JPH02177569A - Manufacture of solar cell - Google Patents

Abstract

PURPOSE:To simplify a manufacturing process of a solar cell of this design by a method wherein a paste-like disperser is printed on a part of a substrate where a photodetective plane electrode is formed, and a deep first diffusion layer formed of a second conductivity type impurity is provided. CONSTITUTION:A paste-like diffusion agent 10 containing impurity of a second conductivity type opposite to that of a semiconductor substrate 1 is printed on a part of the semiconductor substrate 1 where a photodetective plane electrode 5 is formed, the substrate 1 is thermally treated to enable the second conductivity type to diffuse into the surface of the substrate 1, and a first diffusion layer 8 formed of a second conductivity type impurity is formed on the primary face of the substrate 1 located just under a part where the photodetective plane electrode 5 is formed. By this setup, a process can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a solar cell, and particularly to a method for manufacturing a solar cell with improved photovoltaic force on the short wavelength side.

[Conventional technology] A solar cell is an energy converter that uses a PN junction.
For example, a p-type diffusion layer with a thickness of 1 to 3 μm is formed on an n-type St substrate so that light reaches the PN junction from the surface, and the photovoltaic effect is utilized. In such a solar cell, it is generally known that when the diffusion layer is made thinner, the spectral sensitivity on the short wavelength side improves, and the energy conversion efficiency improves. However, when the diffusion layer is thinned, the material for the light-receiving surface electrode formed thereon is limited, and the method for forming the same is also limited. In other words, if the diffusion layer is to be thinned, an electrode material must be selected that will not increase leakage current and destroy the PN junction, and careful attention must be paid to the method of forming it. . Among commercially available solar cells, like space solar cells,
Ti, Pd, Ag
Vapor-deposited electrodes such as these are often used. However, if such materials are used in terrestrial solar cells, the cost will be high not only in terms of material costs but also in terms of process complexity, making it impractical. Therefore, the cost is low and the process is not complicated.
As a method for forming a light-receiving surface electrode of a terrestrial solar cell, a method of printing and firing a conductive silver (Ag) paste has been proposed. However, in this printing and firing method of conductive silver paste, the silver paste material is often fired at a temperature range of 600 to 750°C, and at such temperatures, the glass frit contained in the paste will diffuse. Penetrates into the layer,
For example, in a shallow junction with a depth of 0.2 μm or less, the leakage current of the device increases and the fill factor decreases, resulting in a significant loss of conversion efficiency. Therefore, in this printing and firing method of conductive silver paste, the bonding depth of the diffusion layer is set to 0.3 μm or more, and the sheet resistance value is 40 μm.
It had to be about ~50Ω/mouth. If the diffusion layer is shallower than this, in other words, if the sheet resistance is high, the glass frit contained in the paste will penetrate into the diffusion layer, as described above, and the leakage current of the device will increase, causing the curve The conversion efficiency is significantly impaired due to the reduction of the factor. Therefore, in the printing and firing method of conductive silver paste, it was thought that it would be practically difficult to manufacture an element with improved sensitivity on the short wavelength side.

Therefore, the method to solve the above problems is as follows.
Various proposals have been made in the past.

FIGS. 4A to 4E are cross-sectional views showing the steps of a conventional manufacturing method for a solar cell with improved sensitivity on the short wavelength side.

Referring to FIG. 4A, for example, a p-type silicon substrate 1 is prepared. Next, referring to FIG. 4B, a deep diffusion layer 2 made of an n-type impurity of a conductivity type opposite to that of silicon substrate 1 is formed on the main surface of silicon substrate 1. Next, referring to FIG. Next, referring to FIG. 4C, an acid-resistant resist 3 is printed on the portion where the light-receiving surface electrode is to be provided. Subsequently, referring to FIG. J@4D, the diffusion layer 2 is etched with a dilute hydrofluoric acid-nitric acid based etching solution using the resist 3 as a mask. Then, the portion of the resist 3 other than the diffusion layer immediately below is etched away and becomes thinner, and a shallow diffusion layer 4 is formed. After that, the resist 3 is removed.

Next, referring to FIG. 4E, a light-receiving surface electrode 5 is formed on the deep diffusion layer 2 using a conductive silver paste printing and baking method, and a light-receiving surface electrode 5 is formed on the back surface of the silicon substrate 1 by baking the A1-Ag paste. A back electrode 6 is formed.

