JPH06101570B2 - Solar cell element - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a solar cell device using a semiconductor substrate.

[0002]

2. Description of the Related Art In order for solar power generation, which is still high in power generation cost, to become popular as a general power source, it is necessary to improve conversion efficiency of solar cells and reduce manufacturing costs. Recently, back contact solar cell elements and granular solar cells, which are expected to improve the conversion efficiency of solar cells and reduce their manufacturing cost, have been announced. At present, efforts are being made to reduce the manufacturing cost of these devices, and the 5th International Conference on Solar Cell Science and Technology (199
0), Technical Digest, page 508, discusses back contact solar cell elements suitable for manufacturing processes using screen printing technology. Also, the 22nd
Low cost granular solar cell devices have been discussed at the IEEE International Conference on Solar Cell Experts (1991).

[0003]

The solar cell element in the above-mentioned prior art has an element structure which can be manufactured by a simple process in which the number of steps is greatly reduced, but it is still insufficient in reducing the manufacturing cost. There is. That is, there is a problem that a large number of man-hours are required for the junction separation between the pair of main electrodes and the pair of n + layers and p + layers connected thereto.

An object of the present invention is to solve the above problems and to improve the photoelectric conversion efficiency and reduce the manufacturing cost.

[0005]

The above-mentioned object is to separate the n + layer (or p + layer) forming the pn junction on the main surface of the p-type silicon substrate (or the n-type silicon substrate) into islands,
One part of the n + layer (or p + layer) separated by islands is penetrated by the n + silicon regrowth layer (or p + silicon regrowth layer), and the other part is opposite to the conductivity type of one. The n + layer (or p + layer) and the n + silicon regrowth layer (or p + silicon regrowth layer), which are penetrated by the p + silicon regrowth layer (or n + silicon regrowth layer) and are junction-separated into islands, form a pair of main parts. This is achieved by the structure connected to the electrodes.

The n + silicon regrowth layer is a layer formed by an alloy reaction between gold-antimony and silicon, and the p + silicon regrowth layer is a layer formed by an alloy reaction between aluminum and silicon. This alloy reaction is caused by the silicon oxide film, titanium oxide film, thin film
A silicon alloy layer and a silicon regrowth layer are formed through the n + layer and the thin p + layer. The same applies to the alloy reaction with a paste in which small aluminum particles or small gold antimony particles are mixed in silver paste. On the other hand, an electrode prepared by mixing small aluminum particles or small gold antimony particles in a silver paste to cause an alloy reaction with silicon has good alkali etching resistance. Further, the silicon oxide film and the titanium oxide film have good alkali etching resistance.

From these things, a pn junction is formed on the main surface of a p-type silicon substrate (or an n-type silicon substrate).
On the n + layer (or p + layer), a paste prepared by mixing small aluminum particles in a silver paste serving as one electrode and a small gold antimony particle mixed in a silver paste serving as the other electrode. After printing with paste, firing and alloying reaction,
P-type silicon substrate (or n
Type silicon substrate) n + layer forming a pn junction on the main surface
The above object is achieved by removing (or p + layer) and then removing silicon.

[0008]

In a silicon solar cell, the charges of electrons and holes generated by sunlight are separated by a pn junction,
Holes are accumulated in the type region and electrons are accumulated in the n-type region, and an electromotive force is generated by this charge double layer.

With the above structure, holes are accumulated in the p-type silicon and p + silicon regrowth layers, and electrons are accumulated in the n + layers and n + silicon regrowth layers, and an electromotive force is generated by this charge double layer. This electromotive force causes p-type silicon and p
+ The holes accumulated in the silicon regrowth layer leak to the n + layer in contact with the p + silicon regrowth layer, but by printing the electrode material paste on the n + layer and performing alkali etching, n + Since the layer is separated from the p-type silicon in the form of an island pn junction, the layer is extracted to the pair of main electrodes without leaking to the other pair of n + layers. The electrons accumulated in the n + layer and the n + silicon regrown layer are similarly extracted without leaking to the pair of the other main electrodes.

