JP2013048306A - Crystal solar battery cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal solar battery cell and a method for manufacturing the crystal solar battery cell capable of suppressing deterioration adhesion of a firing electrode even at low firing temperature.SOLUTION: A crystal solar battery cell and a method for manufacturing the crystal solar battery cell comprise: a semiconductor substrate; an impurity diffusion region disposed on a surface of the semiconductor substrate; a passivation film disposed on the surface of the semiconductor substrate; a protrusion which is a part of the passivation film disposed on the impurity diffusion region; and a firing electrode disposed so as to cover the impurity diffusion region and the protrusion separately.

Description

  The present invention relates to a crystalline solar battery cell.

  In recent years, in particular, from the viewpoint of protecting the global environment, solar cells that convert solar energy into electrical energy have been rapidly expected as next-generation energy sources. There are various types of solar cells, such as those using compound semiconductors and those using organic materials, but at present, crystalline solar cells using silicon crystals are the mainstream.

  Currently, the most manufactured and sold crystalline solar cells have an n-electrode formed on the surface on which sunlight is incident (light-receiving surface) and a p-electrode on the surface opposite to the light-receiving surface (back surface). This is a double-sided electrode type solar cell having a configuration in which is formed. Further, development of a back electrode type solar cell in which an electrode is not formed on the light receiving surface of the crystal solar cell and an n electrode and a p electrode are formed only on the back surface of the crystal solar cell is underway.

  For example, in Patent Document 1, an n-type layer is formed on the surface of a p-type silicon wafer, and a dielectric layer and a barrier layer are formed in this order on the back surface of the p-type silicon wafer, and provided on the dielectric layer and the barrier layer. There is described a double-sided electrode type solar cell in which a back contact that is electrically connected to a BSF layer on the back is formed through the formed opening.

  Here, the double-sided electrode type solar cell described in Patent Document 1 is manufactured as follows. First, an n-type layer is formed on the surface of a p-type silicon wafer. Next, a dielectric layer and a barrier layer are formed on the p-type silicon wafer. Next, an etching paste is applied on the surface of the barrier layer and heated to form openings in the dielectric layer and the barrier layer.

  Thereafter, an aluminum paste is applied to the openings of the dielectric layer and the barrier layer on the back surface of the p-type silicon wafer and baked. Thereby, the double-sided electrode type solar cell described in Patent Document 1 is manufactured.

  For example, in Patent Document 2, an n + -type impurity layer region and a p + -type impurity layer region are formed on the back surface of an n-type silicon substrate, and an n-type electrode is formed on the n + -type impurity layer region. , A back electrode type solar cell having a p-type electrode formed on the p + -type impurity layer region is described.

Here, the back electrode type solar cell described in Patent Document 2 is manufactured as follows. First, after forming an n + -type impurity layer region and a p + -type impurity layer region on the back surface of the n-type silicon substrate, a passivation film is formed on the entire back surface of the n-type silicon substrate. Next, an etching paste is applied to a part of the surface of the passivation film, and the passivation film is removed by heating the etching paste. As a result, the n + -type impurity layer region and the p + -type impurity layer region are exposed from the passivation film.

  Thereafter, silver paste is applied to the exposed surfaces of the n + -type impurity layer region and the p + -type impurity layer region and fired. Thus, an n-type electrode is formed on the n + -type impurity layer region, and a p-type electrode is formed on the p + -type impurity layer region, whereby the back electrode type solar cell described in Patent Document 2 is manufactured. Is done.

Special table 2010-527147 gazette JP 2009-21494 A

However, in the back electrode type solar cell described in Patent Document 2, when the silver paste is baked under the same baking temperature condition (about 800 ° C.) as that of the conventional double sided electrode type solar cell, the n-type silicon substrate The n + -type impurity in the n + -type impurity layer region on the back surface and the p-type impurity in the p + -type impurity layer region diffuse to each other and cancel each other, thereby canceling each other. There is a problem that the impurity concentration in the p + -type impurity layer region is lowered, and the characteristics of the back electrode type solar cell are lowered.

  In order to solve this problem, there are a method of lowering the firing temperature of the silver paste and a method of shortening the firing time of the silver paste. When these methods are used, the n-type silicon substrate and There is a problem that the adhesion between the n-type electrode and the p-type electrode is lowered and the fired electrode is peeled off from the n-type silicon substrate.

