KR20090054733A - Manufacturing method of solar cell - Google Patents

Abstract

The present invention relates to a method of manufacturing a solar cell using a plasma surface treatment, comprising: (a) preparing a solar cell substrate doped with impurities of a first conductivity type; (b) plasma reflecting the entire surface of the solar cell substrate to reduce reflectance to sunlight; (c) forming an emitter layer by implanting impurities of a second conductivity type opposite to the first conductivity type onto the solar cell; (d) plasma processing the entire surface of the solar cell substrate to reduce dead layers; (e) plasma-processing the rear surface of the solar cell substrate to remove the second conductive type impurity implantation layer formed when the emitter layer is formed on the rear surface of the substrate, and simultaneously planarize the rear surface of the substrate; (f) forming an anti-reflection film on the entire surface of the solar cell substrate; (g) contacting the front electrode to the emitter layer through the antireflection film; And (h) contacting a rear electrode on 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.

Description

Method for preparing solar cell using plasma surface treatment {Method for preparing of solar cell using 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 that can improve the efficiency of the solar cell by plasma-processing the front and rear surfaces of the solar cell substrate in the solar cell manufacturing process. It is about.

Recently, as the prediction of depletion of existing energy sources such as oil and coal is increasing, interest in alternative energy to replace them is increasing. Among them, solar energy is particularly attracting attention because it is rich in energy resources and has no problems with environmental pollution. There are two methods of using solar energy: solar energy that generates steam required to rotate turbines using solar heat, and solar energy that converts photons into electrical energy using the properties of semiconductors. In general, it refers to a solar cell (hereinafter referred to as a "solar cell").

Referring to FIG. 1 showing the basic structure of a solar cell, a solar cell has a junction structure of a p-type semiconductor 101 and an n-type semiconductor 102 like a diode, and when light is incident on the solar cell, Interaction with the materials that make up the semiconductor causes electrons with negative charge and electrons to escape, creating holes with positive charge, and as they move, current flows. This is called a photovoltaic effect. Among the p-type 101 and n-type semiconductors 102 constituting the solar cell, electrons are directed toward the n-type semiconductor 102 and holes are p-type semiconductors ( Pulled toward 101 and moved to the electrodes 103 and 104 bonded to the n-type semiconductor 101 and the p-type semiconductor 102, respectively, and when the electrodes 103 and 104 are connected by 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 maximum output Pm is defined as the point where the product Ip × Vp of the output current Ip and the output voltage Vp becomes maximum on the output current-voltage curve, and the total light energy incident on the solar cell (S × I: S is The element area, I, is defined as the conversion efficiency η divided by the intensity of light irradiated to the solar cell. 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 voltage Voc (output voltage when I = 0 on the output current-voltage curve) or output current. Increase the fill factor, which represents the square of the voltage curve. The closer the fidelity value is to 1, the closer the output current-voltage curve is to the ideal square and the higher the conversion efficiency η.

Silicon substrates, which are mainly used in solar cell manufacturing, are mirror-finished so they reflect high sunlight. Therefore, it is possible to manufacture a solar cell having a desired photoelectric conversion efficiency only by manufacturing a solar cell by applying a process capable of reducing the reflectance of sunlight on the solar incident surface side.

In addition, the pn junction of the solar cell substrate is a solar cell substrate doped with a p-type or n-type impurities into a diffusion furnace and injecting a gas that can form a different conductivity type from the substrate after the injection into the diffusion furnace This is done by diffusing the surface of the solar cell substrate to form an emitter layer.

Conventionally, there is a tendency to excessively dopants to form a shallow junction to improve the contact characteristics between the front electrode and the substrate and to obtain a high current collection rate when forming the p-n junction. In this case, the top layer of the emitter layer (hereinafter referred to as the 'dead layer') causes the concentration of the doped impurities to increase beyond the solid solubility in the silicon semiconductor. For reference, the dead layer has a thickness of about 50 to 200 nm. As a result, there is a problem that the mobility of the carrier is reduced near the emitter layer surface and the scattering effect with excessive impurities increases the recombination rate of the carrier and decreases the life time of the carrier.

