KR101113503B1 - Method for fabricating silicon solar cell using induced current apparatus - Google Patents

Abstract

The present invention relates to a method for manufacturing a silicon solar cell using an induction current device, comprising: forming a second type silicon layer that becomes an emitter on a first type crystalline silicon substrate, and passivation on the second type silicon layer Forming a film or an anti-reflection film, forming a front metal electrode on the passivation film or an anti-reflection film, and sequentially forming a rear metal electrode on the bottom of the first type crystalline silicon substrate, and using an induction current device. And selectively heat-treating the front metal electrode and forming a back metal electrode contact and a back electric field under the first type crystalline silicon substrate.

Description

Method for manufacturing silicon solar cell using induction current device {METHOD FOR FABRICATING SILICON SOLAR CELL USING INDUCED CURRENT APPARATUS}

The present invention relates to a method for manufacturing a silicon solar cell using an induction current device, by forming a metal electrode on the upper and lower parts of the silicon solar cell and then performing a heat treatment process using an induction current device, as well as the metal electrode already fabricated The present invention relates to a technique for solving the problem of thermal effects on other devices.

Renewable energy using solar energy can be divided into solar power generation system using solar heat and solar cells using solar light.

Among them, solar cells have the opposite principle to LEDs or laser diodes that convert electrical energy into light energy, and are mostly composed of large-area P-N junction diodes.

The solar cell is composed of n-type region and p-type region, where n-type region has large electron density and small hole density, and p-type region is The opposite is true.

In this structure, in the thermal equilibrium, in the diode composed of a junction of a p-type semiconductor and an n-type semiconductor, an unbalance of charge occurs due to diffusion due to a difference in carrier concentration. An electric field is formed so that diffusion of the carrier no longer occurs.

When these diodes are subjected to light above the band gap energy, which is the difference in energy between the conduction band and valence band of the material, they receive this light energy and the electrons are excited from the valence band to the conduction band. (excited)

At this time, the electrons excited by the conduction band can move freely, and holes are generated in the valence band where electrons escape. This is called an excess carrier, and these excess carriers diffuse by concentration differences in the conduction band or the valence band.

At this time, electrons excited in the p-type region and holes made in the n-type region are referred to as minority carriers, and carriers in a p-type or n-type semiconductor before bonding are conventional. , n-type electrons) are called major carriers.

In addition, the main carriers are interrupted by the energy barrier caused by the electric field, but the electrons of the p-type minority carriers toward the n-type region and the holes of the n-type minority carriers toward the p-type region, respectively. I can move it.

The diffusion of a small number of carriers breaks the electrical neutrality of the material, which leads to a potential drop. When the electromotive force generated at the anode terminal of the PN junction diode is connected to an external circuit, it acts as a solar cell. Done.

Such solar cells can be divided into homojunctions and heterojunctions according to the properties of p and n regions used for PN junctions. When combined with.

Here, looking at the structure of a typical silicon solar cell, first, a Group 5 material that can use POCl ₃ , a screen printer, spin coating, or the like is coated on a crystalline silicon substrate (base) front surface with a doping source.

Next, a PN junction structure is formed through a diffusion process at a high temperature, and an oxide film such as SiN _x is deposited as a passivation or antireflection film by using a plasma chemical vapor deposition apparatus (PECVD).

Next, the basic structure of the silicon solar cell is formed by forming a metal such as silver on the front side where light comes in and aluminum or the like on the back side to form a back side electric field, and then forming an electrode contact and a back side field through high temperature heat treatment. Is made.

In this case, as the high temperature process is performed to form contact between the front and rear electrodes of the silicon solar cell, warpage may occur in the case of a thin wafer.

On the other hand, the metal line is formed by a screen printing process and a heat treatment process using a metal paste, looking at the heat treatment process temperature of the electrode for forming the metal line as follows.

1 is a graph showing a process shape according to temperature and time of an electrode heat treatment process according to the prior art.

Referring to FIG. 1, after the electrode is formed, a drying process is performed at a temperature of 200 ° C. or lower, and a burn-out process of removing resin at a temperature of 300 to 400 ° C. is performed. have.

Next, a heat treatment (Firing) process for bonding the metal electrode to the silicon wafer is performed at a temperature of 700 ~ 800 ℃. In this case, the heat treatment process may be referred to as a firing process, but hereinafter, the heat treatment process will be described as a uniform heat treatment.

