JP6796176B2 - Solar cells, solar cell modules, and photovoltaic systems - Google Patents

Description

The present invention relates to a method for manufacturing a high photoelectric conversion efficiency solar cell and a high photoelectric conversion efficiency solar cell.

As one of the solar cell structures having a relatively high photoelectric conversion efficiency using a single crystal or polycrystalline semiconductor substrate, there is a back electrode type solar cell in which all positive and negative electrodes are provided on a non-light receiving surface (back surface). An overview of the back surface of the back electrode type solar cell is shown in FIG. Emitter layers 102 and base layers 101 are arranged alternately, and electrodes (103, 104) are provided on the layers along the respective layers. The width of the emitter layer is several mm to several hundred μm, and the width of the base layer is several hundred μm to several tens of μm. Further, the electrode width is generally about several hundred to several tens of μm, and the electrode is often called a finger electrode.

A schematic view of the cross-sectional structure of the back electrode type solar cell is shown in FIG. The emitter layer 102 and the base layer 101 are formed in the vicinity of the outermost surface layer on the back surface of the substrate 202. The thickness of each layer is at most about 1 μm. Finger electrodes (205, 206) are provided on each layer, and the surface of the non-electrode region is covered with a back surface protective film 207 such as a silicon nitride film or a silicon oxide film. An antireflection film 201 is provided on the light receiving surface side for the purpose of reducing reflection loss.

Japanese Unexamined Patent Publication No. 2006-332273

One of the problems in the manufacturing method of the back electrode type solar cell is the deviation between the base layer and the base electrode. When the electrodes are formed by the printing method, the elongation of the plate changes with time and plate making, so the electrodes having a width of several hundred to several tens of μm are aligned with the base layer having a width of several hundred μm to several tens of μm as described above. It was extremely difficult to form stably. In order to alleviate this deviation, it is easiest in terms of manufacturing method to widen the base layer width, but it is known in Patent Document 1, for example, that widening the base layer width lowers the conversion efficiency. .. The printing method is the most effective in consideration of the manufacturing cost, and it is necessary to establish a method for forming electrodes with good yield by the printing method while maintaining the base layer width.

The present invention has been made in view of the above problems, and provides a method for manufacturing a high photoelectric conversion efficiency solar cell, which can reduce the deviation between the base layer and the base electrode and improve the manufacturing yield of the solar cell. The purpose is to do. Another object of the present invention is to provide a high photoelectric conversion efficiency solar cell in which the deviation between the base layer and the base electrode is small and the characteristics are good. A further object of the present invention is to provide a solar cell manufacturing system capable of reducing the deviation between the base layer and the base electrode and improving the manufacturing yield of the solar cell.

In order to achieve the above object, the present invention comprises a step of preparing a semiconductor substrate having a dielectric film on at least the first main surface.
A step of partially removing the dielectric film of the semiconductor substrate, and
A method for manufacturing a solar cell, which comprises a step of forming an electrode along a region where the dielectric film is partially removed.
The position of the region where the dielectric film is partially removed and the position of the formed electrode with respect to the semiconductor substrate after performing the steps of partially removing the dielectric film and forming the electrodes. Has a process of measuring the relative positional relationship of
Based on the measured positional relationship, the dielectric is adjusted after adjusting the position of the region where the dielectric film is partially removed with respect to the newly prepared semiconductor substrate having the dielectric film on at least the first main surface. Provided is a method for manufacturing a solar cell, which comprises partially removing a body membrane.

In this way, rather than correcting the misalignment of the formed electrodes in-plane, the dielectric film is formed based on the relative positional relationship between the position of the region where the dielectric film is partially removed and the position of the electrodes. By correcting the position of the region to be removed according to the electrodes, the relative positional relationship deviation, that is, the positional deviation can be easily reduced, and the yield of the solar cell can be improved while improving the productivity. Further, the position adjustment is not performed by separately measuring each of the region where the electrode and the dielectric film are removed, but the electrode is actually formed in the region where the dielectric film is removed. It is possible to reduce the factors of variation by observing and carrying out.

At this time, the relative positional relationship is measured for each selected coordinate in the plane of the semiconductor substrate, and the position of the region for partially removing the dielectric film is adjusted for each selected coordinate. It is preferable to carry out.

Since the positional deviation when forming the electrode in the region where the dielectric film has been removed occurs with high probability with reproducibility in the plane, the coordinates of the location where the positional deviation occurs are obtained, and the dielectric is obtained for each of these coordinates. By adjusting the position of the region where the body membrane is partially removed, the misalignment can be easily and effectively reduced.

Further, the in-plane of the semiconductor substrate was divided into a plurality of regions, coordinates representing the regions were assigned to each of the divided regions, and the measurement of the relative positional relationship was assigned to the divided regions. It is preferable to perform each coordinate and to adjust the position of the region for partially removing the dielectric film for each assigned coordinate.

In this way, the in-plane of the semiconductor substrate is divided into a plurality of regions, representative coordinates are assigned to each region, and the relative positional relationship is measured and the dielectric film is partially removed at those coordinates. By adjusting the position of, the number of points to be measured can be thinned out to some extent. As a result, the productivity is increased and the solar cell can be manufactured efficiently. Since it is considered that the systematic misalignment when forming the electrodes in the region where the dielectric film has been removed changes continuously in the plane, it is considered that all the electrodes are necessarily observed when measuring the positional relationship. You don't have to do it.

Further, it is preferable to measure the relative positional relationship only in the direction orthogonal to the longitudinal direction of the electrode.

The problem of the deviation between the position of the region where the dielectric film is partially removed and the position of the electrode is often in the direction orthogonal to the longitudinal direction of the electrode. Therefore, if the positional relationship is measured in the direction orthogonal to the longitudinal direction of the electrode, the time required for measuring the positional relationship can be shortened while sufficiently reducing the positional deviation.

