Glass powder for back silver paste of N-type crystalline silicon cell, preparation method and application thereof

Abstract

The application provides a glass powder for N-type crystalline silicon cell back silver paste, and the glass powder components of the application comprise: main components: Pb-Te-Bi oxides; auxiliary components: Zn-W-Li-Na oxides; through optimization of component types and contents, the contact resistivity and metal composite are well balanced, excellent filling efficiency and conversion efficiency are exhibited, the contact between the conductive layer and the metal matrix is increased, higher wettability and lower thermal expansion volume are achieved, the problems of excessive etching and interface cracking existing in the high-temperature sintering process are solved, and the series resistance and contact resistivity of the cell are effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of crystalline silicon solar cell technology, C03C12 / 00, specifically to a glass powder for silver paste on the back of an N-type crystalline silicon solar cell, its preparation method, and its application. Background Technology

[0002] TOPCon is a tunnel oxide passivated contact solar cell technology based on the selective carrier principle. The back side uses an ultra-thin tunnel oxide layer of 1-2nm and a stacked structure of highly doped polycrystalline silicon (Poly-Si) deposited on its surface. The two together form a passivated contact structure, which reduces surface recombination and metal contact recombination, and comprehensively improves the performance of the cell.

[0003] Crystalline silicon solar cells typically have conductive pastes coated on both the front and back. The front conductive paste forms electrodes that facilitate electron exchange, while the back conductive paste serves as solder joints to connect the cells in series. Currently, the silver paste used for the fine grid on the back of N-type TOPCon crystalline silicon solar cells is mainly composed of silver powder, glass powder, and an organic carrier. The glass powder used in the back silver paste plays a crucial role in etching the silicon nitride layer, forming electrodes, and building electron transport bridges. During the cell metallization process, the high-temperature sintering of the silver paste can etch the silicon nitride layer on the back, forming contact with the Poly-Si layer. However, excessive etching can lead to passivation layer failure. In addition, the properties of the glass powder, such as its type, content, and composition, are important factors affecting the silver paste and the metallization effect. Furthermore, cracking at the interface between the silver paste layer and the aluminum layer can reduce the cell's conductivity, which is also a problem that needs to be addressed.

[0004] Chinese patent CN108666003A discloses a conductive silver paste for photovoltaic cells, which includes a metal microcrystalline glass powder composed of tellurium oxide, bismuth oxide, zinc oxide, tungsten oxide, lithium oxide, bismuth oxide, tungsten dioxide, tin monoxide, indium chloride, and barium chloride. By optimizing the amount and type of each component, the ohmic contact between the silver paste layer and the silicon substrate is improved, thus increasing the conversion efficiency. However, the conversion efficiency is still not high, and there is significant room for improvement. Chinese patent CN 104364851A discloses a glass powder. To improve the adhesion of the silver paste layer to the silicon wafer, the glass powder composition includes at least one of tellurium dioxide, nickel oxide, magnesium oxide, zirconium dioxide, tungsten oxide, AgO, cobalt oxide, and cerium oxide. Although the adhesion strength of the conductive paste layer to the electrode is increased, its filling efficiency and conversion efficiency are not high. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention first provides a glass powder for silver paste on the back of an N-type crystalline silicon battery. The glass powder of this application, through optimization of component types and contents, effectively balances contact resistivity and metal composite, exhibits excellent filling efficiency and conversion efficiency, increases the contact between the conductive layer and the metal substrate, has higher wettability and lower thermal expansion volume, solves problems such as excessive etching and interface cracking during high-temperature sintering, and effectively reduces battery series resistance and contact resistivity.

[0006] Furthermore, the glass powder comprises:

[0007] Main components: oxides of Pb-Te-Bi;

[0008] Auxiliary components: oxides of Zn-W-Li-Na,

[0009] The main component accounts for 30-90% of the total weight of the glass powder, preferably 50-90%, and more preferably 70-89%.

[0010] Furthermore, the Pb-Te-Bi oxide includes PbO, TeO2, and Bi2O3.

