CN111200041B - Etching method and application of silicon nitride in crystalline silicon solar cell - Google Patents

Abstract

The present application discloses an etching method and application of silicon nitride in a crystalline silicon solar cell. The etching method for silicon nitride in a crystalline silicon solar cell of the present application includes using silver tellurite to etch the silicon nitride of the crystalline silicon solar cell. The etching method of the present application uses silver tellurite to etch silicon nitride, and the sintering temperature is low, which can completely replace the existing etchant PbO to achieve lead-free low-temperature sintering; and silver tellurite etches The produced elemental silver can grow into nano-silver in situ two-dimensionally on the silicon emitter, and form a good ohmic contact with the silicon of the emitter, which is beneficial to reduce the silver-silicon contact resistance and improve the efficiency of the solar cell.

Description

Etching method and application of silicon nitride in crystalline silicon solar cells

technical field

The present application relates to the field of crystalline silicon solar cells, in particular to an etching method and application of silicon nitride in crystalline silicon solar cells.

Background technique

Photovoltaic power generation is one of the most promising clean energy sources among renewable energy sources, and silicon solar cells account for more than 90% of the photovoltaic market share. High-efficiency cells are the direction of future development, and one of the keys to improving the efficiency of silicon solar cells is metallization. In the production of silicon solar cells, large-scale use of screen printing silver paste and high temperature sintering to achieve its metallization. The sintering mechanism of solar cells and the silver-silicon ohmic contact mechanism are the focus of research in the field of silicon solar cells. S.Xiong uses the contact terminal voltage measurement technology to deepen the understanding of the silver-silicon contact formation process, according to which the silver paste formulation and sintering process for high-efficiency solar cells can be optimized. DieterK reviewed ohmic contacts for solar cells, introduced the basic principles of metal-semiconductor contacts, including Fermi level pinning of surface states, field emission, thermal/field emission, and tunneling mechanisms for current transport, studied silicon and different The contact resistance of the material. The measurement of ohmic contact is very critical. Ballif.C measured the contact resistivity of silicon solar cells using atomic force microscopy and found that the minimum value of silver-silicon contact is 10 ^-7 Ωcm ² .

The glass frit contained in the silver paste is a very critical material, and its basic functions include etching the silicon nitride film (Si ₃ N ₄ ) anti-reflection layer and forming a silver-silicon ohmic contact with the silicon substrate. Most of the viewpoints believe that in the sintering process, after the glass powder is melted, the silver element in the silver grid lines is dissolved and transported to the surface of the silicon emitter. When the temperature is lowered, silver is precipitated on the silicon surface or in the glass layer, forming contact with silicon. Good silver-silicon The contact can improve the photoelectric conversion efficiency of the cell. X.Cai prepared a new type of lead-free silver paste, which uses a TeO2 _- based glass frit for the front electrode of crystalline silicon solar cells, and the resistivity of the front electrode after sintering is between 3.1-3.7 μΩcm. X.Pi prepared glass samples by melt cooling method, studied the effect of glass powder on the etching of anti-reflection film Si ₃ N ₄ and the resistivity of silver, and found that the tellurium glass made the combination of silver and silicon well. BMChunga studies the formation mechanism of solar cell contact, and believes that silver interacts with oxygen in the atmosphere to dissolve and form Ag ⁺ in the molten glass. It is measured that the concentration of Ag ⁺ increases significantly with the increase of oxygen partial pressure, so the oxidative property of the atmosphere The sintering of the battery plays an important role.

To find and develop new materials for the current metallization of crystalline silicon solar cells, realize low temperature sintering, reduce lead or lead-free, and study its function and mechanism, is an important subject of solar cell metallization.

SUMMARY OF THE INVENTION

The purpose of this application is to provide a new etching method and application of silicon nitride in crystalline silicon solar cells.

