CN102403406A - Preparation method for back contact type silicon solar cell - Google Patents

Abstract

The invention discloses a method for preparing a back-contact silicon solar cell, which comprises the following steps: (1) performing texturing on the light-receiving surface of a silicon wafer, and then opening holes; (2) performing coating source diffusion on the light-receiving surface of the silicon wafer Make a junction, form a PN junction on the light-receiving surface and the hole; (3) set a transparent conductive film on the above-mentioned light-receiving surface and the PN junction in the hole; (5) prepare a through-hole electrode, a back metal electrode, and a back passivation field on the non-coated surface of the above-mentioned silicon wafer to obtain the back-contact silicon solar cell; the through-hole electrode and the transparent The conductive film is in electrical communication. The light-receiving surface of the back-contact silicon solar cell prepared by the invention is not shielded by electrodes, which avoids light-shielding loss and significantly improves the photoelectric conversion efficiency; the number of holes to be opened is also greatly reduced, thereby greatly reducing the fragmentation rate and simplifying the preparation process.

Description

A kind of preparation method of back contact silicon solar cell

technical field

The invention relates to a method for preparing a back-contact silicon solar cell, belonging to the field of crystalline silicon solar cell manufacturing.

Background technique

Conventional fossil fuels are being exhausted day by day. Among the existing sustainable energy sources, solar energy is undoubtedly the cleanest, most common and most potential alternative energy source. At present, among all solar cells, silicon solar cells are one of the solar cells that have been widely commercialized. This is due to the extremely abundant reserves of silicon materials in the earth's crust. With excellent electrical and mechanical properties, silicon solar cells occupy an important position in the field of photovoltaics. Therefore, developing cost-effective silicon solar cells has become one of the main research directions of photovoltaic companies in various countries.

The power generation principle of silicon solar cells is based on the photovoltaic effect of semiconductor PN junctions. At present, there are many types and structures of solar cells. The more common method is to place the positive and negative electrodes of the solar cell on the light-receiving side and the backlight side respectively. Similar solar cells can realize positive and negative interconnection through low-resistance metals. However, this type of solar cell has a large shading loss because many areas on the light-receiving surface are blocked by electrodes, thus losing a part of the current.

In order to improve the loss of photoelectric conversion caused by the above structure, solar cells with various structures have been developed, among which there is a type called "back contact" cell, which is characterized in that the positive and negative electrodes of the cell are both arranged on the backlight surface. The shading loss of the light-receiving surface can be reduced, the photoelectric conversion efficiency can be increased, and the interconnection between solar cells can be facilitated.

In the prior art, there are several schemes for realizing "back contact" solar cell devices:

One is that the PN junction is set on the backlight surface of the device, and there is no PN junction on the light-receiving surface. Please refer to the literature (R.A. Sinton, Y. Kwark, J.Y. Gan, R.M. Swanson, IEEE Electron Device Letters, Vol. ED- 7. No. 10 , October 1986); the cell with this structure needs a silicon wafer with excellent quality (mainly the minority carrier lifetime is large enough) to ensure that the current generated by the light-receiving surface can pass through the entire base region to reach the electrode on the backlight surface; therefore, this type Solar cells are very picky about raw materials, and it is difficult to promote them on a large scale under the current manufacturing level, and the manufacturing cost is very high.

The second solution is MWT battery (Metal wrap through). The PN junction is still made on the light-receiving surface of the device. At the same time, dozens to dozens of holes are made throughout the entire device. The inner wall of the hole is equipped with low-resistance electrodes and light-receiving surface electrodes. Then the photocurrent generated by the light-receiving surface can be conducted from the electrode in the hole to the corresponding electrode on the backlight surface of the device. This solution well solves the aforementioned weakness of the back-contact solar cell, and can use the existing level of silicon wafers to produce solar cells with higher photoelectric conversion efficiency, while hardly increasing the cost. Many patents have disclosed their corresponding technologies, such as WO2010126346, JP2010080576, JP2010080578, US20100276772, US20090188550, US20090178707 and KR1020100098993. The loss affects the further improvement of photoelectric conversion efficiency.

