Inorganic glass powder composition, inorganic glass powder, conductive paste and application thereof

Abstract

The invention provides an inorganic glass powder composition, inorganic glass powder, conductive paste and application thereof. The inorganic glass powder composition comprises an oxide and / or a compound forming the oxide; wherein the composition of cation elements in the composition is Pba-Bib-Sic-Znd-Be-Mf, and M is other cation elements; the molar ratio of a, b, c, d, e and f is as follows: a is 0%-25%, b is 20%-42%, and c is 5%-15%; d is 8%-33%, and e is 0%-15%; a + b + c + d + e + f = 100%. The invention also provides inorganic glass powder prepared from the composition, conductive paste prepared from the inorganic glass powder and a solar cell. The inorganic glass powder or conductive paste can greatly improve the acetic acid corrosion resistance of the Topcon battery, and has excellent contact performance.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to an inorganic glass powder composition suitable for a Topcon cell laser-assisted sintering process, inorganic glass powder and conductive slurry, and applications thereof. Background Art

[0002] Crystalline silicon solar cells generate electricity using the photovoltaic effect. The cell forms a PN junction through diffusion, and then a passivation layer is plated on the front and back to reduce surface recombination. Then, a conductive paste is screen-printed on the passivation layer to form a metal grid line to collect photogenerated carriers. Then EVA and glass are placed on the front of the solar cell, and EVA and a backplane (or glass) are placed on the back through lamination. Finally, they are packaged into photovoltaic modules. The photovoltaic module generally has a lifespan of 25 years, and the reliability requirements of the product are relatively high. During use, the EVA in the module will decompose a small amount of acetic acid to corrode the metal grid of the cell, causing the power attenuation of the photovoltaic module and affecting the service life. Especially for the current mainstream Topcon-LECO (laser-assisted sintering) battery technology route in the market, the velvet on the front of the cell becomes smaller, forming a smoother surface. At the same time, with low unit consumption, cost reduction and efficiency improvement, the reliability requirements for the cell are getting higher and higher. Similarly, higher requirements are also put forward for the acetic acid corrosion resistance of photovoltaic electronic paste.

[0003] However, the existing conductive pastes generally mainly consider how to improve the conversion efficiency and welding tension of solar cells, and lack research on the acetic acid corrosion resistance of the conductive paste.

[0004] After the printing of the cell is completed, the paste enters the high-temperature sintering stage. In this stage, the organic matter in the paste volatilizes or decomposes and eliminates. At the same time, the glass powder reacts with the surface of the silicon wafer to finally form a dense metallic silver conductive layer and complete the sintering contact. The lead oxide, bismuth oxide, etc. in the glass powder will participate in the reaction of the anti-reflection layer silicon nitride and silicon oxynitride on the surface of the silicon wafer to destroy the anti-reflection layer, and promote the glass liquid in the high-temperature molten state to form a contact surface with the silicon substrate. Boron oxide mainly plays a role in reducing the melting point of the glass powder in this process, which is conducive to the flow of the molten glass liquid under high-temperature fast burning. At the same time, it has a certain strengthening effect on the B element doping on the front of the cell, which is more conducive to the reduction of the front resistance. Therefore, the existing glass powder usually contains a considerable amount of lead oxide and boron oxide content to meet the requirements of reducing the contact resistance and forming a good silver-silicon contact. However, lead oxide easily reacts with acetic acid (PbO+2CH3COOH---(CH3COO)2Pb+2H2O), resulting in a decrease in the corrosion resistance of the paste to acetic acid. Summary of the invention

[0005] In order to solve the above-mentioned problem of acetic acid corrosion resistance of Topcon batteries, the present invention proposes an inorganic glass powder composition, inorganic glass powder and conductive slurry and their applications suitable for the laser assisted sintering (LECO) process of Topcon batteries. The inorganic glass powder composition can not only greatly improve the acetic acid corrosion resistance of Topcon batteries, but also meet the metallization process of the front side of N-type batteries to form good contact.

[0006] In order to achieve the above object, the present invention provides an inorganic glass powder composition, which comprises an oxide of a cationic element and / or a compound capable of forming an oxide of a cationic element; wherein the cationic element composition of the composition is: Pb a -Bi b -Si c -Zn d -B e- M f , M is a cationic element other than lead, bismuth, silicon, zinc, and boron;

[0007] a, b, c, d, e, and f are the molar proportions of lead, bismuth, silicon, zinc, boron, and M in the cationic elements of the composition, respectively; the values ​​of a, b, c, d, e, and f satisfy equations 1 to 3 at the same time:

[0008] Formula 1: 0%≤a≤25%, 20%≤b≤42% and 5%≤c≤15% (i.e., all three formulas are satisfied at the same time);

[0009] Formula 2: 8%≤d≤33% and 0%≤e≤15% (both relations are satisfied at the same time);

[0010] Formula 3: a+b+c+d+e+f=100%.

[0011] In the above-mentioned inorganic glass powder composition, the cationic element may specifically include at least one of a metal element and a non-metal element (an element having similar properties to a metal element and capable of forming a cation, such as Si, Te, B, P, etc.).

[0012] In some specific embodiments, the compound capable of forming an oxide includes carbonates, etc. Among them, "carbonate" includes not only various elements and carbonate (CO3 2- ) formed, also includes bicarbonate (acid carbonate) and basic carbonate.