This application adopts the following technical solutions:

A first aspect of the present application discloses a method for etching silicon nitride in a crystalline silicon solar cell, including using silver tellurite (Ag ₂ TeO ₃ ) to etch the silicon nitride of the crystalline silicon solar cell.

Preferably, the etching method of the present application includes adding silver tellurite to the glass powder of the silver paste for solar cells to prepare a mixed glass powder, using the mixed glass powder to prepare the silver paste for solar cells, and using a solar cell containing silver tellurite A silicon solar cell is prepared from a battery silver paste, and the silicon nitride is etched with silver tellurite at the etching temperature.

Preferably, the starting temperature of the etching temperature of silver tellurite is 545°C. Among them, the etching temperature of 545°C is only found in one implementation of this application. When silver tellurite is about 545°C, the TGA curve of the reaction between Ag ₂ TeO ₃ and Si ₃ N ₄ begins to lose weight, indicating that the occurrence of Redox reaction; it can be understood that 545°C is only a reaction node, and redox reactions may also occur before this, but the effect or efficiency is low. Similarly, redox reactions can also occur at higher temperatures, but they will Higher thermal energy is wasted; therefore, the optimal starting temperature for etching is 545°C.

It should be noted that the present application creatively found that silver tellurite can etch silicon nitride of crystalline silicon solar cells, and the etching temperature of silver tellurite is only about 545°C, which is lower than the traditional optimal etchant. The etching temperature of PbO is 160 °C lower, which can replace PbO to achieve lead-free low-temperature sintering; in addition, the etching product of silver tellurite is conductive elemental silver, which is beneficial to reduce the silver-silicon contact resistance and improve the efficiency of solar cells.

It should also be noted that, in this application, silver tellurite is used for silicon nitride etching, and silver tellurite can be used directly, or it can be added to ordinary oxide glass for etching, such as adding it to glass frit. In this way, the elemental silver produced by etching can also optimize the silver-silicon interface and improve the efficiency of solar cells. In addition, the present application uses silver tellurite to etch silicon nitride, and silicon nitride can be etched at low temperature in various atmospheres, and can be etched in an oxygen-free or oxygen-free environment.

A second aspect of the present application discloses a method for preparing a crystalline silicon solar cell, including etching silicon nitride of a crystalline silicon solar cell by using the silicon nitride etching method of the present application.

It can be understood that the key to the preparation method of the crystalline silicon solar cell of the present application is to use the silicon nitride etching method of the present application to etch the silicon nitride of the crystalline silicon solar cell; as for other steps, please refer to the existing crystalline silicon solar cell. The battery preparation method is not specifically limited here.

A third aspect of the present application discloses a crystalline silicon solar cell prepared by the preparation method of the present application.

It should be noted that, in the crystalline silicon solar cell of the present application, since silver tellurite is used for silicon nitride etching, the elemental silver produced by the etching can in situ two-dimensionally grow nano-silver and the emitter on the silicon emitter. The silicon forms a good ohmic contact, thereby improving solar cell efficiency.

A fourth aspect of the present application discloses the application of silver tellurite in silicon nitride etching.

It should be noted that the key point of this application lies in the discovery that silver tellurite can etch silicon nitride; it can be understood that this can not only be applied to the preparation of crystalline silicon solar cells, but also to other applications that require etching of silicon nitride is not specifically limited here.

A fifth aspect of the present application discloses a mixed glass frit containing silver tellurite.

A sixth aspect of the present application discloses a solar cell silver paste containing silver tellurite.

It should be noted that, since the mixed glass powder or silver paste for solar cells of the present application contains silver tellurite, low-temperature sintering can be achieved during the preparation of solar cells, which not only saves energy, but also avoids the unfavorable effects of high-temperature sintering on solar cells. influences. More importantly, when the mixed glass powder or solar cell silver paste containing silver tellurite is etched with silicon nitride, its elemental silver product can form a two-dimensional nanostructure grown in situ on the silicon emitter. Thereby, a good ohmic contact is formed with the silicon of the emitter, and the efficiency of the solar cell is improved.