In order to solve the above problems, some researchers have proposed a new structure battery device (Emitter wrap through, referred to as EWT) with no electrodes on the light-receiving surface; its characteristic is that the PN junction is still made on the light-receiving surface of the device, and tens of thousands of them are made throughout the entire device at the same time. The inner wall of the hole is doped with a high concentration of PN junctions, and is connected to the corresponding electrode on the backlight surface through a low-resistance electrode, so the photocurrent generated by the light-receiving surface can be conducted to the backlight surface of the device by the electrode in the hole.多个专利涉及了相应技术，如US7851696、CA2596827、US7144751、CA2530743、US20090320922、US20110086466、WO2005006402、CA2530684、US7649141、WO2005018007、WO2005076959、WO2005076960、WO2006029250、US7863084以及KR1020110011053。 Although this technology avoids the shading loss caused by the front electrode, in order to ensure that the current on the light-receiving surface is transmitted to the back without loss, tens of thousands of holes need to be set, and high-concentration doping needs to be formed in the holes. These conditions have led to its preparation. The process is very complicated and the cost is high; at the same time, too many holes also affect the mechanical strength of the device, and a large number of silicon wafers will be broken during production.

Contents of the invention

The object of the present invention is to provide a method for preparing a back-contact silicon solar cell.

In order to achieve the above object, the technical solution adopted in the present invention is: a method for preparing a back-contact silicon solar cell, comprising the steps of:

(1) Carry out texturing on the light-receiving surface of the silicon wafer, and then open holes;

(2) Carry out coating source diffusion junction on the light-receiving surface of the above-mentioned silicon wafer, and form a PN junction on the light-receiving surface and the hole;

(3) After removing the phosphosilicate or borosilicate glass, set a transparent conductive film on the light-receiving surface and the PN junction in the hole;

(4) Peripheral etching to remove the transparent conductive film around the silicon wafer; then plate an anti-reflection film on the transparent conductive film on the light-receiving surface of the silicon wafer;

(5) Prepare a through-hole electrode, a back metal electrode, and a back passivation field on the non-coated surface of the above-mentioned silicon wafer to obtain the back-contact silicon solar cell; the through-hole electrode is electrically connected to the transparent conductive film.

In the above, the silicon wafer may be p-type or n-type. The back passivation field is a dopant substance or a dielectric passivation film of the same conductivity type as that of the silicon chip, or both. The back passivation field is electrically connected to the back metal electrode, and the two are isolated from the through-hole electrode only by air insulation, and the electrode polarity is opposite.

The non-coated surface of the silicon wafer in the step (5) refers to the surface of the silicon wafer that is not coated with an antireflection coating, that is, the surface of the silicon wafer that is not coated with an antireflection coating.

The coating source diffusion junction is an existing technology, which refers to the use of screen printing, spin coating or inkjet printing to cover the slurry or solution or ink containing doping elements on the surface of the silicon wafer that needs to be junctioned. After high temperature treatment, a PN junction is obtained. The doping element composition refers to elements containing phosphorus or boron. For example, a p-type silicon chip should be covered with a slurry or solution or ink containing a phosphorus-doped element, while an n-type silicon chip should be covered with a slurry or solution containing a boron-doped element. or ink.

In the above technical solution, the number of holes in the step (1) is 2 to 500. Preferably, the number of holes in the step (1) is 9-100.

In the above technical solution, the transparent conductive film in the step (3) is an ITO film, a SnO ₂ film, an In ₂ O ₃ film, a ZnO film, a Cd ₂ SnO ₄ film or an FTO film. These are all prior art, wherein, ITO thin film refers to tin-doped indium oxide transparent conductive film, and FTO thin film refers to SnO ₂ Doped F transparent conductive film. Certainly, the above-mentioned transparent conductive film may also be selected from CuGaO ₂ , CuInO ₂ , SrCu ₂ O ₂ , or ZnO doped with B, Al, Ga, In, etc.

In the above technical scheme, the thickness of the transparent conductive film in the step (3) is 80-1000 nm. Preferably, the thickness of the transparent conductive film is 100-500 nm.