[0013] In the above inorganic glass powder composition, bismuth-silicon-zinc is the network skeleton of the glass system, which not only has a certain reactivity, but also can prevent excessive damage to the silicon nitride layer, has good glass-forming ability, and has a good glass state. Inorganic glass powder with a good glass state has less crystal precipitation and weak reactivity with acetic acid, so the acid resistance is improved. Lead is a network intermediate that can reduce the softening point of glass and enhance the corrosion of glass to the silicon nitride layer on the surface of the silicon wafer. Boron can adjust the fluidity of the glass.

[0014] In the above inorganic glass powder composition, Bi, Si, Zn, M (such as Cu, Mn, Ti, etc.) can improve the inhibition of glass reaction activity, prevent excessive corrosion, protect the silicon nitride layer, and improve the glass state; Pb, Bi, B, M (Li, Na, etc.) elements can adjust the glass melting point and sintering activity. By improving the glass state and controlling the content of alkali metals and alkaline earth metals, the acid resistance of the glass powder can be improved.

[0015] In the inorganic glass powder composition, a is generally 0%-25%, for example, 0%, 5%, 10%, 15%, 20%, 25% and other specific values, and a range with any two of the above specific values ​​as endpoints. In some specific embodiments, the molar proportion of lead in the metal element can be further controlled to: 5%≤a≤15%.

[0016] In the above inorganic glass powder composition, b is generally 20%-42%, for example, 20%, 25%, 30%, 35%, 40%, 42% and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. In some specific embodiments, the molar proportion of bismuth in the metal element can be further controlled to: 25%≤b≤35%.

[0017] In the above-mentioned inorganic glass powder composition, c is generally 5%-15%, for example, specific values ​​such as 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 21%, 23%, 25%, and ranges with any two of the above-mentioned specific values ​​as endpoints.

[0018] In the above-mentioned inorganic glass powder composition, d is generally 8%-33%, for example, specific values ​​such as 8%, 10%, 15%, 20%, 25%, 30%, 33%, and a range with any two of the above-mentioned specific values ​​as endpoints.

[0019] In the above inorganic glass powder composition, e is generally 0%-15%, for example, specific values ​​such as 0%, 5%, 10%, 15%, and a range with any two of the above specific values ​​as endpoints.

[0020] In some specific embodiments, Formula 2 may be: 8%≤d≤30; 0≤e≤15%.

[0021] In the above-mentioned inorganic glass powder composition, the cationic element composition in the composition can further satisfy the following formula 4: 1:2≤a:b≤1:1.5 and / or 1:2≤c:d≤1:1 on the basis of satisfying formulas 1 to 3.

[0022] In the above inorganic glass powder composition, a and b represent the molar proportions of Pb and Bi, respectively. The oxides corresponding to Pb and Bi, PbO and Bi2O3, are low-melting oxides, with a melting point of 888°C for PbO and 820°C for Bi2O3. Both have the effect of lowering the softening temperature of glass in the glass system, but the reaction activity of PbO to the silicon nitride layer on the surface of the silicon wafer is much higher than that of Bi2O3, so it has an impact on the efficiency of the cell. By controlling the molar ratio of Pb and Bi, the softening temperature of the glass can be lowered while avoiding a significant impact on the efficiency of the cell.

[0023] In the above inorganic glass powder composition, c and d represent the molar proportions of Si and Zn, respectively. Both ZnO and SiO2 have the effect of increasing the softening temperature of glass in glass, but SiO2 has a better protective effect on the silicon nitride layer; excessive Zn content will cause the hardness of the glass powder to be too high, which is not conducive to subsequent grinding into powder. By controlling the molar ratio of Si and Zn, the protective effect and processing performance of inorganic glass powder on silicon nitride can be adjusted.

[0024] In the above-mentioned inorganic glass powder composition, the cationic element composition in the composition can further satisfy the following formula 5: e:a≥1:3 (it can be understood that a is not 0 at this time) on the basis of satisfying formulas 1 to 3 or 1 to 4.

[0025] In the above inorganic glass powder composition, a and e are the molar ratios of Pb and B respectively. PbO can corrode the silicon nitride layer on the surface of the silicon wafer; while the B element can adjust the fluidity of the glass. The glass with a high B element content has better fluidity, but is not reactive. By controlling the molar ratio of Pb and B, the present invention can make the inorganic glass powder have both high reactivity and good fluidity.

[0026] According to a specific embodiment of the present invention, the inorganic glass powder combination that satisfies Formula 4 and / or Formula 5 on the basis of satisfying Formula 1 to Formula 3 may have better acetic acid resistance.

[0027] In the above inorganic glass powder composition, the metal M can adjust the high-temperature melting viscosity of the glass, promote the glass forming ability, and reduce the firing requirements and process requirements for the glass.

[0028] In some specific embodiments, the molar proportion of M in the cationic element can be further controlled to be: 0%≤f≤15%. For example, f can be specific values ​​such as 0%, 5%, 10%, 15%, and a range with any two of the above specific values ​​as endpoints.

[0029] In some specific embodiments, M may include one or more combinations of alkali metals (Li, Na, K, etc.), alkaline earth metals (Ca, Mg, etc.), rare earth metals, Al, Ga, Ge, Sn, P, Sb, transition metals, and the transition metals include one or more combinations of Cu, Sb, Nb, Ta, V, Ti, Mo, Cr, Zr, and Mn. Further, M includes one or more combinations of alkali metals, alkaline earth metals, and transition metal oxides, for example, one or more combinations of Li, Na, K, Mg, Ga, Ca, Ti, and Mn.

