JP2004247595A - Solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form high-concentration diffusion layers of a solar cell under its front-surface electrodes without any additional heat treatment process. <P>SOLUTION: On the side of one principal surface of an one conductive semiconductor substrate 1, the solar cell has many fine protrusions 2, the other conductive impurity diffusion layer 4, and front-surface electrodes 6. Also, on the side of the other principal surface, the solar cell has rear-surface electrodes 7, 8. Fine protrusions 3 present under the front-surface electrodes 6 of the side of the one principal surface have larger aspect ratios, higher heights, and shorter distances between the summits of the adjacent protrusions 3 to each other than the fine protrusions 2 present in the region wherefrom the regions present under the electrodes 6 are excluded. Thereby, high-concentration diffusion layers are formed under the front-surface electrodes 6. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solar cell element, and more particularly to a solar cell element having a large number of fine protrusions on one principal surface side.
[0002]
[Prior art]
FIG. 3 shows a conventional solar cell element. In FIG. 3, 1 is a semiconductor substrate, 2 is a fine projection, 4 is a diffusion layer, 5 is an antireflection film, 6 is a front electrode, 7 is a back electrode (silver electrode), and 8 is a back electrode (aluminum electrode). .
[0003]
For example, a large number of fine protrusions 2 for preventing reflection are formed on one main surface side of a P-type semiconductor substrate 1, and an N-type impurity is diffused to a certain depth over the entire surface near the surface to form an N-type diffusion layer 4. And an anti-reflection film 5 made of a silicon nitride film or the like is provided on one main surface of the semiconductor substrate 1, a surface electrode 6 is provided on one main surface, and an aluminum electrode 8 and a silver electrode 7 are provided on the other main surface. Are provided. A high-concentration P-type diffusion layer (not shown) is formed on the other main surface of the semiconductor substrate 1.
[0004]
In order to form these solar cell elements, a large number of fine projections 2 are formed on one main surface side by using a reactive ion etching method, and an antireflection film 5 is formed. In general, a surface electrode material is applied and baked to melt the antireflection film 5 under the electrode material and directly contact the semiconductor substrate 1 (for example, see Patent Document 1).
[0005]
In a solar cell as shown in FIG. 3, a diffusion layer 2 is formed by uniformly diffusing an impurity of the opposite conductivity type on one main surface side of a semiconductor substrate 1 of one conductivity type. Electron-hole pairs generated inside the semiconductor substrate 1 by the irradiation of sunlight are separated into N-type and P-type regions by a junction electric field at the interface between the P-type semiconductor substrate 1 and the N-type diffusion layer 4. Electric power can be obtained by extracting this from the electrodes on both sides. However, electrons and holes generated inside the semiconductor substrate 1 by light irradiation are partially recombined on the surface of the impurity diffusion layer 2. Therefore, it is important to reduce this surface recombination in order to improve the conversion efficiency of the solar cell. In order to reduce surface recombination, it is preferable that the impurity concentration on the surface is low.
[0006]
However, when the impurity concentration is low at the contact portion between the surface electrode 6 and the diffusion layer 4, the contact resistance increases and the conversion efficiency of the solar cell decreases. In order to prevent an increase in leakage current due to penetration of the electrode, the diffusion layer 4 below the electrode 6 is preferably deep, that is, has a high concentration. As a method of satisfying these contradictory conditions, a selective impurity diffusion method has been devised in which a high concentration diffusion layer is formed in a portion corresponding to the lower part of the electrode on one main surface side, and the other light receiving region is made low concentration ( For example, see Non-Patent Document 1).
[0007]
FIG. 4 is a diagram showing such a solar cell element. In FIG. 4, 1 is a semiconductor substrate, 4 is a diffusion layer, 5 is an antireflection film, 6 is a surface electrode, 7 is a silver electrode, 8 is an aluminum electrode, and 9 is a high concentration diffusion layer.
[0008]
For example, an N-type diffusion layer 4 is provided on the entire surface near the surface of the P-type semiconductor substrate 1 by diffusing N-type impurities, and an antireflection film 5 made of a silicon nitride film or the like is provided on one main surface side of the semiconductor substrate 1. A surface electrode 6 is provided on one main surface side, and a high concentration diffusion layer 9 is formed on the semiconductor substrate 1 below the surface electrode 6. Further, on the other main surface side, there are provided back electrodes 7 and 8 composed of an aluminum electrode 8 and a silver electrode 7. A high-concentration P-type diffusion layer (not shown) is formed on the other main surface of the semiconductor substrate 1.