Further, it is preferable that the electrodes are formed by using a screen printing method.

As described above, if the screen printing method is used, the electrodes can be formed at the lowest cost, and the solar cell can be manufactured at low cost.

Further, it is preferable to partially remove the dielectric film by using a laser.

By removing the dielectric film using a laser in this way, a solar cell can be manufactured at low cost. In addition, laser processing has good processing accuracy, and it is relatively easy to adjust the position of the region where the dielectric film is partially removed.

Further, in the method for manufacturing a solar cell of the present invention, after the step of partially removing the dielectric film and before the step of forming the electrode, impurities are found in the region where the dielectric film is partially removed. Can be diffused to form a diffusion layer.

By forming the diffusion layer in the region where the dielectric film is partially removed in this way, the displacement between the formed diffusion layer and the electrodes on the diffusion layer can be sufficiently reduced.

Further, in the method for manufacturing a solar cell of the present invention, a semiconductor substrate having a diffusion layer on the first main surface can be prepared.

By using such a semiconductor substrate having a diffusion layer on the first main surface, it is possible to easily form contact between the electrodes and the diffusion layer while reducing the displacement of the electrodes.

Further, in the method for manufacturing a solar cell of the present invention, the dielectric film is partially removed to remove the dielectric film by the amount of the dielectric film per unit area in the region where the dielectric film is removed. It is preferable that the amount of the dielectric film is 1/10 or less per unit area of the non-existent region.

By setting the amount of the dielectric film per unit area as such, the effect of removing the dielectric film can be sufficiently obtained. That is, in the case of diffusion using the remaining dielectric film as a mask, diffusion can be sufficiently performed. Further, when the electrode is formed by penetrating the dielectric film, fire-through is not required when forming contact between the electrode and the semiconductor substrate under the electrode, so that the electrode can be co-fired at a low temperature, and a solar cell can be used. The degree of freedom in the manufacturing process can be expanded.

Further, in order to achieve the above object, the present invention has a base layer and an emitter layer adjacent to the base layer on the first main surface of the semiconductor substrate, and electrodes are arranged on the base layer. It ’s a battery,
The base layer has a linear region having a length and a width on the first main surface, and the linear region has a linear region shorter than the length of the linear region. Provided is a solar cell, characterized in that the linear region includes one arranged at a position deviated from the extension of the other linear region of the linear region.

As described above, in the case of a solar cell including a solar cell in which the linear region is arranged at a position deviated from the extension of the other linear region, the base layer when viewed in the plane of the first main surface. The misalignment of the electrodes can be reduced, and a solar cell having good characteristics and small variations in characteristics can be obtained.

At this time, the width of the base layer is preferably 50 μm or more and 250 μm or less, and the width of the electrode is preferably 30 μm or more and 200 μm or less.

With such a width of the base layer and the electrodes, the misalignment between the base layer and the electrodes can be reduced more effectively, and a solar cell having better characteristics can be obtained.

At this time, the emitter layer has a wedge-shaped region that is convex from the emitter layer side at the boundary between the base layer and the emitter layer adjacent to the base layer, and the bottom of the wedge-shaped region. It is preferable that the length of the portion is 1 μm or more and 20 μm or less, and the angle of the top of the wedge-shaped region is 70 ° or more and 110 ° or less.

If the boundary between the base layer and the emitter layer has such a shape, the contact area between the base layer and the electrode increases when the electrode is formed near the boundary as compared with the case where there is no wedge-shaped region, so that it is relative. The contact resistance is reduced, and the adhesive strength of the electrodes is relatively increased.

Further, in order to achieve the above object, the present invention has a first region having a diffusion layer on the first main surface of the semiconductor substrate and a dielectric film having a predetermined thickness on the diffusion layer, and the predetermined region. A solar cell having a dielectric film thinner than the thickness of the above or having a second region without the dielectric film and having electrodes arranged in at least a part of the second region. And
The second region has a linear region having a length and a width on the first main surface, and the linear region has a linear region shorter than the length of the linear region. The linear region includes those arranged at positions deviated from the extension of the other linear regions of the linear region.
The amount of the dielectric film per unit area of the region where the electrode is not formed in the second region is 1/10 or less of the amount of the dielectric film per unit area of the first region. Provide solar cells.

In this way, if the solar cell includes a solar cell in which the linear region is arranged at a position deviated from the extension of the other linear region, the second is when viewed in the plane of the first main surface. The displacement between the area and the electrode can be reduced. Further, the amount of the dielectric film per unit area of the region where the electrode is not formed in the second region is 1/10 or less of the amount of the dielectric film per unit area of the first region. Solar cells do not require fire-through to form contact between the electrodes and the underlying semiconductor substrate during manufacturing. Therefore, since the electrodes can be fired at a low temperature during manufacturing, such a solar cell has a wide degree of freedom in the manufacturing process.

At this time, the width of the second region is preferably 50 μm or more and 250 μm or less, and the width of the electrode is preferably 30 μm or more and 200 μm or less.

With such a width of the second region and the electrode, it is possible to obtain a solar cell in which the misalignment between the second region and the electrode is more effectively reduced.

At this time, the first region has a wedge-shaped region that is convex from the first region side at the boundary between the second region and the first region adjacent to the second region. It is preferable that the length of the bottom portion of the wedge-shaped region is 1 μm or more and 20 μm or less, and the angle of the top portion of the wedge-shaped region is 70 ° or more and 110 ° or less.

When the boundary between the first region and the second region has such a shape, when the electrode is formed in the vicinity of the boundary, an anchor effect is exhibited in the electrode, and the electrode has a shape as compared with the case where there is no wedge-shaped region. Adhesive strength is relatively high.

The present invention also provides a solar cell module characterized in that the above-mentioned solar cell is built-in.

