WO2020096478A1

WO2020096478A1 - Aluminum paste for producing a rear contact of silicon solar cells

Info

Publication number: WO2020096478A1
Application number: PCT/RU2018/000832
Authority: WO
Inventors: Максим Михайлович ВЛАСЕНКО; Вячеслав Геннадиевич ГОЛОВИН; Иван Сергеевич МИТЧЕНКО; Андрей Сергеевич РОДИОНОВ; Алексей Владимирович СЕРДЮК
Original assignee: Общество с ограниченной ответственностью "Научное Предприятие Монокристалл Пасты"
Priority date: 2018-11-08
Filing date: 2018-12-17
Publication date: 2020-05-14
Also published as: CN113169236A; RU2690091C1

Abstract

An aluminum paste for producing a rear contact of silicon solar cells having rear dielectric passivation comprises aluminum powder, organic binder and powdered glass, wherein the paste additionally contains one or a mixture of organometallic compounds of alkaline earth metals with the following component ratio: 68-82 wt% powdered aluminum; not more than 1.0 wt% powdered glass; 0.1-2.0 wt% organometallic compounds of alkaline earth metals; and 15-29 wt% organic binder.

Description

ALUMINUM PASTE FOR THE PRODUCTION OF THE REAR CONTACT

SILICON SOLAR ELEMENTS

Technical field

The invention relates to thick-film electronics, namely, materials for the manufacture by screen printing of the rear current collector contacts of silicon solar cells with rear dielectric passivation PERC (Passivated Emitter and Rear Contact).

State of the art

Solar cells with back dielectric passivation using PERC technology are made on the basis of single-crystal or multicrystalline silicon with p-type conductivity doped with boron or gallium. According to the known manufacturing process of solar cells on a silicon plate with a thickness of 150-220 microns, broken layers on the front and back sides are removed by chemical etching and at the same time a texture is formed on the front side of the solar cell. A method of diffusion or ion implantation on the frontal textured side is used to fabricate a solar cell emitter - a phosphorus-doped layer of a silicon wafer. A non-stoichiometric silicon nitride (SiNx) coating layer is applied over the entire frontal area. Chemical back etching is performed on the back of the silicon wafer in order to remove phosphorus on the back during emitter manufacturing and to remove morphological defects on the back of the silicon wafer before applying two-layer back dielectric passivation.

Two dielectric layers are applied over the entire area of the back side of the solar cell, providing back dielectric passivation. A passivating layer of non-stoichiometric alumina (A120x) or silicon oxynitride (SiNxOy) using PECVD 10-25 pt thick or ALD 5-15 pt thick, respectively. The passivating layer reduces the surface recombination rate of minority charge carriers to a level of 10-50 cm / s. A second protective layer of non-stoichiometric silicon nitride (SiNx) 40-120 nm thick is applied over the entire surface of the passivating layer by PECVD. In the back two-layer dielectric coating by laser ablation, local contacts are made, which are areas with a removed two-layer dielectric, in which the aluminum paste will sinter directly with the silicon wafer when the solar cell is burned (see Fig. 1).

There are three topologies for local contacts (see FIG. 2):

1. Linear-dashed topology of local contacts (see Fig. 2a). Discontinuous lines consisting of strokes with a width of 30-50 microns. The stroke length is 1, 0-8.0 mm and the distance between the strokes in one line is 30-300 microns. The distance between the lines is 600-1400 microns.

2. Linear-point topology of local contacts (see Fig. 26). Lines with a width of 30-50 microns, consisting of individual points with a distance between points in one line of 10-100 microns. The distance between the lines is 600-1400 microns. 3. The point topology of local contacts (see Fig. 2B). Individual points with a diameter of 30-100 microns with a distance between them of 200-700 microns.

On top of the dielectric passivation with local contacts by screen printing, areas of silver paste are applied, followed by drying at a temperature of 150-200 ° C for 15-40 seconds in a conveyor dryer. The pads are used for soldering slip rings.

A contact grid of silver paste is applied to the front side of the solar cell by screen printing, followed by drying at a temperature of 150-200 ° C for 15-40 seconds in a conveyor dryer. The contact grid is used to collect charge carriers and solder the front collector tires.