[0009]
Conventionally, a method of performing diffusion twice has been used to realize this method. That is, first, after the high concentration diffusion layer 9 is formed, the electrode pattern is masked, and the high concentration diffusion layer other than the mask portion is removed by etching. Thereafter, a diffusion layer 4 is formed in the etched portion.
[0010]
[Patent Document 1]
JP-A-11-307792 [Non-Patent Document 1]
Jianhua Zhao, etc. "22.3% EFFICIENT SILICON SOLAR CELL MODULE" 25th Photovoltaic Specialists Conf. (1996) P.A. 1203-1206
[0011]
[Problems to be solved by the invention]
However, according to this method, since the high-temperature heat treatment step of diffusion is performed twice, there is a problem that the substrate is easily broken by thermal shock.
[0012]
Further, after forming the high concentration diffusion layer 9 in a solar cell element having irregularities on one principal surface side as shown in FIG. 2, the electrode pattern is masked, and the high concentration diffusion layer other than the mask portion is etched. If the method of removing by removing is performed, the shape of the fine unevenness 2 formed on the one main surface side of the semiconductor substrate 1 previously formed is broken, and a problem that a sufficient anti-reflection effect cannot be obtained occurs.
[0013]
The present invention has been made in view of such a problem of the related art. In a solar cell element having a large number of fine protrusions on one main surface side of a semiconductor substrate, the surface electrode 6 can be formed without adding a heat treatment step. An object is to provide a solar cell element having a high concentration diffusion layer formed below.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the solar cell element according to claim 1 has a large number of fine protrusions, a diffusion layer of another conductivity type impurity and a surface electrode on one main surface side of the one conductivity type semiconductor substrate, and In the solar cell element having the back surface electrode on the main surface side, the fine projections under the surface electrode on the one main surface side have a larger aspect ratio than the fine protrusions in other regions.
[0015]
Further, in the solar cell element according to the present invention, it is preferable that the fine projections under the surface electrode on the one main surface side have a higher height than the fine projections in other areas.
[0016]
Further, in the solar cell element according to the present invention, the distance between the vertices of adjacent fine projections under the surface electrode on the one main surface side is greater than the distance between the vertices of adjacent fine projections in other regions. It may be short.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a solar cell element according to the present invention. In FIG. 1, 1 is a semiconductor substrate, 2 is fine protrusions, 3 is fine protrusions below the electrodes, 4 is a diffusion layer, 5 is an antireflection film, 6 is a front electrode, 7 is a back electrode (silver electrode), 8 is The back electrode (aluminum electrode) is shown.
[0018]
The solar cell element according to the present invention is substantially the same as the conventional solar cell element. That is, for example, a large number of fine protrusions 2 for preventing reflection are formed on one main surface side of a P-type semiconductor substrate 1, and an N-type impurity is diffused to a certain depth over the entire surface near the surface to provide N-type diffusion. A layer 4 is provided, an antireflection film 5 made of a silicon nitride film or the like is provided on one main surface of the semiconductor substrate 1, a surface electrode 6 is provided on one main surface, and an aluminum electrode 8 and silver are provided on the other main surface. Back electrodes 7, 8 composed of the electrodes 7 are provided. A high-concentration P-type diffusion layer (not shown) is formed on the other main surface of the semiconductor substrate 1.
[0019]
In the present invention, the fine projections 3 below the surface electrode 6 are formed so that the aspect ratio (height of the projections / width of the projections) is larger than that of the fine projections 2 in other regions. By doing so, the fine protrusions 3 under the surface electrode 6 having a large aspect ratio are diffused at a higher concentration than the fine protrusions 2 having a small aspect ratio other than under the surface electrode 6. The high-concentration diffusion layer 9 can be formed under the surface electrode 6 by performing thermal diffusion twice.