In this way, the photoelectric conversion efficiency is improved and p
The manufacturing cost for separating the n-junction is reduced.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of the solar cell element of the present invention. In the figure, reference numeral 1 denotes a semiconductor substrate having a first main surface 11 serving as a light-receiving surface and a second main surface 12 having an uneven surface serving as a back surface, which is an n-type conductive first substrate adjacent to the first main surface 11. The first layer 13, the first layer 13 and the p-type conductive second layer 14, which is adjacent to the concave portions of the second main surface 12 and has a lower impurity concentration than the first layer 13, And an n-type conductive third layer 15, which has a higher impurity concentration than the second layer 14 and is adjacent to the convex portion of the second main surface 12,
The first layer 13 from a plurality of selected locations on the main surface 11 of the
N-type conductive fourth layer 16 having a higher impurity concentration than the second layer 14 extending to the second layer 14 and a plurality of selected portions of the convex portion of the second main surface 12 From the second layer 14 through the third layer 15 to the second layer 14
It is composed of a fifth p-type conductive layer 17 having a higher impurity concentration. 2 is a light antireflection film formed of titanium oxide on the first main surface 11, 3 is a first portion 31 of a gold-silicon alloy which penetrates the light antireflection film 2 and extends into the fourth layer 16, and The first main electrode 4 composed of the second portion 32 of the silver paste formed by mixing the gold antimony grains contacting the first portion 31 formed on the selected portion of the light reflection preventing film 2 is the second The aluminum particles formed on the convex portion of the second main surface 12 and the first portion 41 of the aluminum silicon alloy extending from the convex portion of the main surface 12 into the fifth layer 17 and contacting the first portion 41 Second part of mixed silver paste 4
It is a second main electrode composed of two.

Next, a method of manufacturing the solar cell element having the above structure will be described.

FIG. 2 is a flow chart showing the manufacturing process.

First, the p-type has a specific resistance of 1 Ωcm and a thickness of 220.
Prepare a μm silicon substrate, and add KOH to this surface by several%.
An etching treatment of about 20 μm is performed with an alkaline etching solution containing the processing strained layer to remove the processed strained layer and to form a textured surface.
Phosphorous oxychloride (POCl ₃ ) is diffused on both sides of the etched silicon substrate at 850 ° C. for 30 minutes to form an n + layer having a depth of about 0.5 μm. Next, a titanium oxide film having a thickness of about 500 Å is formed on the surface to be the light receiving surface by atmospheric pressure CVD. Further, on the n + layer formed on the back surface, aluminum particles having a particle size of several tens of μm were added to the silver paste in a weight ratio of 9%.
A mixture of 7% silver and 3% by weight of aluminum particles was mixed, printed, and baked at 750 ° C. for 1 minute to form a p + layer, a second layer.
Forming a first portion and a second portion of the main electrode. Next, on the titanium oxide film, 93% by weight of gold-1% by weight of antimony-6% by weight of silicon, alloy particles with a particle size of several tens of μm from silicon were added to a silver paste at 97% by weight of silver-3% by weight of silver. % Mixture of alloy grains is printed and fired at 750 ° C. for 1 minute to form the first and second portions of the first main electrode. Finally, it is etched by about 2 μm with an alkaline etching solution containing KOH of several%, and the n + layers on both sides are pn-separated into islands in a mesa shape.

The solar cell element thus manufactured is
The production yield was high and the photoelectric conversion efficiency was high.

FIG. 3 is a schematic sectional view showing another embodiment of the solar cell element of FIG. 1, which is different from the embodiment of FIG. 1 in that the conductivity type is opposite.

In the figure, the semiconductor substrate 1 includes a first p-type conductive first layer 131, a first main surface 11 and a first layer 131.
Adjacent to the concave portion of the layer 131 and the second main surface 12 of the first
N-type second conductive layer having a lower impurity concentration than the second layer 131 of
Layer 141, second layer 141, and p-type conductive third layer 151 having a higher impurity concentration than the second layer 141 adjacent to the convex portions of the second main surface 12 and the first main surface 11. Of the p-type conductive fourth layer 161, which has a higher impurity concentration than the second layer 141 extending from the plurality of selected locations through the first layer 131 to the second layer 141. Main surface 12
Of the n-type conductive fifth layer 171 having a higher impurity concentration than the second layer 141 extending from the plurality of selected portions of the convex surface portion of the third layer 151 to the second layer 141. Has become. 3 is a fourth layer 1 which penetrates the antireflection film 2
A first portion 31 of aluminum-silicon alloy extending in 61 and a second portion of a silver paste mixed with aluminum particles formed on a selected portion of the light reflection preventing film 2 and contacting the first portion 31. The first main electrode 32 made of 32 is the first portion 41 of the gold-silicon alloy extending from the convex portion of the second main surface 12 into the fifth layer 171, and the second main surface 12
Is a second main electrode composed of a second portion 42 of a silver paste mixed with gold antimony grains which is formed on the convex surface portion of and contacts the first portion 41. Fourth layer 161 and fifth layer 1
71 is a regrowth layer, respectively.