A seventh aspect of the present application discloses a method for preparing silver tellurite, comprising using at least one of AgNO ₃ , Ag ₂ CO ₃ , Ag ₂ C ₂ O ₄ and Ag ₂ O, with Te, TeO ₂ and At least one of the tellurites is mixed according to a stoichiometric ratio and heated to 250°C-1200°C to synthesize the silver tellurite of the present application.

Preferably, the preparation method of silver tellurite of the present application specifically adopts AgNO ₃ and TeO ₂ to synthesize silver tellurite.

It should be noted that, compared with the existing preparation method, the silver tellurite preparation method of the present application has simpler and more direct synthesis steps, shorter synthesis process, and avoids the introduction of other metal impurities.

The beneficial effects of this application are:

The etching method of the present application uses silver tellurite to etch silicon nitride, and the sintering temperature is low, which can completely replace the existing etchant PbO to achieve lead-free low-temperature sintering; and silver tellurite etches The produced elemental silver can grow into nano-silver in situ two-dimensionally on the silicon emitter, and form a good ohmic contact with the silicon of the emitter, which is beneficial to reduce the silver-silicon contact resistance and improve the efficiency of the solar cell.

Description of drawings

Fig. 1 is the XRD analysis result figure of silver tellurite in the embodiment of the application;

Fig. 2 is the DSC curve of silver tellurite in the embodiment of the application;

Fig. ₃ is the TGA curve of silver tellurite in O atmosphere in the embodiment of the present application;

Fig. 4 is the thermogravimetric and differential thermal curves of Ag ₂ TeO ₃ and Si ₃ N ₄ in O ₂ in the examples of the present application;

Fig. 5 is the TGA curve of Ag ₂ TeO ₃ and Si ₃ N ₄ in the N ₂ environment in the embodiment of the present application;

Fig. 6 is the contrast curve of Ag ₂ TeO ₃ and PbO etching Si ₃ N ₄ in the embodiment of the present application;

Fig. 7 is the XRD diffractogram of Ag ₂ TeO ₃ and Si ₃ N ₄ powder in the embodiment of the present application;

Fig. 8 is the XRD diffractogram of PbO and Si ₃ N ₄ powder in the embodiment of the present application;

Fig. 9 is the XRD analysis result diagram of glass made by melting Ag ₂ TeO ₃ and oxide in the embodiment of the present application;

Fig. 10 is the thermogravimetric curve of the glass prepared by melting Ag ₂ TeO ₃ and oxide and Si ₃ N ₄ powder in the embodiment of the present application, and heating reaction in O ₂ ;

11 is a photo of the silicon solar cell prepared in the examples of the present application;

12 is a cross-sectional view of a solar cell silver grid line FIB slice in an embodiment of the present application;

13 is a structural diagram of a silver-silicon contact interface in an embodiment of the present application;

14 is an interface diagram of a further enlarged Ag-Si contact in the embodiment of the present application;

Fig. 15 is the total surface distribution diagram of the interface energy spectrum of the silver grid line of the solar cell in the embodiment of the present application;

16 is a distribution diagram of Si in the interface energy spectrum of the silver grid line of the solar cell in the embodiment of the present application;

17 is a distribution diagram of Ag in the interface energy spectrum of the silver grid line of the solar cell in the embodiment of the present application;

FIG. 18 is a distribution diagram of O in the interface energy spectrum of the silver grid line of the solar cell in the embodiment of the present application.

Detailed ways

The existing silicon nitride etching usually uses the etchant PbO, which not only has a high sintering temperature, but also has problems such as being unfriendly to the environment due to the use of lead. In the research process of crystalline silicon solar cells, this application creatively found that silver tellurite can etch silicon nitride, and the sintering temperature is low, and the silver produced by etching can also form a good ohmic contact with the silicon of the emitter , to improve the efficiency of solar cells.

