as follows:

[0079] S1. On the back N region of the TOPCon cell, screen-print the conductive silver paste in Comparative Example 2 using a screen (screen parameters: 480 - 11 - M14E4 - 22μm, no mesh knots). Under the condition of a belt speed of 12000 mm / min, dry it at a peak temperature of 200°C for 30 s.

[0080] S2. On the front P region of the TOPCon cell printed with the back N region grid lines, screen-print the conductive paste in Example 1 using a screen (screen parameters: 480 - 11 - M14E4 - 22μm, no mesh knots). Under the condition of a belt speed of 12000 mm / min, dry it at a peak temperature of 200°C for 30 s.

[0081] S3. Place the TOPCon cell obtained in Step S2 into a sintering furnace and sinter it in an air atmosphere under the condition of a belt speed of 12000 mm / min. Among them, the peak temperature is 740°C and the sintering time is 1.5 min.

[0082] Experimental Group 2

[0083] Experimental Group 2 provides an electrode metallization method and a solar cell. The difference from Experimental Group 1 is only that: screen-print the conductive paste in Example 2 on the front P region.

[0084] Experimental Group 3

[0085] Experimental Group 3 provides an electrode metallization method and a solar cell. The difference from Experimental Group 1 is only that: screen-print the conductive paste in Example 3 on the front P region.

[0086] Experimental Group 4

[0087] Experimental Group 4 provides an electrode metallization method and a solar cell. The difference from Experimental Group 1 is only that: screen-print the conductive paste in Example 4 on the front P region.

[0088] Experimental Group 5

[0089] Experimental Group 5 provides an electrode metallization method and a solar cell. The difference from Experimental Group 1 is only that: screen-print the conductive paste in Example 5 on the front P region.

[0090] Experimental Group 6

[0091] Experimental Group 6 provides an electrode metallization method and a solar cell. The difference from Experimental Group 1 is only that: screen-print the conductive paste in Example 6 on the front P region.

[0092] Experimental Group 7

[0093] Experimental group 7 provides a method for electrode metallization and a solar cell, the difference from experimental group 1 being only that: the conductive paste in Example 7 is screen-printed on the front P region.

[0094] Experimental group 8a

[0095] Experimental group 8a provides a method for electrode metallization and a solar cell, the difference from experimental group 1 being only that: the conductive paste in Example 8 is screen-printed on the front P region.

[0096] Experimental group 8b

[0097] Experimental group 8b provides a method for electrode metallization and a solar cell, the difference from experimental group 8a being only that: in step S3, the peak temperature is 710 °C, the sintering time is 1.5 min, to obtain the first sintered cell sheet; and it further includes step S4, laser enhanced sintering the first sintered cell sheet while applying a reverse deflection voltage to complete the metallization of the crystalline silicon solar cell; wherein, the power of the laser beam corresponding to the laser enhanced sintering is 30 W, the scanning time of the laser beam is 1 s, and the reverse deflection voltage is 20 V.

[0098] Experimental group 9

[0099] Experimental group 9 provides a method for electrode metallization and a solar cell, the difference from experimental group 1 being that: the conductive paste in Example 9 is screen-printed on the front P region.

[0100] Experimental group 10

[0101] Experimental group 10 provides a method for electrode metallization and a solar cell, the difference from experimental group 1 being that: the conductive paste in Example 10 is screen-printed on the front P region.

[0102] Experimental group 11

[0103] Experimental group 11 provides a method for electrode metallization and a solar cell, the difference from experimental group 1 being that: the conductive paste in Example 11 is screen-printed on the front P region.

[0104] Experimental group 12

[0105] Experimental group 12 provides a method for electrode metallization and a solar cell, the difference from experimental group 1 being that: the conductive paste in Example 12 is screen-printed on the back N region of the TOPCon cell sheet, and the conductive paste in Comparative Example 1 is screen-printed on the front P region.