At the next technological stage of manufacturing the solar cell, aluminum paste is applied by screen printing on the back surface of the solar cell. There are two printing topologies for aluminum paste (see Fig. 3):

1. A continuous layer of aluminum paste, providing contact with the collector silver-containing sites with an overlap of 0.1 -0.5 mm around the perimeter of each site (see Fig. For);

2. Aluminum paste printed in the form of tracks on top of local contacts in dielectric passivation. The print topology provides contact with silver collector sites with an overlap of 0.1-0.5 mm along the perimeter of each site (see Fig. 36).

After printing the aluminum paste, it is dried in a conveyor dryer with infrared heating or heating with hot air at a temperature of 200-350 ° C for 15-60 seconds.

The final step in the manufacture of a solar cell is the burning of a solar cell in a conveyor furnace with infrared heating at a peak temperature of 750-850 ° C and a burning time of 4-7 seconds above 577 ° C. In the process of firing in local contacts, a local BSF (Back Surface Field) is formed, which is a layer of a silicon wafer doped with acceptor impurities of aluminum and boron from the bulk of the dried paste layer (see Fig. 4).

Depending on the topology of the local contacts, the total area of the dielectric passivation removed by the laser is 0.1-4.5% of the total area of the back surface of the solar cell. In places of local contacts, the aluminum paste directly contacts and sinteres with the silicon wafer during the firing process. In areas where aluminum paste is printed and driven over dielectric passivation, there should be no damage to the dielectric, which leads to a sharp decrease in the quality of rear passivation due to an increase in the surface recombination rate of minority charge carriers.

Under the layer of high-quality dielectric passivation, the surface recombination rate is 10–50 cm / s. In the case of damage to dielectric passivation, the surface recombination rate can significantly exceed 10,000 cm / s, which leads to a sharp drop in the efficiency (hereinafter, the efficiency) of the solar cell.

In local contacts, where the aluminum paste is sintered directly with silicon, the theoretically achievable surface recombination rate is 500-1000 cm / s in the presence of a uniform local BSF layer. With suboptimal composition aluminum paste, the dissolution of silicon from the area of local contact in the bulk of the aluminum layer can lead to the formation of voids in the places of local contacts and the heterogeneity of the local BSF up to its complete absence. The rate of surface recombination at local contacts in the case of an inhomogeneous BSF layer can significantly exceed 10,000 cm / s, which leads to a sharp drop in the efficiency of the solar cell.

The main factor limiting the increase in efficiency and the quality of a solar cell with back dielectric passivation is the non-optimal work of the back contact made by screen printing of aluminum paste.

To obtain a high-quality back contact, aluminum paste must ensure the fulfillment of a set of technical requirements:

1. The absence of damage to the rear dielectric passivation during the burning of the solar cell.

2. A homogeneous local BSF layer and the absence of voids in local contacts located at any point on the back of the solar cell.

3. Minimum layer resistance of the pressed layer of aluminum paste.

4. The absence of aluminum balls on the surface of the smoothed aluminum layer

5. The amount of adhesion of the aluminum layer after firing more than 10 N / cm.

6. The magnitude of the deflection of the solar cell is less than 1.5 mm.

The use of rear dielectric passivation in combination with a specially developed aluminum paste allows increasing the efficiency of the solar cell by 0.2 absolute% by improving the quality of the total passivation on the back of the solar cell under the dielectric passivation layer and in places of local contacts in which the aluminum paste is directly sintered with silicon.

There is a method of forming the back contact of a solar cell with back dielectric passivation using a paste containing silicon in an amount of from 1 to 12 atomic% (patent publication EP 2149155 B1, class IPC H01L 31/0224, H01L 31/18, publ. 10.27.2010 )

The disadvantages of this method are:

1. Selected non-optimal concentration limits of silicon in the paste. The silicon concentration in the paste of less than 3.5 at.% Does not provide a sufficient decrease in the solubility of silicon from the area of local contact in the paste layer during firing.