Among them, Ag ₂ TeO ₃ is a compound that is rarely reported, and the research on its properties and applications is quite lacking. LBSharma reported the synthesis method of Ag ₂ TeO ₃ : First, Na ₂ TeO was prepared by the high temperature reaction of TeO ₂ and sodium carbonate. _3. Dissolve Na ₂ TeO ₃ in water to form a solution; then prepare Ag ₂ TeO ₃ by uniform precipitation method, that is, add AgNO ₃ solution uniformly into Na ₂ TeO ₃ solution to precipitate Ag ₂ TeO ₃ , wash and heat the precipitate to obtain Ag ₂ TeO ₃ crystal; the Ag ₂ TeO ₃ prepared by this method is characterized and thermally analyzed, and the results show that the Ag ₂ TeO ₃ prepared by the precipitation method is a tetragonal crystal.

On the basis of the above research and knowledge, the present application further develops a new preparation method of Ag ₂ TeO ₃ , that is, using at least one of AgNO ₃ , Ag ₂ CO ₃ , Ag ₂ C ₂ O ₄ and Ag ₂ O One is to directly heat and react with at least one of Te, TeO ₂ and tellurate to obtain Ag ₂ TeO ₃ . The Ag ₂ TeO ₃ prepared in this way not only has a simple preparation method, shortens the synthesis process, and avoids the introduction of other metal impurities; but also can well meet the application requirements for etching silicon nitride in the present application.

The present application will be further described in detail below through specific embodiments. The following examples are only to further illustrate the application, and should not be construed as a limitation to the application.

Example

1. Preparation of materials

According to the metering ratio of Ag ₂ TeO ₃ , weigh out AgNO ₃ with a purity of 99.9% and TeO ₂ with a purity of 99.99% and a particle size of D50=100 nm, mix them evenly, and place them in a muffle furnace at a temperature of 10°C/min to 750°C for insulation. 100 min, then cooled with the furnace, and ground to a particle size of D50=10 μm for later use, that is, the Ag ₂ TeO ₃ of this example was obtained.

In this example, the prepared Ag ₂ TeO ₃ is added to the glass powder of the solar cell silver paste to make a mixed glass powder. The mixed glass powder is used to prepare the solar cell silver paste, and the solar cell silver paste containing silver tellurite is used to prepare the silicon solar cell. battery, as follows:

Weigh 70 grams of the prepared Ag ₂ TeO ₃ and melt it with other oxides to make glass. Other oxides include: 1 gram Na ₂ O, 2 grams MgO, 0.5 grams CaO, 0.2 grams TiO ₂ , 3 grams P ₂ O ₅ , 5 grams of SiO ₂ , 6 grams of B ₂ O ₃ , 20 grams of TeO ₂ , the specific conditions for melting into glass are 1000 ° C for 2 hours, then pour the glass melt into water for quenching, and after water quenching, put the glass in In the agate jar, use the agate ball to grind the powder to 1-5 microns to obtain the mixed glass powder of this example.

The silver paste is prepared by mixing 5% of the mixed glass powder and 85% of the silver powder prepared in this example with 9% of the organic solvent and 1% of the resin to prepare the silver paste for the solar cell of this example. Among them, organic solvents and resins are conventional general materials for solar cell silver pastes.

Using a 400-mesh screen, on a silicon solar cell substrate, screen-printed silver grid lines with a line width of 30 μm and a spacing of 1 mm were sintered at 920° C. for 1 min to form a battery.

