KR101474008B1 - Method for preparing of solar cell using plasma-surface-treatment - Google Patents

Abstract

The present invention relates to a method of manufacturing a solar cell using a plasma surface treatment, comprising the steps of: (a) preparing a solar cell substrate doped with an impurity of a first conductivity type; (b) implanting an impurity of a second conductivity type opposite to the first conductivity type into the entire surface of the solar cell to form an emitter layer; (c) reducing a dead layer by plasma-treating the front surface of the solar cell substrate; (d) plasma-treating the rear surface of the solar cell substrate to remove a second conductivity type impurity injection layer formed in forming the emitter layer on the rear surface of the substrate, and planarizing the rear surface of the substrate; (e) forming an antireflection film on the entire surface of the solar cell substrate; (f) contacting the front electrode through the antireflection film to the emitter layer; And (g) forming a back surface field (BSF) on the rear surface of the substrate contacting the rear electrode and contacting the rear electrode on the rear surface of the solar cell substrate.

Solar cell, plasma, emitter layer, BSF, edge isolation

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing a solar cell using a plasma surface treatment,

The present invention relates to a solar cell, and more particularly, to a method of manufacturing a solar cell using a plasma surface treatment capable of improving the efficiency of a solar cell by plasma-treating a front surface and a rear surface of the solar cell substrate in a solar cell manufacturing process .

With the recent depletion of existing energy resources such as oil and coal, interest in alternative energy to replace them is increasing. Among them, solar energy has attracted particular attention because it has abundant energy resources and there is no problem about environmental pollution. The use of solar energy includes solar energy that generates the steam needed to rotate the turbine using solar heat and solar energy that converts photons to electrical energy using the properties of semiconductors, Refers to a photovoltaic cell (hereinafter, referred to as a "solar cell").

1 showing a basic structure of a solar cell, a solar cell, like a diode, has a junction structure of a p-type semiconductor 101 and an n-type semiconductor 102. When light is incident on the solar cell, Electrons and electrons charged by (-) electrons escape from the interaction with the material constituting the semiconductor, and positive holes with positive charges are generated, and current flows while they move. Electrons among the p-type 101 and the n-type semiconductor 102 constituting the solar cell are referred to as the n-type semiconductor 102 and the holes are referred to as p-type semiconductor (hereinafter, referred to as " p- 101 to the electrodes 103, 104 bonded to the n-type semiconductor 101 and the p-type semiconductor 102. When these electrodes 103, 104 are connected by electric wires, electricity flows, Can be obtained.

The output characteristics of the solar cell are evaluated by measuring the output current-voltage curve of the solar cell. The point at which the product Ip x Vp of the output current Ip and the output voltage Vp becomes maximum is defined as the maximum output Pm on the output current-voltage curve, and the total light energy (S x I: S, And I is the intensity of the light irradiated to the solar cell) is defined as a conversion efficiency?. To increase the conversion efficiency η, increase the short-circuit current Jsc (output current when V = 0 on the output current-voltage curve) or open-circuit voltage Voc (output voltage when I = 0 on the output current-voltage curve) - Increase the fill factor, which is close to the square of the voltage curve. The closer the value of fidelity is to 1, the closer the output current-voltage curve is to the ideal square, and the higher the conversion efficiency η.

In the fabrication of such a solar cell, the pn junction of the solar cell substrate is performed by introducing a solar cell substrate doped with p-type or n-type impurity into a diffusion furnace and forming a gas capable of forming a conductivity type different from that of the substrate And then diffuses it on the surface of the solar cell substrate to form an emitter layer.

Conventionally, there has been a tendency to improve the contact characteristics between the front electrode and the substrate during the formation of the p-n junction, and excessively doping the impurity in order to form a shallow junction capable of obtaining a high current collection rate. In this case, the concentration of the doped impurity is increased above the solid solubility in the silicon semiconductor at the top of the emitter layer (hereinafter referred to as a 'dead layer'). For reference, the dead layer has a thickness of about 50 to 200 nm. As a result, the mobility of the carrier decreases in the vicinity of the surface of the emitter layer, and the carrier recombination speed increases due to the scattering effect with excessive impurities and the life time of the carrier decreases.