[0030] In the embodiments of the present invention, Mn is added as the M element, which can, on the one hand, have a positive effect on the resistance of the glass to acetic acid corrosion attenuation; on the other hand, during the firing process of the glass, there may be a certain metal oxide saturation situation. For example, when the amount of alumina and ZnO in the glass containing Al and Zn exceeds a certain ratio (for example, ZnO exceeds 20%) during the firing process, it is difficult to continue to increase the ratio. In this case, the Mn element can be added as a supplement; in addition, the Mn element also has an improving effect on the wettability of the glass.

[0031] The present invention also provides an inorganic glass powder, which is prepared from the inorganic glass powder composition.

[0032] In some specific embodiments, the composition of the cationic elements of the inorganic glass powder is Pb a -Bi b -Si c -Zn d -B e- M f , where M is a cationic element other than lead, bismuth, silicon, zinc, and boron, and a, b, c, d, e, and f are the molar proportions of lead, bismuth, silicon, zinc, boron, and element M in the cationic element, respectively;

[0033] Among them, the values ​​of a, b, c, d, and e satisfy equations 1 to 3 at the same time:

[0034] Formula 1: 0%≤a≤25%, 20%≤b≤42% and 5%≤c≤15%;

[0035] Formula 2: 8% ≤ d ≤ 33% and 0% ≤ e ≤ 15%;

[0036] Formula 3: a+b+c+d+e+f=100%.

[0037] In some specific embodiments, on the basis of satisfying Formula 1 to Formula 3, the cationic element composition in the inorganic glass powder may further satisfy:

[0038] Formula 4: 1:2≤a:b≤1:1.5 and / or 1:2≤c:d≤1:1 (ie, at least one of the relationship formulas is satisfied).

[0039] In some specific embodiments, on the basis of satisfying Formula 1 to Formula 3, or Formula 1 to Formula 4, the cationic element composition in the inorganic glass powder may further satisfy:

[0040] Formula 5: e:a≥1:3 (it can be understood that a is not 0 in this case).

[0041] In some specific embodiments, the inorganic glass powder contains oxygen elements in addition to the above-mentioned cationic elements, and the composition of the cationic elements of the inorganic glass powder is obtained by removing the oxygen element and normalizing the remaining elements.

[0042] In some specific embodiments, the particle size distribution of the inorganic glass powder generally satisfies D50≤10 μm.

[0043] In some specific embodiments, the softening temperature of the inorganic glass powder is generally 600-720°C.

[0044] In some specific embodiments, the inorganic glass powder may be amorphous glass powder, crystalline glass powder, or a combination of amorphous glass powder and crystalline glass powder.

[0045] In some specific embodiments, the method for preparing the inorganic glass powder may include: melting, cooling, and grinding an inorganic glass powder composition to obtain the inorganic glass powder.

[0046] In the above preparation method, the melting temperature is generally controlled to be 900-1400° C. (eg, 900° C.), and the melting time is generally controlled to be 30 min-120 min.

[0047] The present invention further provides a conductive paste, which comprises a conductive phase, an organic carrier and an inorganic adhesive phase, wherein the inorganic adhesive phase comprises the inorganic glass powder provided by the present invention.

[0048] In some specific embodiments, the mass content of the conductive phase in the conductive paste is generally controlled to be 86%-93%, for example, it can be 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93% and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0049] In some specific embodiments, the element of the conductive phase may include one or a combination of two or more conductive metals such as gold, silver, and copper.

[0050] In some specific embodiments, the conductive phase is preferably silver powder.

[0051] In some specific embodiments, the D50 of the silver powder is generally 1 μm-5 μm, and the tap density of the silver powder is generally 5 g / cm 3 -9g / cm 3 .

[0052] In some specific embodiments, the silver powder includes modified silver powder, and the dispersion stability of the silver powder in the conductive paste can be improved by modification.

[0053] Further preferably, the modifier used in the modified silver powder includes one or a combination of two or more of oleic acid, linoleic acid, linolenic acid, silane coupling agent, stearic acid, fatty acid amine, polyvinyl pyrrolidone, fatty alcohol polyoxyethylene ether and block macromolecular surfactant. The block macromolecular surfactant may include a polyamide block macromolecular surfactant, such as N,N-dimethylacrylamide.

[0054] In some specific embodiments, the mass content of the inorganic bonding phase in the conductive paste is generally controlled to be 1%-10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0055] In some specific embodiments, the mass content of the organic carrier in the conductive paste is generally controlled to be 1%-9%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% and other specific values, and a range with any two of the above specific values ​​as endpoints, and can further be 1-6%.

[0056] In some specific embodiments, the organic carrier generally includes a resin and an organic solvent. The mass ratio of the resin to the organic solvent can be controlled to be (50-95): (5-30).

[0057] Furthermore, the organic carrier also includes an auxiliary agent.

[0058] In some specific embodiments, the mass ratio of the resin, the organic solvent and the auxiliary agent can be controlled to be (50-95): (5-30): (0-10). The auxiliary agent is an optional added component, and the minimum mass can be 0.

[0059] In some specific embodiments, the resin may include one or a combination of two or more of cellulose, ethyl cellulose, epoxy resin and acrylic resin.

[0060] In some specific embodiments, the organic solvent may include one or a combination of two or more of terpineol, butyl carbitol acetate, and dodecyl alcohol.

[0061] In some specific embodiments, the auxiliary agent may include one or a combination of two or more of a dispersant, a thixotropic agent, a lubricant, a humectant, and a plasticizer.