  The problem as described above is not a problem limited to the back electrode type solar battery cell, but also a problem of the entire crystal solar battery cell including the double-sided electrode type solar battery cell. In other words, from the viewpoint of reducing manufacturing energy in consideration of manufacturing cost and environment, and preventing damage due to deformation of a heated substrate, which has been greatly affected by thinning of the substrate, lowering the firing temperature during firing electrode formation Is required.

  In view of the above circumstances, an object of the present invention is to provide a crystalline solar battery cell capable of suppressing a decrease in adhesion of a fired electrode even at a low firing temperature.

  The crystalline solar cell of the present invention includes a semiconductor substrate, an impurity diffusion region provided on the surface of the semiconductor substrate, a passivation film provided on the semiconductor substrate, and an impurity diffusion region via a contact hole penetrating the passivation film. And a convex portion is provided in a linear shape in a region corresponding to the contact hole of the impurity diffusion region, and the convex portion is made of the same material as that of the passivation film.

  Here, in the crystalline solar battery cell of the present invention, it is preferable that the convex portion is provided in a linear shape or a circular shape.

  Moreover, it is preferable that the convex part is provided in the center both sides in the area | region corresponding to a contact hole.

  In the crystalline solar battery cell of the present invention, the thickness of the convex portion is preferably 0.03 μm or more and 0.5 μm or less.

  ADVANTAGE OF THE INVENTION According to this invention, the crystalline solar cell which can suppress the fall of the adhesiveness of a baking electrode can be provided even at low baking temperature.

(A)-(i) is typical sectional drawing illustrated about the manufacturing method of the back surface electrode type photovoltaic cell of Embodiment 1. FIG. (A)-(d) is typical sectional drawing illustrated about the formation process of the contact hole shown in FIG.1 (h), and the formation process of the baking electrode shown in FIG.1 (i). FIG. 3 is a schematic plan view of a part of the back surface of the n-type silicon substrate after the contact hole is formed in the first embodiment. FIG. 6 is a schematic plan view of a part of the back surface of an n-type silicon substrate after contact holes are formed in the second embodiment.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In addition, other steps may be included before and after each step described later. Moreover, the order of each process mentioned later may be changed, and at least 2 process of each process mentioned later may be performed simultaneously.

<Embodiment 1>
Hereinafter, with reference to schematic sectional drawing of Fig.1 (a)-FIG.1 (i), manufacture of the back electrode type photovoltaic cell of Embodiment 1 which is an example of the manufacturing method of the crystalline solar cell of this invention. A method will be described.

  First, as shown in FIG. 1A, a step of preparing an n-type silicon substrate 1 as an example of a semiconductor substrate is performed. Here, as the n-type silicon substrate 1, for example, polycrystalline silicon or single-crystal silicon having n-type conductivity can be used.

  Further, as the n-type silicon substrate 1, for example, a substrate from which slice damage caused by slicing a silicon ingot is removed can be used. Here, the removal of the slice damage can be performed, for example, by etching with a mixed acid of a hydrogen fluoride aqueous solution and nitric acid or an alkaline aqueous solution such as a sodium hydroxide aqueous solution.

  The size and shape of the n-type silicon substrate 1 are not particularly limited, but the thickness of the n-type silicon substrate 1 can be, for example, 100 μm or more and 300 μm or less, and the surface shape of the n-type silicon substrate 1 is, for example, one side The length can be a square shape of 100 mm or more and 150 mm or less.

In the present embodiment, the case where n-type silicon substrate 1 is used as an example of a semiconductor substrate will be described. However, a semiconductor substrate other than n-type silicon substrate 1 may be used, for example, a p-type silicon substrate or the like. A semiconductor substrate having a conductive type may be used.

  Next, as shown in FIG. 1B, a step of forming a texture mask 2 on the back surface of the n-type silicon substrate 1 is performed. Here, as the texture mask 2, for example, a silicon oxide film, a silicon nitride film, a stacked body of a silicon oxide film and a silicon nitride film, or the like can be used.

The texture mask 2 can be formed by a method such as a thermal oxidation method, a plasma CVD (Chemical Vapor Deposition) method, or a sputtering method. Also,
The texture mask 2 can be formed to a thickness of 300 nm to 800 nm, for example.

