CN100483750C - Back point-contact silicon solar cell based on silk-screen printing technology and making method - Google Patents

Abstract

The back point contact silicon solar cell based on the screen printing process, the P-type silicon wafer is provided with a PN junction formed by phosphorus diffusion, the front side is provided with a silicon nitride layer or a silicon dioxide layer surface passivation layer and an anti-reflection film, and a positive electrode. The feature is that the back metal layer of the silicon chip forms an ohmic contact through the p-type dot-shaped alloy diffusion region, and a passivation layer is provided between other parts of the back metal and the back side of the silicon chip. The manufacturing method is as follows: the silicon wafer is of P type; the suede surface is made and cleaned; phosphorus is diffused to form a PN junction; the edge is etched by plasma etching; silicon nitride or silicon dioxide is grown on both sides; The method of phase diffusion or selective gas phase diffusion is used to make the concentrated area of P ⁺ in point contact; the front side is printed by screen printing and sintered; the back side is covered with a metal layer. According to the invention, the open-circuit voltage of the battery is greater than 650mV, the current density is greater than 38mA/cm ² , the filling factor is 74%-78%, and the conversion efficiency of the battery can reach 18%-20%.

Description

Fabrication method of back point contact silicon solar cell based on screen printing process

technical field

The invention relates to a solar cell, in particular to a method for manufacturing a backside point-contact silicon solar cell with high efficiency and low cost based on a screen printing process.

Background technique

The silicon solar cell is actually a PN junction device. The photo-generated carriers generated by the light are swept to both sides of the PN junction through the electric field of the PN junction to form a photo-generated current to achieve the effect of photoelectric conversion. In order to increase photogenerated carriers, the surface of the solar cell is made into a textured or pyramid-like structure to increase light absorption, and an anti-reflection film is used to reduce light reflection. In order to reduce the recombination of photogenerated carriers, structures or measures to reduce the recombination mechanism are added in the silicon body and surface. In the body, high-purity, defect-free, low-oxygen silicon single crystal or polycrystalline materials should be selected; high-quality diffusion methods are used in the structure to form high-quality PN junctions, and the concentration on both sides of the PN junction should not be too thick to avoid Form a "dead zone"; the back surface forms a back electric field through diffusion, accelerates the drift speed of photogenerated carriers, and so on. On the surface, use various passivation techniques such as PECVD to grow silicon nitride films to reduce surface recombination; reduce the diffusion area of the concentrated regions on both sides of the silicon wafer, etc.

The manufacturing process of silicon solar cells can be compared to the process of integrated circuits. However, the low cost of solar cells determines that its process technology must be a large-capacity and low-cost process technology. Reducing process manufacturing costs and improving the conversion efficiency of solar cells are the main technical cores. In the manufacturing process of solar cells, the ordinary diffusion process is used for diffusion, and the PECVD process is used for surface passivation. These two processes are similar to the integrated circuit process. Metallization uses screen printing and sintering processes, which are high-throughput and low-cost. Solar cells do not use photolithography.

The main process of conventional screen printing solar cell manufacturing process is as follows:

1. The silicon wafer is P-type 0.5-10 ohm-cm, with a thickness of 0.2μm-0.4μm.

2. Suede production and cleaning:

Texture is formed on both sides of the silicon wafer by chemical etching.

3. Phosphorus diffuses to form a PN junction.

4. Plasma etching corrodes the edges.

5. Silicon nitride grown by PECVD is used as surface passivation and anti-reflection film on the upper surface of the silicon wafer.

6. Screen printing electrodes and sintering, in which the front metal is the main grid line and the sub grid line; the back metal is full-area contact.

The structure diagram is shown in Fig. 1: p-type silicon wafer 1; silicon nitride passivation layer 2 deposited on the front side; back metal 4 on the whole area on the back side.

The efficiency of monocrystalline silicon solar cells produced by the conventional screen printing process is about 16%, the open circuit voltage is about 600mV, the fill factor is about 75%-78%, and the current density is about 35mA/cm ² .