In this method, a deep diffusion layer is formed under the light-receiving surface electrode, so even if the glass frit contained in the silver paste penetrates into the diffusion layer, the junction is deep and the leakage current of the device is reduced. Does not increase. Furthermore, since the portion through which light passes is the thin diffusion layer 4, the spectral sensitivity on the short wavelength side is improved.

FIGS. 5A to 5E are cross-sectional views of another example of a conventional manufacturing method for a solar cell with improved sensitivity on the short wavelength side.

Referring to the fifth AIE, for example, a p-type semiconductor substrate 1 is prepared. Next, referring to FIG. 5B, silicon substrate 1 is heated in an oxygen atmosphere to form silicon dioxide film (S i 02 film) 7 on the front and back surfaces of silicon substrate 1 . Subsequently, referring to FIG. 5C, the silicon dioxide film 7 in the portion where the light-receiving surface electrode will be formed is removed by ordinary photolithography and etching. Next, referring to FIG. 5D, pocu, which is an impurity of the opposite conductivity type to the silicon substrate 1,
.

A deep diffusion layer 2 is formed directly below the portion where the light-receiving surface electrode is formed. Next, silicon dioxide film 7 is removed with hydrofluoric acid. Next, referring to FIG. 5E, an impurity of a conductivity type opposite to that of silicon substrate 1 is diffused into the main surface of silicon substrate 1 to form shallow diffusion layer 4. Finally, a light-receiving surface electrode is formed on the deep diffusion layer 2 by printing and baking a conductive silver paste, and a back electrode 6 is formed on the back surface of the silicon substrate 1 by baking the AfL-Ag paste.
A solar cell is produced. In the solar cell manufactured in this manner, the light-receiving surface electrode 5 is formed on the deep diffusion layer 2. Therefore, in the printing and firing method of conductive silver paste, the glass frit contained in the paste is formed on the deep diffusion layer 2. Even if it penetrates into the interior, the leakage current of the element will not increase because the junction is deep, and the conversion efficiency will not be impaired. On the other hand, since the portion through which light passes is the shallow diffusion layer 4, the spectral sensitivity on the short wavelength side is improved.

[Problems to be Solved by the Invention] A conventional method for manufacturing a solar cell with improved short wavelength sensitivity is configured as described above.

However, the conventional method shown in FIGS. 4A to 4E has a problem in that the steps of printing the resist 3 and removing it are increased, as shown in FIG. 4C. Furthermore, referring to FIG. 4D, the thickness of the diffusion layer 2 is set to 0.4 to 0.5 μm.
When the etching depth is approximately 0.2 μm, there is a problem in that it is extremely difficult to form a shallow diffusion layer 4 of approximately 0.2 μm with good reproducibility using the above-mentioned etching solution.

The conventional techniques shown in Figures msA to 5E also have the following problems in addition to the problem of increasing the number of resist coating and resist removal steps.

That is, referring to FIG. 5D, the diffusion layer 2 has a thickness of approximately 0°6μ.
m, at 950°C in POC1s atmosphere.
It is necessary to perform a diffusion process for 0 minutes, but at this time, if the silicon dioxide film 7 is thin, the impurity phosphorus may be diffused to the part immediately below the silicon dioxide JII 7. In other words, this is because the silicon dioxide film 7 does not function sufficiently as a mask, and in order for the silicon dioxide film 7 to function sufficiently as a mask, the thickness of the silicon dioxide film 7 must be 1500A or more. Ta. In order to obtain such a thick silicon dioxide film, 1100
It was necessary to perform heat treatment at ℃ for 60 minutes.

However, when measuring the characteristics of solar cells formed through such heat treatment, it was found that the long-wavelength sensitivity was significantly reduced compared to conventional elements in which the depth of the diffusion layer was constant. Ta. This was considered to be because the formation temperature of the silicon dioxide film 7 was as high as 1100° C., so that the lifetime of bulk minority carriers was reduced. Therefore, we conducted an experiment to lower the formation temperature of the silicon dioxide film 7, but when forming 1500A silicon dioxide H7 in dry oxygen, it took 3 hours at 1000℃, and 8 hours at 920℃.
This was time consuming and impractical in terms of manufacturing process.

This invention was made to solve the above-mentioned problems, and aims to provide a method for manufacturing a solar cell that can produce a solar cell with improved sensitivity on the short wavelength side using a simple process at low cost. purpose.