As described above, the solar cell of the present invention can be incorporated in the solar cell module.

The present invention also provides a photovoltaic power generation system characterized by having the above-mentioned solar cell module.

As described above, the solar cell module incorporating the solar cell of the present invention can be used in the photovoltaic power generation system.

Further, in order to achieve the above object, the present invention includes at least a dielectric film removing device for partially removing the dielectric film on the first main surface of the semiconductor substrate.
An electrode forming device that forms an electrode along a region where the dielectric film is partially removed,
The first main surface of the semiconductor substrate after the electrodes are formed by the electrode forming apparatus is inspected, and the position of the region where the dielectric film is partially removed is relative to the position of the formed electrodes. A visual inspection device that acquires data on various positional relationships,
A device having a data analysis device for determining a correction value for adjusting the position of a region for partially removing the dielectric film based on the acquired data and feeding back the correction value to the dielectric film removing device. Provided is a solar cell manufacturing system characterized by being.

In this way, the solar cell manufacturing system is provided with a dielectric film removing device, an electrode forming device, a visual inspection device, and a data analysis device, and by linking them, a region and an electrode in which the dielectric film is partially removed can be obtained. It is possible to efficiently reduce the misalignment of the solar cell and improve the manufacturing yield of the solar cell. As a result, the manufactured solar cell can be made inexpensive.

At this time, the visual inspection apparatus divides the in-plane of the semiconductor substrate into a plurality of regions, assigns coordinates representing the regions to each of the divided regions, and divides the relative positional relationship data into the divided regions. It is preferable that the data has a function of acquiring each coordinate assigned to the assigned area.

In this way, the in-plane of the semiconductor substrate is divided into a plurality of regions, representative coordinates are assigned to each region, and the positional relationship is measured and the position of the region where the dielectric film is partially removed is determined by those coordinates. By making adjustments, the measurement points can be thinned out to some extent. As a result, the productivity is increased and the solar cell can be manufactured efficiently. Since it is considered that the systematic misalignment when forming the electrodes in the region where the dielectric film has been removed changes continuously in the plane, it is considered that all the electrodes are necessarily observed when measuring the positional relationship. You don't have to do it.

At this time, it is preferable that the dielectric film removing device is a laser processing device and the electrode forming device is a screen printing device.

As described above, by using the laser processing device and the screen printing device, the misalignment can be reduced at low cost, and an inexpensive solar cell can be manufactured.

According to the method for manufacturing a solar cell of the present invention, it is possible to reduce the displacement between the region where the dielectric film is partially removed and the electrodes formed along the region, and improve the manufacturing yield of the solar cell. .. Further, the solar cell of the present invention can be a high photoelectric conversion efficiency solar cell having small electrode misalignment and good characteristics. Further, according to the solar cell manufacturing system of the present invention, it is possible to reduce the displacement of the electrodes and improve the manufacturing yield of the solar cell.

It is an overview view of a general back electrode type solar cell to which this invention can be applied seen from the back side. It is sectional drawing of the general back electrode type solar cell to which this invention can be applied. It is a process flow diagram which shows an example of the manufacturing method of the back electrode type solar cell which concerns on this invention. It is a top view which shows the shape of the base layer formed by laser processing which concerns on this invention. It is a top surface schematic view which shows the relative position of a base layer and a base electrode which concerns on this invention. It is a top view which shows an example of the shape of the base layer which concerns on this invention. It is sectional drawing of the solar cell which concerns on this invention. It is an overview diagram of the solar cell module which concerns on this invention. It is a schematic diagram inside the back surface of the solar cell module which concerns on this invention. It is sectional drawing of the solar cell module which concerns on this invention. It is a schematic diagram of the photovoltaic power generation system which concerns on this invention. It is the schematic which shows an example of the structure of the manufacturing system of the solar cell which concerns on this invention. It is a figure which showed the in-plane distribution of the misalignment frequency of a base layer and a base electrode which concerns on this invention. It is a figure which showed the in-plane distribution between the base layer and the base electrode gap which concerns on this invention.

As described above, in recent years, the misalignment between the base layer of the solar cell and the base electrode has been a problem. The present inventors have earnestly studied measures for reducing such misalignment and completed the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

Hereinafter, the method for manufacturing a solar cell of the present invention will be described with reference to FIG. 3, taking the case where an N-type substrate is used as the semiconductor substrate as an example.

FIG. 3 is a process flow chart showing an example of a method for manufacturing a back electrode type solar cell to which the present invention is applied.

First, a semiconductor substrate having a dielectric film on at least the first main surface is prepared. For example, the semiconductor substrate can be prepared as follows. An ascut single crystal {100} N-type silicon substrate 202 having a specific resistance of 0.1 to 5 Ω · cm was prepared by doping high-purity silicon with a V-valent element such as phosphorus, arsenic, or antimony (step (a)). , Surface slice damage is etched with a high concentration alkali such as sodium hydroxide or potassium hydroxide having a concentration of 5 to 60%, or a mixed acid of difluoric acid and nitric acid. The single crystal silicon substrate may be produced by either a CZ (Czochralski) method or an FZ (Floating zone) method. The substrate 202 does not necessarily have to be a single crystal silicon substrate, and may be a polycrystalline silicon substrate.

Subsequently, minute irregularities called textures are formed on the surface of the substrate 202. Texture is an effective way to reduce the reflectance of solar cells. For the texture, the substrate 202 is placed in a heated alkaline solution (concentration 1 to 10%, temperature 60 to 100 ° C.) of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium hydrogen carbonate, etc. for about 10 to 30 minutes. It is made by immersing. A predetermined amount of 2-propanol may be dissolved in the above solution to accelerate the reaction.

After forming the texture, it is washed with hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, etc., or a mixed solution thereof in an acidic aqueous solution. Hydrogen peroxide may be mixed to improve the cleanliness.