[0106] Experimental group 13

[0107] Experimental Group 13 provides a method for electrode metallization and a solar cell, which is different from Experimental Group 1 in that: the conductive paste in Example 14 of screen printing on the back N region of the TOPCon cell; the conductive paste in Example 13 of screen printing on the front P region; and in step S3, the peak temperature is 600 °C and the sintering time is 1.5 min to obtain the first sintered cell; and it includes step S4, laser enhanced sintering the first sintered cell while applying a reverse deflection voltage to complete the metallization of the crystalline silicon solar cell; wherein, the power of the laser beam corresponding to the laser enhanced sintering is 30 W, the scanning time of the laser beam is 1 s, and the reverse deflection voltage is 20 V.

[0108] Experimental Group 14

[0109] Experimental Group 14 provides a method for electrode metallization and a solar cell, which is different from Experimental Group 13 only in that: the conductive paste in Example 16 of screen printing on the back N region of the TOPCon cell; the conductive paste in Example 15 of screen printing on the front P region.

[0110] Experimental Group 15

[0111] Experimental Group 15 provides a method for electrode metallization and a solar cell, which is different from Experimental Group 1 in that: the prepared multi-metal conductive paste is used for the metallization of the BC cell; the conductive paste in Example 17 is screen printed on both the N region and the P region.

[0112] Control Group

[0113] Control Group 1a

[0114] Control Group 1a provides a method for electrode metallization and a solar cell, which is different from Experimental Group 1 only in that: the conductive paste in Comparative Example 1 is screen printed on the front P region of the TOPCon cell.

[0115] Control Group 1b

[0116] Control Group 1b provides a method for electrode metallization and a solar cell, which is different from Comparative Example 1a only in that: in step S3, the peak temperature is 710 °C and the sintering time is 1.5 min to obtain the first sintered cell; and it also includes step S4, laser enhanced sintering the first sintered cell while applying a reverse deflection voltage to complete the metallization of the crystalline silicon solar cell; wherein, the power of the laser beam corresponding to the laser enhanced sintering is 30 W, the scanning time of the laser beam is 1 s, and the reverse deflection voltage is 20 V.

[0117] Control Group 2

[0118] The comparative group 2 provides a method for electrode metallization and a solar cell, and the only difference from the experimental group 15 is that: the conductive paste in Comparative Example 3 is screen-printed on both the P region and the N region on the back of the BC cell.

[0119] Performance detection test

[0120] For the solar cells prepared by the metallization methods of the experimental groups 1-15 and the comparative groups 1 and 2 of the present invention, the following performance detections are carried out.

[0121] Electrical performance

[0122] The commercially available IV tester "YP-CX5000" obtained from Ziyuan Spectrum Intelligence is used to characterize the solar cell at 25 °C ± 1.0 °C. The stroboscopic pulsed light simulates sunlight, and its AM1.5 intensity on the cell surface is known to be 1000 W / m 2 . In order to make the simulator have this intensity, the stroboscopic pulsed light flashes several times in a short time until a stable level monitored by the "1.0.0.0" software of the IV tester is reached. The Ziyuan Spectrum IV tester uses a multi-point contact method to measure the current (I) and voltage (V) to determine the IV curve of the cell. All values are automatically determined from this curve by running the software package. As a reference standard sample, a calibrated solar cell obtained from ISE Freiburg and having the same area size, the same wafer material, and using the same front pattern is tested, and the data is compared with the certified values. At least 5 wafers processed in a very same manner are measured, and the data is analyzed by calculating the average value of each value. The software provides the values of conversion efficiency, fill factor, short-circuit current, series resistance, grid line resistance, and open-circuit voltage.

[0123] Tables 3 and 4 show the relevant data of the experimental groups. Among them, the relative gains or attenuations of the conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of experimental groups 1-8a and experimental groups 9-12 compared with control group 1a are shown; the relative gains or attenuations of the conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of experimental group 8b and experimental groups 13, 14 compared with control group 1b are shown; the relative gains or attenuations of the conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of experimental group 15 compared with control group 2 are shown (Note: Due to the confidentiality requirements of the company to which the battery products involved in control group 2 belong, the experimental data of control group 2 are not provided in this application); among them, ΔEta refers to the converted efficiency value of the relative gain or attenuation, and its unit is %, when the conversion efficiency has a relative gain, the data is positive, and when the conversion efficiency has a relative attenuation, the data is negative; ΔUoc refers to the open-circuit voltage value of the relative gain or attenuation, and its unit is mV, when the open-circuit voltage has a relative gain, the data is positive, and when the open-circuit voltage has a relative attenuation, the data is negative; ΔIsc refers to the short-circuit current value of the relative gain or attenuation, and its unit is A, when the short-circuit current has a relative gain, the data is positive, and when the short-circuit current has a relative attenuation, the data is negative; ΔFF refers to the fill factor value of the relative gain or attenuation, and its unit is %, when the fill factor has a relative gain, the data is positive, and when the fill factor has a relative attenuation, the data is negative.