Here, looking at the type of electrode heat treatment process that occurs during the heat treatment process is as follows.

Figure 2 is a graph showing the process form by temperature of the electrode heat treatment process according to the prior art.

Referring to FIG. 2, a drying process is performed in which an organic solvent is evaporated at a temperature of 200 ° C. or less, and a burnout process is performed in which resin is removed at a temperature of 200 to 400 ° C., 400. at a temperature of ~ 600 ℃, the sintering process (sintering Ag) and glass melting process (melting glass) is conducted, at a temperature of 600 ~ 800 ℃ glass -SiN _x / Si reaction _{(glass-SiN x / Si reaction} ) and Ag -Si reaction (Ag-Si reaction) proceeds.

The above-described series of processes are performed in a single-wafer Rapid Thermal Process (RTP) apparatus using a batch furnace (Furnace), a belt furnace (Furnace) or a cold wall (Hot Wall).

Batch furnace (Furnace) and belt furnace (Furnace) is to make the electrode heat treatment process in the thermal equilibrium state obtained by heating for a long time. This can stably raise the temperature of the wafer and has the advantage of high uniformity of processing. Therefore, the throughput per unit time can be increased, but there is a problem that the time and cost for the temperature rise are increased, and the temperature of the wafer cannot be measured directly. In addition, there is a problem that the flexibility of the process is limited because the maintenance is not easy and the pause or additional work cannot be performed while the above series of processes are in progress.

In addition, since the single-wafer type RTP apparatus uses a thermal non-equilibrium state, the single-wafer type RTP apparatus has an advantage of heating in a short time and flexibly processing the process. However, in the case of the RTP apparatus, the throughput per unit time is limited, the temperature measurement method of the wafer is not easy, and the uniformity of the processing may be reduced.

As described above, the conventional batch furnace (Furnace), belt furnace (Furnace) and single-wafer type RTP apparatus all have a problem that the heat treatment must be made at a high temperature of 700 ~ 800 ℃. Under such high temperatures, thermal effects may be applied not only to the metal electrode but also to other devices already manufactured, thereby degrading the performance of the solar cell and failing to achieve desired efficiency.

The technical problem to be achieved by the present invention is to form a metal electrode of a crystalline silicon solar cell by performing a screen printing process using a metal paste and then performing a heat treatment process using an induction current device, only the metal electrode is heated, and already manufactured It is an object of the present invention to provide a silicon solar cell having high efficiency stability and reproducibility without affecting other devices, and to provide a method for manufacturing a silicon solar cell using an induction current device.

In a method of manufacturing a silicon solar cell using an induction current device according to the present invention, forming a second type silicon layer on the first type crystalline silicon substrate, and forming a passivation film or an antireflection film on the second type silicon layer Forming a front metal electrode on the passivation film or an anti-reflection film, sequentially forming a back metal electrode on the bottom of the first type crystalline silicon substrate, and selectively selecting the front metal electrode by using an induction current device. It characterized in that it comprises a step comprising the heat treatment (Firing).

Wherein the first type is p-type, the second type is n-type, the first type is n-type, and the second type is p-type, and the first type crystalline silicon substrate A passivation film is formed at an interface between the second type silicon layers, and the passivation film is selected from SiO ₂ , SiC, SiN _x, and intrinsic amorphous silicon (Intrinsic amorphors-Si). Forming a thickness of 5 ~ 100nm, the front metal electrode is 70 to 80% by weight of Ag powder, 5 to 20% by weight of glass frit (Glass Frit), 5 to 20% by weight of resin (Resin) And a metal paste containing a residual amount of an organic solvent, wherein the Ag powder is a flake or spherical particle having a particle diameter of 1 to 20 μm. 2 types And a passivation film or an anti-reflection film, wherein the front metal electrode is heated to a temperature of 700 to 800 ° C.

The rear metal electrode may be selectively heat-treated by the induction current device, and an electric field forming layer BSF is formed at an interface between the first type silicon substrate and the rear metal electrode by the heat treatment. The heat treatment is characterized in that using an induced current using a frequency having 1,000 ~ 1,000,000 Hz.