The emitter layer 102 is formed on the first main surface of the substrate 202 (step (b)). The emitter layer 102 is a conductive type (P type in this case) opposite to that of the substrate 202 and has a thickness of about 0.05 to 1 μm. The emitter layer 102 can be formed by vapor phase diffusion using BBr ₃ or the like. Specifically, the substrates 202 are placed in a heat treatment furnace in a state of being stacked as a set of two, and a mixed gas of BBr ₃ and oxygen is introduced and heat treatment is performed at 950 to 1050 ° C. Nitrogen or argon is suitable as the carrier gas. The emitter layer 102 can also be formed by applying a coating agent containing a boron source to the entire surface of the first main surface and heat-treating at 950 to 1050 ° C. As the coating agent, for example, an aqueous solution containing 1 to 4% boric acid as a boron source and 0.1 to 4% polyvinyl alcohol as a thickener can be used.

After the emitter layer 102 is formed, the mask 303 for forming the base layer, which is the next step, is formed on both main surfaces of the substrate 202 (step (c)). As the mask 303, a silicon oxide film or a silicon nitride film which is a dielectric film can be used. By using the CVD method, any film can be formed by appropriately selecting the gas type to be introduced. In the case of a silicon oxide film, the substrate 202 can also be formed by thermal oxidation. In that case, the substrate 202 is heat-treated at 950 to 1100 ° C. for 30 minutes to 4 hours in an oxygen atmosphere to form a silicon thermal oxide film of about 100 nm. The film thickness can be arbitrarily changed by appropriately selecting the temperature, time, gas, etc., but the film thickness is preferably 30 to 300 nm in order to combine the mask function and the ease of partial opening in the next step. .. This heat treatment may be carried out in the same batch following the heat treatment for forming the emitter layer 102. In this way, a semiconductor substrate having a dielectric film on at least the first main surface is prepared.

Next, the dielectric film of the semiconductor substrate prepared in this manner is partially removed. For example, the mask of the portion to be the region of the base layer 101 is partially removed (opening) to form the opening 304 (step (d)). Specifically, the opening width of the opening 304 is 50 μm or more and 250 μm or less, and the distance between the openings 304 is about 0.6 mm or more and 2.0 mm or less so that the openings can be formed in a parallel line. A photolithography method or an etching paste can be used for the opening of the mask 303, but the opening with a laser is convenient and preferable. As the laser source, a second harmonic such as YAG system, YVO ₄ system, GdVO ₄ system or the like can be used, but any laser source may be used as long as the wavelength is about 500 to 700 nm. In the future, even shorter wavelength lasers will be available. The laser conditions can be determined as appropriate, but for example, the output is 4 to 20 W, the frequency is 1000 to 100,000 Hz, the fluence is 1 to 5 J / cm ² , the galvo head is provided, and the scanning speed is 100 to 5000 mm / sec. can do. The processing position can be easily specified by linking with CAD (Computer-aided design) data using a personal computer or the like.

After forming the opening 304 in the mask 303, the substrate 202 is immersed in an alkaline aqueous solution such as KOH or NaOH heated to 50 to 90 ° C. to remove (etch) the unnecessary emitter layer 102 of the opening 304 (step). (E)). As a result, the opening 305 from which the emitter layer is removed is formed.

Subsequently, the base layer 101 is formed (step (f)). A vapor phase diffusion method using phosphorus oxychloride can be used to form the base layer 101. By heat-treating the substrate 202 at 830 to 950 ° C. in an atmosphere of a mixed gas of phosphorus oxychloride, nitrogen and oxygen, a phosphorus diffusion layer (N ⁺ layer) to be a base layer 101 is formed. In addition to the vapor phase diffusion method, the base layer 101 can also be formed by spin-coating or printing a phosphorus-containing material and then heat-treating it. After forming the base layer 101, the mask 303 and the glass formed on the surface are removed with hydrofluoric acid or the like.

When the region to be the base layer is formed on the mask by performing the laser processing as described above, since the laser spot is not rectangular, a pattern (shape) peculiar to the boundary between the base layer 101 and the emitter layer 102 is formed. FIG. 4 shows a schematic top view of the base layer 101 formed by laser processing. As shown in FIG. 4, at the boundary between the base layer 101 and the emitter layer 102 adjacent to the base layer 101, a wedge-shaped region 407 that is convex from the emitter layer 102 side is generated. This wedge-shaped region 407 becomes apparent especially after etching. The apex angle 409 of the wedge-shaped region 407 is 70 ° or more and 110 ° or less, and the length 408 of the bottom portion of the wedge-shaped region 407 is about 1 μm or more and 20 μm or less.

Next, the antireflection film 307 is formed on the second main surface, which is the main surface opposite to the first main surface (step (g)). As the antireflection film 307, a silicon nitride film, a silicon oxide film, or the like can be used. In the case of a silicon nitride film, a plasma CVD apparatus is used to form a film with a film thickness of about 100 nm. As the reaction gas, monosilane (SiH ₄ ) and ammonia (NH ₃ ) are often mixed and used, but nitrogen can also be used instead of NH ₃ . Further, hydrogen may be mixed with the reaction gas in order to adjust the process pressure, dilute the reaction gas, and promote the bulk passivation effect of the substrate when polycrystalline silicon is used for the substrate. On the other hand, in the case of a silicon oxide film, it can be formed by the CVD method, but the film obtained by the thermal oxidation method has higher characteristics. Further, in order to enhance the surface protection effect, an aluminum oxide film may be formed on the surface of the substrate in advance, and then the antireflection film 307 may be formed.