FIG. 4 is a flow chart showing a manufacturing process of the solar cell element of FIG.

At the time of manufacture, first of all, it is an n type and has a specific resistance of 1 Ωc.
m, 220 μm thick silicon substrate is prepared, and its surface is about 20 μm with an alkaline etching solution containing KOH of several%.
Etching is performed to remove the work strain layer and to make it a textured surface. Boron tribromide (BBr ₃ ) diffusion is performed on both surfaces of the etched silicon substrate at 900 ° C. for 30 minutes to form a p + layer having a depth of about 0.5 μm. The boron glass produced at this time is removed with hydrofluoric acid. Next, a titanium oxide film having a thickness of about 500 Å is formed on the surface to be the light receiving surface by atmospheric pressure CVD. In addition, on the p + layer formed on the back surface, a weight ratio of 93% gold-1% antimony-weight ratio 6
%, Alloy particles having a particle size of several tens of micrometers were mixed with silver paste in a ratio of 97% by weight of silver and 3% by weight of alloy particles by weight, printed, and baked at 750 ° C. for 1 minute to obtain n +. Forming a layer, a first portion and a second portion of the second main electrode. Next, on the titanium oxide film, aluminum particles having a particle size of several tens of μm were mixed with silver paste at a ratio of 97% by weight of silver and 3% by weight of aluminum particles, and printed, and baked at 750 ° C. for 1 minute. The p + layer, the first part of the first main electrode and the second
Form part of. Finally, the p + layers on both sides are pn-separated into islands in a mesa shape by etching with an alkali etching solution containing KOH of several% for about 2 μm.

The solar cell element thus manufactured is
The production yield was high and the photoelectric conversion efficiency was high.

FIG. 5 is a schematic cross-sectional view showing another embodiment of the solar cell element of the present invention, which is different from the embodiment of FIG.
Of the n-type conductivity having a higher impurity concentration than the second layer 14 extending from the surface to the second layer 14 at the convex portion between the fifth layers 17 of the main surface 12 of Sixth
A first portion 51 of gold-silicon alloy extending from the convex portion of the second main surface 12 into the sixth layer 18, and the first portion formed on the convex portion of the second main surface 12. Part 51
Second silver paste mixed with gold antimony particles that come into contact with
The third main electrode 5 composed of the part 52 is formed. The third main electrode 5 is used with the same potential as the first main electrode 3.

FIG. 6 is a flow chart showing the manufacturing process of the solar cell element of FIG.

After printing a silver paste mixed with aluminum particles on the back surface by the flow chart of FIG. 2, a silver paste mixed with gold antimony particles is printed away from a silver paste mixed with aluminum particles. The difference from FIG. 2 is that steps are added.

This solar cell element has a third surface provided on the back surface.
Since electric power can be taken out from the main electrode 5 of, the photoelectric conversion efficiency can be further improved.

FIG. 7 is a schematic cross-sectional view showing another embodiment of the solar cell element of FIG. 5, which is different from the embodiment of FIG.
Of the p-type conductivity having a higher impurity concentration than the second layer 141 extending from the surface to the second layer 141 at the convex portion between the fifth layers 171 of the main surface 12 of A sixth layer 181 is provided and is formed on the convex portion of the second main surface 12 and the first portion 51 of the aluminum silicon alloy extending from the convex portion of the second main surface 12 into the sixth layer 181. The third main electrode 5 is formed of a second portion 52 of a silver paste mixed with aluminum particles that contacts the first portion 51. The third main electrode 5 is used with the same potential as the first main electrode 3.