2. Testing and Characterization

Adopt XRD (Bruker, D8), step size 0.1s, angle 10°-80°, test Ag ₂ TeO ₃ , Ag ₂ TeO ₃ mixed with oxide glass, Ag ₂ TeO ₃ and Si ₃ N ₄ , PbO The X-ray diffraction pattern of the reaction product with Si ₃ N ₄ , wherein the purity of Si ₃ N ₄ is 99.95%, and the particle size is D50=0.5 μm. Specifically, using a comprehensive thermal analyzer (Mettler-Toledo, TGA/DSC professional type), in an O ₂ atmosphere, at 10 ° C/min, heated to 1000 ° C, the thermal properties of Ag 2 TeO ₃ and Ag ₂ TeO 3 were measured. Reaction differential thermal and thermogravimetric curves of ₂ TeO ₃ , PbO and Si ₃ N ₄ powder; solar cell efficiency was measured with a photoelectric simulator, FIB (FEI, Scios) was used for sample preparation, and TEM (Japan Electronics, JEM-3200FS) was used to observe the interface Element distribution and morphological characteristics.

3. Results and discussion

(1) XRD analysis results of silver tellurite samples

The XRD analysis result of the silver tellurite synthesized in this example is shown in Figure 1, and its PDF card number is 83-1779, indicating that Ag ₂ TeO ₃ was successfully synthesized in the experiment in this example. Compared with the existing Ag ₂ TeO ₃ synthesis method, the synthesis of AgNO ₃ and TeO ₂ is simpler in this example, which avoids the pollution of other metal ions and improves the experimental quality.

(2) Thermal analysis results of silver tellurite

The DSC curve of the silver tellurite synthesized in this example is shown in Figure 2. Its melting point is 600 °C, while the melting points of TeO ₂ and PbO are 730 ° C and 888 ° C, respectively. The melting point of silver tellurite is 130 °C lower than that of TeO ₂ ℃, 288℃ lower than PbO. The lower melting point of silver tellurite facilitates the etching reaction.

The TGA curve of the silver tellurite synthesized in this example in O ₂ atmosphere, as shown in Figure 3, shows that the material is stable before 800 °C, starts to decompose after 800 °C, and decomposes at 900 °C.

(3) Ag ₂ TeO ₃ etching Si ₃ N ₄

The TGA curve of the reaction of Ag ₂ TeO ₃ with Si ₃ N ₄ is shown in Figure 4, which is the thermogravimetric and differential thermal curves of Ag ₂ TeO ₃ and Si ₃ N ₄ in O ₂ , where the solid line is the thermogravimetric curve curve, the dotted line is the differential heat curve.

Specifically, in this example, 20mg Ag ₂ TeO ₃ and 5mg Si ₃ N ₄ are taken to compare the stable states of Ag ₂ TeO ₃ in the O ₂ environment. The results in Figure 4 show that the curve begins to lose weight when the sample is about 545 ° C, indicating that the occurrence of The oxidation-reduction reaction is based on the reaction equation (1), the system releases _N2 gas, and the reaction occurs below the melting point of the two materials, indicating that the reaction is a solid-phase reaction. The DSC curve shows that there is exotherm at 450℃-800℃, and the peak value is reached at 600℃, indicating that the redox exothermic reaction mainly occurs at about 600℃, which is beneficial to increase the temperature of the system and accelerate the progress of the reaction.

6Ag ₂ TeO ₃ +Si ₃ N ₄ =12Ag+3SiO ₂ +6TeO ₂ +2N ₂ ↑ (1)

2Ag ₂ TeO ₃ +Si ₃ N ₄ +2O ₂ =4Ag+3SiO ₂ +2TeO ₂ +2N ₂ ↑ (2)

The curve begins to increase in weight at around 750°C, and the weight gain reaches the peak at 900°C, indicating that the reaction is dominated by equation (2). After 800 °C, the weight of the TGA curve increases significantly, but the exotherm is weak, indicating that the absorption of oxygen by the system is an endothermic reaction, and the exothermic heat of the etching reaction may cancel each other, so there is a dynamic change of energy.

In this example, the TGA curves of 10mg Ag ₂ TeO ₃ and 2.5mg Si ₃ N ₄ under N ₂ environment were also tested, and the results are shown in Figure 5. The results show that the TGA curve in the _N2 environment is compared with that in the aerobic environment, which shows weight loss at the same temperature, the reaction is equation ( ₁ ), and it is also proved that in the _O2 environment _Ag2TeO3 and _{Si3N4 are} in The weight gain after 750°C is due to the participation of O ₂ in the reaction. Also after 900 °C, the weight loss is accelerated and Ag ₂ TeO ₃ is decomposed.