[0124] Table 3

[0125]

[0126] Table 4

[0127]

[0128] The following details the technical effects of this application with respect to the test data.

[0129] From the test data of experimental groups 1-15, it can be seen that for the multi-metal conductive paste in this application, on the one hand, due to the use of lead-based or lead-boron-based glass powder, the activity of lead is greater than that of copper, silver, and other precious metals. Therefore, during sintering, the lead-containing glass will dissolve the metal into the vitreous body during the heating process and flow and spread to the gaps between the metal powders. When cooling, the metals in the glass will precipitate simultaneously and grow on the surface of the powders, filling the metal components in the powder gaps and interfaces to form a dense contact, resulting in the Seebeck effect occurring between the mutually contacting metal powders after illumination, generating a microscopic electric field. The microscopic electric field can help carriers cross the grain boundaries, accelerating the movement of carriers, thereby reducing the recombination rate of carriers at the interface and increasing Isc and Uoc; on the other hand, due to the addition of tungsten, molybdenum metals or their alloys with poor conductivity, the wire resistance increases, thereby reducing FF, causing a negative effect. Therefore, the increase in Eta depends on these positive and negative effects.

[0130] From the test data of experimental groups 1-3, it can be seen that in this application, conductive pastes are prepared from Ag-W metal powders with three different mixing ratios (Ag:W by mass ratio of 4:1, 99:1, 3:2), and screen-printed on the P region of the front side of TOPCon solar cells. For the conductive paste prepared by mixing Ag and W in a mass ratio of 99:1 in experimental group 2, the Eta increases by 0.01%. This shows that with only a very small addition amount, the Seebeck effect can be generated, thereby increasing Eta. As the content of tungsten powder increases, Eta first increases and then decreases. This is because the increase in the content of tungsten powder causes the Seebeck effect to become stronger, thereby increasing Eta. However, when the content of tungsten powder is too high, the line resistance increases, resulting in a decrease in FF. The negative effect is close to the positive gain generated by the Seebeck effect, ultimately leading to a decrease in the Eta increase amount. Therefore, the addition of tungsten powder can increase Eta due to the Seebeck effect, and when the amount of tungsten powder is controlled at an appropriate level, the increase in Eta can be more significant. At the same time, the addition of tungsten powder can reduce the amount of silver used, achieving the effect of cost reduction and efficiency improvement.

[0131] From the test data of experimental groups 4-7, it can be seen that in experimental groups 4-5, silicon powder is added, and silver-silicon alloy is formed by silicon and silver at high temperature. While in experimental groups 6-7, titanium-molybdenum alloy and tungsten-molybdenum alloy are directly added. The Seebeck coefficient of pure metals is small, and that of alloys is large. Therefore, the Eta of experimental groups 4-7 increases significantly. However, due to the conductivity: tungsten > molybdenum > titanium, the line resistances formed after sintering are different, and the negative effects caused by the line resistance loss are different, resulting in different improvement ranges of the conversion efficiency.

[0132] From the test data of control group 1a and control group 1b, it can be seen that in this application, compared with the sintering in air at 740 °C in control group 1a, control group 1b using the process of sintering in air at 710 °C and then combining with laser enhanced sintering can obtain TOPCon solar cells with higher conversion efficiency. This is because laser enhanced sintering maximally retains the original passivation layer and avoids the carrier recombination caused by the direct contact between the metal and the silicon matrix, improving Uoc, thereby increasing Eta. From the test data of experimental groups 8a and 8b, it can be seen that due to the existence of the Seebeck effect, the conversion efficiency can be further increased on the basis of laser enhanced sintering. At the same time, because the Seebeck coefficients of silver and copper are the same, silver-coated copper can be directly used instead of silver as the conductive phase to achieve the effect of cost reduction and efficiency improvement.