After the p-n junction is formed through the diffusion of the impurity, the same conductivity type is formed on the entire surface of the solar cell substrate, and the front electrode and the rear electrode formed thereafter are electrically connected to each other to cause a decrease in efficiency of the solar cell. Conventionally, in order to prevent this, an impurity injection layer of another conductivity type formed at the edge of the side of the solar cell substrate is removed by mechanical scribing or using a laser. However, in the case of using mechanical scribing, there is a problem that the process time is long. In the case of using a laser, not only a long process time is required but also a portion where the hardened portion is melted by a high- Therefore, after the laser process is applied, it is troublesome to remove the damaged area due to the laser by a separate etching process.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems of the prior art, and it is an object of the present invention to eliminate the edge isolation process by treating a front surface and a rear surface of a solar cell substrate with a plasma to reduce a dead layer formed in an emitter layer of a solar cell And a method of manufacturing a solar cell using a plasma surface treatment capable of forming a uniform BSF on the rear surface and improving the efficiency of the solar cell.

According to another aspect of the present invention, there is provided a method of manufacturing a solar cell using a plasma surface treatment, comprising the steps of: (a) preparing a solar cell substrate doped with an impurity of a first conductivity type; (b) implanting an impurity of a second conductivity type opposite to the first conductivity type into the entire surface of the solar cell to form an emitter layer; (c) reducing a dead layer by plasma-treating the front surface of the solar cell substrate; (d) plasma-treating the rear surface of the solar cell substrate to remove a second conductivity type impurity injection layer formed in forming the emitter layer on the rear surface of the substrate, and planarizing the rear surface of the substrate; (e) forming an antireflection film on the entire surface of the solar cell substrate; (f) contacting the front electrode through the antireflection film to the emitter layer; And (g) forming a back surface field (BSF) on the rear surface of the substrate contacting the rear electrode and contacting the rear electrode on the rear surface of the solar cell substrate.

In the present invention, the step (c) is a surface treatment step using a plasma using any one selected from CF ₄ , SF ₆ , Cl and O ₂ , or a mixed gas thereof. At this time, the plasma treatment can be performed under an atmospheric pressure or a vacuum atmosphere.

In the present invention, the step (d), CF _4, SF _6, and any one or a mixed gas with O ₂ is selected from Cl This is a surface treatment step by plasma using gas mixed gas. At this time, the plasma treatment can be performed under an atmospheric pressure or a vacuum atmosphere.

According to the present invention, the thickness of the dead layer formed at the top of the emitter layer can be reduced by forming the emitter layer by the impurity diffusion process during the manufacture of the solar cell, and then treating the front and rear surfaces of the solar cell substrate with plasma. In addition, the impurity injection layer of another conductivity type formed on the back surface of the solar cell substrate can be removed and planarized, so that a separate edge isolation process can be eliminated and a uniform BSF can be formed on the rear surface of the substrate. As a result, the efficiency of the solar cell can be improved by increasing the short-circuit current and the open-circuit voltage of the solar cell.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

2 to 6 are process sectional views sequentially illustrating a method of manufacturing a solar cell using a plasma surface treatment according to a preferred embodiment of the present invention.

In the method of manufacturing a solar cell according to the present invention, as shown in FIG. 2, a solar cell substrate 201 doped with an impurity of a first conductivity type is prepared. Preferably, the solar cell substrate 201 is a single crystal, a polycrystalline silicon substrate, or an amorphous silicon substrate. However, the present invention is not limited to this. The solar cell substrate 201 is wet-etched by sawing damage generated on the surface of the solar cell substrate 201 during the slicing process by a pre-treatment process.

Then, as shown in FIG. 3, an impurity of a second conductivity type opposite to the first conductive type is implanted into the entire surface of the solar cell substrate 201 to form an emitter layer 202. When the emitter layer 202 is formed, a p-n junction is formed on the solar cell substrate 201. Here, both the p-type and n-type solar cell substrates 201 can be used, and among them, the p-type substrate is most preferable because the lifetime and mobility of the minority carriers are large Lt; / RTI > The p-type substrate is typically doped with Group 3 elements such as B, Ga, and In. When the substrate is p-type, the n-type emitter layer is formed by diffusing the Group 5 elements such as P, As, and Sb.

In forming the emitter layer 202 of the second conductivity type, the solar cell substrate 201 is first placed in a diffusion furnace, and an oxygen gas and an impurity gas of a second conductivity type are implanted to form impurities Thereby forming the introduced oxide film. Here, when the solar cell substrate 201 is p-type, POCl ₃ may be used as the impurity gas. Then, impurities in the oxide film are driven-in to the surface of the solar cell substrate 201 through a high-temperature heat treatment. Then, the PSG film, which is an oxide film remaining on the substrate surface, is removed. Then, an emitter layer 202 having a predetermined thickness is formed on the solar cell substrate 201.

