CN105858623A - Preparation method for silver tellurite, crystalline solar cell positive pole silver paste and preparation method therefor - Google Patents

Abstract

The invention discloses a method for preparing silver tellurite by reacting silver ammonia solution and tellurite, and provides the silver tellurite by directly adding the silver tellurite prepared by the above method and improving the inorganic glass powder on the basis of the original raw materials. A new anode silver paste for crystalline solar cells and a method for preparing the anode silver paste for crystalline solar cells. The invention is exquisitely designed, and by directly adding silver tellurite and highly selective corrosive inorganic glass powder, conditions are created for the formation of silver-silicon ohmic contact, and at the same time, high temperature conditions required for the precipitation of sufficient silver tellurite from the glass powder are avoided , to ensure that the integrity of the PN junction will not be affected by high temperature, thus solving the contradiction between the two and widening the window of sintering temperature.

Description

Preparation method of silver tellurite, crystalline solar cell cathode silver paste and preparation method thereof

technical field

The invention belongs to the field of solar cells, and in particular relates to a preparation method of silver tellurite, a positive electrode silver paste of a crystalline solar cell containing the above silver tellurite and a preparation method of the silver paste.

Background technique

Solar energy is an inexhaustible and inexhaustible clean energy. Solar power generation is the direct conversion of solar radiation energy into electrical energy. It is the most direct way to convert solar energy with the fewest conversion links among all clean energy sources.

At present, crystalline silicon solar cells are the main solar cells, and the front silver paste of crystalline silicon solar cells is used as the positive electrode of the cell, which is an important part of the cell, and its composition includes organic carrier, silver powder and inorganic glass. At present, the standards for measuring the performance of silver paste include adhesion, series resistance, parallel resistance, and printing performance.

The mechanism of action of the front-side silver paste for current cells is: during the sintering process, the inorganic glass is first decomposed by heat, and penetrates the silicon nitride by means of the glass's corrosion of silicon nitride and silicon, but it also penetrates the silicon nitride while penetrating the silicon nitride. To get the ohmic contact of silver silicon.

In this process, the integrity of the PN junction should be kept intact as far as possible to ensure the high open circuit voltage of the cell, and form a good enough silver-silicon contact surface to reduce the contact resistance of the front electrode.

However, in order to effectively ensure the ohmic connection of silver-silicon, there must be sufficient energy in the overshoot of sintering, which requires a high temperature of nearly 800°C, and it is a great challenge to keep the integrity of the PN junction from being damaged, that is, High temperature will damage the PN junction. In general, the higher the temperature, the greater the probability of damage to the PN junction. Therefore, how to solve the contradiction between the high temperature requirement for silver-silicon ohmic contact and the low temperature requirement for the integrity of the PN junction becomes Questions that require research.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, by improving the components of the silver paste, directly adding silver tellurite or improving the inorganic glass powder on the basis of the original components to provide a new positive electrode for crystalline solar cells Silver paste and preparation method thereof; another object of the present invention is to provide a silver tellurite preparation method for providing silver tellurite raw material for the preparation of the positive electrode silver paste of crystalline solar cells.

The purpose of the present invention is achieved through the following technical solutions:

The preparation method of silver tellurite, comprises the steps,

S11, the step of forming tellurite: reacting tellurium oxide with XOH solution to produce tellurite, wherein X is K or Na;

S12, the step of generating silver ammonia solution: adding ammonia water dropwise to the silver nitrate solution of a specified amount, shaking while dripping, until the dissolution of the initially formed precipitate stops, and obtaining a silver ammonia solution;

S13, step of forming silver tellurite: mixing and reacting tellurite with silver ammonia solution to form silver tellurite precipitation.

Preferably, the preparation method of silver tellurite, wherein: the mass fraction of the XOH solution is 2-5%.

Preferably, the preparation method of silver tellurite, wherein: the molar ratio of tellurium oxide to sodium hydroxide or potassium hydroxide is 1:2.

Preferably, the preparation method of silver tellurite, wherein: the concentration of the silver nitrate solution is 0.05-0.12mol/L, the mass fraction of the ammonia solution is 8-15%, the silver nitrate and ammonia water The molar or weight ratio is 1:1.

Preferably, the preparation method of silver tellurite, wherein: the silver ammonia solution and tellurite solute ratio is 2:1.