Also on the first main surface, a silicon nitride film or a silicon oxide film can be used as the back surface protective film 207. The film thickness of the back surface protective film 207 is preferably 50 to 250 nm. Similar to the second main surface (light receiving surface) side, the back surface protective film 207 can be formed by the CVD method in the case of the silicon nitride film and by the thermal oxidation method or the CVD method in the case of the silicon oxide film. Further, in order to enhance the surface protection effect, an aluminum oxide film may be formed on the surface of the substrate in advance, and then a silicon nitride film, a silicon oxide film, or the like may be formed.

The electrode is then formed along the region where the dielectric film (mask 303) has been partially removed. This electrode formation can be performed as follows. The base electrode 103 is formed by, for example, a screen printing method (step (h)). For example, a plate making having an opening width of 30 μm or more and 200 μm or less and a parallel line pattern at intervals of 0.6 to 2.0 mm is prepared, and an Ag paste obtained by mixing Ag powder and glass frit with an organic binder is applied along the base layer 101. To print. Although the dielectric film (mask 303) itself is completely removed, the region where the base layer 101 exists is a portion where the dielectric film of the semiconductor substrate is partially removed in the step (d). Similarly, the Ag paste is printed as the emitter electrode 104. The Ag paste for the base electrode 103 and the Ag paste for the emitter electrode 104 may be the same or different ones. After the above electrode printing, Ag powder is passed through a silicon nitride film or the like by heat treatment (fire-through), and the electrode and the silicon under it are made conductive. The base electrode 103 and the emitter electrode 104 can be fired separately. Baking is usually carried out by treating at a temperature of 700 ° C. or higher and 850 ° C. or lower for 5 to 30 minutes.

Since the number of the base layer 101 and the base electrode 103 reaches 80 to 260, it is not easy to align them. This is because the electrode is formed by combining misalignment factors such as misalignment during laser processing, misalignment during electrode printing, and plate elongation. It is conceivable to measure the position of the laser and the position of the electrode with a length measuring machine or the like in advance, but it is not effective because the cause of the deviation is not the only one.

In the method for manufacturing a solar cell of the present invention, the position of the region where the dielectric film is partially removed with respect to the semiconductor substrate after performing the steps of partially removing the dielectric film and forming the electrodes. It has a step of measuring the relative positional relationship between the positions of the formed electrodes. In the case of this example, specifically, the relative positional relationship between the base layer 101 and the base electrode 103 is measured by observing the substrate on which the base layer 101 and the base electrode 103 are actually formed by using, for example, a microscope. To do. Then, based on the measured positional relationship, the position of the region where the mask 303 is partially removed with respect to the newly prepared semiconductor substrate 202 having the mask (dielectric film) 303 on at least the first main surface. After adjusting, the mask 303 is partially removed. That is, in the present invention, the measured relative positional relationship is fed back to the processing position of the laser, and then the dielectric film of another substrate is partially removed by the laser. The points to be observed and measured may be the entire base electrode, or the in-plane of the substrate may be divided into regions such as 3 × 3 and 6 × 7, and each region may be observed one by one.

The number of substrates 202 to be observed for measuring the relative positional relationship is preferably a plurality, but may be one. The entire number of printed substrates 202 may be observed, or may be observed at a frequency of once every several to several hundreds in a sampling inspection, and may be appropriately determined from the scale of production and the time required for observation. .. Further, it does not necessarily have to be a product, and may be a dummy substrate that has undergone at least a base layer region forming step and an electrode forming step in which the dielectric film is partially removed.

As a specific method for measuring the relative positional relationship, there is a method for measuring the distance between the base electrode end and the base region (base layer) end. Since deviation is mainly a problem in the direction orthogonal to the longitudinal direction of the electrode, the measurement may be performed only in this direction. FIG. 5 shows a schematic top view showing the relative positions of the base layer 101 and the base electrode 103. The distance between the base electrode end and the base layer end can be defined by two distances, an upper distance 504 and a lower distance 505. As shown in FIG. 5A, if the base electrode 103 is completely contained in the base layer 101, a finite (non-zero) value can be obtained for both the distances 504 and 505. On the other hand, as shown in FIG. 5B, when the deviation occurs, the upper distance 504 is measured as 0. In other words, if any of the distances 504 and 505 is 0, it is determined that the deviation has occurred. As a method of determining the deviation amount, there are a method of using the larger value of the distances 504 and 505, a method of simultaneously measuring the electrode width and the base region width, and a method of estimating the protrusion amount by addition and subtraction.

Once the amount of deviation is determined, the amount of correction for the base layer formation position is determined. In order to arrange the base electrode 103 in the center of the base layer 101, it is preferable to correct the distances 504 and 505 so that the values are the same for each selected coordinate in the substrate surface. Convergence will be faster if the distances 504 and 505 are redefined with the amount of protrusion as a negative value and then the amount of correction is determined.

Further, instead of obtaining a specific amount of deviation, a method of obtaining the frequency of deviation may be used. That is, whether or not the base electrode 103 is contained in the base layer 101 is observed (measured) on a plurality of substrates, and the frequency (probability) of deviation is calculated. More specifically, coordinate data in which either the distance 504 or the distance 505 is 0 is accumulated, and the upward deviation (distance 504 is 0) and the downward deviation (distance 505 is 0) for each coordinate in the substrate. For each case of 0), the number of occurrences of deviation ÷ the number of observations × 100 (%) is calculated as the frequency of occurrence of deviation. The larger the amount of deviation (position), the greater the frequency of deviation. In this case, the correction amount of the base layer forming position is preferably 1 to 50 μm each time. This is because if you make large adjustments at once, the overall balance will be lost.

When the operation of adjusting the base layer forming position for each region in the substrate is repeated as described above, as shown in FIG. 6, a portion 607 in which the center line 606 of the base layer 101 is discontinuous is generated, and the base layer is formed. 101 is no longer formed in a straight line. By adopting such a structure in the base layer 101, the misalignment between the base layer 101 and the base electrode 103 can be reduced.

