JP3173392B2 - Solar cell element and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved solar cell device and a method for manufacturing the improved solar cell device.

[0002]

2. Description of the Related Art In order to improve the performance of a solar cell, it is necessary to improve the carrier transfer characteristics of a silicon wafer serving as a substrate. However, ordinary silicon substrates have
Crystal lattice defects, mixed oxygen atoms, contamination impurities, etc.
These become recombination centers for capturing the carriers moving in the silicon substrate, and lower the carrier movement characteristics.
Therefore, in order to improve the carrier transfer characteristics, it is necessary to reduce the recombination centers, ie, defects, which capture and annihilate the carriers, and allow the carriers generated by sunlight to reach the electrodes without loss.

In order to reduce defects in a silicon substrate, efforts have been made to improve the quality of a silicon substrate used in a solar cell device. For this reason, for example, a method of forming a silicon substrate by a floating zone (FZ) method has been used. However, even by such a method, the quality of the silicon substrate cannot be sufficiently improved.
There has been a limit in improving the performance of solar cell elements.

On the other hand, in the field of semiconductor devices (IC, LSI), defects are moved to a part of the substrate by heat treatment or the like.
There is known a technique called gettering, which forms a layer in a substrate with a very reduced number of defects for concentrating and forming each element. This gettering is disclosed in "Ultra High Speed MOS Device", written by Susumu Kayama, published on February 10, 1986. Therefore, it is conceivable to apply this gettering also to a silicon substrate used for a solar cell element.

[0005]

However, the above-mentioned gettering does not reduce the defects in the semiconductor substrate, but collects and concentrates the defects in one part of the substrate to reduce the defects in other parts. Things. For example,
As shown in FIG. 9, in the case of an IC, an LSI, or the like, the element formation region 100 is formed only near the surface of the silicon substrate 10. There is no element formation region 100 in the back surface region opposite to 100. Therefore, the defect concentration regions 12 where the defects in the silicon substrate 10 are collected in these portions.
And the gettering described above can be used.

On the other hand, FIGS. 10 and 11 are cross-sectional views of a solar cell element. In FIG. 10, a diffusion layer 14 and an electrode 16 are formed on the front and back surfaces of a silicon substrate 10. In FIG. 11, a diffusion layer 14 and an electrode 16 are formed on the back surface of the silicon substrate 10. In both cases shown in FIGS. 10 and 11, the carriers generated by sunlight move on the entire surface of the silicon substrate 10 in the thickness direction. For this reason, as shown in FIGS. 10 and 11, if there is a defect concentration region 12 in the central layer region of the silicon substrate 10, carriers are captured and disappear here. Therefore, in the solar cell element, there is a problem that the formation of the defect concentration region 12 by the gettering in the central layer region or the back surface region of the silicon substrate 10 rather than the usual semiconductor device causes a deterioration in characteristics.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a solar cell element having improved carrier movement characteristics by gettering and a method for manufacturing the same.

[0008]

According to a first aspect of the present invention, there is provided a back electrode type crystalline silicon solar cell device having an electrode formed on the back surface of a light receiving portion, wherein the periphery of the light receiving portion is provided. Is characterized in that a reinforcing portion is formed, and a region where defects existing in the silicon substrate are concentrated exists only in the reinforcing portion.

According to a second aspect of the present invention, there is provided a back electrode type crystalline silicon solar cell element in which an electrode is formed on a back surface of a light receiving portion, wherein a reinforcing portion is formed around the light receiving portion, and the silicon substrate is provided with a reinforcing portion. The region where the existing defects are concentrated is present in the reinforcing portion and the back surface region of the reinforcing portion.

A third invention is a method of manufacturing a solar cell device according to the first invention, wherein the step of concentrating defects in the silicon substrate in the surface layer region or the central layer region of the substrate by gettering; Etching the silicon substrate deeper than the defect concentration region while leaving the reinforcing portion around the silicon substrate.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial sectional view of one embodiment of a solar cell element according to the present invention. In FIG. 1, a reinforcing portion 18 for maintaining mechanical strength is formed around a silicon substrate 10. In a portion surrounded by the reinforcing portion 18, the silicon substrate 10 is thinned by etching to form a power generation region 20. An antireflection film 22 is formed on the surface of the power generation region 20, and the light receiving portion 24 is formed.
Is composed. On the back side of the power generation region 20, the diffusion layer 1
4 and the electrode 16 are formed, and the carrier generated by the incident light 26 incident on the light receiving portion 24 can be taken out from the back surface of the power generation region 20. The power generation area 20
Are formed thinly because the generated carrier is the electrode 1
This is for shortening the distance to 6 and improving the power generation characteristics.