The anode silver paste for crystalline silicon solar cells comprises the above-mentioned silver tellurite, organic carrier, high selectivity corrosive inorganic glass powder and silver powder, the weight percentage of each of the above components is: silver tellurite: 0-4wt%, organic Carrier: 7-11wt%, inorganic glass powder: 2-4wt%, silver powder: 87-90wt%.

Preferably, the anode silver paste for crystalline silicon solar cells, wherein: the average particle size of the silver tellurite is 1-4 μm.

Preferably, the anode silver paste for crystalline silicon solar cells, wherein: the high selectivity corrosive inorganic glass powder is Pb-Te-O system inorganic glass.

Preferably, the anode silver paste for crystalline silicon solar cells, wherein: the silver powder is in spherical form, spheroidal form, flake form and a combination of one or more, and the average particle diameter of the silver powder is 1- 5 μm.

The preparation method of crystalline silicon solar cell anode silver paste, it comprises the steps:

S1, silver tellurite preparation steps: prepare silver tellurite according to the above silver tellurite preparation method;

S2, organic carrier preparation step: add organic components alcohol ester dodeca, butyl carbitol acetate, butyl carbitol, ethyl cellulose and thixatrol st into the container according to the specified weight ratio, and heat up to 75°C, heat preservation for 2 hours to obtain an organic carrier;

S3, silver paste preparation steps: mix silver tellurite, organic vehicle, highly selective corrosive inorganic glass powder and silver powder according to the specified weight ratio, adjust the paste, roll and grind it with a three-roller until the fineness is less than 10 μm, and the viscosity 200-250mpa·s to prepare the front silver paste of the solar cell.

Substantive features and progress of the technical solution of the present invention are mainly reflected in:

1. The design of the present invention is exquisite. By directly adding silver tellurite and using highly selective corrosive inorganic glass powder, conditions are created for the formation of ohmic contact between silver and silicon, and at the same time, it avoids the precipitation of enough silver tellurite from ordinary glass powder. The required high temperature condition ensures that the integrity of the PN junction will not be affected by high temperature, solves the contradiction between the two, and widens the window of sintering temperature.

2. By using highly selective corrosive inorganic glass powder and silver tellurite, the purpose of low contact resistance of the positive electrode is achieved and the high conversion efficiency of the battery is ensured.

3. The preparation method of silver tellurite provided by the present invention is simple and easy, the raw materials are convenient to obtain, the cost is low, and the environmental hazard is small, which creates basic conditions for the preparation of silver paste.

detailed description

The scheme of the present invention will be further described below:

The present invention separates the process that the inorganic glass powder not only corrodes silicon nitride but also promotes the ohmic connection of silver and silicon in the sintering process, that is, corrodes the silicon nitride layer by highly selective corrosive inorganic glass powder, and directly adds The silver tellurate and Pb-Te-O system precipitates silver tellurite at a relatively low temperature, which promotes the formation of ohmic contacts between silver and silicon, thereby solving the need for high temperature and The stability of the PN junction requires a relatively low temperature paradox.

The present invention specifically provides a positive electrode silver paste for a crystalline silicon solar cell, comprising silver tellurite, an organic carrier, highly selective corrosive inorganic glass powder and silver powder, the weight percentage of each of the above components: silver tellurite: 0- 4wt%, organic vehicle: 7-11wt%, inorganic glass powder: 2-4wt%, silver powder: 87-90wt%.

Moreover, the average particle size of the silver tellurite is 1-4 μm. Since the inorganic glass is an insulator, too much addition will increase the series resistance of the solar cell. By directly adding the silver tellurite, the inorganic glass can be greatly reduced. The amount of glass added to improve the performance of solar cells.

The organic vehicle has the ability to form an ink suitable for screen printing after mixing the inorganic components and the organic medium. This is because the ink has a certain consistency and rheological properties, and has suitable viscosity, thixotropy, Yield value, etc., and has good burning performance.

The highly selective corrosive inorganic glass powder refers to an inorganic glass powder with a large corrosion rate difference between SiNx and Si, which has good corrosion performance to silicon nitride as a reflective layer, but very low corrosion performance to Si; The corrosive inorganic glass powder with high selectivity ratio is preferably the inorganic glass powder of Pb-Te-O system, wherein Pb-Te-O system refers to that the main material is composed of Te, Pb, O, and the Pb-Te-O system is formed during the sintering process. There will be the formation of silver tellurite, which is beneficial to further increase the total amount of silver tellurite in the reaction and promote the ohmic contact of silver and silicon.