According to the method of manufacturing a silicon solar cell using an induction current device according to an embodiment of the present invention, it is possible to minimize the thermal damage generated in the passivation film or the anti-reflection film in the Ag electrode heat treatment process as the front metal electrode, the second type emitter To minimize heat loss. In addition, since only the Ag electrode is heated by using the induction current device, only the metal electrode can be adjusted to be accurately connected to the emitter.

In addition, since high heat of 700-800 ° C. does not affect other devices other than the electrode, it is possible to minimize interference generated between the devices by heat and to reduce interface defects, thereby improving the characteristics of the PN diode. The increase in battery fill rate can be maximized. In addition, the present invention provides an effect that can maximize the solar cell conversion efficiency.

Hereinafter, a highly efficient silicon solar cell and a method of manufacturing the same will be described in detail based on the technology of the present invention described above.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

3 and 4 are cross-sectional views showing an electrode heat treatment process using an induced current according to the present invention.

3 and 4 are cross-sectional views of a silicon solar cell according to an embodiment of the present invention. The first type silicon substrate 100, the second type silicon layer 120, the passivation film or the anti-reflection film 130, A front metal electrode 150, a field forming layer (BSF, 135) and a back metal electrode 140 is included.

Here, the first type and the second type means p or n type, respectively, and may not be the same type. Hereinafter, for convenience of description, the first type and the second type are n type. Explain only to.

First, the first type silicon substrate 100 is a crystalline p-type silicon substrate, which may be either single crystal or polycrystal.

Next, the second type silicon layer 120 used as an emitter is a crystalline n-type silicon layer, which may also be an n-type of a material other than crystalline silicon.

Next, a passivation film or an anti-reflection film 130 is formed on the second type silicon layer 120.

In addition, by reducing interface defects occurring at the interface between the second type silicon layer 120 and the first type silicon substrate 100, minimizing recombination of electrons and holes, A passivation film (not shown) may be formed in order to improve the efficiency to show stable efficiency.

In other words, in the case of crystalline silicon, the defect density at the crystalline interface is the biggest factor that determines the characteristics of the solar cell, and to minimize the plasma damage and the dopant damage that cause the defect density. In order to passivate the crystalline with a material that can minimize defect generation at the interface between the crystalline, it is possible to lower the interface defect density, thereby lowering the recombination rate of the carriers at the interface.

Such a passivation film must be able to move holes, which are minority carriers of the first type silicon substrate 100, to the n-type silicon layer 120, and electrons (e) that are minority carriers of the n-type silicon layer 120. Since it must be possible to move-) to the p-type silicon substrate 100, it must be connected to a certain gap.

As described above, the passivation film is formed of a material capable of minimizing PN interface defects to serve as a buffer layer layer that minimizes PN interface defects, and at the same time passes through the top and bottom surfaces of the passivation film. By forming a plurality of pores (through holes), it is a layer that functions to free the movement of the minority carriers described above.

However, when such a passivation film is provided, the PN junction is not formed entirely, but the first type crystalline silicon substrate 100 and the second type silicon layer 130 are formed by point contact or partial surface contact only through voids. As a result, the collecting capacity or the moving force of the minority carriers may be reduced, but the collecting capacity due to the diffusion of the minority carriers may be increased in the bulk region due to passivation of the surface.

Therefore, the passivation film is formed of a material capable of minimizing defects in the PN interface as described above. Specifically, the passivation film is formed of one selected from SiO ₂ , SiC, SiN _x, and intrinsic a-Si: H. It is desirable to.

In the above passivation film, it is preferable that the proportion of the voids based on the planar surface area is in the range of 50% or less of the total surface area based on the planar view, and the distance d between the centers of the neighboring pores is several µm to several hundred µm. It can be freely determined in the range, specifically 5 μm to 100 μm. And the shape of the voids can be freely designed in the form of squares, triangles, circles, ovals, and other polygons when viewed from the top view.

As described above, specific details of the voids formed in the passivation film have been described, but in order to smoothly perform the function of the passivation film described above, that is, collection of electrons and holes by the internal field effect through PN diode formation is possible. In order to be able to do so, the size of the pores and the spacing between neighboring pores need to be properly adjusted.

For this purpose, the thickness of the passivation film is preferably several nm to several hundred nm. That is, it is preferable to deposit about 80 nm in the case of the passivation film (SiN _x ) which serves as the anti-reflection film, and in the range of 5 to 10 nm as a condition for minimizing the reflectance when using the silicon passivation film while using SiN _x as the anti-reflection film. It is desirable to be freely determined at.