The back of the solar cell produced by the conventional screen printing process is a full-area metal contact, without surface passivation, and the surface state is poor. The open circuit voltage and short circuit current of the cell are greatly affected, and the adverse effect on cell efficiency is obvious. .

Contents of the invention

Aiming at the shortcomings of low open-circuit voltage and small short-circuit current caused by the all-metal contact structure on the back of the silicon solar cell produced by the above-mentioned conventional screen printing process, the present invention will provide a new structure of silicon solar cell based on the conventional screen printing process: Silicon solar cells with point contact on the back, this kind of silicon solar cells with point contact structure on the back can significantly improve the performance of solar cells, so that the open circuit voltage of the cell is >650mV, the current density is >38mA/cm ² , and the fill factor can reach 74%~78 %, the conversion efficiency of the battery can reach 18% to 20%. At the same time, the invention will also provide the manufacturing method of the silicon solar cell.

The solution for accomplishing the above-mentioned invention task is: based on the backside point contact silicon solar cell of the screen printing process, the P-type silicon wafer is provided with a PN junction formed by phosphorus diffusion, and the front side is provided with a silicon nitride layer or a silicon dioxide layer for surface passivation. layer and anti-reflection coating, and the positive electrode. It is characterized in that the back metal layer of the silicon chip forms an ohmic contact through the p-type dot-shaped alloy diffusion region, and a passivation layer is provided between other parts of the back metal and the back side of the silicon chip.

In other words, the front structure of the silicon solar cell according to the present invention is the same as that of the solar cell produced by the conventional screen printing process. Metalization. The new structure means: it increases the back passivation layer and the back point contact of the solar cell.

至3000

之间即可，太薄有针孔，太厚则加长工艺时间，增加成本。The back passivation layer means that the back passivation layer can be formed by growing silicon nitride by PECVD, or by thermal oxidation to form a passivation layer of silicon dioxide. The thickness of the passivation layer is not critical, at 1000

to 3000

If it is too thin, there will be pinholes; if it is too thick, the process time will be prolonged and the cost will be increased.

The point contact on the back side refers to: the back side passes through the point diffusion region as a contact with the back side electrode. The back side is point contact alloy diffusion. The point area of point contact can be more than 200μm×200μm. The point contact points are arranged in a surface array, and the distance between points is controlled within 1mm. The ratio is controlled between 0.1% and 20%: the smaller the ratio, the higher the open circuit voltage and the larger the short circuit current, but the fill factor decreases, and the opposite is true if the ratio is large. Optimizing the area ratio of point contacts can find the best conversion efficiency.

Under the condition that the resistivity of the p-type silicon substrate is 1Ω-CM, the typical point contact area ratio is 0.5-2.5%, and about 1.5% is recommended in this application.

The size of the point contact area is determined by the accuracy of screen printing; the printed paste can be aluminum paste, silver-aluminum paste, etc., or a mixed paste mainly composed of aluminum and other three-group elements; after sintering and diffusion Form ohmic contact with the p-type silicon of the body and obtain a certain depth. The temperature of sintering and diffusion can be controlled at about 680°C to 1150°C. The higher the temperature, the deeper the depth of diffusion.

Printing paste This application recommends the use of aluminum-boron paste or a mixed paste of three group elements mainly composed of aluminum.

The manufacturing method of the above structure is: on the basis of the existing general screen printing process, the diffusion source of the point contact on the back is printed by screen printing to achieve the purpose of selective diffusion, and then connected to the back electrode through the sintering process . The structure and process method are widely applicable to the solar cell production process of screen printing, and the solar cell produced according to the method can increase the absolute conversion efficiency by 2% to 4%.

More specifically and more optimally, the structure of the above-mentioned backside point-contact silicon solar cell with high efficiency and low cost based on the screen printing process is characterized by:

1. The contact of the base area on the back of the battery is a point contact and is composed of a P ⁺ concentrated area. The concentration of the concentrated area can be above 10 ¹⁸ /cm ³ , and the junction depth of the concentrated area can be above 0.5 μm.

The upper limit of the concentration in the concentrated area is restricted by the manufacturing cost, and the higher the concentration, the better the technical effect if possible.

