KR20120060582A - High efficiency cellular cell manufacturing method - Google Patents

Abstract

PURPOSE: A method for manufacturing a solar cell with high efficiency is provided to reduce manufacturing costs by using a thin film wafer and reducing an amount of paste of the solar cell. CONSTITUTION: A substrate(11) is prepared. An emitter layer(12) is formed on the substrate. An anti-reflection layer(13) is formed on the emitter layer. A groove(14) is formed on the anti-reflection layer and the emitter layer. A selective emitter(15) is formed in the groove. An electrode(16) is formed in the selective emitter by a gravure offset printing method.

Description

High efficiency solar cell manufacturing method {HIGH EFFICIENCY CELLULAR CELL MANUFACTURING METHOD}

The present invention relates to a method for manufacturing a high efficiency solar cell, and more particularly, to a method of forming an emitter by simultaneously applying patterning and diffusion using a laser and a method of manufacturing a solar cell using gravure offset printing. will be.

Recently, with increasing interest in environmental problems and energy depletion, there is a growing interest in solar cells as an alternative energy with abundant energy resources, no problems with environmental pollution, and high energy efficiency.

Solar cells can be divided into solar cells that generate steam required to rotate a turbine using solar heat, and solar cells that convert photons into electrical energy using properties of semiconductors. Among them, researches on solar cells that convert light energy into electrical energy by using electrons and holes generated by absorbed photons have been actively conducted.

Silicon solar cells, which are representative examples of such solar cells (hereinafter abbreviated as "solar cells"), generally have an n-type semiconductor layer on the front side of a Si substrate and a p-type semiconductor on the back side. It is prepared by forming each layer. The front surface of the n-type semiconductor layer acts as an emitter, and in order to minimize the reflection of the irradiated light, the anti-reflection layer of the silicon nitride film or the oxide film is coated and then the electrodes are wired.

Wiring of the front electrode is generally accomplished by screen printing a metal paste, which has a problem of high contact resistance between the silicon surface and the front electrode. Therefore, in order to lower the contact resistance between the silicon surface and the front electrode, the front electrode is wired after forming a high concentration of emitter on the front surface of the Si substrate.

However, when a high concentration of emitters are formed up to the site where the front electrode is not located, a high concentration of dopants present on the surface are present in the silicon, resulting in formation of aggregates, thereby resulting in the life of the charge. lifetime decreases, which ultimately lowers the operating efficiency of the solar cell.

Accordingly, US Patent No. 5928438, etc., proposes a method for solving the above problem by forming a portion where the front electrode is wired in a solar cell with a relatively high concentration of emitter. Emitters of this structure are sometimes referred to as selective emitters.

Referring to the general manufacturing method of the selective emitter, first, an oxide film pattern is formed on the surface of the silicon wafer by a photolithography process, and then impurities are implanted to form a high concentration impurity layer, an oxide layer is removed, and a low concentration impurity layer Forming a film, applying an anti-reflection film on the front surface, forming a high concentration impurity region on the front surface, and forming an electrode on the back surface.

1 schematically shows a series of processes for some of them. Referring to FIG. 1, first, an oxide film 2 is formed on a silicon wafer 1, and a photosensitive film 3 is applied thereon. The photosensitive film is exposed using a photo mask and partially etched to form a patterned photosensitive film 3. After removing the oxide film 2 exposed through the patterned photosensitive film 3 with the etching solution, the photosensitive film 3a is removed. Next, after making the high concentration impurity region 4 which is a portion where the electrode is to be formed using thermal diffusion, the patterned oxide film 2 is removed and the thermal diffusion process is performed once more to form the low concentration impurity region 5 as a whole. do.

However, in the method, the impurity implantation process is performed twice, and the overall process is complicated because the overall process is complicated such as requiring an exposure mask, a photosensitive material, and an etchant for the photolithography process. The efficiency of the liver is not uniform and there are various problems such as high manufacturing cost.

In Korean Patent Application Publication No. 2002-0049718 (Patent No. 366353), an oxide film is formed on a surface of a silicon wafer, a photosensitive film is applied thereon, and partially etched by a photolithography process, and then selectively exposed. A method of fabricating a selective emitter by thermally diffusing impurities into a silicon wafer is presented. The method has the advantage of performing only one impurity implantation process, but has a fundamental problem that the manufacturing process is complicated because the photolithography process is still required for the selective formation (patterning) of the oxide film.

On the other hand, as in the patent, a silicon oxide film is preferably considered as a film that acts as a partially penetrable barrier in the process of thermal diffusion of impurities. However, in order to have flexibility in the process of forming such a partially permeable barrier, a metal oxide film, a nitride film, an amorphous silicon film, or the like may be substituted for the silicon oxide film.

However, these thin films are difficult to increase the manufacturing cost of solar cells or to obtain a desired level of impurity permeability compared to silicon oxide films, and more harsh conditions are required to completely remove them after completion of the impurity thermal diffusion process. do.