[0062] Among the above-mentioned auxiliary agents, the dispersant is generally a macromolecular dispersant, for example, it may include one or a combination of two or more of polyether, polyester, polyamide, polysilicone, etc.

[0063] Among the above-mentioned auxiliary agents, the thixotropic agent may include one or a combination of two or more of hydrogenated castor oil, polyamide, fumed silica, etc.

[0064] Among the above-mentioned auxiliary agents, the lubricant may include a surfactant and / or silicone oil.

[0065] Among the above-mentioned auxiliary agents, the moisturizing agent may include one or a combination of two or more of diethylene glycol, triethylene glycol, PEG400, glycerol, ethylene glycol, sorbitol, 1,2-propylene glycol, diethylene glycol, diethylene glycol butyl ether, monoethylene glycol, polyethylene glycol, N-methyl-2-pyrrolidone, a condensation product of a polyol and ethylene oxide, and xylitol.

[0066] Among the above-mentioned auxiliary agents, the plasticizer may include one or a combination of two or more of aliphatic dibasic acid esters, phthalates, terephthalates, polybenzoates, benzoates, polyol esters, epoxides, citrates, and polyesters.

[0067] In some specific embodiments, the average scraper fineness of the conductive silver paste is generally controlled to be less than 10 μm, preferably less than 5 μm.

[0068] According to a specific embodiment of the present invention, the method for preparing the conductive paste may include:

[0069] (1) mixing a resin and an organic solvent in a certain proportion, stirring them uniformly at room temperature or under heating to obtain an organic carrier intermediate;

[0070] (2) Adding a conductive phase and an inorganic adhesive phase to the intermediate of the organic carrier, mixing, grinding and dispersing with a three-roll mill, and the average scraper fineness reaches 10 μm or less (preferably 5 μm or less), to obtain the conductive paste.

[0071] When the organic carrier contains an auxiliary agent, the above preparation process also includes the operation of adding the auxiliary agent. Specifically, the auxiliary agent can be completely added in step (1) (thereby preparing the organic carrier), or can be completely added in step (2) of preparing the slurry, or part of the auxiliary agent can be added in step (1) and the remaining part of the auxiliary agent can be added in step (2).

[0072] The present invention also provides the use of the inorganic glass powder composition, the inorganic glass powder, or the conductive paste in a Topcon battery laser-assisted sintering process.

[0073] The present invention also provides a solar cell, the raw materials for preparing the solar cell include the above-mentioned conductive paste.

[0074] In some specific embodiments, the solar cell may be a TOPCon cell made by a laser assisted sintering (LECO) process using the above conductive paste as a raw material.

[0075] TOPCon cell is a solar cell technology with tunneling oxide passivation contact. Its cell structure is an N-type silicon substrate cell. An ultra-thin layer of silicon oxide is prepared on the back, and then a thin layer of doped silicon is deposited. The two together form a passivation contact structure, which effectively reduces surface recombination and metal contact recombination.

[0076] The preparation process of the TOPCon battery may include the following main steps:

[0077] 1. Cleaning + alkali texturing: After the silicon wafer is cut, its edge is damaged, the silicon lattice structure is destroyed, and the surface is seriously compounded. The main purpose of cleaning and texturing is to remove surface damage, surface impurities, etc., and form a pyramid light-trapping structure on the surface to increase light absorption and improve minority carrier lifetime. The commonly used alkali solution is KOH / NaOH solution.

[0078] 2. Boron diffusion + etching: The inert gas (N2) carries the B source (BBr3) to react in a high-temperature diffusion furnace, and the B atoms are diffused to the surface of the silicon wafer to form a PN junction. The purpose of the diffusion process is to form a PN junction on the silicon wafer to realize the conversion of light energy into electrical energy, and at the same time form a layer of borosilicate glass on the surface of the silicon wafer.

[0079] After diffusion is completed, the silicon wafer passes through a chain etcher to clean and remove the borosilicate glass (remove BSG), and then the back of the silicon wafer is polished with alkaline solution to improve the back reflectivity of the silicon wafer.

[0080] 3. Preparation process of tunnel oxide layer and polysilicon layer:

[0081] The core process of TOPCon battery is to make tunnel oxide layer and polysilicon layer. The preparation of tunnel oxide layer and polysilicon layer refers to depositing a 1-4nm silicon oxide film and a 70-150nm doped amorphous silicon film on the back of N-type silicon wafer. The crystallinity of amorphous silicon film changes during the subsequent annealing process, from microcrystalline amorphous mixed phase to polycrystalline, thus realizing the passivation contact structure. According to the different preparation methods of the two layers of film, it can be divided into LPCVD, PECVD and PVD.

[0082] 4. Preparation of anti-reflection film:

[0083] The anti-reflection film is composed of a multilayer film of silicon oxide (SiOx) / silicon oxynitride (SiONx) / silicon nitride (SiNx), that is, the anti-reflection film helps the cell improve its absorption of sunlight, reduce optical losses, increase photocurrent, and thus improve conversion efficiency. More importantly, the anti-reflection film also has a passivation effect. The hydrogen atoms generated during the film formation process passivate the cell surface and reduce the surface recombination rate of the emitter junction, thereby promoting the improvement of photoelectric conversion efficiency and extending the service life of the cell.