2. The method of introducing silicon into the finished paste commercially available on the market does not ensure the industrial applicability of the invention. The introduction of 1-12 at.% Silicon powder into the finished paste will require additional adjustment of the paste composition with an organic binder.

Known aluminum paste for the back electrode of a solar cell with back dielectric passivation (publication of national application JP 2013-143499 A, class IPC H01L 31/04, H01L 21/28, H01L 21/288, publ. 22.07.2013). The paste contains a mixture of aluminum powder, aluminum alloy powder with silicon (Al-Si) and silicon powder. The total concentration of silicon in the mixture of three powders per due to Al-Si powder and pure silicon powder lies in the range of 10-40 wt.%. The concentration of silicon in the Al-Si alloy is in the range of 5-40 wt.%.

The disadvantages of the known aluminum paste are:

1. The presence of a part of silicon in the paste in the form of a silicon powder, which, having abrasive properties, mechanically damages (scratches) the back passivation layer of the solar cell during paste printing. This leads to an increase in the rate of back surface recombination and a decrease in the efficiency of the solar cell.

2. The presence of abrasive silicon powder in the paste leads to increased wear of the screen mesh and the doctor blade during printing.

3. Non-optimal choice of the range of total silicon concentration. At a silicon concentration of more than 22 wt.%, There is a sharp increase in the layer resistance of the veneered back contact and a decrease in the solar cell efficiency due to an increase in the series resistance.

Known aluminum paste for the back electrode of a solar cell with back dielectric passivation (publication of international application WO2016 / 178386A1, class IPC H01L 31/0224, H01B 1/22, H01L 31/068, publ. 10.11.2016). The paste contains a mixture of aluminum powder and powder of an alloy of aluminum with silicon (Al-Si). The concentration of silicon in the Al-Si alloy lies in the range of 3.0-30.0 wt.%. And the silicon concentration in the mixture of aluminum powder and Al-Si alloy powder lies in the range of 3.0-15.0 wt.%.

The paste contains one or a mixture of two glass fiber, not containing lead and alkali metals, but containing boron oxide B203.

The disadvantages of the known aluminum paste are:

Non-optimal choice of silicon concentration range in Al-Si alloy. A silicon concentration of less than 13 wt.% Does not provide a sufficient decrease in the solubility of silicon from the area of local contact in the paste layer during firing.

The closest in technical essence and the achieved positive effect - the prototype - is a conductive composition used in the formation of thick-film electrodes of solar cells with rear dielectric passivation and local contacts (publication of international application W02013 / 109466A1, class IPC Н01В 1/16, H01L 31/18 published on 07.25.2013). The paste contains: 40-80 wt.% Aluminum powder; glass frits 0.1-10 wt.%, organic binder 5.0-30.0 wt.% and 0.1-10 wt.% organic or inorganic additives. Organic additives include one or a mixture of organometallic compounds of boron, silicon, vanadium, phosphorus, antimony, yttrium, titanium, nickel, cobalt, zirconium, zinc and lithium. Inorganic additives include up to 20 mass. % non-eutectic and eutectic alloys of aluminum with silicon.

The disadvantages of the known composition are:

1. The use of organoboron compounds as a source of acceptor impurities of boron. In the process of burning pasta as a result of pyrolysis Organoboron compounds are formed of boron oxide and its evaporation, which leads to contamination of the exhaust system of the furnace.

2. The concentration limits of the silicon content in the Al-Si alloy and in the paste have not been determined, which ensure the formation of a uniform local BSF layer and at the same time low layer resistance.

Disclosure of invention

The problem to which the claimed invention is directed is to create a composition (composition) of an aluminum conductive paste, which, with a reduced mass of the imprint of the paste, allows to obtain a high-quality back contact, which provides an increase in the efficiency of a solar cell with back dielectric passivation and local contacts with linear dashed, linear - point or point topologies.

The technical result achieved by the implementation of the claimed invention is to reduce the damage to dielectric passivation by the paste during the burning of the contact system of the solar cell while improving the quality of the back aluminum contact and the quality of passivation in local contacts by obtaining a uniform local BSF layer, which leads to a significant reduction in defectiveness and increasing the efficiency of the solar cell when the mass of the print of aluminum paste is less than 0.7 grams per solar cell.