[0020]
This will be described in more detail with reference to the drawings. 2A and 2B are schematic diagrams for explaining a diffusion state to protrusions having different aspect ratios. FIG. 2A is a diagram illustrating a protrusion having a large aspect ratio, and FIG. 2B is a diagram illustrating a protrusion having a small aspect ratio. In the figure, 2 indicates fine projections, and 4 indicates a diffusion layer. For example, when phosphorus is diffused as an impurity into the silicon substrate 1, the concentration and depth of the diffusion layer 4 are determined by the diffusion coefficient of phosphorus with respect to silicon, the maximum solubility of phosphorus in silicon, the diffusion temperature, the diffusion time, and the like. From this, if the diffusion is performed simultaneously, the protrusions having a large aspect ratio as shown in FIG. 3A will be diffused from the left and right, and eventually all of the protrusions will become a phosphorus diffusion layer. . On the other hand, in the projections having a small aspect ratio as shown in (b), the diffusion layer 4 is formed uniformly on the surface.
[0021]
In the present invention, the fine projections 3 under the surface electrode 6 are preferably higher in height than the fine projections 2 in the other areas. By doing so, the high concentration diffusion layer 9 can be formed under the surface electrode 6 more effectively by a single thermal diffusion. In addition, even if an electrode material containing silver powder as a main component is applied to form the surface electrode 6, the electrode material does not enter gaps smaller than the particle diameter of the silver powder. The diffusion layer 4 is further deeper by the height of the fine projections 2 because it contacts only the portion having the particularly high concentration diffusion layer at the top of 3.
[0022]
Further, in the present invention, the distance between the vertices of the adjacent fine projections 3 below the surface electrode 6 may be shorter than the distance between the vertices of the adjacent fine projections 2 in other regions. By doing so, the high concentration diffusion layer 9 can be formed under the surface electrode 6 more effectively by a single thermal diffusion. Further, the depth of the electrode material entering between the fine projections 3 becomes shallower, and the surface electrode 6 contacts only a portion having a particularly high concentration diffusion layer at the top of the fine projections 3, and the diffusion layer 4 becomes finer. The projection 2 is deeper by the height of the projection 2.
[0023]
An example of a method for manufacturing a solar cell element according to the present invention will be described. First, a large number of fine protrusions 2 are formed on the entire main surface of a P-type silicon substrate 1 having a P-type as a semiconductor substrate 1 by using a reactive ion etching method or the like. The fine projections 2 confine incident light, reduce the reflectance, and increase the short-circuit current of the solar cell element. The width of the fine projections 2 is desirably 2 μm or less. When the thickness is 2 μm or more, the etching processing time is prolonged, but the reflectance on the one main surface side of the silicon substrate 1 is not reduced so much.
[0024]
Next, a plasma-resistant resist is printed on a portion of the light-receiving area other than the electrode forming area, and fine projections 3 below the surface electrode 6 are formed in the electrode forming area again by a reactive ion etching method or the like. At this time, the width of the fine projections 3 to be formed is desirably 1 μm or less. The reason is that the depth of the diffusion layer 4 formed by the impurity diffusion to be performed later is about 0.5 μm or less. Therefore, when the width of the projection is 1 μm or more, the concentration of the impurity does not occur, and the projection diffused at a high concentration. Is difficult to form.
[0025]
Further, the aspect ratio of the projection is desirably 0.5 or more. If the aspect ratio is less than 0.5, the root portion of the fine projection 3 under the surface electrode 6 becomes thick, and a portion that is not diffused at a high concentration is formed. If the surface electrode 6 is formed in this portion, the junction is likely to break through, the leak current increases, and the output characteristics of the solar cell element deteriorate.
[0026]
The formation of the fine projections 2 and 3 is preferably performed by a reactive ion etching method. In the reactive ion etching method, the shape of the projections can be arbitrarily changed by adjusting the gas component ratio and the etching time, and the shapes of the fine projections 2 and 3 of the solar cell element according to the present invention are compared. It can be easily formed. The fine projections 3 can be formed by flowing chlorine at a flow rate 3 to 5 times that of forming the fine projections 2.
[0027]
Thereafter, diffusion treatment is performed by performing a heat treatment in a gas containing an impurity element such as POCl _3, or by applying a chemical solution containing the impurity element to the substrate surface and then performing a heat treatment. Thus, in one diffusion, a diffusion layer 4 is formed under the fine protrusions 2 in a region other than below the surface electrode 6, and locally under the fine protrusions 3 under the surface electrode 6, a high concentration diffusion is performed. Layer 9 is formed.
[0028]
Next, an antireflection film 6 is formed on one main surface side of the semiconductor substrate 1 by a CVD device or the like, and the diffusion layer 4 is separated.