Another corresponding technical solution, a method for preparing a back-contact silicon solar cell, comprises the following steps:

(1) Open holes on the surface of the silicon wafer, and then make texture on the light-receiving surface;

(2) Carry out coating source diffusion junction on the light-receiving surface of the above-mentioned silicon wafer, and form a PN junction on the light-receiving surface and the hole;

(3) After removing the phosphosilicate or borosilicate glass, set a transparent conductive film on the light-receiving surface and the PN junction in the hole;

(4) Peripheral etching to remove the transparent conductive film around the silicon wafer; then plate an anti-reflection film on the transparent conductive film on the light-receiving surface of the silicon wafer;

(5) Prepare a through-hole electrode, a back metal electrode, and a back passivation field on the non-coated surface of the above-mentioned silicon wafer to obtain the back-contact silicon solar cell; the through-hole electrode is electrically connected to the transparent conductive film.

In the above technical solution, the number of holes in the step (1) is 2 to 500.

In the above technical solution, the transparent conductive film in the step (3) is an ITO film, a SnO ₂ film, an In ₂ O ₃ film, a ZnO film, a Cd ₂ SnO ₄ film or an FTO film.

In the above technical scheme, the thickness of the transparent conductive film in the step (3) is 80-1000 nm.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

1. The present invention has prepared a new back-contact silicon solar cell. Compared with the existing MWT cell, the light-receiving surface of the cell of the present invention has no electrode shielding, avoids the loss of light shielding, and significantly improves the photoelectric conversion efficiency; compared with the existing MWT cell Compared with the EWT battery, the battery of the present invention needs to greatly reduce the number of holes, thereby greatly reducing the debris rate and simplifying the preparation process.

2. The preparation method of the invention is simple and does not require high-quality silicon chips, so the cost is low and it is suitable for large-scale production.

3. The invention uses a transparent conductive film to replace the electrodes on the light-receiving surface, taking into account both light transmission and current collection, so there is no shielding by the electrodes on the light-receiving surface, the photoelectric conversion efficiency is significantly improved, and the appearance is uniform and beautiful.

Description of drawings

Accompanying drawing 1～8 is the preparation process schematic diagram of the embodiment of the present invention one;

FIG. 9 is a schematic structural diagram of a back-contact silicon solar cell in Embodiment 1 of the present invention.

Among them: 1. Silicon wafer; 2. PN junction; 3. Transparent conductive ITO film; 4. Hole; 5. Anti-reflection film; 6. Through-hole electrode; 7. Back metal electrode; 8. Back passivation field.

Detailed ways

The present invention will be further described below in conjunction with embodiment:

Embodiment one

Referring to Figures 1 to 9, a method for preparing a back-contact silicon solar cell, the silicon wafer is p-type, includes the following steps:

The first step is texturing, the purpose of which is to form an uneven structure on the surface of the original bright silicon wafer through chemical reaction to prolong the propagation path of light on its surface, thereby improving the absorption of light by the silicon wafer 1; the silicon wafer after texturing The schematic diagram of the structure is shown in Figure 1;

The second step is to open holes 4 on the silicon wafer, the number of which is 100. Its function is to set electrodes in the holes 4 to lead the current from the light-receiving surface of the battery sheet to the backlight surface of the battery sheet, so that the positive electrode of the battery sheet Both the negative electrode and the negative electrode are located on the back of the cell; the holes can be opened by laser, mechanical drilling or chemical etching; the structural diagram of the silicon wafer after opening is shown in Figure 2;

The third step is to screen-print phosphorus-containing paste on the light-receiving surface of the silicon wafer, and form a PN junction 2 on the light-receiving surface after heat treatment at 800°C. At the same time, a PN junction 2 is also formed on the inner wall of the hole 4, and then remove the phosphosilicate glass with hydrofluoric acid; The schematic diagram of the structure after forming the PN junction is shown in Figure 3;

The fourth step is to plate a 500nm thick transparent conductive ITO film 3 on the PN junction, including the inner wall of the hole 4 and the periphery of the silicon wafer, as shown in Figure 4; the purpose of the transparent conductive ITO film here is to replace the traditional metal electrode, effectively Collect the photocurrent generated by conducting the light-receiving surface without blocking the incident light; there are many methods for coating ITO thin films, such as magnetron sputtering, organic metal vapor deposition, vacuum evaporation, chemical vapor deposition, spray coating, sol-gel Glue method, electrostatic spray assisted vapor deposition and other methods; in this embodiment, the ITO thin film is coated by magnetron sputtering;