[Means for Solving the Problems] The present invention relates to a method of manufacturing a solar cell in which a light-receiving surface electrode is formed on the main surface of a semiconductor substrate. and,
In order to solve the above-mentioned problems, a step of preparing the semiconductor substrate of a first conductivity type, and a step of preparing the semiconductor substrate of the first conductivity type; printing a paste-like diffusing agent containing impurities of a second conductivity type that is an opposite conductivity type; and performing heat treatment on the semiconductor substrate on which the paste-like diffusing agent is printed;
The impurity of the second conductivity type is diffused into the main surface of the semiconductor substrate, and the impurity of the second conductivity type is formed on the main surface of the semiconductor substrate located directly below the portion where the light-receiving surface electrode is formed. After forming the deep first diffusion layer, forming a shallow second diffusion layer made of impurities of a second conductivity type on the main surface of the semiconductor substrate. It includes a step of.

[Operation] A paste-like diffusing agent containing an impurity of a second conductivity type, which is the opposite conductivity type to that of the semiconductor substrate, is printed on the main surface of the semiconductor substrate on the part where the light-receiving surface electrode is to be formed. The step of forming a deep first diffusion layer made of impurities of the second conductivity type on the main surface of the semiconductor substrate located directly below the portion where the light-receiving surface electrode is to be formed is performed using a conventional method (see FIG. 4A). ~
This is a very simple process compared to FIGS. 4E and 5A to 5E).

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1A to 1D are cross-sectional views showing the steps of an embodiment of the present invention.

Referring to FIG. 1A, the semiconductor substrate is, for example, p-type,
A 100 mmφ silicon single crystal substrate having a specific resistance value of 1 Ω·cm is prepared. Next, referring to FIG. 1B, paste containing an n-type impurity, which is the opposite conductivity type to that of the semiconductor substrate 1, is applied to the main surface of the semiconductor substrate 1 in a portion where the light-receiving surface electrode is to be formed. The diffuser 10 is applied by screen printing.

This paste-like diffusing agent was produced as follows.

80 cc of ethyl alcohol was added to the beaker, and then 5 g of P2O as impurities, 10 cc of ethyl silicate, and 5 cc of acetic acid were further added and stirred to dissolve them. 3
After an hour, the mixture was heated at a temperature of 150° C. to vaporize the solvent into a glass material containing phosphorus (P). On the other hand, another beaker was prepared, and in this beaker, α-terpineol and butylcarpitol acetate were heated and mixed at 70° C., ethyl cellulose resin was added, and the mixture was sufficiently mixed, and then cooled to room temperature. The above-mentioned glass substance containing phosphorus was added to this and mixed to obtain a paste-like diffusing agent.

Next, referring to FIG. 1C, the semiconductor substrate 1 on which the pasty diffusing agent 10 is printed is heated at 200° C. for 10 minutes, dried, and then heated at 950° C. for 30 minutes in an atmosphere of oxygen and nitrogen. Heat treatment was performed to form a deep diffusion layer 8 with a depth of approximately 0.6 μm. Thereafter, the surface was cleaned with a hydrofluoric acid solution to remove the paste-like diffusing agent 10 from the main surface of the semiconductor substrate 1.

Next, referring to FIG. 1D, the main surface of semiconductor substrate 1 is
It was exposed to an OCIL s atmosphere and subjected to diffusion treatment at 850° C. for 15 minutes. As a result, a shallow diffusion layer 9 of about 0.2 μm was formed on the main surface of the semiconductor substrate 1. Next, CV
A TiO2 antireflection film 11 was formed on the main surface of the semiconductor substrate 1 by method D. Next, a high concentration P+ layer 13 was formed on the back surface of the semiconductor substrate 1 by baking the All paste, and the baked AfL paste was used as the back electrode 12. lastly,
A conductive silver base plate was directly printed on the TiO2 antireflection film 11 and fired at 600°C to penetrate the TiO□ film to provide a light-receiving surface electrode 5, thereby producing a solar cell.

In the solar cell manufactured in this manner, the portion directly below the light-receiving surface electrode 5 is a deep diffusion layer 8, so the junction is deep and leakage current is small. Furthermore, since the portion other than the portion immediately below the light-receiving electrode 5 is formed by the shallow diffusion layer 9, the spectral sensitivity on the short wavelength side is improved and the conversion efficiency is improved.

FIG. 2 shows an investigation of the voltage-current characteristics of the solar cell formed as described above. In the figure, the curve indicated by A is a characteristic diagram of a solar cell manufactured by the manufacturing method of the present invention. The curve indicated by B is a characteristic diagram of a device in which the entire surface of the diffusion layer has a shallow junction depth (approximately 0.2 μm). C is
5E is a characteristic diagram of a device having a shallow junction depth (0.2 μm) and a deep junction depth; FIG. As is clear from FIG. 2, element A of the present invention (junction depth of about 0.2 μm) has a small leakage current, and compared to conventional element C, the short circuit current density has improved by about 1.2 mA/cm2. I found out that In addition, the conversion efficiency is 0.0% compared to the conventional element C's 15°696. A value of 16.1%, which is 5% higher, was obtained.