The quality of the rear aluminum contact additionally means the fulfillment of three technical requirements simultaneously:

1. Lack of formation during the burning process of aluminum balls of any size on the surface of the waxed aluminum layer;

2. The value of adhesion of the smoothed aluminum layer is not less than 10 N / cm;

3. Deflection of the solar cell due to the difference in the coefficients of linear thermal expansion of the aluminum paste and silicon wafer is less than 1.5 mm.

The specified technical result is achieved in that the aluminum paste for silicon solar cells includes aluminum powder with an optimized particle size distribution in a concentration of 68-82 mass. %, organic binder 15-29 wt. %, powder or a mixture of glass powders not more than 1.0 mass. % (hereinafter glass powder), one or a mixture of organometallic compounds from a number of oleates, stearates or octoates of magnesium, calcium, strontium, barium 0.1 -2.0 mass. %, as well as a powder or a mixture of powders of an alloy of aluminum with silicon (Al-Si) doped with boron in the optimal range of boron concentrations of 0.04-0.20 mass. % (hereinafter referred to as alloy powder). Alloy powder is introduced into the paste due to aluminum powder. At the same time, the total concentration of aluminum powder and alloy powder remains unchanged. The optimal range of silicon concentrations in the alloy powder is 15-40 mass. % The optimal concentration range of the alloy powder in the paste is 33-40 mass. %

The use of glass powder with a concentration in the paste of not more than 1.0 mass. % in a combination of organometallic compounds of alkaline earth metals (Mg, Ca, Sr, Ba) in the paste allows to increase the efficiency of the solar cell by reducing damage to the dielectric passivation by glass during the paste firing process, and also ensuring a uniform flow of the sintering process at the boundary with the silicon wafer in places of local contacts due to organometallic compounds.

The additive powder of the alloy (Al-Si), doped with boron, with an optimal range of silicon concentrations in the alloy 15-40 mass. % and in the optimal range of alloy concentrations in the paste 33-40 wt. % allows you to further increase the efficiency of the solar cell by reducing the dissolution of silicon in the paste layer from the area of local contacts during the burning process of the paste, which increases the uniformity of the local BSF layer and is especially effective for the construction of a solar cell with point local contacts in dielectric passivation.

The additive powder of the alloy (Al-Si) doped with boron in the optimal range of boron concentrations of 0.04-0.20 mass. % allows you to compensate for the decrease in boron content while lowering the concentration of glass powder in the paste and further contributes to a significantly more uniform distribution of boron in the paste, which leads to an increase in the efficiency of the solar cell.

Brief Description of the Drawings

In FIG. 1 shows the structure of a solar cell with back dielectric passivation before printing, drying and burning aluminum paste.

In FIG. 2 shows three topologies of local contacts in the rear dielectric passivation:

a) Line-dashed topology of local contacts. Discontinuous lines consisting of strokes with a width of 30-50 microns. The stroke length is 1, 0-8.0 mm and the distance between the strokes in one line is 30-300 microns. The distance between the lines is 600-1400 microns.

b) Linear point topology of local contacts. Lines with a width of 30-50 microns, consisting of individual points with a distance between points in one line of 10-100 microns. The distance between the lines is 600-1400 microns.

c) Point topology of local contacts. Individual points with a diameter of 30 - 10Okm with a distance between them of 200-700 microns.

In FIG. Figure 3 shows the back of solar cells with two print topologies of aluminum paste:

a) A continuous layer of aluminum paste, providing contact with the collector silver-containing sites with an overlap of 0.1 -0.5 mm around the perimeter of each site.

b) Aluminum paste is printed in the form of tracks on top of local contacts in dielectric passivation. The print topology provides contact with silver collector pads with an overlap of 0.1-0.5 mm around the perimeter of each pad.

In FIG. 4 shows the structure of a solar cell with back dielectric passivation after printing, drying and burning aluminum paste.

The following notation is used in the figures:

1. A silicon wafer with p-type conductivity doped with boron or gallium. 2. Solar cell emitter - A layer of silicon on the frontal textured surface of a solar cell doped with phosphorus.