[0084] 5. Screen printing and laser assisted sintering (LECO):

[0085] Using a printing machine, the slurry is placed above the screen, and the scraper is pressed on the screen with a certain pressure, so that the screen is deformed and contacts the surface of the silicon wafer. The slurry is squeezed through the opening gap of the screen and printed on the surface of the silicon wafer. It is usually completed in four steps: back main grid, back fine grid, front main grid, and front fine grid.

[0086] Then, the slurry on the front of the silicon wafer is metallized through laser-assisted rapid sintering (LECO), so that the slurry on the front of the silicon wafer forms a good ohmic contact with the silicon wafer. The significant advantage of laser-assisted sintering is that it can achieve local sintering by utilizing the high energy and high concentration of the laser, thereby changing the area covered by the original slurry to be fully burned through into a local burn-through, and the metallized surface contact becomes "small and numerous" point contacts. Therefore, while achieving good contact, the passivation layer can be protected to the greatest extent, greatly improving the conversion efficiency of the battery cell. The core equipment for this process is the screen sintering furnace, light injection furnace, and laser machine.

[0087] 6. Test and sorting: This process mainly uses an IV tester to test the battery cells according to their efficiency and pack the battery cells with the same efficiency level.

[0088] The solar cell mentioned above can also be prepared by other conventional methods in the art.

[0089] The beneficial effects of the present invention are:

[0090] 1. The inorganic glass powder composition provided by the present invention is suitable for the laser assisted sintering (LECO) process of TOPCon batteries. The composition has obvious low Pb and low B, or Pb-free and B-free ratio characteristics. Compounding with other metal elements can not only greatly improve the acetic acid corrosion resistance of the TOPCon battery, but also meet the metallization process of the front side of the N-type battery, forming good contact, and can match the wide range of the front side resistance of the Topcon battery.

[0091] 2. The inorganic glass powder provided by the present invention will corrode the passivation layer of the solar cell and dissolve a small amount of the conductive phase in the slurry during the sintering process of the conductive slurry printed on the solar cell. When the temperature is lowered, the conductive phase precipitates from the glass and forms a good ohmic contact with silicon. In addition, the glass powder of the present invention will wet the conductive metal and form a protective layer on the surface of the conductive metal, thereby reducing the corrosion of the conductive metal by the acetic acid decomposed in the EVA component, that is, improving the ability to resist acetic acid corrosion, increasing the reliability of the photovoltaic module, and increasing the service life of the photovoltaic module. DETAILED DESCRIPTION

[0092] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0093] Example 1, Comparative Example 1 and Comparative Example 2

[0094] Example 1 provides inorganic glass powders numbered 1 to 10, and Comparative Examples 1 and 2 provide inorganic glass powders. The cation element composition of each inorganic glass powder is Pb a -Bi b -Si c -Zn d -B e- M f , where M is a cationic element other than lead, bismuth, silicon, zinc, and boron, a, b, c, d, and e are the molar proportions of lead, bismuth, silicon, zinc, and boron in the cationic element, respectively, and f is the molar proportion of M in the cationic element.

[0095] Table 1 shows the composition of cationic elements in the above-mentioned inorganic glass powders.

[0096] Table 1

[0097]

[0098] The preparation methods of the inorganic glass powders in the above embodiments and comparative examples are as follows:

[0099] An inorganic glass powder composition containing an oxide of the above-mentioned cationic element and / or a substance that can generate the oxide of the above-mentioned cationic element through reaction is used, the inorganic glass powder composition is mixed in proportion, heated at 1200°C in a muffle furnace for 50 minutes, and glass crushed pieces are obtained after water quenching and steel plate cooling. The fragments are further crushed and then ball-milled with a planetary ball mill to obtain a glass product of an inorganic reaction system with a particle size distribution D50 of 0.1μm-5μm, namely, the inorganic glass powder.

[0100] Example 2

[0101] This embodiment provides a conductive paste prepared from the inorganic glass powder obtained in Example 1, Comparative Example 1 and Comparative Example 2. The preparation method of the conductive paste is as follows:

[0102] 1. A mixture of pine alcohol, butyl carbitol acetate, and dodecyl alcohol ester in a mass ratio of 1:7:2 is selected as the organic solvent, a mixture of ethyl cellulose and acrylic resin in a mass ratio of 1:2 is selected as the resin, and a mixture of hydrogenated castor oil and silicone oil (mass ratio 1:1) is selected as the auxiliary agent. The mass ratio of the above organic solvent, resin, and auxiliary agent is 78:20:2. Heat the resin and the organic solvent at 70-100°C and stir them fully. After the resin is completely dissolved, add the auxiliary agent to obtain an organic carrier.

[0103] 2. Select D50 of 1μm-5μm and tap density of 5g / cm 3 -9g / cm 3 of silver powder as the conductive phase.

[0104] 3. According to the total weight of the conductive paste as 100 parts, weigh 88.5 parts of silver powder, 2.5 parts of inorganic glass powder (prepared in Example 1, Comparative Example 1 or Comparative Example 2), and 9 parts of organic carrier, mix and stir evenly, grind and disperse on a three-roll mill, and select an average scraper fineness of less than 10 μm to obtain a conductive paste.

[0105] Example 3

[0106] This embodiment provides a solar cell, and the preparation method thereof includes:

[0107] 1. Cleaning + alkali texturing: Clean the cut silicon wafers, and then use alkali liquid to texturing to form a pyramid light-trapping structure on the surface. The commonly used alkali liquid is KOH / NaOH solution.