[0133] It can be seen from the test data of experimental groups 9-11 that experimental groups 9-11 used C-type, A-type, and B-type glass powders respectively. Among them, the efficiency improvement of experimental group 10 was the largest, and that of experimental group 9 was the smallest. The conductive phase of experimental groups 9-11 all adopted tin-coated copper powder. The difference is that both experimental group 10 and experimental group 11 used lead glass powder containing Bi, while experimental group 9 used lead glass powder without Bi. The reason for the smallest efficiency improvement in experimental group 9 is as follows:

[0134] In terms of metal activity, there is a relationship of K>Ca>Na>Mg>Al>Zn>Fe>Sn>Pb>Cu>Hg>Ag>Pt>Au. Both Pb and Bi are common elements in glass design for photovoltaic applications, and both can achieve good contact effects. Among them, Pb has always been a difficult element to replace because of its stronger reaction activity and better contact effect. Pb glass powder will react with silver at the beginning stage of the electrode metallization process to form silver oxide. However, because the activity of Pb is stronger than that of Ag, Ag will be redeposited as a single substance in the later stage of the reaction and become the conductive component in the electrode (the one with stronger activity will eventually exist in the form of an oxide). Pb glass powder cannot produce the optimal effect when coating with tin-coated copper. The reason is that base metals (such as Sn) will also be replaced by lead to form oxides in the early stage of the reaction, and because the activity of Sn is stronger than that of Pb, it will not be redeposited as a single metal in the later stage of the reaction but will always remain in the form of an oxide, which reduces the proportion of the conductive component in the electrode and increases the proportion of the non-conductive phase, which is not conducive to the improvement of the fill factor and conversion efficiency. By using Bi element to replace a part of Pb element, not only can the contact effect of the electrode paste be ensured, but also the oxidation of base metals such as Sn can be reduced. Therefore, the paste containing high-activity metals such as tin-coated copper has a better effect with Bi-containing glass powder (note: Bi cannot completely replace Pb because using relatively low-activity elements will require a higher sintering temperature, which will damage the battery chip. Therefore, a sufficient amount of Pb is needed to ensure the Ohmic contact of the electrode under instantaneous high temperature. If Bi element is used completely, a higher sintering temperature will be required, which is not conducive to the final conversion efficiency of the battery chip. Therefore, experimental groups 10 and 11 used lead glass powder containing Bi, which is a balance sought after considering the reaction activity, oxidation degree, and sintering temperature of substances).

[0135] Therefore, the effect of using Bi-containing glass powder in the multi-metal conductive paste containing tin-coated copper is the best.

[0136] It can be seen from the test data of experimental group 8a and experimental group 12 that in this application, no matter whether the multi-metal conductive paste is printed on the front P region or the back N region of the TOPCon battery chip, the positive gain of Eta caused by the Seebeck effect always exists, but the efficiency improvement is greater when the multi-metal conductive paste is printed on the front P region of the TOPCon battery chip.

[0137] From the test data of experimental groups 13 - 14, it can be seen that in experimental group 13, the conductive paste in Example 14 composed of silver - silver - coated copper - tungsten with glass powder of type C was printed on the back N - region of the TOPCon cell, and the conductive paste in Example 13 composed of silver - silver - coated copper - tungsten with glass powder of type C was printed on the front P - region; in experimental group 14, the conductive paste in Example 16 composed of silver - tin - coated copper - tungsten with glass powder of type B was printed on the back N - region of the TOPCon cell, and the conductive paste in Example 15 composed of silver - tin - coated copper - tungsten with glass powder of type A was printed on the front P - region. Moreover, the metallization method in experimental groups 13 - 14 was sintering in air at 600 °C combined with the laser - enhanced sintering process. The sintering temperature was significantly reduced (low - temperature sintering has less damage to the cell and has an energy - saving effect), and the conversion efficiency still had a large increase.