2. The P ⁺ concentration zone in point contact can be made by solid phase-solid phase diffusion and selective gas phase diffusion.

3. The method for forming the point contact area, that is, the "solid-solid phase diffusion, selective gas phase diffusion method" can be:

a. Silicon nitride or silicon dioxide is grown on both sides of the silicon wafer after phosphorus is diffused on the front side to form a PN junction. On the back, screen printing is used to print silver-aluminum paste or other dot matrix point contact sources containing group III elements. After high-temperature sintering, it burns through silicon nitride or silicon dioxide and then diffuses into the silicon body to form a dense diffusion region and ohmic contact. Finally, the metallization is formed by conventional sintering of silver and aluminum paste on the back side.

b. Silicon nitride or silicon dioxide is grown on both sides of the silicon wafer after phosphorous diffusion forms a PN junction on the front side. Laser drilling is used to drill out the point-contact dot matrix area on the back, and then the metallization is formed after the conventional full-printed silver-aluminum paste is sintered and diffused on the back.

c. After the array of point contacts is made by laser, the point contact depth can be several μm deep. Then the point contact hole is cleaned by alkali corrosion, and concentrated boron diffusion is formed in the point contact hole through conventional boron diffusion. Finally, the metallization is formed by conventional sintering of silver and aluminum paste on the back side.

d. The boron-concentrated area of point contact can also be realized by the "lift-off" process. The so-called "lift-off" process refers to the use of screen printing to print the point-contact diffusion source on the back of the silicon wafer ( This diffusion source can be composed of group III elements such as boron and aluminum sources, but it is best to have aluminum elements). Solid-solid diffusion is then carried out, and the diffusion temperature is between 950°C and 1150°C. Through such solid-solid diffusion, a p-type diffusion region with a concentration exceeding 10 ¹⁸ /cm ³ and a junction depth of several μm is generally formed. After the point contact on the back is formed, the phosphorus diffusion on the front and the passivation layer on both sides are done. The corrosion of the nitric acid etching solution will corrode the solid-solid diffusion source in point contact on the back, and the passivation layer attached to the solid-solid diffusion source will also fall off at the same time, and the point of the p-type concentrated area on the back will be The contact holes are exposed. Next, the double-sided metallization contact can be realized through the conventional metallization process.

4. Silicon nitride or silicon dioxide can be grown on both sides of the battery as passivation protection on both sides, and the passivation layer on the front side is also an anti-reflection layer.

5. A and b in the above third point are metallization after solid-solid phase diffusion, and c in the above third point is metallization after selective gas phase diffusion.

The present invention is based on the manufacturing method of the back point contact silicon solar cell of screen printing process, comprises the following steps:

The silicon chip is P-type 0.5-10 ohm-cm, with a thickness of 0.2μm-0.4μm;

suede making and cleaning;

Phosphorus diffuses to form a PN junction;

Plasma etching and corroding edges;

Silicon nitride or silicon dioxide grown on both sides;

On the back side, a point-contact P ⁺ concentrated area is made by screen printing by means of solid-solid diffusion or selective gas-phase diffusion;

The front side is screen-printed with electrodes and sintered;

Full-area metal layer on the back.

In the above-mentioned manufacturing method, the "concentrated region of point-contact P ⁺ made by solid phase-solid phase diffusion or selective gas phase diffusion" can be specifically selected from the following methods:

a. The back of the silicon wafer is screen-printed with silver-aluminum paste or other dot matrix point contact sources containing group III elements. After high-temperature sintering, it burns through silicon nitride or silicon dioxide and then diffuses into the silicon body to form a dense diffusion region and ohmic contact. Finally, the metallization is formed by conventional sintering of silver and aluminum paste on the back;

b. Use laser drilling to punch out the point-contact dot matrix area on the back, and then form metallization after sintering and diffusing the conventional full-printed silver-aluminum paste on the back;

c. After the array of point contacts is made by laser, the point contact depth can be several μm deep. Then the point contact hole is cleaned by alkali corrosion, and concentrated boron diffusion is formed in the point contact hole through conventional boron diffusion. Finally, the metallization is formed by conventional sintering of silver and aluminum paste on the back;