[0011] Furthermore, the mass ratio of PbO, TeO2, and Bi2O3 in the Pb-Te-Bi oxide is (1-6):(2-5):(0.5-3). In this application, PbO can significantly reduce the softening temperature of glass powder and improve the wettability between the glass powder and the matrix material, exhibiting strong silver-dissolving ability. However, due to the toxicity of lead oxide, this application further optimizes the types and contents of components to reduce the use of PbO. TeO2 itself has a low melting point and can be used as a liquid-phase sintering aid to lower the glass transition temperature of glass powder and accelerate the sintering and densification of silver powder. In addition, tellurium dioxide has a strong silver-dissolving ability and can form a conductive path, enhancing the conductivity of the Si-Ag interface and further reducing contact resistance. Bi2O3 can lower the glass softening point, significantly reduce glass viscosity, improve wettability, and regulate the glass thermal expansion coefficient. When the Bi2O3 content is low, it enters the glass system as a glass network modifier and does not participate in the construction of the glass network structure. As the Bi2O3 content increases, bismuth oxide exists in the glass network structure in the form of [BO3] and [BO4]. 3+ The high polarizability of Pb can hinder the movement of ions outside the glass network in the network voids, reduce the compatibility between the glass powder and silver, and cause the volume resistivity of the glass to increase continuously. Therefore, it is necessary to control the content of each component in the Pb-Te-Bi oxide to better increase the silver dissolving ability of the glass powder and the wetting performance of the matrix material, and reduce the contact resistivity.

[0012] Preferably, the mass ratio of PbO, TeO2, and Bi2O3 in the Pb-Te-Bi oxide is (3-4.5):(3-4):(1-2).

[0013] Furthermore, the auxiliary components account for 7%-55% of the total mass of the glass powder, preferably 10-15%.

[0014] Furthermore, the oxides of Zn-W-Li-Na include ZnO, WO3, Li2O, and Na2O.

[0015] Preferably, in the Zn-W-Li-Na oxide, the mass ratio of ZnO, WO3, Li2O, and Na2O is (0.2-5):(2-15):(1-15):(0.2-10); ZnO can lower the softening point of glass, giving the glass appropriate fluidity during melting; during the sintering process, zinc oxide is used as a byproduct of ZnO. 2+ The alkali metals are dissolved into the molten glass, reducing its viscosity at high temperatures and promoting the etching reaction of Si on the glass. Li₂O and Na₂O accelerate the melting of glass at high temperatures, and both can reduce the coefficient of thermal expansion of the glass powder. The small ionic radius and high electric field of alkali metals also provide a certain fluxing effect, significantly influencing the glass transition temperature and improving the electrical conductivity of the glass. Optimizing the relative amounts of alkali metal oxides utilizes the dual-alkali effect of Li₂O and Na₂O to enhance the chemical and thermal stability of the glass system.

[0016] This application unexpectedly discovered that when the mass ratio of TeO2 to WO3 is (5-8):1, more preferably (5-7):1, the contact resistivity of the glass powder can be further reduced; the reason for this is that during the melting process of the glass powder, W... 6+ With Te 4+ Ions can form WO-Te bonds, improving the compatibility and connectivity within the glass network structure and further enhancing the stability of the glass structure. However, if too much WO3 is added, the glass powder will reduce the metal-semiconductor contact, resulting in a decrease in contact efficiency.

[0017] Furthermore, the glass powder also includes 0-20% of modifying components, which include at least one of transition metal oxides, rare earth metal oxides, non-metal oxides, thallium oxide, aluminum oxide, tin oxide, and antimony oxide.

[0018] Preferably, the modifying component includes at least one of transition metal oxides, rare earth metal oxides, and non-metal oxides.

[0019] Furthermore, the transition metal oxide includes, but is not limited to, at least one of Fe2O3, ferrous oxide, AgO, CuO, VO2, MoO3, Cr2O3, NiO, Nb2O5, and ZrO4.

[0020] In one embodiment, the modifying component includes a transition metal oxide, used in an amount of 1-10%, including at least one of Fe2O3, AgO, CuO, and MoO3.

[0021] In a preferred embodiment, the transition metal oxide is Fe2O3, and the amount used is 1.5-4.5% of the total mass of the glass powder. In the presence of Bi2O3, Fe2O3 will significantly reduce the coefficient of thermal expansion of the glass and increase the network structure of the glass, thereby increasing the chemical stability of the glass. However, if the amount added is too much, it will lead to a decrease in glass density, an increase in molar volume, and an increase in volume resistivity.

[0022] In a preferred embodiment, the transition metal oxide is AgO, which accounts for 2-5% of the total mass of the glass powder. AgO has a melting point of about 100°C. Its addition can significantly reduce the glass transition temperature, increase the co-solubility of glass and silver powder, and enable the glass to spread and wet better on the silicon substrate. However, the content of AgO should not be too high, and the system should be adjusted to have a suitable glass transition temperature.