[0138] From the test comparison data between experimental group 15 and control group 2, it can be seen that the conductive paste prepared with the conductive phase of silver - silver - coated copper - tungsten mixed in a mass ratio of 2:2:1 and glass powder of type C in Example 17 was used for metallization of the back P - region and N - region of the BC cell. With the assistance of the lead - based glass powder, the Seebeck effect was generated at the metal interface junction, creating a microscopic electric field, accelerating the movement of carriers, reducing the carrier recombination rate, and improving Eta; at the same time, due to the addition of W, the amount of silver used was reduced, achieving the effect of cost reduction and efficiency improvement.

[0139] The specific embodiments of the present invention have been described above. Through the above - described description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention.

Claims

1. A method for metallizing the electrodes of a solar cell, characterized in that, It includes the following steps: Screen-print multi-metal paste for solar cells on the surface of solar cell wafers, dry, and sinter in air at 500 - 750 °C to obtain sintered cell wafers; The multi-metal paste for solar cells includes metal powder, glass powder, and an organic carrier; The metal powder includes a first additive phase and a second additive phase; the first additive phase is selected from any at least one of silver powder, gold powder, platinum powder, iridium powder, silver-coated copper powder, and tin-coated copper powder; the second additive phase is selected from any at least one of tungsten powder, molybdenum powder, tungsten alloy powder, and molybdenum alloy powder; The glass powder is lead-based glass powder; During sintering, the lead-containing glass melts the metal during the heating process and enters the glass body, flowing and spreading into the gaps between each metal powder. When cooling, the metal in the glass precipitates simultaneously and grows on the surface of the powder, filling the metal components in the powder gaps and interfaces to form a dense contact, resulting in the Seebeck effect occurring between the metal powders in contact after illumination.

2. The method for metallizing a solar cell electrode according to claim 1, wherein The metal powder further includes a third additive phase, and the third additive phase is silicon powder.

3. The method for metallizing the electrode of a solar cell according to claim 2, wherein, The first additive phase is any at least one of silver powder and silver-coated copper powder.

4. The method for metallization of a solar cell electrode according to claim 1, characterized in that, The glass powder is Bi-containing glass powder.

5. The method for metallizing a solar cell electrode according to claim 1, wherein The tungsten alloy powder is selected from any at least one of tungsten molybdenum alloy powder, niobium tungsten alloy powder, tungsten cobalt alloy powder, tungsten nickel alloy powder, and tungsten titanium alloy powder; the molybdenum alloy powder is selected from any at least one of titanium molybdenum alloy powder, molybdenum rhenium alloy powder, and hafnium molybdenum alloy powder.

6. The method for metallizing a solar cell electrode according to claim 1, characterized in that, The tungsten alloy powder is tungsten molybdenum alloy powder, and the molybdenum alloy powder is titanium molybdenum alloy powder.

7. The method for metallizing a solar cell electrode according to claim 1, characterized in that, By mass percentage, the composition of the metal powder is: 60% - 99% of the first additive phase and 1% - 40% of the second additive phase.

8. The method for metallizing a solar cell electrode according to claim 2, wherein By mass percentage, the composition of the metal powder is: 60% - 99% of the first additive phase, 1% - 40% of the second additive phase, 0.01% - 20% of the third additive phase, and the total amount of the metal powder is 100%.

9. The method for metallizing a solar cell electrode according to claim 1, wherein By mass percentage, the composition of the paste is: 45% - 95% of the metal powder, 0.1% - 10% of the glass powder, and 5% - 55% of the organic carrier, and the total amount of the paste is 100%.

10. The method for metallizing a solar cell electrode according to claim 1, characterized in that, It further includes the following steps: subject the obtained sintered cell wafers to laser enhanced sintering and apply a reverse deflection voltage simultaneously to complete the metallization of the solar cell wafers.

11. A solar cell, characterized in that, Prepared by using the method for metallizing the solar cell electrode according to any one of claims 1 to 10.

12. The solar cell according to claim 11, characterized in that, The solar cell is a solar cell with a front P region and a back N region, or a front N region and a back P region, or a BC back-contact solar cell with a back P region and a back N region.

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