Therefore, there is a high need for a technique capable of forming selective emitters by a simple process while exhibiting high operating efficiency.

The present invention is to overcome the above-mentioned conventional problems, an object of the present invention is to improve the conversion efficiency of a polycrystalline silicon solar cell, controlling the diffusion depth to reduce the surface recombination of the excited electron hole pair short circuit current And prevent the leakage current by forming the emitter selectively, and also control the electrode structure of the front part where the sunlight is incident finely and high to reduce the shadow shadowing and short circuit current, open voltage, fidelity ( The present invention provides a method for manufacturing a high efficiency solar cell having a high fill factor.

As an example of a high efficiency solar cell manufacturing method according to the present invention,

Preparing a substrate; forming a thin emitter layer on the substrate; forming an antireflection film on the emitter layer; forming a groove in the antireflection film and the emitter layer; Heavy doping (n ++) is coated with a high concentration of impurities with a dopant applicator, and selectively diffused using an annealing laser to diffuse the high concentration of impurities to form a selective emitter, and a selective emi with gravure offset printing. Forming an electrode on the part consisting of the rotor,

The gravure offset printing method includes the step of applying a paste to the pattern groove of the pattern roll by using a squeeze, and the step of arranging the paste to be inserted into the pattern groove of the pattern roll using a doctor and leaving no paste in other portions thereof. And transferring the paste in the pattern groove to the outer diameter of the blanket roll while the blanket roll is rotated on the pattern roll, and the paste on the blanket roll is transferred onto the wafer while the blanket roll is rotated on the wafer. Consists of the following steps,

The grooving laser serves to open the anti-reflection film formed on the surface of the substrate so that the process for forming the selective emitter is carried out as a single device, and at the same time, the dopant applicator is applied to annealing by applying impurities in a uniform amount. The laser is used for both patterning and partial diffusion.

The high efficiency solar cell manufacturing method according to the present invention has the following effects.

1. In order to make a high efficiency solar cell, i) it needs to receive a lot of light and effectively capture it, ii) generate the maximum electric charge with the captured light. Therefore, various studies have been conducted to approach these characteristics. In the present invention, a selective emitter and an electrode forming method of maximizing a light receiving area can be applied to a solar cell manufacturing process.

2. High-efficiency silicon solar cells can be manufactured, increasing the amount of power produced per unit area (5 inches or 6 inches).

3. It is possible to reduce the manufacturing defect rate due to the cracking of the wafer because the metal paste transferred to the roll is printed on the wafer compared to the pressure of printing the metal paste on the existing screen by pressing with a squeeze.

4. Cost reduction by using paste of solar cell and thin wafer.

What has been described herein is just one embodiment for carrying out the method of manufacturing a high efficiency solar cell according to the present invention, and the present invention is not limited to the present embodiment, and the scope of the present invention as claimed in the following claims. Without departing from the technical spirit of the present invention to the extent that any person of ordinary skill in the art to which the present invention pertains various modifications can be made.

1 is a process chart of a conventional solar cell manufacturing method
2 is a process chart of a method of manufacturing a high efficiency solar cell according to the present invention
3 is a process chart of the gravure offset printing method
4 is a cross-sectional view of the gravure offset printing method
5 illustrates a selective emitter manufacturing process

Referring to FIG. 2 (a), the substrate 11 used in the present invention is a p-type polycrystalline silicon, which is formed in a tube or belt diffusion path using P (phosphorus) in a liquid state as an impurity to have semiconductor characteristics. To spread. The emitter layer 12 is formed on the substrate 11, wherein the thickness of the emitter layer 12 of n + has a property of approximately 70 to 100 mW / cm 2 and preferably may be fluid depending on the plasticity property. . The emitter layer 12 may include impurities of a type opposite to that of the substrate 11, that is, the n-type emitter layer is doped in the p-type semiconductor, and the p-type emitter layer is doped in the n-type semiconductor to form a pn junction. Form.

Referring to FIG. 2 (b), a material such as silicon nitride (SiNx) or SiNx / SiO 2 may be PECVD to minimize reflection of light incident on a surface of a semiconductor substrate having a thin emitter layer 12 formed thereon and to passivate the substrate. Plasma chemical vapor deposition) is used to form an anti-reflection coating (13). The reason for the passivation is to disable the dangling bonds or defects at the exposed silicon wafer substrate, thereby reducing the possibility of charge recombination by reducing the disappearance of charges such as electrons and holes generated when light enters To give.

    Referring to FIG. 2 (c), the grooves 14 are formed in the anti-reflection film 13 and the emitter layer 12 by a long or short wavelength grooving laser.

    Referring to FIG. 2 (d), the groove 14 is coated with a dopant applicator such as a dispenser or a spray for heavy doping (n ++), and a high concentration of impurities is coated to spread the high concentration of impurities. The short wavelength or long wavelength annealing laser is used to selectively diffuse to form the selective emitter 15.