  Next, as shown in FIG. 1C, a step of forming the texture structure 3 on the surface of the n-type silicon substrate 1 is performed. The step of forming the texture structure 3 includes, for example, using the etching solution obtained by heating a solution obtained by adding isopropyl alcohol to an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide to 70 ° C. or higher and 80 ° C. or lower. This can be done by etching the surface.

  Next, as shown in FIG. 1D, a step of removing the texture mask 2 on the back surface of the n-type silicon substrate 1 is performed. The step of removing the texture mask 2 can be performed, for example, by immersing the texture mask 2 in a hydrogen fluoride aqueous solution or a phosphoric acid aqueous solution.

  Next, as shown in FIG. 1E, a step of forming an n-type impurity diffusion region 5 and a p-type impurity diffusion region 6 on the back surface of the n-type silicon substrate 1 is performed.

  Here, the n-type impurity diffusion region 5 is formed by, for example, vapor phase diffusion using a gas containing an n-type impurity such as phosphorus or coating diffusion in which a solution containing an n-type impurity such as phosphorus is applied and then heated. Can be formed.

  The p-type impurity diffusion region 6 is formed by, for example, a vapor phase diffusion using a gas containing a p-type impurity such as boron, or a coating diffusion in which a solution containing a p-type impurity such as boron is applied and then heated. Can be formed.

  The n-type impurity diffusion region 5 and the p-type impurity diffusion region 6 are each formed in a strip shape extending to the front side and / or the back side of the paper surface of FIG. The regions 6 are alternately arranged at predetermined intervals on the back surface of the n-type silicon substrate 1.

  N-type impurity diffusion region 5 is not particularly limited as long as it includes an n-type impurity and exhibits n-type conductivity. The p-type impurity diffusion region 6 is not particularly limited as long as it includes a p-type impurity and exhibits p-type conductivity.

  Next, as shown in FIG. 1F, a step of forming a passivation film 8 on the back surface of the n-type silicon substrate 1 is performed. Here, in the step of forming the passivation film 8, for example, a silicon oxide film, a silicon nitride film, or a stacked body of a silicon oxide film and a silicon nitride film is formed by a method such as a thermal oxidation method or a plasma CVD method. Can be done.

Next, as shown in FIG. 1G, a step of forming an antireflection film 7 on the texture structure 3 of the n-type silicon substrate 1 is performed. Here, the step of forming the antireflection film 7 can be performed by forming a silicon nitride film or the like, for example, by plasma CVD.

  Next, as shown in FIG. 1H, a step of forming contact holes 9 and contact holes 10 in the passivation film 8 formed on the back surface of the n-type silicon substrate 1 is performed. Here, the contact hole 9 is formed linearly so that the n-type impurity diffusion region 5 is exposed linearly, and the contact hole 10 is formed linearly so that the p-type impurity diffusion region 6 is exposed linearly. The

  Next, as shown in FIG. 1 (i), a step of forming the n-type fired electrode 11 on the n-type impurity diffusion region 5 and forming the p-type fired electrode 12 on the p-type impurity diffusion region 6 is performed. Do. Here, the n-type fired electrode 11 is formed so as to be in contact with the n-type impurity diffusion region 5 through the contact hole 9, and the p-type fired electrode 12 is in contact with the p-type impurity diffusion region 6 through the contact hole 10. Formed.

  Thus, the back electrode type solar battery cell of Embodiment 1 is completed.

  In the manufacturing method of the back electrode type solar cell of the first embodiment, the contact hole forming step shown in FIG. 1 (h) and the fired electrode forming step shown in FIG. 1 (i) are shown in FIGS. It is characterized in that it is performed as shown in the schematic sectional view of 2 (d).

  That is, first, as shown in FIG. 2A, a step of applying an etching paste 21 to a location on the surface of the passivation film 8 corresponding to the upper portion of the n-type impurity diffusion region 5 is performed. For the step of applying the etching paste 21, for example, a method such as application by a dispenser, application by inkjet printing, application by screen printing, application by roll coater printing, or application by offset printing can be used.

  Here, as the etching paste 21, for example, an etching component capable of etching the passivation film 8 and a component containing water, an organic solvent, a thickener, and the like as components other than the etching component can be used.