d. The boron-concentrated area of point contact can also be realized by the "lift-off" process. The so-called "lift-off" process refers to the backside of the silicon wafer printed with the point-contact diffusion source by screen printing ( This diffusion source can be composed of group III elements such as boron and aluminum sources, preferably aluminum). Solid-solid diffusion is then carried out, and the diffusion temperature is between 950°C and 1150°C. Through such solid-solid diffusion, a p-type diffusion region with a concentration exceeding 10 ¹⁸ /cm ³ and a junction depth of several μm is generally formed. After the point contact on the back is formed, the phosphorus diffusion on the front and the passivation layer on both sides are done. The corrosion of the nitric acid etching solution will corrode the solid-solid diffusion source in point contact on the back, and the passivation layer attached to the solid-solid diffusion source will also fall off at the same time, and the point of the p-type concentrated area on the back will be The contact holes are exposed. Next, the double-sided metallization contact can be realized through the conventional metallization process.

The back point contact silicon solar cell based on the screen printing process of the present invention obviously improves the performance of the cell, and can make the open circuit voltage of the cell > 650mV, the current density > 38mA/cm ² , and the fill factor of 74% to 78%. The conversion efficiency can reach 18% to 20%. The manufacturing method is simple and practical, and can be directly used in industrialized production.

specific implementation plan

Example 1:

Basic requirements for silicon wafers: p-type silicon wafers, resistivity: 0.5~10Ω-CM, thickness: 250~400μm.

The production process is:

cleaning;

Suede production: (1) Alkali corrosion (usually 100 crystal orientation single crystal silicon). Corrosion depth 5 ~ 15μm.

(2) Acid etching (usually monocrystalline silicon or polycrystalline silicon other than 100 crystal orientation) etching depth of 5-15 μm.

(3) Cleaning, HF rinse

Phosphorus diffusion: sheet resistance 50～100Ω-CM

。Silicon nitride deposited on both sides: PECVD, thickness ~ 1000

.

。Or thermally oxidized silica: thickness ~ 1000

.

Laser engraved point contact area on the back: the point contact area ratio is 0.5-20%, and the point contact depth is 3-5 μm.

Alkali corrosion, cleaning.

The positive electrode is screen-printed on the front side and sintered.

Full area back metal screen printed on the back, sintered.

Example 2:

Basic requirements for wafers: p-type silicon wafers, resistivity: 0.5~10Ω-CM, thickness: 250~400μm.

to clean

Suede production: (1) Alkali corrosion (usually 100 crystal orientation single crystal silicon). Corrosion depth 5 ~ 15μm.

(2) Acid etching (usually monocrystalline silicon or polycrystalline silicon other than 100 crystal orientation) etching depth of 5-15 μm.

(3) Cleaning, HF rinse

Phosphorus diffusion: sheet resistance 50～100Ω-CM

。Silicon nitride deposited on both sides: PECVD, thickness ~ 1000

.

。Or thermally oxidized silica: thickness ~ 1000

.

Laser engraved point contact area on the back: the point contact area ratio is 0.5-20%, and the point contact depth is 3-5 μm.

Alkali corrosion, cleaning.

Boron diffusion: sheet resistance 50～200Ω-CM

The positive electrode is screen-printed on the front side and sintered.

Full area back metal screen printed on the back, sintered.

Example 3:

Basic requirements for silicon wafers: p-type silicon wafers, resistivity: 0.5~10Ω-CM, thickness: 250~400μm.

to clean

Suede production: (1) Alkali corrosion (usually 100 crystal orientation single crystal silicon). Corrosion depth 5 ~ 15μm.

(2) Acid etching (usually monocrystalline silicon or polycrystalline silicon other than 100 crystal orientation) etching depth of 5-15 μm.

(3) Cleaning, HF rinse

Phosphorus diffusion: sheet resistance 50～100Ω-CM

Silicon nitride deposited on both sides: PECVD, thickness ~ 1000 ;

。Or thermally oxidized silica: thickness ~ 1000

.