(4) Comparison of Ag ₂ TeO ₃ and PbO etching Si ₃ N ₄

Figure 6 shows the comparison curves of Ag ₂ TeO ₃ and PbO etching Si ₃ N _4. In Figure 6, the solid line is the thermogravimetric curve of PbO etching Si ₃ N ₄ , and the dotted line is Ag ₂ TeO ₃ etching Si ₃ Thermogravimetric curves of _N4 . The results in Figure 6 show that the quality of the thermogravimetric curve of PbO remains basically stable before 700 °C, and the weight gain accelerates after 710 °C, without the phenomenon of weight loss, indicating that the reaction of PbO etching Si ₃ N ₄ is mainly caused by the environment. O ₂ is involved. Its reaction equations are (3) and (4):

6PbO+Si ₃ N ₄ =6Pb+3SiO ₂ +2N ₂ ↑ (3)

2Pb+O2=2PbO (4)

Comparing the thermogravimetric curves of Ag ₂ TeO ₃ and PbO, there is a significant difference between the two. The etching reaction of Ag ₂ TeO ₃ starts at about 540 ° C, which is 160 ° C lower than that of lead oxide etching, and the etching temperature of Ag ₂ TeO ₃ is 160 ° C lower. The thermogravimetric curve loses weight at first, indicating that the reaction mainly comes from oxygen in Ag ₂ TeO ₃ . As the temperature increases, more O ₂ in the environment participates in the reaction, and the curve begins to gain weight. The advantage of Ag ₂ TeO ₃ is that the reaction temperature is lower and the source of oxygen is more abundant.

In this example, 10g of PbO and Ag ₂ TeO ₃ were mixed with 2.5g of Si ₃ N ₄ powder respectively, heated to 750°C at 10K/min and reacted, and the XRD diffraction pattern of the product was measured. The results are shown in Figure 7 and Figure 8. FIG. 7 is the XRD diffraction pattern of Ag ₂ TeO ₃ and Si ₃ N ₄ powder, and FIG. 8 is the XRD diffraction pattern of PbO and Si ₃ N ₄ powder. Comparing and analyzing the results of Fig. 7 and Fig. 8 shows that the reaction of Ag ₂ TeO ₃ and Si ₃ N ₄ powder has a peak of silver element, indicating that silver is produced in the reaction product. Therefore, adding Ag ₂ TeO ₃ to the glass component of the silver paste can help the sintering of the paste and improve the ability of the interface to conduct electricity. The PbO reaction products are mainly amorphous glass and unreacted residues, no metal lead, that is, no conductive substances are produced. Other reaction residues appear in the diffractogram because the _SiO2 generated by the reaction will hinder the progress of the etching reaction, resulting in an incomplete reaction.

(4) Slurry and solar cell I-V, TEM

In this example, the prepared Ag ₂ TeO ₃ and oxide are melted into glass, that is, mixed glass powder. The XRD results are shown in Fig. 9 . The results in FIG. 9 show that the mixed glass frit material is dominated by a disordered structure. The glass was mixed with Si ₃ N ₄ powder, and the thermogravimetric curve of the mixture heated in O ₂ was measured by TGA. The results are shown in Figure 10. The results show that the mass change is similar to the reaction of Ag ₂ TeO ₃ with Si ₃ N ₄ , indicating that the properties of Ag ₂ TeO ₃ are successfully transplanted into glass, that is, the glass contains Ag ₂ TeO ₃ . Therefore, the silver paste prepared with the glass can better etch the silicon nitride during the sintering process of the solar cell, generate more silver particles, and improve the performance of the solar cell.