3. A layer of antireflection coating of non-stoichiometric silicon nitride (SiNx).

4. Passivation layer of non-stoichiometric alumina or silicon oxynitride.

5. The protective dielectric layer of non-stoichiometric silicon nitride

(SiNx).

6. Local contacts - areas with remote laser ablation by a two-layer dielectric.

7. Sites made of silver-containing paste for soldering current collector tires.

8. A layer of aluminum paste.

9. Contact grid made by screen printing of silver-containing paste on the front side of the solar cell.

10. Local BSF - an aluminum-doped silicon layer during the burning of contacts of a solar cell.

11. Sites made of silver-containing paste for soldering slip rings.

The implementation of the invention

As the aluminum powder in the paste, a spherical fine powder or a mixture of aluminum powders with a known particle size ratio is used to ensure maximum packing density after printing, drying and burning of aluminum paste. The average particle size D50 of an aluminum powder or a mixture of aluminum powders is in the range of 2-4 microns. The increase in the average particle size D50 more than 4.0 microns leads to a deterioration of the printing properties of the paste with a target mass of the print of the paste is not more than 0.7 grams per plate. A decrease in the average particle size D50 of aluminum powder below 2.0 μm leads to an increase in the resistance of the pasted layer of the paste, an increase in the series resistance of the solar cell and a decrease in efficiency.

As the glass frit, a single powder or a mixture of powders of commercially available glasses of silicon-bismuthate, lead-borosilicate, antimony-borosilicate and other systems with a softening temperature in the range of 200-400 ° C and an average particle size of D50 of not more than 3.0 μm can be used, preferably 1, 0-2.0 microns. The upper dielectric passivation protective layer made of silicon nitride (SiNx) is chemically inert with respect to a wide range of chemical elements. However, during the paste firing process, particles of glass powder, regardless of the chemical composition of the glass, damage the dielectric passivation layer during cooling due to the difference in the temperature expansion coefficients of the glass and the dielectric passivation layer. Reducing the concentration of glass powder in the paste can reduce the degree of damage to dielectric passivation, which leads to increased efficiency. However, at the same time, the uniformity of sintering of the paste with a silicon wafer at the places of local contacts decreases, which leads to the formation of an uneven local BSF layer and a decrease in the efficiency of the solar cell. A decrease in the glass content in the paste further leads to a decrease in adhesion a primed layer of paste. The glass powder in the paste performs the function of a flux providing uniform and sufficient sintering of aluminum particles in the volume of the paste layer, with dielectric passivation and in the places of local contacts with the silicon wafer.

To reduce the degree of damage to the particles of glass dielectric passivation during the burning process of the paste, the total concentration of glass powders should not exceed 1.0 mass. % Preferably not more than 0.5 mass. %

To increase the uniformity of the physical and chemical processes of sintering, one or a mixture of organometallic compounds of alkaline-earth metals from a number of oleates, stearates or octoates Mg, Ca, Sr, Ba in a concentration range of 0.1 - 2.0 masses is introduced into the paste with a reduced concentration of glass. % In the process of kneading and grinding the paste, organometallic compounds are dissolved in the organic binder of the paste and are evenly distributed over the volume of the paste. A concentration of organometallic compounds of less than 0.1% does not provide a sufficient improvement in the size and uniformity of the sinterability of the paste layer, which leads to a decrease in adhesion and efficiency due to the formation of an inhomogeneous local BSF layer and an increase in the resistance of the aluminum layer. Introduction to the composition of the paste more than 2.0 mass. % of organometallic compounds of alkaline earth metals leads to a sharp increase in the deflection of the solar cell after burning and the formation of aluminum balls on the surface of the waxed aluminum layer.

In known compositions of aluminum pastes, glass powder additionally serves as a source of boron, which, like aluminum, is an acceptor impurity in silicon, but has a greater solubility limit in silicon than aluminum. The concentration of acceptor impurities in the local BSF layer determines the quality of its work to reduce the surface recombination rate in the region of local contacts. The higher the concentration of acceptor impurities in the BSF layer, the lower the surface recombination rate and the higher the efficiency of the solar cell.