Next, the first embodiment of the solar cell of the present invention will be described with reference to FIG. 6 and the like. The solar cell of the first embodiment of the present invention has a base layer 101 and an emitter layer 102 adjacent to the base layer 101 on the first main surface of the semiconductor substrate, and the base electrode 103 is arranged on the base layer 101. In the solar cell, the base layer 101 has a linear region 612 having a length and a width on the first main surface, and the linear region 612 is based on the length of the linear region 612. It has a short linear region 614, the linear region 614 including those located offset from the extension of the other linear region 614 of the linear region 612.

As described above, if the solar cell includes a solar cell in which the linear region 614 is arranged at a position deviated from the extension of the other linear region 614, when viewed in the plane of the first main surface, The misalignment between the base layer 101 and the base electrode 103 can be reduced, and a solar cell having good characteristics and small variations in characteristics can be obtained.

Further, it is preferable that the width of the base layer 101 is 50 μm or more and 250 μm or less, and the width of the base electrode 103 is 30 μm or more and 200 μm or less. With such a width of the base layer 101 and the base electrode 103, the misalignment between the base layer 101 and the base electrode 103 can be more effectively reduced, and a solar cell having better characteristics can be obtained.

Further, as shown in FIG. 4, the emitter layer 102 has a wedge-shaped region 407 that is convex from the emitter layer 102 side at the boundary between the base layer 101 and the emitter layer 102 adjacent to the base layer 101. It is preferable that the length 408 of the bottom portion of the wedge-shaped region 407 is 1 μm or more and 20 μm or less, and the angle 409 of the top of the wedge-shaped region 407 is 70 ° or more and 110 ° or less. If the boundary between the base layer 101 and the emitter layer 102 has such a shape, the contact area between the base layer 101 and the base electrode 103 when an electrode is formed near the boundary is compared with the case where there is no wedge-shaped region 407. Therefore, the contact resistance is relatively reduced, and the adhesive strength of the electrodes is also relatively large.

In the above, an example of application of the present invention to a back electrode type solar cell has been described. However, the present invention is not limited to this, and is also applicable to a method for manufacturing a solar cell in which a protective film (dielectric film) on the surface of a substrate is removed by a laser and an electrode is directly formed at a portion where the protective film is removed. Can be done. That is, the substrate whose surface is protected by a dielectric film such as a silicon nitride film or a silicon oxide film is locally irradiated with a laser in a pattern to open an opening for electrode contact with the silicon nitride film or the silicon oxide film. Is provided. The amount of protective film (= thickness of protective film x area) can be removed to 1/10 or less by laser treatment. This eliminates the need for fire-through, enables low-temperature firing of electrodes, and expands the degree of freedom in the manufacturing process of solar cells.

A second embodiment of the solar cell of the present invention corresponding to the above-described method for manufacturing the solar cell of the present invention will be described with reference to FIGS. 7 (a) and 7 (b). As shown in FIG. 7A, the solar cell of the second embodiment of the present invention has a diffusion layer 720 on the first main surface of the semiconductor substrate 702, and a dielectric having a predetermined film thickness is placed on the diffusion layer 720. It has a first region 724 having a body film (passion film) 722 and a second region 726 having a dielectric film thinner than a predetermined thickness or not having a dielectric film, and having a second region. A solar cell in which electrodes 728 are arranged in at least a part of region 726. The second region 726 has a linear region 712 having a length and a width on the first main surface as shown in FIG. 7 (b), and the linear region 712 is the linear region 712 of the linear region 712. It has a linear region 714 shorter than the length, the linear region 714 including one arranged at a position offset from the extension of the other linear region 714 of the linear region 712. The amount of the dielectric film per unit area of the region where the electrode 728 is not formed in the second region 726 is 1/10 or less of the amount of the dielectric film per unit area of the first region 724.

As described above, in the case of a solar cell including a solar cell in which the linear region 714 is arranged at a position deviated from the extension of the other linear region 714, as described above, in the plane of the first main surface. When viewed, the misalignment between the second region 726 and the electrode 728 can be reduced. Further, the amount of the dielectric film per unit area of the region where the electrode 728 is not formed in the second region 726 is 1/10 or less of the amount of the dielectric film per unit area of the first region. As described above, since the need for fire-through is eliminated when forming contact between the electrode 728 and the substrate under the electrode 728, low-temperature firing of the electrode 728 becomes possible, and the degree of freedom in the manufacturing process of the solar cell can be expanded. ..

Further, it is preferable that the width of the second region 726 is 50 μm or more and 250 μm or less, and the width of the electrode 728 is 30 μm or more and 200 μm or less. With such a width of the second region 726 and the electrode 728, the solar cell can be obtained in which the misalignment between the second region 726 and the electrode 728 is more effectively reduced.

Further, the first region 724 has a wedge-shaped region that is convex from the first region 724 side at the boundary between the second region 724 and the first region 724 adjacent to the second region 724. It is preferable that the length of the bottom portion of the wedge-shaped region is 1 μm or more and 20 μm or less, and the angle of the top portion of the wedge-shaped region is 70 ° or more and 110 ° or less. If the boundary between the first region 724 and the second region 726 has such a shape, when an electrode is formed near the boundary, an anchor effect is exhibited in the electrode, as compared with the case where there is no wedge-shaped region. The adhesive strength of the electrodes is relatively large.

The solar cell of the present invention described above can be incorporated in the solar cell module. FIG. 8 shows an overview of an example of a solar cell module incorporating the solar cell of the present invention. FIG. 8 shows an example of a solar cell module having a built-in back electrode type solar cell, but the present invention is not limited to this, and a solar cell module containing another type of solar cell of the present invention may be used. it can. The solar cell 800 of the present invention described above has a structure in which the solar cell module 860 is laid out in a tile shape.