[0108] 2. Boron diffusion + etching: The inert gas (N2) carries the B source (BBr3) to react in a high-temperature diffusion furnace, and the B atoms are diffused to the surface of the silicon wafer to form a PN junction. After the diffusion is completed, the silicon wafer passes through a chain etcher to clean and remove the borosilicate glass (remove BSG), and then the back of the silicon wafer is polished with alkaline solution to improve the back reflectivity of the silicon wafer.

[0109] 3. Preparation process of tunnel oxide layer and polysilicon layer:

[0110] A 1-4nm silicon oxide film and a 70-150nm doped amorphous silicon film are deposited on the back of the N-type silicon wafer. The crystallinity of the amorphous silicon film changes during the subsequent annealing process, from a microcrystalline amorphous mixed phase to a polycrystalline phase, thereby realizing a passivated contact structure. According to the different preparation methods of the two-layer film, it can be divided into LPCVD, PECVD, and PVD. PECVD is used in this embodiment.

[0111] 4. Preparation of anti-reflection film:

[0112] The anti-reflection film is composed of a multilayer thin film of silicon oxide (SiOx) / silicon oxynitride (SiONx) / silicon nitride (SiNx).

[0113] 5. Screen printing and laser assisted sintering (LECO):

[0114] Using a printing machine, the slurry is placed above the screen, and the scraper is pressed on the screen with a certain pressure, so that the screen is deformed and contacts the surface of the silicon wafer. The slurry is squeezed through the opening gap of the screen and printed on the surface of the silicon wafer. It is usually completed in four steps: back main grid, back fine grid, front main grid, and front fine grid.

[0115] Then, laser-assisted rapid sintering (LECO) is used to metallize the slurry on the front side of the silicon wafer, so that the slurry on the front side of the silicon wafer and the silicon wafer form a good ohmic contact. The core equipment of the laser-assisted sintering process is the screen sintering furnace, light injection furnace, and laser machine.

[0116] 6. Testing and sorting: This process mainly uses an IV testing machine to test the cells according to their efficiency, and packages the cells with the same efficiency level to obtain solar cells.

[0117] Test Example 1

[0118] This test example provides a test of the acetic acid corrosion resistance of solar cells. The cells used for the test are commercially available blue film cells printed with the conductive paste to be tested. The test method is:

[0119] 1. Prepare acetic acid solution of a certain concentration in a container. The height of the solution on the bottom net of the container is about 0.5-1cm.

[0120] 2. Take 3 pieces of battery cells that have been tested for electrical performance and insert them vertically into a flower basket. Then place the flower basket in a container of prepared acetic acid (concentration is 0.1 mol / L). Place the container with acetic acid in a heating box and maintain the temperature at 85°C. Use acetic acid vapor to corrode the battery cells. After 15 hours, take out the battery cells and test the electrical performance again. Compare the conversion efficiency of the solar cells before and after corrosion, and calculate the efficiency attenuation percentage after corrosion.

[0121] The electrical performance test method of the battery cell is: using a solar energy simulation electrical efficiency tester, testing under standard conditions, air quality AM1.5, light intensity 1000W / m 2 , test temperature 25℃. The test standards for photovoltaic cells mainly include the following aspects:

[0122] Electrical performance test:

[0123] Conversion efficiency test (Eff): Evaluates the ability of a cell to convert solar energy into electrical energy, calculated by measuring input power and output power.

[0124] Table 2 shows the conversion efficiency results of solar cells made of various inorganic glass powders before and after acid corrosion.

[0125] Table 2

[0126] Inorganic glass powder serial number Initial conversion efficiency Conversion efficiency after acetic acid corrosion Attenuation 1 26.06％ 20.42％ 21.64％ 2 26.12％ 20.80％ 20.37％ 3 25.98％ 21.39％ 17.67％ 4 26.15％ 21.02％ 19.62％ 5 25.87％ 22.56％ 12.79％ 6 26.09％ 22.89％ 12.27％ 7 26.07％ 23.78％ 8.78％ 8 26.07％ 20.92％ 19.75％ 9 26.11％ 20.47％ 21.60％ 10 25.94％ 20.25％ 21.94％ Comparative Example 1 25.98％ 14.79％ 43.07％ Comparative Example 2 26.05％ 12.43％ 52.28％

[0127] As can be seen from Table 2, in the inorganic glass powders of Comparative Examples 1 and 2, the glass system with mainstream Pb-Si-B or Pb-Si-Zn-B-Al (Mg, Ti) as the skeleton, the efficiency of the battery cells made therefrom is significantly attenuated (greater than 40%) in the acetic acid environment; while the inorganic glass powder provided by the present invention (Bi-Si-Zn skeleton compounded with low Pb, low B or no Pb and no B) is used to prepare the slurry, and the acetic acid test is performed after printing the battery cells. The results show that the acetic acid attenuation corresponding to the present invention is weak, and the attenuation value can be controlled within 10% at the lowest. It can be seen from this that the inorganic glass powder of the present invention can improve the corrosion resistance of the battery cells after being made into a conductive slurry, and the components made of this battery have less attenuation during use and higher long-term reliability.

[0128] The laboratory has grouped 100 pieces to test the proportion of foggy black spots after sintering of cells printed with slurries made of different systems of inorganic glass powder. The test method is as follows:

[0129] This experiment uses a MAXWELL MX-FTSH-30L tester with a light intensity of 1000W / m 2 The efficiency of the battery cell was tested at a test temperature of 25°C and a power supply of 12V&10A. The sintering foggy black spots of the battery cell were observed through EL imaging. The black spots whose blackened edges exceeded the edge of the battery cell by 0.25mm were judged as foggy black spots and included in the foggy black spot ratio. The black spots whose blackened edges did not exceed the edge of the battery cell by 0.25mm were not included in the foggy black spot ratio.