[0029]
Thereafter, an electrode material made of silver or the like is applied on the fine projections 3 below the surface electrode 6, and an electrode material mainly containing aluminum and an electrode material mainly containing silver are applied to the other main surface side. Is applied and baked to form the front surface electrode 6 and the back surface electrodes 7 and 8, thereby obtaining the solar cell element shown in FIG.
[0030]
The present invention is not limited to the above embodiment, and many modifications and changes can be made within the scope of the present invention. For example, the method for manufacturing a solar cell element according to the present invention is not limited to this, and the order and method of forming fine projections are one example.
[0031]
【The invention's effect】
As described in detail above, the solar cell element according to the present invention has a large number of fine protrusions and a diffusion layer of another conductive type impurity and a surface electrode on one main surface side of the one conductive type semiconductor substrate, In the solar cell element having the back electrode on the other main surface side, the fine projections under the surface electrode on the one main surface have an aspect ratio larger than those of the other regions. By doing so, the fine protrusions under the surface electrode having a large aspect ratio are diffused at a higher concentration than the fine protrusions having a small aspect ratio in the other regions, and a single thermal diffusion A high concentration diffusion layer can be formed under the surface electrode. That is, a solar cell having a high-concentration diffusion layer below the surface electrode for reducing the surface impurity concentration at the same time as reducing the surface recombination and at the same time reducing the contact resistance and suppressing the increase in the leak current due to the electrode penetration. The battery element can be obtained by one heat diffusion.
[0032]
Further, the height of the fine projections under the surface electrode is set higher than the height of the fine projections in the other regions. By doing so, a high concentration diffusion layer can be formed under the surface electrode more effectively by one heat diffusion, and an electrode material mainly composed of silver powder is applied to form the surface electrode. However, since the electrode material does not enter gaps smaller than the particle size of the silver powder, the surface electrode contacts only the portion having the particularly high-concentration diffusion layer at the top of the fine projection, and the diffusion layer It becomes deeper by the height of the projection.
[0033]
Further, the distance between the vertices of the adjacent fine projections under the surface electrode may be shorter than the distance between the vertices of the adjacent fine projections in the other region. By doing so, a high concentration diffusion layer can be formed under the surface electrode more effectively by one heat diffusion. In addition, the depth of the electrode material entering between the fine protrusions becomes shallower, and the surface electrode contacts only the top of the fine protrusions, particularly the portion having the high-concentration diffusion layer. It will be deep.
[Brief description of the drawings]
FIG. 1 is a view showing one embodiment of a solar cell element according to the present invention.
FIGS. 2A and 2B are schematic diagrams for explaining a diffusion state of a solar cell element according to the present invention into projections having different aspect ratios, wherein FIG. 2A is a projection having a large aspect ratio and FIG. 2B is a projection having a small aspect ratio. FIG. 3 is a view showing one example of a conventional solar cell element.
FIG. 4 is a view showing another embodiment of a conventional solar cell element.
DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Fine protrusion, 3 ... Fine protrusion under surface electrode, 4 ... Diffusion layer, 5 ... Antireflection film, 6 ... Surface electrode, 7 ... back electrode (silver electrode), 8 ... back electrode (aluminum electrode), 9 ... high concentration diffusion layer

Claims (3)

A solar cell element having a large number of fine protrusions, a diffusion layer of another conductivity type impurity and a surface electrode on one main surface side of one conductivity type semiconductor substrate, and having a back surface electrode on the other main surface side. A solar cell element wherein fine projections below a surface electrode on the surface side have a larger aspect ratio than fine projections in other regions. A solar cell element having a large number of fine protrusions, a diffusion layer of another conductivity type impurity and a surface electrode on one main surface side of one conductivity type semiconductor substrate, and having a back surface electrode on the other main surface side. 2. The solar cell element according to claim 1, wherein the fine projections below the surface-side surface electrode are higher than the fine projections in other areas. A solar cell element having a large number of fine protrusions, a diffusion layer of another conductivity type impurity and a surface electrode on one main surface side of one conductivity type semiconductor substrate, and having a back surface electrode on the other main surface side. 2. The solar cell element according to claim 1, wherein the distance between the vertices of the fine projections adjacent to each other under the surface-side surface electrode is shorter than the distance between the vertices of the fine projections adjacent to each other in the other region. .

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