FIG. 8 is a flow chart showing the manufacturing process of the solar cell element of FIG.

After printing the silver paste mixed with gold antimony grains on the back side by the flow chart of FIG. 4, the silver paste mixed with aluminum grains is printed away from the silver paste mixed with gold antimony grains. The difference from FIG. 4 is that the step of adding is added.

This solar cell element has a third surface provided on the back surface.
Since electric power can be taken out from the main electrode 5 of, the photoelectric conversion efficiency can be further improved.

FIG. 9 is a schematic cross-sectional view showing still another embodiment of the solar cell element of the present invention, which is different from the embodiment of FIG. 5 in the fourth layer 1.
6 and the first main electrode 3 are removed so that the entire surface of the first main surface 11 serves as a light receiving surface.

FIG. 10 is a flow chart showing a manufacturing process of the solar cell element of FIG.

The flow chart of FIG. 6 is characterized in that the step of printing a silver paste in which gold antimony particles are mixed on the light receiving surface is removed.

In this solar cell element, since there is no sunlight shield on the light receiving surface, the photoelectric conversion efficiency can be further improved as compared with the embodiment of FIG.

FIG. 11 is a schematic sectional view showing another embodiment of the solar cell element of the present invention, which is different from the embodiment of FIG. 7 in the fourth layer 16
The difference is that the first and the first main electrodes 3 are removed so that the entire surface of the first main surface 11 becomes the light receiving surface.

FIG. 12 is a flow chart showing the manufacturing process of the solar cell element of FIG.

The flow chart of FIG. 7 is characterized in that the step of printing a silver paste in which aluminum particles are mixed on the light receiving surface is removed.

Since this solar cell element does not have a sunlight shield on the light receiving surface, the photoelectric conversion efficiency can be further improved as compared with the embodiment of FIG.

FIG. 13 is a schematic cross-sectional view showing still another embodiment of the solar cell element of the present invention, which is characterized in that a large number of solar cell balls are provided on a supporting substrate.
In the figure, 20 is a support substrate made of ceramics,
Reference numeral 21 is a solar cell sphere, and 22 and 23 are a pair of electrodes of the solar cell sphere 21 for bonding the solar cell sphere 21 to the support substrate 20. The solar cell sphere 21 includes a p-type base body 211 having a spherical shape as a whole, two n + layers 212 formed separately on the surface portion of the base body 211 facing the supporting substrate 20, and from one n + layer 212 surface to the base body 211. The n + layer 213 extends, the p + layer 214 extends from the surface of the other n + layer 212 to the base body 211, and the titanium oxide film 24 formed on the surface of the base body 211 opposite to the side facing the support substrate 20. One electrode 22 is a first portion 221 of gold-silicon alloy extending into the n + layer 213 of the adjacent solar cell sphere 21,
And a second part 222 of a silver paste formed by mixing n + layer 212 and n + layer 213 with gold antimony grains that are in contact with the first part 221 and the other electrode 23 is an adjacent solar cell sphere. 21 a first portion 231 of aluminum silicon alloy extending into the p + layer 214 and the n + layer 2
12, a second portion 232 of silver paste mixed with aluminum grains formed on the p + layer 214 and contacting the first portion 231.

FIG. 14 is a flow chart showing the manufacturing process of the solar cell element of FIG.

In the flow chart shown in FIG. 10, the p-type silicon substrate is replaced with p-type silicon spheres (grains), texture etching is stopped, phosphorus diffusion is performed, and silver paste and aluminum in which gold antimony grains are premixed are used. The method further comprises a step of spraying and adhering the silver paste mixed with the particles onto the printed support substrate 20, and then firing. Since the silicon spheres (grains) are lower in price than the silicon substrate in principle, the manufacturing cost can be reduced as compared with the above-mentioned embodiment.

FIG. 15 is a schematic sectional view showing another embodiment of the solar cell element of FIG. 13, which is different from that of FIG. 13 in that the conductivity type is reversed.