[0130] The test results are shown in Table 3. The results of the experimental group "Bi-Si-Zn system" in Table 3 are the average test results of the inorganic glass powders of No. 5, No. 6, and No. 7 in the above embodiments; the results of the comparative group "Pb-Si-B" in Table 3 are the average test results of the inorganic glass powders of Comparative Examples 1 and 2.

[0131] Table 3

[0132]

[0133] As can be seen from Table 3, the proportion of sintering foggy black spots of the glass powder with Bi-Si-Zn framework of the present invention is significantly superior to that of sintering foggy black spots of the glass with Pb-Si-B framework. This is because the melting point of Bi2O3 (820-825°C) is lower than that of PbO (888°C), the glass forming range is wider, and the fluidity of glass is stronger. Therefore, during the printing and sintering process of the cell, the glass powder is easier to flow and spread, the glass is more evenly distributed, and the probability of local glass aggregation is lower, so the proportion of poor cell sintering and EL foggy black spots will be reduced.

[0134] The contact resistance of solar cells made of inorganic glass powder of different systems is tested. The test method is as follows:

[0135] The contact resistance meter TLM-SCAN+ is used to test the contact resistance, contact resistivity and other parameters of the battery cells. The above parameters can be directly read from the instrument. The contact resistivity of each group of battery cells is measured and the average value of each group is calculated.

[0136] The test results are shown in Table 4. The results of the experimental group "Bi-Si-Zn system" in Table 4 are the average test results of the inorganic glass powders of No. 5, No. 6, and No. 7 in the above embodiments; the results of the comparative group "Pb-Si-B" in Table 4 are the average test results of the inorganic glass powders of Comparative Examples 1 and 2.

[0137] Table 4

[0138]

[0139] It can be seen from Table 4 that compared with the conventional Pb-Si-B skeleton glass powder, the Bi-Si-Zn skeleton glass powder provided by the present invention has a wider range of contact resistance applicable to the battery cell with a diffusion square resistance in the range of 600-850Ω / sq. Specifically, when the diffusion square resistance is 600Ω / sq, the contact resistivity of the experimental group is close to that of the control group; when the diffusion square resistance is close to or greater than 800Ω / sq, the contact resistivity of the experimental group is less than that of the control group, so the sintering window is wider and the applicable square resistance range is wider. In the current technology, battery cells exceeding 850Ω / sq are not easy to produce. Therefore, in the current application range, the inorganic glass powder of the present invention has good contact properties and can match a wider range of front square resistance of solar cells.

[0140] The same laboratory grouped 100 pieces for statistics to evaluate the slurry's tolerance to the laser voltage. The test method is as follows:

[0141] Laser induced sintering equipment is used for testing. The specific manufacturer model is DR-M4XS-LIF-1000. The battery cell enters the laser area through a transmission device, and the laser generator emits a laser to scan the front of the battery cell. The voltage of the laser generator can be adjusted. The higher the voltage, the stronger the energy at the scanning position. When the energy is too large, the silver paste grid line will be burned through, forming laser breakdown, which is included in the breakdown ratio. Therefore, the higher the scanning voltage that can be withstood and the lower the breakdown ratio, the better the anti-breakdown performance.

[0142] The test results are shown in Table 5. The results of the experimental group "Bi-Si-Zn system" in Table 5 are the average test results of the inorganic glass powders of No. 5, No. 6, and No. 7 in the above embodiments; the results of the comparative group "Pb-Si-B" in Table 5 are the average test results of the inorganic glass powders of Comparative Examples 1 and 2.

[0143] Table 5

[0144]

[0145] When the laser voltage is high, the output energy will be high, and local grid line sintering breakdown will occur in the battery cell. The data in Table 5 shows that compared with the conventional Pb-Si-B skeleton glass powder, the Bi-Si-Zn skeleton glass provided by the present invention has a wider range of laser voltage tolerance and a lower breakdown ratio under high laser voltage.

[0146] Compared with the PERC cell process, the TOPcon-LECO cell process has a laser-assisted sintering (LECO) process, so the corrosion requirements for glass are weaker. The glass of the Te-Pb-Bi-Si-Li system used in the PERC front slurry will have a significant reduction in opening voltage and a large loss of efficiency on the TOPcon-LECO cell. For the TOPcon-LECO process, the inorganic glass powder system with a Bi-Si-Zn skeleton provided by the present invention not only has improved resistance to acetic acid corrosion, but also has an opening voltage advantage over the glass of the Pb-Si-B system because the corrosion ability of Bi2O3 is weaker than that of PbO. When combined with silver powder with high sintering activity, there is a large room for efficiency optimization.

[0147] The current development trend of photovoltaic electronic paste is to pursue the balance of paste in conversion efficiency, sintering performance, acetic acid attenuation resistance, unit consumption, etc. The above conductive paste provided by the present invention can improve the comprehensive performance of the paste's conversion efficiency and acetic acid attenuation resistance without affecting other performance aspects.