With a decrease in the concentration of glass powder in the paste, it is necessary to compensate for the decrease in the concentration of boron. At the same time, in order to increase the efficiency of the solar cell, it is necessary to increase the uniformity of boron distribution over the paste volume due to its low solubility and diffusion rate in aluminum and silicon. At the ignition temperature of the solar cell, the solubility limit of boron in aluminum is about 0.16 mass. % The solubility of boron in silicon does not exceed 0.1 mass. % The equilibrium concentration of boron in the local BSF at room temperature is 0.03 mass. %

A known effect in the process of burning aluminum paste in the design of a solar cell with dielectric passivation is to reduce the uniformity of the local BSF due to the dissolution of silicon from the area of local contacts in the volume of aluminum paste. At the solar cell burning temperature of 750 ° C, the solubility of silicon in aluminum reaches 15 mass. %

The introduction into the paste of a powder of an alloy of aluminum with silicon (Al-Si) doped with boron can effectively solve both problems: 1. Introduce the optimal amount of boron into the paste, while increasing the uniformity of its distribution over the volume of the printed paste layer relative to glass powder used previously as a source of boron;

2. To increase the uniformity of the local BSF layer by reducing the dissolution of silicon from the area of local contact during the burning of the paste layer.

As a powder of an alloy (Al-Si) doped with boron, a spherical fine powder or a mixture of powders with an average particle size of D50 in the range of 2-4 microns is used. Exceeding the average particle size D50 of the alloy powder of more than 4.0 μm leads to a deterioration in the printing properties of the paste with a target mass of the print of the paste of not more than 0.7 grams per plate. The decrease in the average particle size D50 of the alloy powder less than 2.0 microns leads to a significant increase in the resistance of the pasted layer of pastes and lower efficiency.

The optimal range of boron concentrations in the alloy is 0.04-0.20%. An increase in the concentration of boron in the paste to a level comparable to its solubility in aluminum and silicon leads to an increase in the efficiency of the solar cell. An increase in boron content above the solubility limit leads to the formation of morphological defects - aluminum balls on the surface of the waxed layer of aluminum paste.

The optimal range of silicon concentrations in the alloy is 15-40 mass. % At silicon concentrations less than 15 mass. % effective suppression of the dissolution of silicon from the area of local contact in the volume of the paste layer is not provided. The excess of silicon concentration in the alloy is more than 40 mass. % leads to an increase in the layer resistance of the paste paste layer and the formation of aluminum balls on the surface of the paste paste layer due to local saturation with silicon, which leads to a decrease in the solar cell efficiency.

The optimal range of alloy concentrations in the paste is 33-40 mass. % The decrease in the concentration of the alloy in the paste is less than 33 mass. % does not provide an effective suppression of the dissolution of silicon from the area of local contact in the volume of the paste layer. The increase in alloy concentration in the paste is more than 40 mass. % leads to an increase in the layer resistance of the paste paste layer and the formation of aluminum balls on the surface of the paste paste layer due to local saturation with silicon, which leads to a decrease in the solar cell efficiency.

The content of the organic binder in the paste is in the range of 15-29 mass. % Organic binder includes one or a mixture of polymers (acrylate polymers, polymethyl methacrylates, ethyl cellulose, polyvinyl butyral, etc.) as a film-forming. An organic binder is prepared by dissolving the polymer in high boiling organic solvents. Butylcarbitol, butylcarbitol acetate, terpineol, texanol, etc. can be used as solvents. Dispersants, wetting agents, and thixotropic agents can be used as additives in the organic binder. The composition of the organic binder is selected in such a way as to ensure high-quality drying of the paste at temperatures of 200-350 ° C for 15-60 seconds, as well as an additional minimum spreading of the tracks during printing and drying of the paste in the design of the solar cell, where the aluminum paste is printed in the form tracks over local contacts in dielectric passivation. The optimality of the quantitative composition of the paste is confirmed by the fact that with the introduction of its constituent components in quantities higher or lower than the declared limits, the required parameters of the solar cell are not provided (table 2).