The fifth step, peripheral etching, the purpose is to remove the transparent conductive ITO film around the porous silicon wafer to avoid short circuit; in the embodiment of the present invention, the side of the silicon wafer 1 is etched for 15 minutes with plasma gas, wherein SF in the plasma gas ₆ The flow rate of _O2 is 200scm, the flow rate of O2 is 30scm, the flow rate of _N2 is 300scm, the pressure is selected as 100Pa, and the glow power is selected as 700W; the schematic diagram of the silicon wafer after etching is shown in Figure 5;

The sixth step is to coat the silicon nitride anti-reflection film 5 on the transparent conductive ITO film 3. The effect of this film is to reduce the reflection of sunlight and maximize the use of solar energy; in this embodiment, PECVD (Plasma Enhanced Chemical Vapor Deposition, plasma-enhanced chemical vapor deposition method) forms an anti-reflection film on the silicon wafer; the schematic diagram of the structure of the silicon wafer after the anti-reflection film 5 is coated is shown in Figure 6;

The seventh step is to screen-print the through-hole electrode 6 on the non-plated anti-reflection film surface of the silicon wafer as the negative electrode; in this embodiment, the through-hole electrode 6 can also be deposited on the silicon wafer 1 by vacuum evaporation, sputtering, etc. Above; the through-hole electrode 6 is prepared to be electrically connected with the transparent conductive ITO film 3, and its structural schematic diagram is shown in FIG. 7 ;

In the eighth step, screen print the back metal electrode 7 on the non-plated anti-reflection film surface of the silicon wafer as the positive electrode; in this embodiment, the back metal electrode 7 can also be deposited on the silicon wafer by methods such as vacuum evaporation and sputtering ; The structural schematic diagram of preparing the back electrode 7 is shown in FIG. 8 ;

The ninth step is to screen-print the aluminum back passivation field 8 on the non-plated antireflection film surface of the silicon wafer; in this embodiment, the aluminum back passivation field can also be deposited on the silicon wafer by methods such as vacuum evaporation and sputtering. Above; a schematic diagram of the structure of the aluminum back passivation field 8 is shown in FIG. 9 ; wherein, the back passivation field 8 is electrically connected to the back metal electrode 7 , and the two are isolated from the through-hole electrode 6 only by air insulation.

Fig. 9 is a schematic structural view of a back-contact silicon solar cell prepared according to the method of the present invention.

Embodiment two

A method for preparing a back-contact silicon solar cell, the silicon wafer is n-type, comprising the steps of:

The first step is texturing; its purpose is to form an uneven structure on the surface of the originally bright silicon wafer through chemical reaction to prolong the propagation path of light on its surface, thereby improving the absorption of light by the silicon wafer;

The second step is to open holes on the silicon wafer, the number of which is 60, and its function is to set electrodes in the through holes to lead the current from the light-receiving surface of the battery to the backlight surface of the battery, so that the positive electrode and the backlight of the battery can be connected. The negative electrodes are all located on the back of the battery sheet; in this embodiment, laser, mechanical drilling or chemical etching can be used to open holes;

The third step is to screen-print boron-containing paste on the surface of the silicon wafer, and form a PN junction on the light-receiving surface after heat treatment at 800 ° C. At the same time, a PN junction is also formed on the inner wall of the hole, and the borosilicate glass is removed with hydrofluoric acid;

The fourth step is to plate a 300 nm thick transparent conductive SnO ₂ :F film (FTO) on the PN junction, including the inner wall of the hole and the periphery of the silicon wafer; the purpose of the transparent conductive SnO ₂ :F film here is to replace the traditional metal electrode, Effectively collect the photocurrent generated by conducting the light-receiving surface without blocking the incident light; there are many methods for coating SnO ₂ : F thin films, such as magnetron sputtering, organic metal vapor deposition, vacuum evaporation, chemical vapor deposition, spraying method, sol-gel method, electrostatic spray assisted vapor deposition and other methods; in the embodiment, the SnO ₂ :F film is coated by magnetron sputtering method;

The fifth step, peripheral etching; the purpose is to remove the surrounding transparent conductive SnO ₂ : F thin film and PN junction, to avoid short circuit; in an embodiment, adopt plasma gas to etch the side of the silicon wafer for 15min, wherein SF in the plasma gas ₆ The flow rate of O2 is 200scm, the flow rate of _O2 is 30scm, the flow rate of _N2 is 300scm, the pressure is 100Pa, and the glow power is 700W;