As shown in FIG. 1, the electrodes 16 are arranged on the back side of the power generation area 20 in a shape as shown in FIG. The electrode 16 has a configuration in which positive electrodes and negative electrodes are alternately arranged.

A defect concentration region 12 exists in a central layer region substantially at the center of the reinforcing portion 18 in the thickness direction.
This defect concentration region 12 is used to move and concentrate the defects in the silicon substrate 10 to the central layer region by gettering before forming the power generation region 20 by etching the silicon substrate 10, and then perform an etching process. , Reinforcement part 1
No. 8 remained only in the central layer region. By such a process, the defect concentration in the power generation region 20 is significantly reduced. For this reason, in the solar cell element shown in FIG. 1, the carrier movement characteristics are improved, and the performance of the solar cell element can be improved. The defect in this case is a recombination center such as a heavy metal element, an alkali metal element, a crystal lattice defect, or dissolved oxygen mixed in the silicon substrate 10.

As described above, by concentrating defects in the central layer region of the silicon substrate 10 and removing them, the defect concentration in the power generation region 20 can be greatly reduced, and the carrier mobility characteristics can be improved. As a result, the power generation characteristics of the solar cell can be improved. Since the reinforcing portion 18 hardly contributes to photovoltaic power generation, the defect concentration region 12 left in the reinforcing portion 18 hardly affects the characteristics of the solar cell element.

FIGS. 2 and 3 show a method of manufacturing the solar cell element shown in FIG. In FIG. 2, an intrinsic gettering process is performed using a single-crystal silicon substrate 10 having a predetermined thickness, for example, about 600 μm. This silicon substrate 10 is formed by the CZ (Czochralski) method, contains about 5 to 50 ppm (atomic number) of oxygen, and contains many lattice defects.

After cleaning the silicon substrate 10, the silicon substrate 10 is placed in a heat treatment furnace having excellent cleanliness, and is subjected to 1000-1
An intrinsic gettering process is performed by performing a heat treatment at 200 ° C. for 2 to 50 hours. With this process,
The defect concentration in the vicinity of the front and back surfaces of the silicon substrate 10 can be reduced, and as shown in FIG.
The defect concentration region 12 is formed in the central portion in the thickness direction of the substrate, that is, in the central layer region. The defect concentration region 12 is formed by performing a heat treatment from above and below the silicon substrate 10 so that oxygen and lattice defects contained in the silicon substrate 10 move to the central layer region.

Next, as shown in FIG.
In order to improve the power generation characteristics of the power generation region 0, the power generation region 20 is made thinner. First, an insulating film 28 is formed on the entire back surface of the silicon substrate 10 and a portion to be left as the reinforcing portion 18 on the front surface, and only the portion where the insulating film 28 is not formed is formed by TM.
AH (tetramethylammonium hydroxide)
The etching is performed by heating an aqueous solution or the like. This TMAH does not contain an alkali metal element or the like that becomes a defect of the silicon substrate 10 and lowers the electrical characteristics.

By this etching, the power generation region 20 is thinned, for example, to a thickness of about 100 μm. In this case, the silicon substrate 10 is etched deeper than the defect concentration region 12 where the defects are concentrated by the gettering process. For this reason, all the defect concentration regions 12 existing above the portion to be the power generation region 20 are removed, and the power generation region 20 does not have the defect concentration region 12, so that the defect concentration can be greatly reduced. . Further, the reinforcing portion 18 left without being etched around the power generation region 20 has a thickness of 600 μm, which is the original thickness of the silicon substrate 10.
The thickness of the silicon substrate 10 is kept small, and the mechanical strength of the thinned silicon substrate 10 with the power generation region 20 formed is maintained.

Next, the insulating film formed on the entire back surface of the silicon substrate 10 and on the reinforcing portion 18 is removed, and a diffusion layer 14 and an electrode 16 are formed on the back surface.
Then, an anti-reflection film 22 is formed to complete the solar cell element having the structure shown in FIG.

By the steps described above, the silicon substrate 10
The defects originally present therein are concentrated in the defect concentration region 12 by the gettering process, and the defect concentration in other portions is significantly reduced. Further, the defect concentration region 12 exists only in the reinforcing portion 18. As a result, the power generation area 20
Carrier characteristics of the solar cell element can be improved, and the output voltage and current density of the solar cell element can be improved. In the present embodiment, the output power in standard sunlight can be improved by about 5 to 12%. Furthermore, in the present embodiment, the output power when sunlight is condensed and made incident on the light receiving surface 24 is particularly greatly improved.
Approximately 17% could be improved.