The concentration of the n-type impurity implanted into the emitter layer 202 through the above-described impurity diffusion process is highest at the surface of the emitter layer 202 and decreases with the Gaussian distribution or error function as it enters the emitter layer 202 . Since the process conditions are adjusted so that a sufficient amount of the n-type impurity is diffused in the diffusion process, a dead layer 202 'doped with the n-type impurity is present in the uppermost portion of the emitter layer 202 at a concentration higher than the solid solubility do. In addition to the emitter layer 202 formed on the front surface of the solar cell substrate 201 having undergone the above-described impurity diffusing process, the impurity injection layer 207 of the second conductivity type is also formed on the side surface and the rear surface, do.

When the emitter layer 202 is formed through the above-described processes, surface treatment using plasma is performed on the front surface and the rear surface of the solar cell substrate 201, as shown in FIG. Plasma refers to the generation of active substances such as electrons, ions, free radicals, etc. by exciting energy with neutral gas molecules. The electrons are accelerated by the potential difference in the electric field. During the acceleration of electrons, they collide with other gas molecules and emit excited energy. The impacted atoms are excited and emit electrons again. In this way, the plasma process is simultaneously present in electrons, ions, free radicals, and neutral molecules, which is called the plasma state. Basically, the plasma gas is composed of gas partially dissociated and particles having the same amount of positive charge and negative charge, and the gas contained therein has high activity.

When the front surface and the rear surface of the solar cell substrate 201 are subjected to plasma treatment, the surface of the solar cell substrate 201 is first placed in a vacuum or atmospheric pressure chamber for plasma treatment A plasma gas is injected into the chamber. As the plasma gas to be injected at this time, any one selected from CF ₄ , SF ₆ , Cl and O ₂ , or a mixed gas thereof is used. Then, the injected plasma gas is reacted to plasma-treat the entire surface of the solar cell substrate 201.

When the plasma surface treatment for the entire surface of the solar electric substrate 201 is completed, the plasma gas is injected into the vacuum or atmospheric chamber while being positioned so that the rear surface of the solar cell substrate 201 can be surface-treated again. As the plasma gas to be injected at this time, it is possible to use the plasma gas for treating the front surface of the solar cell substrate 201, but it is preferable that the O ₂ gas is added when the rear surface of the solar cell substrate 201 is processed. The O ₂ gas promotes the oxidation of the solar cell substrate 201 during the plasma treatment.

When the plasma gas is injected, the plasma chamber is operated to excite the injected plasma gas into the plasma, thereby surface-treating the rear surface of the solar cell substrate 201 with plasma. At this time, when O ₂ is added to the plasma gas, the oxidation of the solar cell substrate 201 is promoted by the added O ₂ gas. The oxidized surface layer of the solar cell substrate 201 is etched by the fluorine (F ₂ ) gas generated during the plasma treatment. Preferably, the etching rate at the time of processing the rear surface of the solar cell substrate 201 is controlled to be larger than that at the time of processing the front surface of the solar cell substrate 201. In order to process the rear surface of the solar cell substrate 201 more smoothly than the front surface, the etch rate of the back surface of the solar cell substrate 201 is rapidly increased. On the other hand, since the present invention is not limited by the order of plasma processing on the front and rear surfaces of the solar cell substrate 201, it is apparent that plasma processing can be performed in the reverse order.

5, when the plasma processing of the solar cell substrate 201 is completed through the above-described processes, the front surface of the solar cell substrate 201 is irradiated with the n-type impurity at a concentration higher than the solubility of solids in the uppermost portion of the emitter layer 202 Type impurity-doped dead layer 202 'is removed by the etching of the plasma. The rear surface of the solar cell substrate 201 has a structure in which the impurity implantation layer 207 of the second conductivity type formed in the impurity diffusion step is removed by the etching action of the plasma and the surface structure of the back surface of the solar cell substrate 201 Thereby achieving planarization. On the other hand, the impurity implantation layer 207 of the second conductivity type formed on the back surface of the solar cell substrate 201 was removed by plasma treatment. As described above, when the impurity injection layer 207 is removed, there is no fear that the front electrode and the rear electrode are electrically connected to each other. In this case, since a separate edge isolation process for removing the side edge of the solar cell substrate 201 during the solar cell manufacturing process can be omitted, it is possible to simplify the manufacturing process of the solar cell. And will be apparent to those skilled in the art.