In the solar cell module 860, several to several tens of adjacent solar cells 800 are electrically connected in series to form a series circuit called a string. An overview of the strings is shown in FIG. FIG. 9 corresponds to a schematic view of the back side inside the module, which is normally invisible to the public. Also, finger electrodes and busbars are not shown. As shown in FIG. 9, the P bus bar (bus bar electrode connected to the finger electrode bonded to the P type layer of the substrate) and the N bus bar (N type layer of the substrate) of the adjacent solar cell 800 are connected in series. (Busbar electrodes connected to the finger electrodes joined to the above) are connected to each other by a tab lead wire 861 or the like.

A schematic cross-sectional view of the solar cell module 860 is shown in FIG. As described above, the string is composed of a plurality of solar cells 800 connected to the bus bar electrode 822 with a lead wire 861. The string is usually sealed with a translucent filler 872 such as EVA (ethylene vinyl acetate), the non-light receiving surface side is a weather resistant resin film 873 such as PET (polyethylene terephthalate), and the light receiving surface is soda lime glass. It is covered with a light receiving surface protective material 871 that is translucent and has strong mechanical strength. As the filler 872, polyolefin, silicone and the like can be used in addition to the above EVA.

In addition, this module can be used to manufacture and configure photovoltaic systems. FIG. 11 shows the basic configuration of a photovoltaic power generation system in which the modules of the present invention are connected. A plurality of solar power modules 16 are connected in series by wiring 15 and supply generated power to the external load circuit 18 via the inverter 17. Although not shown in FIG. 11, the system may further include a secondary battery for storing the generated power.

In the above, the case of the N-type substrate has been described as an example, but in the case of the P-type substrate, phosphorus, arsenic, antimony, etc. may be diffused to form the emitter layer, and boron, Al, etc. may be diffused to form the base layer. , It is obvious that the P-type substrate can be applied to the method for manufacturing a solar cell of the present invention and a solar cell.

Next, the solar cell manufacturing system of the present invention will be described with reference to FIG. FIG. 12 is a schematic view showing an example of the configuration of the solar cell manufacturing system according to the present invention. The solar cell manufacturing system 900 includes at least a dielectric film removing device 902 that partially removes the dielectric film on the first main surface of the semiconductor substrate, and electrodes along the region where the dielectric film is partially removed. The first main surface of the semiconductor substrate after the electrodes were formed by the electrode forming apparatus 904 and the electrode forming apparatus 904 was inspected to form the position of the region where the dielectric film was partially removed. Based on the visual inspection device 906 that acquires the data of the relative positional relationship of the electrode positions and the acquired data, a correction value for adjusting the position of the region where the dielectric film is partially removed is determined, and the correction value is determined. It has a data analysis device 908 that feeds back the value to the dielectric film removing device 902. As described above, the solar cell manufacturing system includes the dielectric film removing device 902, the electrode forming device 904, the visual inspection device 906, and the data analysis device 908, and by linking them, the dielectric film is partially removed. The misalignment between the region and the electrode can be efficiently reduced, and the manufacturing yield of the solar cell can be improved. As a result, the manufactured solar cell can be made inexpensive.

The dielectric film removing device 902 may be a laser processing device, and the electrode forming device 904 may be a screen printing device. For example, after screen printing with a screen printing device (electrode forming device 904), a visual inspection is performed with the visual inspection device 906, and the obtained data is used to adjust the laser processing position with the data analysis device 908, and the laser processing device (dielectric material) is used. It feeds back to the laser processing recipe of the film removing device 902). As described above, by using the laser processing device and the screen printing device, the misalignment can be reduced at low cost, and an inexpensive solar cell can be manufactured. Further, the data analysis device 908 may be provided independently, or may be integrated with the visual inspection device 906 and the laser processing device 902. If the image data is converted into an electric signal using a CCD camera or the like and the visual inspection device 906, the data analysis device 908, and the laser processing device 902 are connected to the network, it is possible to automatically perform all the series of operations.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1)
A solar cell was manufactured using the method for manufacturing a solar cell of the present invention. First, 20 phosphorus-doped {100} N-type ascut silicon substrates having a thickness of 200 μm and a specific resistance of 1 Ω · cm were prepared. Next, the damaged layer of the silicon substrate was removed with a hot concentrated potassium hydroxide aqueous solution. Then, it was immersed in a potassium hydroxide / 2-propanol aqueous solution at 72 ° C. to form a texture, and then washed in a hydrochloric acid / hydrogen peroxide mixed solution heated to 75 ° C.

Next, a P-type diffusion layer (emitter layer) was formed on the substrate. The substrates were placed in a heat treatment furnace in a state of being stacked as a set of two, and a mixed gas of BBr ₃ and oxygen and argon was introduced and heat treatment was performed at 1000 ° C. for 10 minutes. As a result of measuring the P-type diffusion layer formed on the substrate by the four-probe method, the sheet resistance was 50Ω.

This substrate was thermally oxidized at 1000 ° C. for 3 hours in an oxygen atmosphere to form a mask (dielectric film) on the surface of the substrate. The mask on the back of the substrate was opened with a laser. The laser source used was the second harmonic of Nd: YVO ₄ . The opening pattern was a parallel line with an interval of 1.2 mm. The output was 18 W and the scan speed was 600 mm / sec. The substrate on which the opening was formed was immersed in KOH at 80 ° C. to remove the emitter layer of the opening.

Next, in an atmosphere of phosphorus oxychloride, heat treatment was performed at 870 ° C. for 40 minutes with the light receiving surfaces of the substrates overlapped with each other to form a phosphorus diffusion layer (base layer) at the opening. After that, the mask and the surface glass were removed by immersing the substrate in hydrofluoric acid having a concentration of 12%.