The silver powder is a combination of one or more of spherical form, spherical form and flake form, and the average particle size of the silver powder is 1-5 μm.

Further, the present invention also discloses a method for preparing a positive electrode silver paste for a crystalline silicon solar cell, which includes the following steps:

S1, silver tellurite preparation steps: prepare silver tellurite according to the following steps:

S11, the step of generating tellurite: reacting tellurium oxide with XOH solution to produce tellurite, wherein X is K or Na; the mass fraction of the XOH solution is 2-5%, preferably 4%, and the The molar ratio of tellurium oxide to sodium hydroxide or potassium hydroxide is 1:2.

Taking NaOH as an example, its reaction equation is as follows:

TeO ₂ +2NaOH==Na ₂ TeO ₃ +H ₂ O.

S12, silver ammonia solution generation steps:

First, inject a small amount of sodium hydroxide solution into the test tube, oscillate, then heat to boil, pour out the sodium hydroxide, and then wash it with distilled water for later use.

Preparation of solution: Inject 1mL of silver nitrate solution into a clean test tube, then add ammonia water drop by drop, shake while dripping, until the initially formed precipitate just dissolves, the specific reaction process is as follows:

After adding ammonia water drop by drop into the silver nitrate solution, the silver nitrate and ammonia water will first precipitate AgOH according to the chemical reaction AgNO ₃ +NH ₃ ·H2O==AgOH↓+NH ₄ NO ₃ reaction; since AgOH is extremely unstable at room temperature, according to the reaction Formula: 2AgOH==Ag ₂ O↓+H ₂ O is decomposed into Ag ₂ O dark brown precipitate; continue to drop ammonia water, and Ag ₂ O precipitates according to the reaction formula: Ag ₂ O+4NH _3· H ₂ O＝2Ag(NH ₃ ) ₂ ⁺ +2OH ^- +3H ₂ O dissolves: at the same time, the generated OH ^- reacts with the NH ₄ ⁺ (AgNO ₃ +NH ₃ ·H2O==AgOH↓+NH ₄ NO ₃ ) generated by the previous reaction: OH ^- +NH ₄ ⁺ ==NH ₃ ·H ₂ O.

Therefore, the total ion equation for adding dilute ammonia water to the AgNO ₃ solution until the precipitate dissolves is: Ag ⁺ +2NH3·H2O==Ag(NH3)2++2H2O At this time, the solution only contains NO ₃ ^- and Ag(NH ₃ ) ²⁺ , namely to get Ag(NH3) ₂ NO ₃ .

In the generation process of silver ammonia solution, the concentration of described silver nitrate solution is 0.05-0.12mol/L, the mass fraction of described ammonia solution is 8-15%, the concentration of preferred described silver nitrate solution is 0.1mol/L , the mass fraction of the ammonia solution is 15%, and the molar ratio of the silver nitrate and ammonia is 1:1.

S13, silver tellurite generation step: mix tellurite with silver ammonia solution to generate silver tellurite precipitation, wherein, the molar ratio of the silver ammonia solution and tellurite is 2:1, they are as follows Reaction equation: Na ₂ TeO ₃ +2Ag(NH3) ₂ NO3==Ag ₂ TeO ₃ ↓+2NaNO ₃ .

In order to facilitate the application of the anode silver paste for crystalline silicon solar cells in the present invention, the generated silver tellurite is ball milled to control the average particle size at 1-4 μm, which is suitable for screen printing.

S2, organic carrier preparation step: add organic components alcohol ester dodeca, butyl carbitol acetate, butyl carbitol, ethyl cellulose and thixatrol st into the container according to the specified weight ratio, and heat up to 75°C, heat preservation for 2 hours to obtain an organic carrier;

S3, silver paste preparation steps: mix the raw materials according to the ratio of silver tellurite: 0-4wt%, organic vehicle: 7-11wt%, inorganic glass powder: 2-4wt%, silver powder: 87-90wt%, and adjust the paste shape, rolling and grinding with a three-roll mill until the fineness is less than 10 μm, and the viscosity is 200-250 mpa·s to prepare the front silver paste of the solar cell.

Of course, there is no strict restriction on the sequence of the steps of silver tellurite generation, organic carrier preparation and glass frit preparation, as long as the raw materials corresponding to the above three steps are prepared before the silver paste preparation step.