The analysis of the prior art showed that the claimed combination of essential features set forth in the claims is unknown. This allows us to conclude that the claimed technical solution meets the condition of patentability “novelty”.

A comparative analysis showed that in the prior art no solutions have been identified that have features that match the distinctive features of the claimed invention, and the popularity of the influence of these signs on the technical result is not confirmed. Thus, the claimed technical solution satisfies the condition of patentability "inventive step".

Example 1

To prepare the conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 76.9 mass. %, glass powder of the antimony-boron-silicon system in an amount of 1.1 mass. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the sticks is shown in table 1. The parameters of a solar cell made using paste are shown in table 2.

Example 2

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in the amount of 77.6 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 3

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in the amount of 76.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, calcium oleate in an amount of 1, 1 mass. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2

Example 4

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 75.4 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, calcium oleate in an amount of 2.2 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 5

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 40.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %., aluminum-silicon alloy powder (Al-Si) undoped with boron in an amount of 36.0 mass. % with a silicon content in the alloy of 34.2 mass. %, calcium oleate in an amount of 1.1 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 6

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 40.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, powder alloy aluminum silicon (Al-Si), doped with boron, in the amount of 36.0 mass. % with a silicon content in the alloy of 12.3 mass. % and boron content in the alloy of 0.11 mass. %, calcium oleate in an amount of 1.1 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 7

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 46.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, powder alloy aluminum silicon (Al-Si), doped with boron, in an amount of 30.0 wt. % with silicon content in the alloy 32.7 wt. % and boron content in the alloy of 0.09 mass. %, calcium oleate in an amount of 1.1 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the sticks is shown in table 1. The parameters of a solar cell made using paste are shown in table 2.

Example 8

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 40.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, powder alloy aluminum silicon (Al-Si), doped with boron, in the amount of 36.0 mass. % with silicon content in the alloy 32.7 wt. % and boron content in the alloy of 0.09 mass. %, calcium oleate in an amount of 1.1 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 9

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 41.6 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, powder alloy aluminum silicon (Al-Si), doped with boron, in the amount of 36.0 mass. % with silicon content in the alloy 32.7 wt. % and boron content in the alloy of 0.09 mass. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 10 For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 34.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, powder alloy aluminum silicon (Al-Si), doped with boron, in the amount of 42.0 mass. % with silicon content in the alloy 32.7 wt. % and boron content in the alloy of 0.09 mass. %, calcium oleate in an amount of 1.1 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 11

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 40.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, powder alloy aluminum silicon (Al-Si), doped with boron, in the amount of 36.0 mass. % with a silicon content in the alloy of 42.4 mass. % and boron content in the alloy of 0.12 mass. %, calcium oleate in an amount of 1.1 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Example 12

For the preparation of conductive paste used: aluminum powder with a particle size of D50 3.2 μm in an amount of 40.5 mass. %, glass powder of the antimony-boron-silicon system in an amount of 0.4 mass. %, powder alloy aluminum silicon (Al-Si), doped with boron, in the amount of 36.0 mass. % with a silicon content in the alloy of 33.5 mass. % and boron content in the alloy of 0.32 mass. %, calcium oleate in an amount of 1.1 wt. %, the rest is an organic binder, a 10% solution of ethyl cellulose in a mixture of terpineol and butylcarbitol. The actual composition of the paste is shown in table 1. The parameters of the solar cell made using the paste are shown in table 2.

Table 1. The composition of the pastes and the parameters of solar cells made using these pastes. All components of the pastes are given in mass. %

Table 2. Parameters of solar cells with rear dielectric passivation and point local contacts.

The mass of the fingerprint was measured on a Sartorius CPA6202S electronic balance. The measurement error is not more than ± 0.005 mm. In the mass industrial production of solar cells, the mass of the imprint of aluminum paste should be in the range of 1.0-0, 4 g. More preferably 0.8-0.6 g.

The deflection of solar cells was measured on a Keyence LK-036 laser optical system. The measurement error is not more than ± 0.025 mm. In the mass industrial production of solar cells, the deflection should be less than 1.5 mm.