  As the etching component, for example, at least one selected from phosphoric acid, hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride can be used.

  Examples of the organic solvent include alcohols such as isopropyl alcohol and diethylene glycol; ethers such as ethylene glycol monobutyl ether and diethylene glycol monobutyl ether; esters such as 2,2-butoxyethyl acetate and propylene carbonate; or N-methyl-2-pyrrolidone What contains at least 1 sort (s), such as ketones, etc. can be used.

  Further, as the thickener, for example, a cellulose derivative such as ethyl cellulose or sodium carboxymethyl hydroxyethyl cellulose; a polyamide resin such as nylon 6; or a polymer containing at least one polymer such as polyvinyl pyrrolidone polymerized with vinyl groups is used. Can do.

  Next, as shown in FIG. 2B, a step of forming a recess 21a in the etching paste 21 is performed. The step of forming the recess 21a is not particularly limited, but can be performed, for example, by heating the etching paste 21.

Here, it is preferable that the etching paste 21 is heated to a temperature lower than the temperature at which the etching paste 21 starts etching the passivation film 8. By heating the etching paste 21 in this way, the etching paste 21 can be agglomerated toward the center of the application region of the etching paste 21, so that the recess 21 a where the thickness of the etching paste 21 is locally thinned is formed. It can form suitably.

  Such a recess 21a can be formed, for example, by heating the etching paste 21 to a temperature of 250 ° C. or higher and 400 ° C. or lower.

  The thickness t of the recess 21a of the etching paste 21 is preferably 0.5 μm or more and 1.5 μm or less. In this case, in the process described later, a tendency that a convex part having a suitable height can be formed on the n-type impurity diffusion region 5 is increased.

  Next, as shown in FIG. 2C, a step of etching the passivation film 8 is performed. Thereby, a contact hole 9 exposing a part of the surface of the n-type impurity diffusion region 5 is formed.

  Here, the step of etching the passivation film 8 is performed using the etching paste 21 in which the recesses 21 a are formed so that the protrusions 8 a that are part of the passivation film 8 remain on the n-type impurity diffusion region 5. .

  Such etching of the passivation film 8 can be performed, for example, by heating the etching paste 21 in which the recess 21 a is formed to a temperature equal to or higher than the temperature at which the etching paste 21 starts etching the passivation film 8. As a result, the passivation film 8 can be completely etched in a portion having a predetermined thickness other than the convex portion 8a of the etching paste 21, so that the surface of the n-type impurity diffusion region 5 is exposed. On the other hand, since the thickness of the recess 21 a of the etching paste 21 is smaller than that of other portions of the etching paste 21, the etching of the passivation film 8 is incomplete, and the passivation is formed on the surface of the n-type impurity diffusion region 5. The convex part 8a which is a part of the film 8 remains.

  Here, the thickness T of the convex portion 8a which is a part of the passivation film 8 is preferably 0.03 μm or more and 0.5 μm or less. When the thickness T of the convex portion 8a is 0.03 μm or more, the contact area of the n-type fired electrode 11 tends to be increased, and the thickness T of the convex portion 8a is 0.5 μm or less. In such a case, there is a tendency that damage to the convex portion 8a due to the convex portion 8a becoming too high can be more effectively suppressed.

  FIG. 3 shows a schematic plan view of a part of the back surface of n-type silicon substrate 1 after formation of contact hole 9 in the first embodiment. Here, from the contact hole 9, the surface of the n-type impurity diffusion region 5 is exposed, a convex portion 8 a extending linearly on the surface of the n-type impurity diffusion region 5, and the convex portion 8 a A broken line-like convex portion 8a that extends in parallel with a gap and is partially missing is also exposed.

  Note that the convex portion 8 a is not limited to the shape shown in FIG. 3, and may be formed on a part of the surface of the n-type impurity diffusion region 5.

  Next, a step of applying a conductive paste on n-type impurity diffusion region 5 and protrusion 8a exposed by etching is performed. Here, the step of applying the conductive paste can be performed by applying a conductive paste such as a commercially available silver paste by screen printing or the like.

Next, as shown in FIG. 2D, a step of forming the n-type fired electrode 11 by firing the conductive paste is performed. Here, the n-type fired electrode 1 by firing the conductive paste
1 is formed by firing the conductive paste at a firing temperature lower than the firing temperature of a conventional double-sided electrode type solar battery cell (for example, about 400 ° C.).