6, an anti-reflection film 203 is formed on the emitter layer 202 formed on the entire surface of the solar cell substrate 201. [ The antireflection film 203 is formed to lower the reflectivity to sunlight and typically includes silicon nitride. The antireflection film 203 may be formed of a material selected from the group consisting of plasma enhanced chemical vapor deposition (PECVD), chemical vapor deposition (CVD), and sputtering May be formed by the method selected. A front electrode 206 is formed to penetrate the antireflection film 203 and to be in contact with the emitter layer 202. A back electrode 206 is formed on the opposite surface of the solar cell substrate 201 on which the antireflection film 203 is formed, (204). The order of forming the front electrode 206 and the rear electrode 204 is not limited, and any electrode may be formed first.

The front electrode 206 may be formed by applying a conventional front electrode forming paste including silver and glass frit on the antireflection film 203 according to a predetermined pattern and then performing heat treatment, Is punched through the antireflection film 203 and is contacted with the emitter layer 202. The front electrode 206 includes silver and is excellent in electrical conductivity.

The rear electrode 204 may be formed by applying a conventional rear electrode forming paste containing aluminum to the rear surface of the solar cell substrate 201 and then performing a heat treatment, An electrode forming material Al is doped from a surface in contact with the electrode 204 to a predetermined depth to form a back surface field (BSF) 205. Since the back electrode 204 includes aluminum, it has excellent electrical conductivity and good affinity with silicon, so that the bonding property is excellent. In addition, aluminum forms a P ⁺ layer, that is, a BSF 205, at the interface with the solar cell substrate 201 as a Group 3 element so that the carriers do not disappear from the surface but gather in the BSF direction. In the present invention, since the rear surface of the solar cell substrate 201 is planarized by the plasma surface treatment, the formation of the BSF 205 can be more uniform than the conventional one, and the effect of the BSF 205 is improved, The efficiency can be increased.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be understood that various modifications and changes may be made without departing from the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given above, serve to further the understanding of the technical idea of the invention, And should not be construed as interpretation.

1 is a schematic view showing a basic structure of a solar cell.

2 to 6 are process sectional views sequentially illustrating a method of manufacturing a solar cell using a plasma surface treatment according to a preferred embodiment of the present invention.

<Reference Numbers in the Drawings>

201: solar cell substrate 202: emitter layer

202 ': Dead layer 203: Antireflection film

204: rear electrode 205: BSF

206: front electrode 207: impurity implantation layer

Claims (5)

(a) preparing a solar cell substrate doped with an impurity of a first conductivity type; (b) implanting an impurity of a second conductivity type opposite to the first conductivity type into the entire surface of the solar cell to form an emitter layer; (b-1) forming a dead layer at the top of the emitter layer by the emitter layer forming step; (c) reducing the dead layer by plasma-treating a front surface of the solar cell substrate; (d) plasma-treating the rear surface of the solar cell substrate to remove a second conductivity type impurity injection layer formed in forming the emitter layer on the rear surface of the substrate, and planarizing the rear surface of the substrate; (e) forming an antireflection film on the entire surface of the solar cell substrate; (f) contacting the front electrode through the antireflection film to the emitter layer; And (g) contacting the rear electrode to the rear surface of the solar cell substrate and forming a back surface field (BSF) on the rear surface of the substrate in contact with the rear electrode, Wherein the step of reducing the dead layer removes the dead layer formed at the top of the emitter layer by the step of forming the emitter layer. The method of claim 1, wherein the step (c) And a step of plasma etching the entire surface of the solar cell substrate using an atmospheric plasma or a vacuum plasma. 3. The method of claim 2, wherein in the step (c) Wherein the plasma reaction gas is any one selected from the group consisting of CF ₄ , SF ₆ , Cl, and O ₂ , or a mixed gas thereof. The method of claim 1, wherein the step (d) Wherein the plasma etching is a step of plasma-etching the rear surface of the solar cell substrate using an atmospheric plasma or a vacuum plasma. 5. The method of claim 4, wherein in step (d) Wherein the plasma reaction gas is a gas obtained by mixing O ₂ with any one selected from CF ₄ , SF _6, and Cl, or a mixed gas thereof.

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