Although the defect concentration region 12 is formed in the central layer region of the silicon substrate 10 in the above embodiment, it may be formed on the surface of the silicon substrate 10.

FIG. 4 is a partial sectional view of another embodiment of the solar cell element according to the present invention. In FIG. 4, the defect concentration region 12 is formed not only in the central layer region of the reinforcing portion 18 but also in the back surface region of the reinforcing portion 18.

With this configuration, the number of defect concentration regions 12 increases, and the defect concentration remaining in the power generation region 20 can be reduced by that amount, and the power generation characteristics of the power generation region 20 are further improved. In particular, there is a great effect in reducing defects in the vicinity of the surface on the back surface side of the power generation region 20, that is, in the region where the diffusion layer 14 is formed.

FIG. 5 shows a method of manufacturing the solar cell element shown in FIG. In FIG. 5, a single crystal silicon substrate 10 having a thickness of about 600 μm formed by the CZ method was used, and two layers of defect concentration regions 12 were formed on the front and back surfaces of the silicon substrate 10. For this, first, the silicon substrate 1
After cleaning 0, an oxide film of 200 to 700 nm, that is, an insulating film 28 is formed on both front and back surfaces of the silicon substrate 10 by a thermal oxidation method. Next, the insulating film 28 other than the back surface of the portion to be the power generation region 20 is removed by photolithography. Subsequently, a thin film containing a high-concentration phosphorus (P) element is formed in a portion other than the portion where the insulating film 28 remains by a thermal diffusion method.
At 00 ° C., phosphorus is diffused into the silicon substrate 10 at a high concentration. Next, after the thin film containing a high concentration of phosphorus element is removed by etching, the silicon substrate 10 is placed in a heat treatment furnace having excellent cleanliness, and is subjected to 1000 to 120 in a nitrogen atmosphere.
Heat treatment is performed at 0 ° C. for 2 to 50 hours. Thereby, the defects can be concentrated on the phosphorus diffusion portion of the silicon substrate 10, and the defect concentration of the silicon substrate 10 can be reduced.

Next, in order to form the power generation region 20, etching is performed in the same manner as in FIG. As the etching solution, the above-mentioned TMAH aqueous solution or the like can be used. Since this etching is performed deeper than the defect concentration region 12 formed on the surface side of the silicon substrate 10 as shown in FIG. 5, the defect concentration region 12 does not remain in the etched portion as a result. become. As a result, the defect concentration region 12 does not exist in the power generation region 20.

Next, the diffusion layer 14 and the electrode 16 are formed on the back surface of the power generation region 20, and the antireflection film 22 is formed on the front surface side, thereby completing the solar cell device having the structure shown in FIG.

By the above-described gettering process, the defect concentration in the power generation region 20 is greatly reduced, so that the carrier transfer characteristics of this portion are improved, and the output voltage and current density are further improved.

FIGS. 6 and 7 show another method of manufacturing the silicon substrate 10 used in the solar cell element according to the present invention.

In FIG. 6, the thickness is about 600 μm.
Cleaning the single crystal silicon substrate 10 formed by the CZ method,
This is placed in a heat treatment furnace having excellent cleanliness, and heat treatment is performed at 1000 to 1200 ° C. in an atmosphere of an inert gas such as nitrogen. By such an intrinsic gettering process, a defect concentration region 12 is formed in the central layer region of the silicon substrate 10 as shown in FIG.

Thereafter, the silicon substrate 10 including the portion where the defect concentration region 12 is formed is removed from the silicon substrate 10 by a method such as etching or polishing, and a solar cell is formed using the remaining silicon substrate 10.

In FIG. 7, after cleaning the single-crystal silicon substrate 10 similar to that of FIG. 6, a thin film containing a high concentration of phosphorus element is formed on one side by a vapor deposition method. Heat treatment is performed at 950 to 1100 ° C. in an atmosphere to diffuse phosphorus into the silicon substrate 10 at a high concentration.
At this time, contaminant impurities such as heavy metals, alkali metals or oxygen and defects such as lattice defects existing inside the silicon substrate 10 are concentrated in the phosphorus diffusion portion, and a defect concentration region 12 is formed on the surface side of the silicon substrate 10. You.

Next, the surface on which the defect concentration region 12 is formed is etched or polished to thereby form the defect concentration region 1.
The part containing 2 is removed. At this time, the etching or polishing is performed about 200 μm from the phosphorus diffusion surface, leaving a thickness of about 400 μm as a part for forming a solar cell.