In addition, after the p-n junction is formed through the diffusion of impurities, 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, which causes a decrease in efficiency of the solar cell. Conventionally, in order to prevent this, another conductive type impurity implantation layer formed on the edge of the side end of the solar cell substrate has been removed using mechanical scribing or laser. However, when using mechanical scribing, there is a problem that the process takes a long time, and when using a laser, the process takes a long time, and a part that is melted and hardened by a high temperature laser causes loss of efficiency. Therefore, after applying the laser process, there was a need to remove the damage caused by the laser by a separate etching process.

The present invention has been made to solve the above-mentioned problems of the prior art, and before the emitter layer is formed, the entire surface of the solar cell substrate is treated with plasma to reduce the reflectivity of sunlight to increase the short circuit current, and after the emitter layer is formed, Plasma treatment of the front and back of the substrate to remove dead layers from the emitter layer while simultaneously eliminating surface defects to increase short-circuit current and open-circuit voltage, while eliminating the edge isolation process, while maintaining a uniform BSF on the back of the substrate It is an object of the present invention to provide a method for manufacturing a high efficiency solar cell that can improve the open voltage by forming a.

According to an aspect of the present invention, there is provided a method of manufacturing a solar cell using plasma surface treatment, the method comprising: (a) preparing a solar cell substrate doped with impurities of a first conductivity type; (b) plasma reflecting the entire surface of the solar cell substrate to reduce reflectance to sunlight; (c) forming an emitter layer by implanting impurities of a second conductivity type opposite to the first conductivity type onto the solar cell; (d) plasma processing the entire surface of the solar cell substrate to reduce dead layers; (e) plasma-processing the rear surface of the solar cell substrate to remove the second conductive type impurity implantation layer formed when the emitter layer is formed on the rear surface of the substrate, and simultaneously planarize the rear surface of the substrate; (f) forming an anti-reflection film on the entire surface of the solar cell substrate; (g) contacting the front electrode to the emitter layer through the antireflective film; And (h) contacting a rear electrode on 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.

In the present invention, step (b) or step (d) is a surface treatment step by 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 may proceed under atmospheric pressure or under a vacuum atmosphere.

In the present invention, the step (e), CF ₄ , SF ₆ and Cl selected from any one or a mixed gas and O ₂ It is a surface treatment step by the plasma using the gas which mixed gas. At this time, the plasma treatment may proceed under atmospheric pressure or under a vacuum atmosphere.

According to one aspect of the invention, it is possible to increase the short circuit current by reducing the reflectivity of sunlight.

According to another aspect of the present invention, it is possible to remove the dead layer from the emitter layer while simultaneously removing the surface defects to increase the short circuit current and the open voltage.

According to another aspect of the present invention, it is possible to simplify the solar cell manufacturing process by eliminating the edge isolation process, and to improve the open voltage by forming a uniform BSF on the rear surface of the solar cell substrate.

The increase in short-circuit current and open voltage as described above enables the manufacture of high efficiency solar cells.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

2 to 7 are process cross-sectional views sequentially illustrating a method of manufacturing a solar cell using 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, first, as shown in FIG. 2, a solar cell substrate 201 doped with impurities 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 thereto. The solar cell substrate 201 was wet-etched to remove saw damage generated on the surface of the solar cell substrate 201 during slicing by a pretreatment process.

3, the solar cell substrate 201 is loaded into the plasma chamber, and then the entire surface of the solar cell substrate 201 is plasma treated to reduce the reflectance of sunlight. The decrease in reflectivity of sunlight results from the fine etching of the plasma. When the reflectivity of sunlight is reduced by the plasma surface treatment, the short-circuit current Jsc rises and the solar cell efficiency can be improved by that much.

In the present invention, the plasma refers to a state in which a neutral gas molecule is excited with a high energy active material including electrons, ions, free radicals, and the like. In the plasma chamber, electrons are accelerated by the potential difference in the electric field. The electrons collide with gas molecules during the acceleration of the electrons, radiate the excited energy, and emit the electrons again when the shocked atoms are excited. As the process is repeated, electrons, ions, free groups, and heavy components exist simultaneously, which is called a plasma state. Basically, the plasma gas is composed of partially dissociated gas and particles having the same amount of positive and negative charges, among which the dissociated gas has high activity.