Referring to FIG. 5, in the present invention, the process for forming the selective emitter 15 is performed in principle in one equipment (module). That is, the grooving laser serves to open the anti-reflection film 13 formed on the surface of the substrate, and at the same time, by applying a dopant applicator in a uniform amount, the patterning and partial diffusion are simultaneously performed using the annealing laser. Through this, the cost for the further process can be reduced and the characteristics of the bottom resistance (heavy doping) of 10 ~ 20Ω / ㎠ are obtained.

    Referring to FIG. 2 (E), a part of the selective emitter 15 configured by a gravure offset printing method capable of minimizing the electrode area and maximizing the light receiving area so that shadows and light are not absorbed in the front part of the solar cell. The electrode 16 is formed in the.

The gravure offset method is an indirect printing using a blanket made of rubber or silicon, which is an intermediate transfer material, without transferring the paste directly from the plate making to the printed material. This method requires a smaller printing pressure than the direct transfer method, and uses an intermediate transition material made of rubber or silicon, so that a thin silicon solar cell wafer is less likely to be damaged during the process and less damage to the printed pattern is possible. The solar cell electrode forming printing method is suitable and the printing method is as follows.

Referring to FIG. 3A, the paste 50 is applied to the pattern groove of the pattern roll 20 using the squeeze 22. The pattern roll 20 is made of stainless steel, which is a metal material, and then plated with copper, and its life is semi-permanent. The line width of the solar cell finger electrode is realized up to 10 microns, and the height of the electrode is repeated through repeated printing. I can raise it.

Then, as shown in FIG. 3 (b), the paste 50 is inserted into the pattern groove of the pattern roll 20 using the doctor 26, and the paste is arranged so that the paste is not left in other portions.

Then, as shown in FIG. 3 (c), the paste 50 in the pattern groove is transferred to the outer diameter of the blanket roll 30 while the blanket roll 30 is rotated on the pattern roll 20. Then, the paste 50 does not remain on the pattern roll 20 as shown in FIG.

Then, as shown in FIG. 3 (e), the blanket roll 30 is rotated on the wafer 40 while the paste 50 on the blanket roll 30 is transferred onto the wafer 40 to complete the electrode. do.

Referring to FIG. 4, specifically, the blanket roll 30 receives the paste 50 from the pattern roll 20 which rotates in a reverse direction at a constant pressure and is printed on the wafer 40 passing through the electrode pattern shape.

In order to form different electrodes on the upper and lower surfaces of the wafer 40, a separate pattern roll 20 and a blanket roll 30 are required.

A solar cell that realizes a fine line width maximizes the light conversion efficiency by adjusting the distance between the finger electrodes to maximize the light receiving area and minimize the resistance component value.

The electrode to which the gravure offset printing method is applied may have characteristics of a line width of a finger electrode of about 30 to 100 μm and a height of 10 to 40 μm, and the value of the width may be changed according to the line width and depth of the selective emitter groove. have.

The semiconductor substrate on which the pn junction is formed is excited by the incidence of sunlight, and the separated electron and hole pairs are separated and moved to the emitter layer and the rear field layer, respectively, and the structure is that charges are collected through the front metal electrode and the rear metal electrode, respectively. do.

11 substrate 12 emitter layer
13: antireflection film 14: groove
15: optional emitter 16: electrode
20: pattern roll 22: squeeze
26: Doctor 30: Blanket Roll
40: wafer 50: paste

Claims (3)

Preparing a substrate;
Forming a thin emitter layer on the substrate;
Forming an anti-reflection film on the emitter layer;
Forming grooves in the anti-reflection film and the emitter layer;
Coating a heavily doped impurity with a heavy doping (n ++) dopant applicator in the groove, and selectively diffusing a high concentration of impurities using an anneal laser to form a selective emitter, and
Forming an electrode on the part composed of the selective emitter by gravure offset printing
High efficiency solar cell manufacturing method characterized in that consisting of.
The method of claim 1,
The gravure offset printing method
Applying a paste to the pattern groove of the pattern roll by using a squeeze,
Arranging such that a paste is inserted into the pattern groove of the pattern roll using a doctor and no paste is left in other portions;
Transferring the paste in the pattern groove to the outer diameter of the blanket roll while the blanket roll is rotated on the pattern roll; and
As the blanket roll is rotated on the wafer, the paste on the blanket roll is transferred onto the wafer to complete the electrode.
High efficiency solar cell manufacturing method characterized in that consisting of.
The method according to claim 1 or 2,
The grooving laser serves to open the anti-reflection film formed on the surface of the substrate so that the process for forming the selective emitter is carried out as a single device, and at the same time, the dopant applicator is applied to annealing by applying impurities in a uniform amount. High efficiency solar cell manufacturing method characterized in that the patterning and partial diffusion at the same time using a laser.

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