Example 1:

Preparation of organic vehicle: according to the ratio of ingredients: ethyl cellulose 3wt%, thixatrol st5wt% thixatrol, alcohol ester twelve 60wt%, butyl carbitol acetate 20wt%, butyl carbitol 12wt% ratio, add Stir in the container and raise the temperature to 75°C and keep it warm for 2 hours.

Mix 87wt% of silver powder, 10wt% of organic carrier, 2wt% of high selectivity corrosion glass powder, and 1wt% of silver tellurite to make a paste, roll and grind it with a three-roller until the fineness is less than 10 μm, and the viscosity is 200-250mpa·s, the solar cell front silver paste was prepared as a comparison paste.

Example 2:

Preparation of organic vehicle: according to the ratio of ingredients: ethyl cellulose 3wt%, thixatrol st5wt% thixatrol, alcohol ester twelve 60wt%, butyl carbitol acetate 20wt%, butyl carbitol 12wt% ratio, add Stir in the container and raise the temperature to 75°C and keep it warm for 2 hours.

According to the ratio of 88wt% of silver powder, 10wt% of organic carrier, and 2wt% of high selectivity corrosion glass powder, they are mixed evenly, adjusted into a paste, rolled and ground with a three-roller until the fineness is less than 10 μm, and the viscosity is 200-250mpa·s. Preparation Obtain the silver paste on the front side of the solar cell as a contrast paste.

Example 3:

Preparation of organic vehicle: according to the ratio of ingredients: ethyl cellulose 3wt%, thixatrol st5wt% thixatrol, alcohol ester twelve 60wt%, butyl carbitol acetate 20wt%, butyl carbitol 12wt% ratio, add Stir in the container and raise the temperature to 75°C and keep it warm for 2 hours.

According to the ratio of 87wt% of silver powder, 9wt% of organic carrier, 2wt% of high selectivity corrosion glass powder, and 2wt% of silver tellurite, they are mixed evenly, adjusted into a paste, rolled and ground with a three-roller until the fineness is less than 10 μm, and the viscosity is 200-250mpa·s, the solar cell front silver paste was prepared as a comparison paste.

Comparative example 1:

Preparation of organic vehicle: according to the ratio of ingredients: ethyl cellulose 3wt%, thixatrol st5wt% thixatrol, alcohol ester twelve 60wt%, butyl carbitol acetate 20wt%, butyl carbitol 12wt% ratio, add Stir in the container and raise the temperature to 75°C and keep it warm for 2 hours.

Mix 87wt% of silver powder, 10wt% of organic carrier, and 3wt% of PSGS-2014 traditional inorganic glass powder to make a paste, roll and grind it with a three-roller until the fineness is less than 10μm, and the viscosity is 200-250mpa·s. A silver paste on the front side of the solar cell was prepared as a comparison paste.

Comparative example 2:

Preparation of organic vehicle: according to the ratio of ingredients: ethyl cellulose 3wt%, thixatrol st5wt% thixatrol, alcohol ester twelve 60wt%, butyl carbitol acetate 20wt%, butyl carbitol 12wt% ratio, add Stir in the container and raise the temperature to 75°C and keep it warm for 2 hours.

87wt% of silver powder, 10wt% of organic carrier, 3wt% of silver tellurite, adjusted into a paste, rolling and grinding with a three-roller until the fineness is less than 10μm, and the viscosity is 200-250mpa·s, to prepare the front silver paste of the solar cell as a comparison paste.

After the positive electrode silver paste is prepared by the preparation method of the above silver paste and the corresponding examples, it is transferred to a polysilicon wafer with a sheet resistance of 90Ω/□ by screen printing; through a despatch sintering furnace with a peak temperature of 770°C, test 156× The efficiency of 156 polycrystalline solar cells at different temperatures, and the comparison test results of the silver pastes prepared in the above examples are shown in the table below:

Sintering peak (℃) Series resistance Rs(mohm) Conversion efficiency (%) Example 1 770 3.57 15.45 Example 1 700 3.42 15.21 Example 2 770 6.22 13.25 Example 3 700 3.01 16.01 Comparative example 1 770 2.43 17.44 Comparative example 1 700 25.28 9.66 Comparative example 2 770 132.08 1.12

It can be seen from the data of the temperature conditions of Example 1 and Comparative Example 1 in the above table at 770°C and 700°C that under a very wide window, the solar cell obtained by adding silver tellurite and high selectivity corrosive inorganic glass powder The various properties have basically remained unchanged, so even under low temperature conditions, it not only meets the low temperature requirements for PN junction stability, but also can effectively meet the requirements for forming silver-silicon ohmic contacts; while in the traditional process, although at 770 ° C, the traditional process The performance of the obtained solar cell is excellent, but as the sintering temperature decreases, the performance of the solar cell drops sharply, and the best values of series resistance and efficiency can only be expressed in a small window, so the traditional process cannot effectively solve the problem of PN junction. The conflict between the low-temperature requirements for stability and the high-temperature requirements for the precipitation of silver tellurite from conventional inorganic glasses to achieve silver-silicon ohmic contacts.