As a source gas for forming the plasma used in the process shown in FIG. 3, any one selected from CF ₄ , SF ₆ , Cl, and O ₂ or a mixed gas thereof is used. However, the present invention is not limited thereto. The plasma is formed under vacuum or atmospheric conditions.

Subsequently, as shown in FIG. 4, an impurity of the second conductivity type opposite to the first conductivity 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, the p-type substrate and the n-type solar cell substrate 201 may be used, and the p-type substrate has a long life and mobility of minority carriers (in the case of p-type electrons are minority carriers), the most preferable. Can be used. The p-type substrate is typically doped with group III elements such as B, Ga, and In. When the substrate is p-type, the n-type emitter layer is formed by diffusing Group 5 elements such as P, As, and Sb.

When the emitter layer 202 of the second conductivity type is formed, the solar cell substrate 201 is first placed in a diffusion furnace, and an oxygen gas and an impurity gas of the second conductivity type are injected to impurity on the substrate. This inflow oxide film is formed. 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 drive-in to the surface of the solar cell substrate 201 through high temperature heat treatment. Then, the PSG film, which is an oxide film remaining on the substrate surface, is removed. Then, the emitter layer 202 having a predetermined thickness is formed on the solar cell substrate 201.

The concentration of the n-type impurity injected into the emitter layer 202 through the impurity diffusion process described above is the highest on the surface of the emitter layer 202 and decreases according to 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 n-type impurities can be diffused during the diffusion process, the dead layer 202 ′ doped with n-type impurities at a concentration higher than the solid solubility is present at the top of the emitter layer 202. do. In addition, in addition to the emitter layer 202 formed on the front surface, the second conductive type impurity injection layer 207 is formed on the solar cell substrate 201 that has undergone the above-described impurity diffusion process. do.

When the emitter layer 202 is formed through the above-described process, as shown in FIG. 5, surface treatment using plasma is performed on the front and rear surfaces of the solar cell substrate 201.

Specifically, when plasma treating the front surface and the back surface of the solar cell substrate 201, first, the front surface of the solar cell substrate 201 is surface-treated in a plasma chamber in a vacuum or atmospheric pressure atmosphere for plasma processing. Plasma source gas is injected into the chamber in a position where it can be positioned. In this case, any one selected from CF ₄ , SF ₆ , Cl, and O ₂ or a mixed gas thereof is used as the source gas to be injected. Then, the injected source gas is excited in a plasma state to treat the entire surface of the solar cell substrate 201 by plasma surface treatment.

When the plasma surface treatment of the front surface of the solar cell substrate 201 is completed, the solar cell substrate 201 is placed in a plasma chamber in a vacuum or atmospheric pressure atmosphere so that the rear surface of the solar cell substrate 201 is surface-treated again. Inject the plasma source gas. In this case, although the plasma source gas used to treat the entire surface of the solar cell substrate 201 may be used as the source gas to be injected, it is preferable to further add O ₂ gas when treating the rear surface of the solar cell substrate 201. Do. When the plasma source gas is injected, the injected source gas is excited by plasma to surface-treat the rear surface of the solar cell substrate 201 with plasma. Preferably, the etching rate when the rear surface of the solar cell substrate 201 is controlled is larger than that when the front surface of the solar cell substrate 201 is processed. On the other hand, the present invention is not limited by the plasma processing order of the front and rear of the solar cell substrate 201, it is apparent that the plasma processing can be performed in the reverse order.

When the plasma processing of the front and rear surfaces of the solar cell substrate 201 is completed through the above-described process, as shown in FIG. 6, the front surface of the solar cell substrate 201 is solid at the top of the emitter layer 202. The dead layer 202 ′ doped with n-type impurities at a concentration higher than the solubility is removed by etching the plasma. In addition, the back surface of the solar cell substrate 201 is removed from the second conductive type impurity injection layer 207 formed during the impurity diffusion process described above by the etching of plasma and the surface structure of the back surface of the solar cell substrate 201. This flattening is achieved. On the other hand, the impurity injection layer 207 of the second conductivity type formed on the back surface of the solar cell substrate 201 was removed by plasma treatment. As such, when the impurity injection layer 207 is removed, there is no fear that the front electrode and the rear electrode are electrically connected. In this case, since the separate edge isolation process for removing the side edges of the solar cell substrate 201 in the solar cell manufacturing process can be omitted, there will be an advantage that can simplify the solar cell manufacturing process It is obvious to those skilled in the art.