Next, the front metal electrode 150 is formed on the passivation film or the anti-reflection film 130 to allow the solar cell to be connected to the external conductor, but maintains a constant interval for the incident light from the outside. To form.

Here, the front metal electrode 150 is formed by a screen printing process and a heat treatment process using a metal paste, the metal paste is preferably formed using one or more of Al, Pt, Au, Cu and Ag.

In particular, when using an Ag paste, 70 to 80% by weight of Ag powder, 5 to 20% by weight of glass frit, 5 to 20% by weight of resin, and the remaining amount of organic solvent are used. It is preferable to form with the metal paste containing. At this time, Ag powder is preferably used to flake (Flake) or spherical particles having a particle diameter of 1 ~ 20㎛.

When Ag powder is added at less than 70% by weight, it may not have sufficient conductivity as an electrode, and the induced current efficiency may be reduced. In addition, since the content of the glass frit or resin is relatively reduced when it exceeds 80% by weight, the heat treatment process for the front metal electrode may not be normally performed.

The glass frit lowers the melting point of the metal and induces bonding between metal powders or metal-silicon, thereby etching the insulating layer formed on the surface of the silicon substrate during the heat treatment process. Therefore, when the addition amount of the glass frit is less than 5% by weight may cause a problem that the melting point is not lowered, and when the addition amount exceeds 20% by weight there is a risk that the insulation layer is excessively etched and shunt (Shunt) occurs.

Resin serves to control the degree of dispersion of the paste and to control the viscosity. Therefore, if the amount of resin added is less than 5% by weight, the screen printing process may not be normally performed. If the amount is 20% by weight, the dispersion degree of paste may become severe after the screen printing process, and thus the shape of the electrode pattern may not be formed normally. Problems may arise.

All of the composition ranges as described above can obtain the optimum efficiency when using the induction current device according to the present invention.

When the induction current device is placed on top of the front metal electrode 150 and an induction current is applied, the metal paste is heated to perform a heat treatment process. In this case, the heat treatment is preferably performed so that the frequency band of the induction current device is adjusted between 1,000 ~ 1,000,000 Hz. If the induction current frequency band is less than 1,000 Hz, the front metal electrode in a non-contact state is formed and heat treatment cannot be performed completely. If the induction current frequency band exceeds 1,000,000 Hz, the front metal electrode in a shunt state is formed. The electrode may melt.

Here, the process of the heat treatment of the front metal electrode 150 by the induction current device is as follows.

First, a drying process is performed in which an organic solvent is evaporated at a temperature of 200 ° C. or less, and a burnout process is performed in which resin is removed at a temperature of 200 to 400 ° C.

Next, silver sintering and glass melting proceed at a temperature of 400-600 ° C. and glass-SiN _x / Si reaction (Glass-SiN _x /) at a temperature of 600-800 ° C. Si reaction) and Ag-Si reaction (Ag-Si reaction) proceed.

Here, since only the front metal electrode is heated by the induction current device, a heat treatment process in which the front metal electrode is stably connected to the second type silicon substrate 120 without affecting other elements even at a high temperature of 700 to 800 ° C. Can proceed.

Next, the back metal electrode 140 of the solar cell according to the present invention is formed under the first type silicon substrate 100, and the back metal electrode 140 is the same as the front metal electrode 150 described above. In addition, it may be formed using one or more of Al, Pt, Au, Cu and Ag having excellent electrical conductivity.

In addition, the rear metal electrode 140 may also be heat treated using an induction current device. As a result, as shown in FIG. 4, an electric field is formed at an interface between the first type silicon substrate 100 and the rear metal electrode 140. A structure to which the forming layer BSF 135 is applied may be formed. The backside field forming layer 135 is formed by applying a metal layer as a backside metal electrode and then performing heat treatment. The backside electric field forming layer 135 acts as an impurity on the back side of the crystalline silicon substrate by the metal layer of the backside metal electrode to p + The p + layer reduces the back recombination of holes generated by light, increasing the efficiency of the solar cell.

Although not shown, a surface of a texturing structure may be formed at an interface between the above-described layers by an etching process. Such a texturing structure may lower reflectance and improve light collection. Make sure

As described above, the silicon solar cell according to the present invention is characterized in that the heat treatment by selectively heating the metal electrode using an induction current device. Therefore, an efficient front metal electrode forming process may be performed and a basic embodiment thereof may be described as follows.