The sixth step is to use PECVD (Plasma Enhanced Chemical Vapor Deposition, plasma enhanced chemical vapor deposition method) to coat the silicon dioxide anti-reflection film on the SnO ₂ :F film. The function of this film is to reduce the reflection of sunlight and maximize the Utilize solar energy; in this embodiment, form anti-reflection film on silicon chip;

The seventh step is to screen-print a through-hole silver electrode on the non-plated anti-reflection film surface of the silicon wafer as the positive electrode; in this embodiment, the through-hole electrode can also be deposited on the silicon wafer by methods such as vacuum evaporation and sputtering; Prepare the through-hole electrode to be electrically connected with the transparent conductive SnO ₂ :F film;

In the eighth step, screen print the back silver electrode on the non-plated anti-reflection film surface of the silicon wafer as the negative electrode; in this embodiment, the back electrode can also be deposited on the silicon wafer by methods such as vacuum evaporation and sputtering;

The ninth step is to screen-print phosphorous paste doping on the non-plated anti-reflection film surface of the silicon wafer and grow silicon nitride by PECVD method as a composite back passivation field; wherein, the composite back passivation layer is electrically connected to the back silver electrode , the two are isolated from the through-hole silver electrode only by air insulation; the back contact silicon solar cell can be obtained.

The above descriptions are only preferred embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the present application will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. the preparation method of a back contact silicon solar cell is characterized in that, comprises the steps:

(1) sensitive surface at silicon chip carries out making herbs into wool, offers hole then;

(2) sensitive surface at above-mentioned silicon chip is coated with source diffusion system knot, in sensitive surface and hole, forms PN junction;

(3) behind removal phosphorus silicon or the Pyrex, on the PN junction in above-mentioned sensitive surface and hole nesa coating is set;

(4) peripheral etching, the nesa coating of removal silicon chips periphery; Antireflective coating is established in plating on the nesa coating of silicon chip sensitive surface then;

(5) preparation perforation electrode, back of the body metal electrode, back of the body passivation field on the non-plated film face of above-mentioned silicon chip can obtain said back contact silicon solar cell; Said perforation electrode and nesa coating electric connection.

2. the preparation method of back contact silicon solar cell according to claim 1 is characterized in that: the quantity of hole is 2 ~ 500 in the said step (1).

3. the preparation method of back contact silicon solar cell according to claim 2 is characterized in that: the quantity of hole is 9 ~ 100 in the said step (1).

4. the preparation method of back contact silicon solar cell according to claim 1 is characterized in that: the nesa coating in the said step (3) is ito thin film, SnO ₂Film, In ₂O ₃Film, ZnO film, Cd ₂SnO ₄Film or FTO film.

5. the preparation method of back contact silicon solar cell according to claim 1 is characterized in that: the thickness of the nesa coating in the said step (3) is 80 ~ 1000 nm.

6. the preparation method of back contact silicon solar cell according to claim 5 is characterized in that: the thickness of said nesa coating is 100 ~ 500 nm.

7. the preparation method of a back contact silicon solar cell is characterized in that, comprises the steps:

(1) offers hole at silicon chip surface, carry out making herbs into wool at its sensitive surface then;

(2) sensitive surface at above-mentioned silicon chip is coated with source diffusion system knot, in sensitive surface and hole, forms PN junction;

(3) behind removal phosphorus silicon or the Pyrex, on the PN junction in above-mentioned sensitive surface and hole nesa coating is set;

(4) peripheral etching, the nesa coating of removal silicon chips periphery; Antireflective coating is established in plating on the nesa coating of silicon chip sensitive surface then;

(5) preparation perforation electrode, back of the body metal electrode, back of the body passivation field on the non-plated film face of above-mentioned silicon chip can obtain said back contact silicon solar cell; Said perforation electrode and nesa coating electric connection.

8. the preparation method of back contact silicon solar cell according to claim 7 is characterized in that: the quantity of hole is 2 ~ 500 in the said step (1).

9. the preparation method of back contact silicon solar cell according to claim 7 is characterized in that: the nesa coating in the said step (3) is ito thin film, SnO ₂Film, In ₂O ₃Film, ZnO film, Cd ₂SnO ₄Film or FTO film.

10. the preparation method of back contact silicon solar cell according to claim 7 is characterized in that: the thickness of the nesa coating in the said step (3) is 80 ~ 1000 nm.

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