After the above processing, silicon nitride films were formed on both sides of the substrate using a plasma CVD apparatus. The film thickness of the silicon nitride film was 100 nm on both the front and back surfaces. At this point, when the base layer width was measured using a microscope, it was approximately 190 μm on the plurality of substrates.

Next, the Ag paste was printed on the base layer and the emitter layer, respectively, to form a base electrode, and dried. This was fired in an air atmosphere of 780 ° C. With the above, a substrate (the substrate of the first cycle) for measuring the relative positional relationship between the base layer and the base electrode was prepared.

With respect to the completed 20 substrates of the first cycle, the vicinity of the base electrode was observed using a microscope to determine the positional deviation between the base layer and the base electrode. The inside of the substrate surface was divided into 42 regions of 6 × 7, and one point was observed in each region. The results of mapping the frequency of occurrence of substrate displacement in the first cycle in the substrate plane are shown in FIGS. 13 (a) and 13 (b). The case where the base electrode is displaced upward with respect to the base layer is (a), and the case where the base electrode is displaced downward is (b). Comparing FIGS. 13A and 13B, in this first cycle substrate, the base electrode is frequently displaced upward with respect to the base layer, and the displacement is particularly large on the lower right side of the substrate. You can see that. It is probable that the base electrodes did not become completely parallel lines and could not completely match the base layer because the amount of elongation of the printing plate making was different in the plane.

Based on this measurement result, the first laser machining position was adjusted. Specifically, the lower right of the substrate was modified to 30 μm and the lower left was modified to 2 μm, respectively, on the upper side in the figure. Laser processing was performed at this position, and after the KOH etching process, 20 cells were produced in the same process as described above (second cycle substrate). The vicinity of the electrodes of the 20 completed substrates was observed, and the misalignment was determined. Similar to the above, FIG. 13 (c) shows a case where the base electrode is displaced upward with respect to the base layer, and FIG. 13 (d) is a case where the base electrode is displaced downward with respect to the base layer. It can be seen that the shift frequency on the right side of the substrate is improved as compared with FIGS. 13 (a) and 13 (b), but the shift frequency on the upper side is still slightly higher.

Based on this measurement result, the laser machining position was adjusted for the second time. Specifically, the regions of the lower part of the substrate having a high deviation frequency were corrected to 20 μm each on the upper side in the drawing. Laser processing was performed at this position, and after the KOH etching process, cells were produced in the same process as described above (the substrate in the third cycle). The vicinity of the electrodes of the 20 completed substrates was observed, and the misalignment was determined. FIG. 13 (e) shows a case where the base electrode is displaced upward with respect to the base layer, and FIG. 13 (f) is a case where the base electrode is displaced downward. The misalignment was hardly seen in the plane.

(Example 2)
One substrate of the first cycle produced in Example 1 was extracted, and the distance between the base layer end and the base electrode end (that is, the amount of the gap between the base layer end and the electrode end, the distances 504 and 505 in FIG. 5 was set. (Equivalent) was measured. The inside of the substrate surface was divided into 42 regions of 6 × 7, and one point was measured in each region. At this time, the electrode width was also measured at the same time. At the location where the electrode protrudes from the base layer, the value of the distance between the base layer end and the base electrode end was extended to a negative number using the following equation.
(Distance between the base layer end and the base electrode end where the electrode protrudes from the base layer)
= (Base layer width)-(Distance between electrode end and base layer end)-(Electrode width)
... Equation (1)

The results of mapping the amount of the gap in the substrate surface are shown in FIGS. 14 (a) and 14 (b). The upper gap (corresponding to the upper distance 504 in FIG. 5) is (a), and the lower gap (corresponding to the lower distance 505 in FIG. 5) is (b). Negative numbers indicate that the base electrode protrudes from the base layer. Focusing on the negative numbers, it can be seen that the base electrodes are shifted upward at the lower left and lower right of the substrate, and slightly downward at the upper right of the substrate.

Based on this measurement result, the laser machining position was adjusted to 15 μm above the lower left of the substrate, 25 μm above the lower right, and 5 μm below the upper right. Laser processing was performed at the adjusted position, and after the KOH etching step, cells were manufactured in the same steps as described above. One sheet was taken out from the completed substrate again, and the gap was measured. Similar to the above, the upper gap is shown in FIG. 14 (c) and the lower gap is shown in FIG. 14 (d) with respect to the base layer. Compared with FIGS. 14 (a) and 14 (b), the variation in the value (gap) was reduced and stabilized around 30 μm, and more negative numbers (that is, the electrodes were protruding) were hardly seen.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any one having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. It is included in the technical scope of the invention.

Claims (4)

A first region having a diffusion layer on the first main surface of the semiconductor substrate and a dielectric film having a predetermined thickness on the diffusion layer and a dielectric film thinner than the predetermined film thickness are provided. A solar cell having a second region without the dielectric film and having electrodes arranged in at least a part of the second region.
The second region has a linear region having a length and a width on the first main surface, and the linear region has a linear region shorter than the length of the linear region. The linear region includes those arranged at positions deviated from the extension of the other linear regions of the linear region.
The amount of the dielectric film per unit area of the region where the electrode is not formed in the second region is 1/10 or less of the amount of the dielectric film per unit area of the first region.
The first region has a wedge-shaped region that is convex from the first region side at the boundary between the second region and the first region adjacent to the second region. A solar cell characterized in that the length of the bottom portion of the wedge-shaped region is 1 μm or more and 20 μm or less, and the angle of the top portion of the wedge-shaped region is 70 ° or more and 110 ° or less. The solar cell according to claim 1, wherein the width of the second region is 50 μm or more and 250 μm or less, and the width of the electrode is 30 μm or more and 200 μm or less. A solar cell module comprising the solar cell according to claim 1 or 2. A photovoltaic power generation system comprising the solar cell module according to claim 3.