[0023] In a preferred embodiment, the transition metal oxide is CuO, and its amount accounts for 1-3% of the total mass of the glass powder. The applicant has found that the addition of CuO can appropriately increase the softening temperature of the glass, compensate for the problem of low viscosity of the glass powder in the high-temperature region, and ensure that the silver layer can be better sintered in the high-temperature stage, making the sintering of the silver electrode more dense and increasing the volume conductivity. However, copper oxide will introduce copper ions into the glass network system, and the metallicity of the glass powder will be significantly enhanced. When the amount of copper oxide added is too much, it will increase the metal composite.

[0024] In a preferred embodiment, the transition metal oxide is MoO3, and its dosage accounts for 1.6-3.5% of the total mass of the glass powder. The melting point of MoO3 is about 795°C. Compared with the high melting and sintering temperature of conductive paste, the addition and melting of MoO3 can drive the glass powder system to slowly become molten, thus controlling the glass transition temperature of the glass powder. However, if the amount added is too much, it will lead to over-melting or over-burning.

[0025] In a preferred embodiment, the transition metal oxides are CuO and MoO3, and the total amount of the two accounts for 1.5-3.2% of the total mass of the glass powder.

[0026] Preferably, the mass ratio of CuO to MoO3 is (0.5-2):1; more preferably, it is 1:1.

[0027] Furthermore, the rare earth metal oxides include, but are not limited to, at least one of LaO3, CeO2, Nd2O3, Pr2O3, and Yb2O3.

[0028] In a preferred embodiment, the rare earth metal oxide is LaO3, and its dosage accounts for 2.2-4.5% of the total mass of the glass powder. The addition of lanthanum oxide can effectively regulate the thermal expansion properties of the glass powder, improve its chemical stability, and further improve the electrical performance of the silver paste or battery.

[0029] Furthermore, the non-metallic oxide is selected from at least one of P2O5 and SiO2.

[0030] In a preferred embodiment, the non-metallic oxide is SiO2, and the amount used is 3-5% of the glass powder. The silicon-oxygen tetrahedra in silicon oxide increase the stability of the overall glass structure and reduce its coefficient of thermal expansion. Appropriate addition can improve the viscosity and surface tension of the glass. However, excessive addition of silicon oxide will lead to a reduction in the wetting effect of the glass on the silicon matrix.

[0031] In another preferred embodiment, the modifying components include transition metal oxides and non-metal oxides, specifically Fe2O3 and SiO2, with the total amount of both accounting for 2-4% of the glass powder mass.

[0032] Preferably, the mass ratio of Fe2O3 to SiO2 is (1-2):(1.5-5); more preferably, it is (1-2):3.

[0033] Furthermore, the particle size D50 of the glass powder is 0.5-4.5 μm, preferably 1.0-3.0 μm, and more preferably 1.4-2.5 μm.

[0034] Furthermore, the glass transition temperature (Tg) of the glass powder is 250-600℃, preferably 300-500℃, and even more preferably 320-450℃.

[0035] Furthermore, this application also provides a method for preparing the glass powder, comprising the following steps:

[0036] S1. Weigh the components of the glass powder and mix them.

[0037] S2. The mixture is placed in a crucible and melted at a high temperature of 900-1200℃ for 30-90 minutes.

[0038] S3. Quickly dry-quench the molten glass and then dry it to obtain glass slag;

[0039] S4. Crush the glass shards to the target particle size and then dry them.

[0040] Furthermore, in step S3, the dry quenching method includes, but is not limited to, any one of cold water quenching and stainless steel rod dry quenching.

[0041] Furthermore, in step S4, the pulverization method includes, but is not limited to, at least one of planetary ball milling and air jet milling.

[0042] Furthermore, this application also provides the application of the glass powder in the conductive silver paste of the fine grid on the back side of an N-type TOPCon crystalline silicon solar cell.

[0043] Furthermore, the glass powder is added to the silver paste at a mass of 1.5-5%, and the sintering temperature of the silver paste is 750-780℃.

[0044] Beneficial effects

[0045] 1. This application uses Pb-Te-Bi oxide as the main component. By adjusting the relative content of the three components, the glass transition temperature of the glass powder is effectively reduced, so that the glass powder has good melting temperature, melting state and melting viscosity, which effectively improves the wetting performance of silver paste and matrix material, the density of sintered silver paste, and the etching of silicon nitride layer on the back of N-type TOPCon crystalline silicon solar cell and forms good contact with Poly-Si layer.

[0046] 2. This application optimizes the types and amounts of main components, auxiliary components and modifying components, effectively enhancing the structural stability of the glass, reducing volume thermal expansion, reducing the contact resistance between metal and semiconductor and the metal-induced recombination rate, and increasing the open circuit voltage and electrical performance.