Claims

1. An inorganic glass powder composition, comprising an oxide of a cationic element and / or a compound capable of forming an oxide of a cationic element; wherein: The cationic elements in the composition are: Pb a -Bi b -Si c -Zn d -B e- M f , M is a cationic element other than lead, bismuth, silicon, zinc, and boron; a, b, c, d, e, and f are the molar proportions of lead, bismuth, silicon, zinc, boron, and M in the cationic elements of the composition, respectively; the values ​​of a, b, c, d, e, and f satisfy equations 1 to 3 at the same time: Formula 1: 0%≤a≤25%, 20%≤b≤42% and 5%≤c≤15%; Formula 2: 8% ≤ d ≤ 33% and 0% ≤ e ≤ 15%; Formula 3: a+b+c+d+e+f=100%.

2. The inorganic glass powder composition according to claim 1, wherein The cationic element composition of the inorganic glass powder composition further satisfies: Formula 4: 1:2≤a:b≤1:1.5 and / or 1:2≤c:d≤1:

1.

3. The inorganic glass powder composition according to claim 1 or 2, wherein: The cationic element composition of the inorganic glass powder composition further satisfies: Formula 5: e:a≥1:

3.

4. The inorganic glass powder composition according to claim 1, wherein 5％≤a≤15％。 5. The inorganic glass powder composition according to claim 1, wherein 25％≤b≤35％。 6. The inorganic glass powder composition according to claim 1, wherein 0％≤f≤15％。 7. The inorganic glass powder composition according to claim 1, wherein The M includes one or a combination of two or more of alkali metals, alkaline earth metals, rare earth metals, Al, Ga, Ge, Sn, P, Sb, and transition metals; Preferably, M includes one or a combination of two or more of Li, Na, K, Mg, Ga, Ca, Ti, and Mn.

8. An inorganic glass powder, which is prepared from the inorganic glass powder composition according to any one of claims 1 to 7; Preferably, the particle size distribution of the inorganic glass powder satisfies D50≤10 μm; Preferably, the softening temperature of the inorganic glass powder is 600-720°C.

9. The inorganic glass powder according to claim 8, wherein: The method for preparing the inorganic glass powder comprises: melting, cooling and grinding the inorganic glass powder composition to obtain the inorganic glass powder; Preferably, the melting temperature is 900-1400° C., and the melting time is 30 min-120 min.

10. A conductive paste, comprising a conductive phase, an organic carrier and an inorganic adhesive phase, wherein the inorganic adhesive phase comprises the inorganic glass powder according to claim 8 or 9; Preferably, the average scraper fineness of the conductive paste is 10 μm or less, preferably 5 μm or less.

11. The conductive paste according to claim 10, wherein: The mass content of the conductive phase in the conductive paste is 86%-93%; The mass content of the inorganic adhesive phase in the conductive paste is 1%-10%; The mass content of the organic carrier in the conductive paste is 1%-9%.

12. The conductive paste according to claim 10 or 11, wherein: The metal element in the conductive phase includes one or a combination of two or more of gold, silver and copper; Preferably, the conductive phase comprises silver powder; the D50 of the silver powder is preferably 1 μm-5 μm, and the tap density of the silver powder is preferably 5 g / cm 3 -9g / cm 3 ; More preferably, the conductive phase comprises modified silver powder; Further preferably, the modifier used in the modified silver powder includes one or a combination of two or more of oleic acid, linoleic acid, linolenic acid, silane coupling agent, stearic acid, fatty acid amine, polyvinyl pyrrolidone, fatty alcohol polyoxyethylene ether and block macromolecular surfactant; Preferably, the block macromolecular surfactant comprises a polyamide block macromolecular surfactant; More preferably, the block macromolecular surfactant comprises N,N-dimethylacrylamide.

13. The conductive paste according to any one of claims 10 to 12, wherein: The organic carrier includes a resin and an organic solvent; preferably, the organic carrier also includes an auxiliary agent; Preferably, the mass ratio of the organic solvent to the resin is (50-95):(5-30); more preferably, the mass ratio of the organic solvent to the resin to the additive is (50-95):(5-30):(0-10); Preferably, the resin comprises one or a combination of two or more of cellulose, ethyl cellulose, epoxy resin and acrylic resin; Preferably, the organic solvent includes one or a combination of two or more of terpineol, butyl carbitol acetate, and dodecyl alcohol; Preferably, the auxiliary agent includes one or a combination of two or more of a dispersant, a thixotropic agent, a lubricant, a humectant and a plasticizer.

14. The conductive paste according to claim 13, wherein: The dispersant includes one or a combination of two or more of polyether, polyester, polyamide and polysilicone; The thixotropic agent includes one or a combination of two or more of hydrogenated castor oil, polyamide, and fumed silica; The lubricant includes a surfactant and / or silicone oil; The moisturizing agent includes one or a combination of two or more of diethylene glycol, triethylene glycol, PEG400, glycerol, ethylene glycol, sorbitol, 1,2-propylene glycol, diethylene glycol, diethylene glycol butyl ether, ethylene glycol acetal, polyethylene glycol, N-methyl-2-pyrrolidone, a condensate of a polyol and ethylene oxide, and xylitol; The plasticizer includes one or a combination of two or more of aliphatic dibasic acid esters, phthalic acid esters, terephthalic acid esters, polyphenylene esters, benzoic acid esters, polyol esters, citrate esters, and polyesters.

15. Use of the conductive paste according to any one of claims 10 to 14 in a Topcon battery laser-assisted sintering process.

16. A solar cell, wherein the raw materials for preparing the solar cell include the conductive paste according to any one of claims 10 to 14; Preferably, the solar cell comprises a TOPCon cell manufactured by a laser-assisted sintering process.

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