  Thus, in the manufacturing method of the back electrode type solar cell of Embodiment 1, the passivation film 8 is etched by using the etching paste 21 having the concave portion 21a which is a locally thin portion, thereby allowing passivation. The convex portion 8 a that is a part of the film 8 is left on the surface of the n-type impurity diffusion region 5. Then, a conductive paste is applied on the surface of the convex portion 8a and the n-type impurity diffusion region 5, and then fired to form the n-type fired electrode 11. Therefore, for the n-type fired electrode 11, the contact area between the n-type impurity diffusion region 5 and the passivation film 8 can be increased by the amount of the surface of the convex portion 8a. Thereby, even when the firing temperature of the conductive paste at the time of forming the n-type fired electrode 11 is low, the adhesion of the n-type fired electrode 11 can be improved. Separation from the silicon substrate 1 can be effectively prevented.

  2A to 2D, the contact hole 9 and the n-type fired electrode 11 are formed. However, the contact hole 10 and the p-type fired electrode 12 are formed in the same manner. Needless to say, this can be done.

  Moreover, in the above, although the case where a back electrode type photovoltaic cell was manufactured was demonstrated, this invention is applied also to other crystal solar cells, such as a double-sided electrode type solar cell other than a back electrode type solar cell. Needless to say, you can.

<Embodiment 2>
Hereinafter, the manufacturing method of the back surface electrode type photovoltaic cell of Embodiment 2 which is another example of the manufacturing method of the crystalline solar cell of this invention is demonstrated. The manufacturing method of the back electrode type solar cell of the second embodiment is characterized in that the shapes of the contact hole 9 and the convex portion 8a are different from those of the first embodiment.

  FIG. 4 shows a schematic plan view of a part of the back surface of n-type silicon substrate 1 after formation of contact hole 9 in the second embodiment. Here, the contact hole 9 is formed in a circular shape, and the convex portion 8a disposed inside the contact hole 9 is also formed in a circular shape.

  Thus, even when the contact hole 9 and the convex portion 8a are formed, the contact area between the n-type impurity diffusion region 5 and the passivation film 8 is about the surface of the convex portion 8a. Can be increased.

  Therefore, also in Embodiment 2, even when the firing temperature of the conductive paste when forming the n-type fired electrode 11 is low, the adhesion of the n-type fired electrode 11 can be improved. Peeling of the fired electrode 11 from the n-type silicon substrate 1 can be effectively prevented.

  The circular contact hole 9 and the convex portion 8a are formed by applying an etching paste 21 on the passivation film 8 and forming a part of the etching paste 21 into a concave portion 21a having a circular shape and a reduced thickness. Can do.

  Since the description other than the above in the present embodiment is the same as that in the first embodiment, the description thereof is omitted.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICABILITY The present invention can be used for a crystal solar cell and a method for manufacturing the crystal solar cell, and in particular, a crystal solar cell and a crystal solar in which a fired electrode is formed by removing a part of a passivation film with an etching paste It can utilize suitably for the manufacturing method of a battery cell.

1 n-type silicon substrate, 2 texture mask, 3 texture structure, 5 n-type impurity diffusion region, 6 p-type impurity diffusion region, 7 antireflection film, 8 passivation film, 8a convex portion, 9,10 contact hole, 11 n-type Firing electrode, 12 p-type firing electrode, 21 etching paste, 21a recess.

Claims (4)

A semiconductor substrate;
An impurity diffusion region provided on a surface of the semiconductor substrate;
A passivation film provided on the semiconductor substrate;
A fired electrode connected to the impurity diffusion region through a contact hole penetrating the passivation film,
A crystalline solar cell in which a convex portion is provided in a line shape in a region corresponding to the contact hole in the impurity diffusion region, and the convex portion is made of the same material as the passivation film . The crystal solar battery cell according to claim 1, wherein the convex portion is provided in a linear shape or a circular shape.   The crystal solar cell according to claim 1, wherein the convex portion is provided on both sides of the center in a region corresponding to the contact hole. The thickness of the said convex part is a crystalline solar cell in any one of Claim 1 to 3 which are 0.03 micrometer or more and 0.5 micrometer or less.