Then, as shown in FIG. 7, the anti-reflection film 203 is formed on the emitter layer 202 formed on the entire surface of the solar cell substrate 201. The anti-reflection film 203 is formed to lower reflectance to sunlight, and may be typically including silicon nitride, and in the group consisting of plasma chemical vapor deposition (PECVD), chemical vapor deposition (CVD), and sputtering It can be formed by the method selected. The front electrode 206 is formed to penetrate the anti-reflection film 203 and contact the emitter layer 202, and a rear electrode on a surface opposite to the surface on which the anti-reflection film 203 of the solar cell substrate 201 is formed. 204 is formed. The order of forming the front electrode 206 and the back electrode 204 is not limited, and any electrode may be formed first.

The front electrode 206 may be formed by screen printing 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. 206 penetrates the antireflection film 203 and contacts the emitter layer 202. The front electrode 206 includes silver and has excellent electrical conductivity.

The back electrode 204 may be formed by screen printing a conventional back electrode forming paste including aluminum on the back surface of the solar cell substrate 201 and then performing heat treatment. The solar cell substrate 201 may be formed by heat treatment. A back surface field (205) is formed by doping the electrode forming material (Al) from a surface in contact with the silver back electrode 204 to a predetermined depth. Since the rear electrode 204 includes aluminum, not only the electrical conductivity is excellent, but also the affinity with silicon is excellent, and the bonding property is excellent. In addition, aluminum forms a P ⁺ layer, that is, BSF 205 at the interface with the solar cell substrate 201 as a group 3 element, so that the carriers are collected in the BSF direction without disappearing from the surface. In the present invention, by flattening the rear surface of the solar cell substrate 201 through plasma surface treatment, the formation of the BSF 205 can be more uniform than the conventional, the effect of the BSF 205 is improved to improve the The efficiency can be increased.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

The following drawings attached to this specification are illustrative of the preferred embodiments of the present invention, and together with the detailed description of the invention serves to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to.

1 is a schematic diagram showing the basic structure of a solar cell.

2 to 7 are process cross-sectional views sequentially illustrating a method of manufacturing a solar cell using plasma surface treatment according to a preferred embodiment of the present invention.

Claims (11)

Forming an emitter layer having a second conductivity type opposite to the first conductivity type on a substrate having a first conductivity type, Plasma-processing the front and rear surfaces of the substrate on which the emitter layer is formed; Forming a first electrode connected to the emitter layer, and Forming a second electrode separated from the first electrode and connected to the substrate Method for manufacturing a solar cell comprising a. In claim 1, The plasma treatment step, Positioning the substrate in which the emitter layer is formed in a chamber, Injecting a plasma source gas into the chamber, and Exciting the plasma source gas into a plasma state Method for manufacturing a solar cell comprising a. In claim 2, The plasma source gas is one of CF ₄ , SF ₆ , Cl and O ₂ or a mixed gas thereof manufacturing method of a solar cell. In claim 2, The chamber is a method of manufacturing a solar cell having a vacuum or atmospheric pressure atmosphere. In claim 1, And plasma-treating one side of the substrate before the emitter layer forming step. In claim 5, The plasma-treated substrate surface is an incident surface to which light is incident. In claim 1, And forming an anti-reflection film on the emitter layer after the emitter layer forming step. In claim 7, The forming of the first electrode may include applying a first electrode forming paste on the antireflective film and heat treating the substrate on which the first electrode forming paste is applied, so that the first electrode forming paste is formed on the antireflective film. Forming a first electrode connected to the emitter layer through the solar cell. In claim 1, Forming the second electrode includes forming a BSF between the substrate and the second electrode, The second electrode is connected to the substrate through the BSF Method for manufacturing a solar cell. In claim 1, The substrate is a silicon substrate manufacturing method of a solar cell. In claim 10, Wherein said substrate is one of a single crystal silicon substrate, a polycrystalline silicon substrate, and an amorphous silicon substrate.

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