The positive electrode is screen-printed on the front side and sintered.

Back metal with back screen printed point contacts, sintered.

Back screen printing back metal, low temperature sintering.

Example 4:

Basic requirements for wafers: p-type silicon wafers, resistivity: 0.5~10Ω-CM, thickness: 250~400μm.

to clean

Suede production: (1) Alkali corrosion (usually 100 crystal orientation single crystal silicon). Corrosion depth 5 ~ 15μm.

(2) Acid etching (usually monocrystalline silicon or polycrystalline silicon other than 100 crystal orientation) etching depth of 5-15 μm.

(3) Cleaning, HF rinse

Screen printing point contact pattern on the back: The diffusion source can be a solid-solid diffusion source such as boron aluminum.

Solid-solid diffusion on the back: sheet resistance ~ 100Ω-CM, junction depth of several μm.

Positive phosphorus diffusion: square resistance 50～100Ω-CM

Silicon nitride deposited on both sides: PECVD, thickness ~ 1000 .

Or thermally oxidized silica: thickness ~ 1000 .

Nitric acid "lift-off": Ultrasonic corrosion in a nitric acid-based corrosion solution.

The positive electrode is screen-printed on the front side and sintered.

Back metal with back screen printed point contacts, sintered.

Back screen printing back metal, low temperature sintering.

Claims (2)

1, a kind of manufacture method of the back point-contact silicon solar cell based on silk-screen printing technique may further comprise the steps:

Silicon chip is selected the P type for use, and resistivity is 0.5～10 ohm-cm, thickness 0.2 μ m～0.4 μ m;

Matte is made and is cleaned;

Phosphorous diffusion forms PN junction;

Plasma etching corrosion edge;

Two sides grown silicon nitride or silicon dioxide;

The back side is made the P of a contact by silk screen printing with the method for solid phase-solid-state diffusion or selective vapor diffusion ⁺Dense district;

Positive by screen printing electrode and sintering;

Back side gross area adds metal level.

According to the manufacture method of the described back point-contact silicon solar cell based on silk-screen printing technique of claim 1, it is characterized in that 2, described " method with solid phase-solid-state diffusion or selective vapor diffusion is made the P of a contact ⁺Dense district ", be selected from one of following method:

A. silicon chip is positive through behind the phosphorous diffusion formation PN junction, two sides grown silicon nitride or silicon dioxide, the back side adopts silk screen printing to print silver-colored aluminium paste or other contain the some contact source of the dot matrix of group iii elements, burn silicon nitride or silicon dioxide through high temperature sintering and diffuse into silicon body again and form dense diffusion region and ohmic contact, form metallization through conventional back side all print silver aluminium paste sintering at last;

B. silicon chip is positive through behind the phosphorous diffusion formation PN junction, two sides grown silicon nitride or silicon dioxide; Utilize laser drilling to get the dot matrix zone of back side point contact, form metallization through conventional all print silver aluminium paste sintering diffusion back, the back side again;

C. after laser is made out the array of a contact, this some contact degree of depth is cleaned a some contact hole through caustic corrosion again in the 3-5 mu m range, and the boron diffusion by routine forms dense boron diffusion in a contact hole; Form metallization through conventional back side all print silver aluminium paste sintering at last;

D. Jie Chu concentrated boron area also the technology mode by " lift-off " realize that described " lift-off " technology is meant, the silicon chip back side that utilizes the method for silk screen printing will put the diffuse source seal of contact; Carry out solid-solid diffusion again, diffusion temperature forms concentration and surpasses 10 at 950 ℃ to 1150 ℃ ¹⁸/ cm ³With the p-type diffusion region of junction depth more than 0.5 μ m; After the some contact at the back side forms, do the passivation layer on positive phosphorous diffusion and two sides again; Utilize the corrosion of nitric acid corrosive liquid, the solid-solid diffusion source of back side point contact is eroded, the passivation layer that is attached on the solid-solid diffusion source also refutes simultaneously, and the some contact holes exposing in the dense district of p-type at the back side is come out; Realize the double-sided metal contact by conventional metallization process then.