FIG. 3 shows a device A of the present invention and a conventional device C shown in FIG. 5E.
This figure shows a comparison of the spectral sensitivity characteristics of a device in which the entire surface of the diffusion layer has a conventional junction depth (0.degree. 3 .mu.m). As is clear from FIG. 3, in the device A of the present invention, approximately 500 nm
It was found that the following sensitivity on the short wavelength side was improved. Note that the decrease in spectral sensitivity on the long wavelength side of element C is due to the 5B
This is probably because the silicon dioxide film 7 shown in the figure was formed at a high temperature of 1000°C.

In the above embodiment, a single crystal silicon substrate is used as the semiconductor substrate, but the present invention is not limited to this, and even if a polycrystalline silicon substrate is used, the same effects as in the embodiment can be obtained. Realize.

Further, in the above embodiment, a case where a P-type silicon substrate is used as the silicon substrate is exemplified, but even if an n-type silicon substrate is used and p-type impurities are diffused, the same effect as in the embodiment can be achieved. do.

Furthermore, in the above example, P is used as a raw material to become an N-type impurity.
2O, is shown as an example, but the present invention is not limited thereto.

This invention has been described above with reference to specific examples, but
The preferred embodiments described herein are illustrative and not restrictive. The scope of the present invention is indicated by the claims, and all modifications that come within the meaning of the claims are intended to be included in the present invention.

[Effects of the Invention] As explained above, according to the present invention, a second conductivity type that is the opposite conductivity type to that of the semiconductor substrate is formed on the main surface of the semiconductor substrate in the portion where the light-receiving surface electrode is formed. A paste-like diffusing agent containing an impurity is printed, and then the semiconductor substrate on which the paste-like diffusing agent is printed is subjected to heat treatment to diffuse the impurity of the second conductivity type to the main surface of the semiconductor substrate, and the above-mentioned A deep first diffusion layer made of m2 conductivity type impurities is formed on the main surface of the semiconductor substrate located directly below a portion where a light-receiving surface electrode is to be formed. Such a process is a simple process, does not require much cost, and provides an element with low leakage current. After forming the deep first diffusion layer, a shallow second diffusion layer made of impurities of the second conductivity type is formed on the main surface of the semiconductor substrate. A battery is obtained.

[Brief explanation of the drawing]

FIGS. 1A to 1D are cross-sectional views showing the steps of an embodiment of the present invention. FIG. 2 is a diagram comparing voltage-current characteristics between the device of the present invention and a conventional device. FIG. 3 is a comparison diagram of spectral sensitivity characteristics between the device of the present invention and a conventional device. FIGS. 4A to 4E are process diagrams of a conventional method for manufacturing a solar cell. FIGS. 5A to 5E are process diagrams of other examples of the conventional solar cell manufacturing method. In the figure, 1 is a semiconductor substrate, 5 is a light-receiving surface electrode, 8 is a deep diffusion layer, 9 is a shallow diffusion layer, and 10 is a paste-like diffusion agent. Note that in each figure, the same parts indicate the same or equivalent parts. Figure 1A Figure 1B Figure 1C Figure 3 Figure 1D Castle length 800 1αη (ηvi) Figure 4A Figure 4B Figure 5A Figure 58

Claims (1)

[Claims] A method for manufacturing a solar cell in which a light-receiving surface electrode is formed on the main surface of a semiconductor substrate, comprising: preparing the semiconductor substrate of a first conductivity type; and the main surface of the semiconductor substrate. printing a paste-like diffusing agent containing an impurity of a second conductivity type, which is an opposite conductivity type to that of the semiconductor substrate, on a portion where the light-receiving surface electrode is to be formed; is printed on the semiconductor substrate to diffuse the impurity of the second conductivity type into the main surface of the semiconductor substrate, and to diffuse impurities of the second conductivity type into the main surface of the semiconductor substrate located directly below the portion where the light-receiving surface electrode is to be formed. the second on the surface
a step of forming a deep first diffusion layer formed with an impurity of a conductivity type; and after forming the deep first diffusion layer, forming an impurity of a second conductivity type on the main surface of the semiconductor substrate; a step of forming a shallow second diffusion layer; and a method of manufacturing a solar cell.