The above results show that Ag ₂ TeO ₃ alone or added to oxide glass can effectively etch Si ₃ N ₄ , and can achieve low-temperature etching in various atmospheres. The etching can be performed in oxygen or without carried out in an oxygen environment.

In this example, seven silicon solar cell samples were repeatedly fabricated, labeled Solarcell-01 to Solarcell-07 in sequence. The photos of the silicon solar cells are shown in Figure 11, and the test results of various parameters of the seven silicon solar cells are shown in Table 1. Show.

Table 1 Performance test results of silicon solar cells

The results in Table 1 show that the current density of the battery reaches a maximum of 38.37mA/cm ² , the open voltage is about 0.638V, the photoelectric conversion efficiency reaches a maximum of 18.41%, and the average value is greater than 18%, indicating that the silver grid lines of the battery have good charge collection capability. .

The solar cell silver grid lines of the silicon solar cell samples prepared in this example were observed by FIB slices, and the results are shown in Figures 12 to 14, wherein Figure 12 is a cross-sectional view of the FIB slice, and Figure 13 is the structure of the silver-silicon contact interface Figure 14 is an interface diagram of the Ag-Si contact. The results shown in Figures 12 to 14 show that the silver grid lines on the pyramid textured surface of the silicon-based surface have a contact interface structure with silicon; the surface of the silicon produces silver with a thickness of 50 nm along the surface length of 300-500 nm, which is the most common in glass. Ag ₂ TeO ₃ etches the product of Si ₃ N ₄ ; and the charge can be directly or tunneled from the surface of the silicon emitter to the silver gate line to complete the collection and transmission of the charge.

The interface energy spectrum diagrams of the silver grid lines of the solar cell are shown in FIGS. 15 to 18 , wherein FIG. 15 is the overall surface distribution diagram, and FIGS. 16 to 18 are the distribution diagrams of Si, Ag, and O in sequence. It can be seen from the element distributions of the energy spectra in Figures 15 to 18 that silver and oxygen are separated, indicating that the interface etching product is silver elemental.

The distribution position and morphology of silver particles have a great influence on the battery performance. When C. Ballif measured the resistance of the direct silver-silicon contact, it was found that the resistivity of some areas was 4 orders of magnitude lower than the typical value, indicating that some contacts of silver and silicon can significantly reduce the contact resistance of the battery and better collect the charge . L. Liang studied the key features of the battery interface micro-region: in addition to the residual SiNx, another large part is a thin glass layer with nano-Ag colloids, and the surface of the silicon emitter is attached with nano-sized 10-100nm Ag particles. However, it can also be seen that the silver particles are discretely distributed and interfaced, and the average spacing is greater than 50 nanometers, which is unfavorable for electrical conductivity. When C. Ballif measured the silver-silicon contact resistance, he found that in the cross-sectional transmission electron microscope, the interface was composed of Ag crystals with a diameter of 200-500nm, and the average penetration of silicon was 130nm. The smaller silver crystals had an epitaxial relationship with the Si substrate. Silver is believed to have grown from glass melts. Likewise, the silver particles also exhibit a discrete distribution. The nano-silver in this example is shown as a strip in the cross-section. Obviously, it needs a higher concentration of silver ions during the growth process, which is directly related to the addition of Ag ₂ TeO ₃ , that is, Ag ₂ TeO ₃ More silver can be produced after etching Si ₃ N ₄ , so that the silver particles separated at low concentrations can be continuous. The addition of Ag ₂ TeO ₃ can generate regenerated silver after etching silicon nitride, which directly contacts with silicon to collect charges, and then outputs through silver grid lines, thereby improving the efficiency of solar cells.

The above results show that the addition of Ag ₂ TeO ₃ to the glass of the silver paste can achieve low-temperature sintering of silver grid lines on the one hand, and on the other hand, the reaction product of Ag ₂ TeO ₃ and Si ₃ N ₄ is conductive metallic silver, Compared with other materials, its conductive advantages are very obvious, and the effect of improving the efficiency of silicon solar cells is particularly prominent.