5 and 6 are cross-sectional views illustrating an electrode heat treatment process according to the present invention.

5 and 6, the bottom metal electrodes 240 and 340, the back field forming layers 235 and 325, the first type silicon substrates 210 and 310, and the second type silicon layers 220 and 320 from the bottom. And passivation films or anti-reflection films 230 and 330.

Next, the first front surface metal electrodes 250 and 350 in the screen printing state are provided. When the front metal electrode is heat-treated (fired) by using an induction current device, the third front metal electrode of ohmic contact state is formed on the second front metal electrodes 260 and 360 in a non-contact state. 270, 370).

In this case, the induction current device does not affect other devices, and uniformly heats only the front metal electrode, thus changing the state of all the third front metal electrodes 270 and 370 on the passivation film or the anti-reflection film 230 and 330. The same can be adjusted.

Here, when some of the induced current process is excessively performed, fourth front surface metal electrodes 280 and 380 in a shunt state may be formed. In this case, like the fourth front metal electrode 280 of FIG. 5, a shape in which the first type silicon substrate 210 and the fourth front metal electrode 280 are short-circuited occurs. In the conventional case, the heat treatment atmosphere is released. In order to perform a separate process from, there was a problem that the process is complex and time lag.

However, the present invention does not use a heat treatment furnace (Furnace) or RTP apparatus, there is no need for a separate heat treatment ambience release process. Therefore, it is possible to quickly perform the doping process only on the electrode portion, and as a result, it is possible to form a self-doping second type silicon layer 315 as shown in FIG. The electrode 390 may be formed.

As described above, when the silicon solar cell according to the embodiments of the present invention, the stability and reproducibility of the solar cell efficiency can be very excellent according to the electrode forming process using the induction current device.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments and can be modified in various forms, and having ordinary skill in the art to which the present invention pertains. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Figure 1 is a graph showing the process shape over time and temperature of the electrode heat treatment process according to the prior art.

Figure 2 is a graph showing the process form by temperature of the electrode heat treatment process according to the prior art.

3 and 4 are cross-sectional views showing an electrode heat treatment process using an induced current according to the present invention.

5 is a cross-sectional view showing an electrode heat treatment process according to an embodiment of the present invention.

6 is a cross-sectional view showing an electrode heat treatment process according to another embodiment of the present invention.

Claims (11)

Forming a second type silicon layer on the first type crystalline silicon substrate; Forming a passivation film or an anti-reflection film on the second type silicon layer; Forming a front metal electrode on the passivation layer or an anti-reflection film and sequentially forming a rear metal electrode on the lower portion of the first type crystalline silicon substrate; And And selectively heat-treating the front metal electrode by using an induction current device. The method of claim 1, A passivation film is formed at an interface between the first type crystalline silicon substrate and the second type silicon layer. The method of claim 1, The passivation film is a silicon solar cell manufacturing method, characterized in that selected from SiO ₂ , SiC, SiNx and intrinsic amorphous silicon (Intrinsic amorphors-Si). The method of claim 1, The passivation film is a silicon solar cell manufacturing method, characterized in that formed to a thickness of 5 ~ 100nm. The method of claim 1, The front metal electrode is formed of a metal paste including 70 to 80% by weight of Ag powder, 5 to 20% by weight of glass frit, 5 to 20% by weight of resin, and a residual amount of organic solvent. Method for producing a silicon solar cell, characterized in that. The method of claim 5, The Ag powder is a method of manufacturing a silicon solar cell, characterized in that the flake (Flake) or spherical particles having a particle diameter of 1 ~ 20㎛. The method of claim 1, And the front metal electrode is connected to the second type silicon layer. The method of claim 1, The front metal electrode is a method of manufacturing a silicon solar cell, characterized in that heated to a temperature of 700 ~ 800 ℃. The method of claim 1, The back metal electrode is a method of manufacturing a silicon solar cell, characterized in that the heat treatment (Firing) selectively by the induction current device. The method of claim 9, And a field forming layer (BSF) is formed at the interface between the first type silicon substrate and the back metal electrode by the heat treatment. The method of claim 9, The heat treatment is a method of manufacturing a silicon solar cell, characterized in that using an induction current using a frequency having a frequency of 1,000 ~ 1,000,000 Hz.

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