From the data in Example 1 and Example 2, it can be seen that the direct addition of silver tellurite can reduce the series resistance and conversion efficiency of solar cells, that is, silver tellurite participates in the silver-silicon contact and reduces the ohmic contact resistance.

From the data in Example 1 and Example 3, it can be seen that when adding silver tellurite, the contact resistance of solar cells can be further reduced and the conversion efficiency can be improved. However, after the content continues to increase, the contact resistance declines no longer. Obviously, the improvement range of the conversion efficiency is also small, and the performance change is relatively stable.

It can be seen from the data in Comparative Example 2 that silver tellurite does not have the ability to penetrate silicon nitride at high temperature. Only under the premise of penetrating silicon nitride through inorganic glass can silver tellurite play the role of promoting ohmic contact. Features.

The above are only preferred embodiments of the present invention, and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still belong to the technology of the present invention. within the scope of the program.

Claims (10)

1. the preparation method of silver tellurite is characterized in that: comprise the steps, S11, the step of forming tellurite: reacting tellurium oxide with XOH solution to produce tellurite, wherein X is K or Na; S12, the step of generating silver ammonia solution: adding ammonia water dropwise to the silver nitrate solution of a specified amount, shaking while dripping, until the dissolution of the initially formed precipitate stops, and obtaining a silver ammonia solution; S13, step of forming silver tellurite: mixing and reacting tellurite with silver ammonia solution to form silver tellurite precipitation. 2. the preparation method of silver tellurite according to claim 1 is characterized in that: the mass fraction of described XOH solution is 2-5%. 3. The method for preparing silver tellurite according to claim 1, characterized in that: the molar ratio of tellurium oxide to sodium hydroxide or potassium hydroxide is 1:2. 4. the preparation method of silver tellurite according to claim 1 is characterized in that: the concentration of described silver nitrate solution is 0.05-0.12mol/L, and the massfraction of described ammonia solution is 8-15%, so The molar ratio of silver nitrate and ammonia water is 1:1. 5. the preparation method of silver tellurite according to claim 1 is characterized in that: the mol ratio of described silver ammonia solution and tellurite is 2:1. 6. Anode silver paste for crystalline silicon solar cells, characterized in that: comprising the silver tellurite described in any one of claims 1-5, organic vehicle, highly selective corrosive inorganic glass powder and silver powder, the weight percentage of each of the above components For: silver tellurite: 0-4 wt%, organic vehicle: 7-11 wt%, high selectivity corrosive inorganic glass powder: 2-4 wt%, silver powder: 87-90 wt%. 7. The anode silver paste for crystalline silicon solar cells according to claim 6, characterized in that: the average particle diameter of the silver tellurite is 1-4 μm. 8. The anode silver paste for crystalline silicon solar cells according to claim 6, characterized in that: the high selectivity corrosive inorganic glass powder is Pb-Te-O system inorganic glass. 9. The anode silver paste for crystalline silicon solar cells according to claim 6, characterized in that: the silver powder is a spherical form, a spherical form, a flake form and one or more combinations, the average of the silver powder The particle size is 1-5μm. 10. A method for preparing a positive electrode silver paste for a crystalline silicon solar cell, characterized in that it comprises the following steps: S1, silver tellurite preparation step: prepare silver tellurite according to the silver tellurite preparation method described in any one of claims 1-5; S2, organic carrier preparation step: add organic components alcohol ester dodeca, butyl carbitol acetate, butyl carbitol, ethyl cellulose and thixatrol st into the container according to the specified weight ratio, and heat up to 75°C, heat preservation for 2 hours to obtain an organic carrier; S3, silver paste preparation step: mix silver tellurite, organic carrier, highly selective corrosive inorganic glass powder and silver powder according to the specified weight ratio, adjust the paste, roll and grind it with a three-roller until the fineness is less than 10 μm, The viscosity is 200-250 mpa·s, and the front silver paste of the solar cell is prepared.