Therefore, compared with the prior art, this example has the following advantages:

a. In this example, AgNO ₃ and TeO ₂ are used to directly synthesize Ag ₂ TeO ₃ , the synthesis process is short, and the introduction of other metal impurities is avoided; Ag ₂ CO ₃ , Ag ₂ C ₂ O ₄ or Ag ₂ O can replace AgNO ₃ . In addition to TeO ₂ , the Te source can also directly use Te or common tellurate; all of them can prepare Ag ₂ that meets the needs of this example. TeO ₃ , but the heating temperature is different, about 250℃-1200℃.

b. In this example, Ag ₂ TeO ₃ is used to etch Si ₃ N ₄ , and the etching temperature is about 545 ℃, which realizes the low temperature etching of Si ₃ N ₄ , which is about 160 ℃ lower than the etching temperature of PbO.

c. In this example, Ag ₂ TeO ₃ was successfully applied to the silver paste of silicon solar cells, and the current density of the prepared cells reached 38.37 mA·cm ^-2 , and the average efficiency was greater than 18%.

d. The silver-silicon interface was observed by TEM/EDS, and it was found that after doping Ag ₂ TeO ₃ in this example, silver with a length of 300-500 nm and a thickness of 50 nm was grown along the surface of the silicon emitter. It shows that Ag ₂ TeO ₃ is not only an excellent low-temperature etching material, but more importantly, it provides a higher concentration of silver ions for the interface; this silver can better collect and transport charges after being generated, and can collect and transport charges. to the silver grid lines, thereby helping to reduce contact resistance and improve solar cell efficiency.

e. This example opens up a new direction for the metallization of silicon solar cells from the perspective of material development, and promotes the development of low-temperature sintered silver paste with less lead and no lead.

The above content is a further detailed description of the present application in conjunction with specific embodiments, and it cannot be considered that the specific implementation of the present application is limited to these descriptions. For those of ordinary skill in the technical field to which the present application pertains, some simple deductions or substitutions can also be made without departing from the concept of the present application.

Claims (9)

1. A method for etching silicon nitride in a crystalline silicon solar cell is characterized by comprising the following steps: the method comprises the steps of etching silicon nitride of a crystalline silicon solar cell by silver tellurite, specifically, adding the silver tellurite into glass powder of a solar cell silver paste to prepare mixed glass powder, preparing the solar cell silver paste by using the mixed glass powder, preparing the silicon solar cell by using the solar cell silver paste containing the silver tellurite, and etching the silicon nitride by using the silver tellurite at an etching temperature;

in the mixed glass powder, the weight ratio of the silver tellurite is greater than that of the glass powder of the solar cell silver paste.

2. The etching method according to claim 1, characterized in that: the initial temperature of the etching temperature was 545 ℃.

3. A preparation method of a crystalline silicon solar cell is characterized by comprising the following steps: the method comprises the step of etching silicon nitride of the crystalline silicon solar cell by using the etching method of claim 1 or 2.

4. The crystalline silicon solar cell prepared by the preparation method according to claim 3.

5. The application of silver tellurite in silicon nitride etching.

6. A mixed glass frit is characterized in that: the mixed glass powder contains silver tellurite, and the weight ratio of the silver tellurite is larger than the sum of other components in the mixed glass powder.

7. The solar cell silver paste is characterized in that: the solar cell silver paste is prepared by adopting the mixed glass powder in the claim 6.

8. A preparation method of silver tellurite is characterized in that: comprises the use of AgNO₃、Ag₂CO₃、Ag₂C₂O₄And Ag₂At least one of O, Te and TeO₂And tellurate, mixing according to stoichiometric ratio, and heating to 250-1200 deg.C to synthesize the silver tellurite.

9. The method of claim 8, wherein: in particular AgNO₃And TeO₂And synthesizing the silver tellurite.

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