[0047] 3. This application optimizes the particle size of the glass powder and its dosage in the silver paste, which not only promotes the rapid formation of silver microcrystals during the silver paste sintering process and reduces the erosion of the Poly-Si layer, but also balances the contact resistivity and metal composite to a greater extent, and increases the adhesion of the silver paste layer to the substrate after sintering. Detailed Implementation

[0048] Example

[0049] Example 1

[0050] This embodiment provides a glass powder for silver paste on the back of an N-type crystalline silicon solar cell. The glass powder, by total mass, comprises:

[0051] 84.5% of the main components: 35.3% PbO, 33.3% TeO2, 15.9% Bi2O3;

[0052] 13.1% auxiliary components: 0.8% ZnO, 5.3% WO3, 5.8% Li2O and 1.2% Na2O;

[0053] 2.4% of the modifying component: the modifying component is Ag2O;

[0054] The method for preparing the glass powder is as follows:

[0055] S1. Accurately weigh the above glass powder components and mix them evenly;

[0056] S2. Transfer the above mixture to a crucible, heat it to 1100℃ for high-temperature melting, and hold it at that temperature for 60 minutes.

[0057] S3. Quickly pour the molten glass into cold water for water quenching, and then dry it to obtain glass slag;

[0058] S4. The glass slag is crushed in an air jet mill until its D50 particle size reaches the specified value, and then dried to obtain the finished glass powder.

[0059] Example 2-10

[0060] The results are basically the same as in Example 1, and specific information is shown in Table 1.

[0061] In Example 9, the modifying components are Fe2O3 and SiO2, with a mass ratio of 2:3.

[0062] The modifying components in Example 10 are CuO and MoO3 in a mass ratio of 1:1.

[0063] Example 11

[0064] It is basically the same as Example 1, except that the main components of the 84.5% are: 35.3% PbO, 14.2% TeO2, and 35.00% Bi2O3.

[0065] Example 12

[0066] It is basically the same as Example 1, except that the 13.1% auxiliary components are: 5.8% ZnO, 5.3% WO3, 0.8% Li2O and 1.2% Na2O.

[0067] Example 13

[0068] It is basically the same as Example 1, except that the 13.1% auxiliary components are: 5.8% ZnO, 8.33% WO3, 2.77% Li2O and 1.2% Na2O.

[0069] Example 14

[0070] It is basically the same as Example 1, except that the particle size of the glass powder is 5.5 μm.

[0071] In the above embodiments, the PbO has a purity ≥ 97%; the TeO2 has a purity ≥ 99.99%; the ZnO has a purity ≥ 99%; the WO3 has a purity ≥ 99.9%; and the Bi2O3, Li2O, and Na2O are all AR grade.

[0072] Table 1

[0073]

[0074] Performance testing methods:

[0075] The glass powder provided in the examples was tested for its glass transition temperature (Tg) using a thermal analyzer, and the results are shown in Table 2. Conductive silver paste for the back grid of N-type TOPCon crystalline silicon solar cells was prepared with a glass powder content of 2.6 wt%. The prepared silver paste was screen-printed onto the back of the N-type TOPCon crystalline silicon solar cells, and sintered in a sintering furnace at a peak temperature of 750–760 °C. Finally, the obtained cells were subjected to current-voltage performance testing, and the data included open-circuit voltage (Voc), series resistance (Rs), fill factor (FF), and conversion efficiency (Eta). The contact resistivity (ρc) of the N-type TOPCon crystalline silicon solar cell electrodes was tested using a TLM device, and the results are shown in Table 2.

[0076] Table 2

[0077]

Claims

1. A glass powder for silver paste on the back of an N-type crystalline silicon solar cell, characterized in that, The glass powder comprises, by total mass, the following components: 84.5% of the main components: 35.3% PbO, 33.3% TeO2, 15.9% Bi2O3; 13.1% auxiliary components: 0.8% ZnO, 5.3% WO3, 5.8% Li2O and 1.2% Na2O; 2.4% of the modifying component: The modifying component is Ag2O; The method for preparing the glass powder is as follows: S1. Accurately weigh the above glass powder components and mix them evenly; S2. Transfer the obtained mixture to a crucible and heat it to 1100℃ for high-temperature melting, holding it at that temperature for 60 min. S3. Quickly pour the molten glass into cold water for water quenching, and then dry it to obtain glass slag; S4. The glass slag is crushed in an air jet mill until its D50 particle size reaches the specified particle size, and then dried to obtain the finished glass powder.

2. The application of the glass powder according to claim 1 in the conductive silver paste for the fine grid on the back side of an N-type TOPCon crystalline silicon solar cell, characterized in that, The glass powder is added to the silver paste at a mass of 1.5-5%.

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