As described above, on the silicon substrate 10 obtained by the method shown in FIGS. 6 and 7, an n-type diffusion layer is formed on the front side and a high concentration p ⁺ -type diffusion layer is formed on the back side.
A comb-shaped electrode is formed on the front surface side on which the mold diffusion layer is formed, and the electrode is formed on almost the entire back surface. Further, an antireflection film or the like is further formed on the front surface side. Thereby, a double-sided electrode type solar cell element as shown in FIG. 8 can be formed.

Using the silicon substrate 10 obtained as shown in FIGS. 6 and 7 to form a back electrode type solar cell element having a reinforcing portion 18 around it as shown in FIG. Of course, it is possible.

Since the silicon substrate 10 obtained as shown in FIGS. 6 and 7 has no defect concentration region 12,
Carrier movement characteristics can be improved, and output voltage and current density can be improved. This allows
In the solar cell as shown in FIG. 8, the output power under standard sunlight could be improved by about 4 to 10%.

In the above example, the silicon substrate 1
Although the single crystal silicon formed by the CZ method is used as 0, the performance can be improved by gettering even when other methods, for example, single crystal silicon or polycrystalline silicon formed by the FZ method are used. it can. Further, the present invention is also effective for compound semiconductors such as gallium arsenide and indium phosphide, and semiconductors using other group IV elements such as germanium. Further, application to a thin film material such as amorphous silicon is also possible.

As the gettering, two examples of intrinsic gettering and high-concentration diffusion of the phosphorus element have been described. However, the present invention is not limited thereto, and one side of the silicon substrate 10 may be subjected to sandblasting or scribe processing. A method of forming a processing strain or a method of high-concentration diffusion using ion implantation or another impurity element can be similarly used.

[0039]

As described above, according to the present invention,
Defects concentrated on a part of the silicon substrate by gettering are left only in the reinforcing part that does not operate as an element, so there is no defect in the power generation area, carrier carrier characteristics are improved, and the performance of the solar cell element is improved. Can be achieved. In addition, since a defect is left only in the reinforcing portion, a gettering method which cannot be applied to the conventional solar cell element can be applied.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of one embodiment of a solar cell element according to the present invention.

FIG. 2 is an explanatory diagram of a method of manufacturing the solar cell element shown in FIG.

FIG. 3 is an explanatory diagram of a method of manufacturing the solar cell element shown in FIG.

FIG. 4 is a partial cross-sectional view of another embodiment of the solar cell element according to the present invention.

FIG. 5 is an explanatory diagram of a method of manufacturing the solar cell element shown in FIG.

FIG. 6 is an explanatory diagram of an example of a method for manufacturing a silicon substrate used for a solar cell according to the present invention.

FIG. 7 is an explanatory view of another example of a method for manufacturing a silicon substrate used for a solar cell according to the present invention.

FIG. 8 is a perspective view of a double-sided electrode solar cell element manufactured using the silicon substrate shown in FIG. 6 or FIG.

FIG. 9 is an explanatory diagram of gettering when a conventional semiconductor device is manufactured.

FIG. 10 is an explanatory diagram in a case where a conventional gettering method is applied to a silicon substrate used for a solar cell element.

FIG. 11 is an explanatory diagram when a conventional gettering method is applied to a silicon substrate used for a solar cell element.

[Explanation of symbols]

Reference Signs List 10 silicon substrate, 12 defect concentration region, 14 diffusion layer, 16 electrodes, 18 reinforcing portion, 20 power generation region, 22
Anti-reflection film, 24 light receiving section, 26 incident light, 28 insulating film.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-204214 (JP, A) JP-A-8-213642 (JP, A) JP-A-4-192474 (JP, A) JP-A-6-204 342798 (JP, A) JP-A-2-302039 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078 H01L 21/322

Claims (3)

(57) [Claims] 1. A back electrode type crystalline silicon solar cell element having an electrode formed on the back surface of a light receiving portion, wherein a reinforcing portion is formed around the light receiving portion, and a defect existing in the silicon substrate is provided. A solar cell element in which a region where is concentrated is present only in the reinforcing portion. 2. A back-side electrode type crystalline silicon solar cell element having an electrode formed on the back surface of a light receiving portion, wherein a reinforcing portion is formed around the light receiving portion, and a defect existing in the silicon substrate is provided. A solar cell element, wherein a region where is concentrated is present in the reinforcing portion and a back surface region of the reinforcing portion. 3. The method of manufacturing a solar cell element according to claim 1, wherein the step of concentrating defects in the silicon substrate in a surface layer region or a central layer region of the substrate by gettering; Leaving the reinforcing part around
A step of etching deeper than the defect concentration region.