The efficiency of the solar cell and other current-voltage characteristics (Voc is the open circuit voltage, Jsc is the short circuit current density and FF is the factor) were measured using the H.A.L.M. cetisPV-Celltest3 (Germany). Measurement class installation "AAA". In the mass industrial production of solar cells, each of these parameters should be the maximum possible.

The heterogeneity of the local BSF layer and damage to the back dielectric passivation was determined as the percentage of black areas with an increased recombination rate of the total area of local contacts on the electroluminescence maps obtained with the H.A.L.M. cetisPV-Celltest3 (Germany). In mass industrial production of solar cells, the total area of black areas with an increased recombination rate on electroluminescence maps should be no more than 5%. More preferably, the complete absence of black patches.

The resistance of the borne layer of aluminum paste was measured using a H.A.L.M. cetisPV-Celltest3 (Germany). In the mass industrial production of solar cells, the resistance of the driven layer of aluminum paste should be as low as possible.

The presence of aluminum balls was evaluated visually using a wide-field microscope Wild (Germany). For a quantitative assessment, a five-point scale was used, where “0” - aluminum balls are completely absent, “5” - the maximum number of balls. In the mass industrial production of solar cells, the number of balls should not exceed the level of "1". More preferably, the complete absence of balls.

Adhesion after lamination was measured on a MEGEON-03050 digital dynamometer. The measurement error is not more than ± 0.5 N / cm. For the manufacture of samples of laminated solar cells, a Panamac DM 12 laminator (Italy) and an ethylene vinyl acetate laminate were used. In the mass industrial production of solar cells, adhesion after lamination should be more than 10 N / cm. Adhesion greater than 20 N / cm is more preferred. Industrial applicability

In the aluminum paste for silicon solar cells with rear dielectric passivation, according to the invention, a lower concentration of glass powder in the paste is used with the simultaneous use of organometallic compounds of alkaline earth metals, including in combination with an alloy powder (Al-Si) doped with an optimal amount of boron, which distinguishes her from famous pastes. This composition of conductive paste provides an increase in the efficiency of the solar cell due to low damage to the quality of the back dielectric passivation during the burning of the paste and the formation of a uniform local BSF in local contacts. At the same time, the paste, according to the invention, allows to obtain a set of consumer requirements for the solar cell, namely: low deflection of less than 1.0 mm, adhesion after lamination above 20 N / cm, the complete absence of aluminum balls on the surface of the paste layer of paste.

An aluminum paste made in accordance with the invention can be used in the production of silicon solar cells with back dielectric passivation to form a back electrode with linear-dashed, linear-point and point local contacts.

Claims

Claim

1. Aluminum paste for the manufacture of the rear contact of silicon solar cells with rear dielectric passivation, including aluminum powder, an organic binder, glass powder, characterized in that the paste additionally contains one or a mixture of organometallic compounds of alkaline earth metals, in the following ratio, in mass. %:

aluminum powder 68-82;

glass powder not more than 1, 0; organometallic compounds of alkaline earth metals 0.1 -2.0;

organic binder 15-29.

2. The aluminum paste according to claim 1, characterized in that as the organometallic compounds it contains one or a mixture of substances from a number of oleates, stearates or octoates of magnesium, calcium, strontium or barium.

3. The aluminum paste according to claim 1, characterized in that it further comprises a powder of boron-doped Al-Si alloy, which partially replaces the aluminum powder, at a constant total concentration of aluminum powder and boron-doped Al-Si powder, in the following ratio of components in mass. %:

a mixture of aluminum powders and an Al-Si alloy doped with boron 68-82;

glass powder not more than 1.0; organometallic compounds of alkaline earth metals 0.1 -2.0;

organic binder 15-29.

4. Aluminum paste according to claim 3, characterized in that the paste uses the following ratio of components, in mass. %:

aluminum powder 35-42;

Al-Si alloy doped with boron 33-40;

glass powder not more than 1.0; organometallic compounds of alkaline earth metals 0, 1 -2.0;

organic binder 15-29.

5. Aluminum paste according to claim 3, characterized in that the boron concentration in the powder of the Al-Si alloy doped with boron is in the range 0.04-0.2 mass. %, at the same time the concentration of silicon lies in the range of 15-40 mass. %