In this figure, a solar cell sphere 25 is an n-type base 251 having a spherical shape as a whole, and two p + formed separately on the surface portion of the base 251 facing the support substrate 20.
The layer 252, the p + layer 253 extending from one p + layer 252 surface to the base 251, the n + layer 254 extending from the other p + layer 252 surface to the base 251, and the surface of the base 251 opposite to the side facing the support substrate 20. It is composed of the formed titanium oxide film 24. One electrode 26 has a first portion 261 of aluminum silicon alloy extending into the p + layer 253 of the adjacent solar cell sphere 25, and the p + layer 252, p.
Second portion 262 of silver paste mixed with aluminum grains formed on + layer 253 and contacting first portion 261.
And the other electrode 27 is adjacent to the solar cell sphere 25.
A first portion 271 of a gold-silicon alloy extending into the n + layer 254 and a second silver paste mixed with gold antimony grains formed on the p + layer 252 and the p + layer 254 and contacting the first portion 271. Part 272.

FIG. 16 is a flow chart showing the manufacturing process of the solar cell element of FIG.

It differs from the flow chart of FIG. 14 in that the starting substrate is n-type and that phosphorus diffusion is used instead of boron diffusion.

[0045]

According to the present invention, by using the screen printing technique and the alkali etching, the junction separation between the n + layer and the p layer can be achieved with a high yield, and a high photoelectric conversion efficiency can be obtained. It has the effect of improving efficiency and economy.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of a solar cell element of the present invention.

2 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

FIG. 3 is a schematic sectional view showing another embodiment of the solar cell element of FIG.

4 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

FIG. 5 is a schematic sectional view showing another embodiment of the solar cell element of the present invention.

FIG. 6 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

7 is a schematic cross-sectional view showing another embodiment of the solar cell element of FIG.

FIG. 8 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

FIG. 9 is a schematic cross-sectional view showing another embodiment of the solar cell element of the present invention.

FIG. 10 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

FIG. 11 is a schematic cross-sectional view showing another embodiment of the solar cell element of the present invention.

12 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

FIG. 13 is a schematic cross-sectional view showing another embodiment of the solar cell element of the present invention.

14 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

FIG. 15 is a schematic cross-sectional view showing another embodiment of the solar cell element of FIG.

16 is a flowchart showing an example of a method for manufacturing the solar cell element of FIG.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Antireflection Film 3 First Main Electrode 4 Second Main Electrode 5 Third Main Electrode 11 Main Surface 12 Main Surface 13 n-Type First Layer 14 p-Type Second Layer 15 n-Type Third layer 16 n-type fourth layer 17 p-type fifth layer 31 first portion of the first main electrode 32 second portion of the first main electrode 41 of the second main electrode 1st part 42 1st 2nd part of 2nd main electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideyuki Yagi, Inventor 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor, Satoshi Omata 3-chome, Hitachi-shi, Ibaraki No. 1 In stock company Hitachi Ltd. Hitachi factory (72) Inventor Yasuaki Uchida 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Incorporated company Hitachi Ltd. Hitachi factory (72) Inventor Kimio Hatsumi Hitachi City, Ibaraki Prefecture 3-1, 1-1 Sachimachi Hitachi, Ltd. Hitachi factory (72) Inventor Tadao Asahi 3-1-1, Sachimachi Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi factory

Claims (4)

[Claims] 1. An n + island-like separated structure having a mesa structure formed on one main surface of a p-type conductive silicon substrate which is a light-receiving surface.
-Type conductive first n + layer, a titanium oxide film for preventing light reflection formed on the first n + layer, and formed through the titanium oxide film and the first n + layer And a first main electrode of the pair of gold-silicon alloy main electrodes, the first main electrode and the first n + layer are in contact with each other, and are in contact with the p-type silicon substrate at a pn junction. A second n + layer of regrown n + type conductive silicon and the first of the one
Of the second main electrode formed by firing a silver paste mixed with gold-antimony particles in contact with the main electrode of the above, and the other main surface serving as a back surface opposite to the one main surface. N + type conductive third separated island-shaped structure
N + layer, the other first main electrode of the pair of aluminum-silicon alloy main electrodes formed so as to penetrate through the third n + layer, the other first main electrode and the third n + layer A first p + layer for re-growth of p + -type conductive silicon, which is formed so as to be in contact with the p-type silicon substrate, the third n + layer, the other first main electrode, and the first p + layer. A solar cell element comprising: the other second main electrode formed by firing a silver paste mixed with aluminum particles in contact with each other. 2. A p + formed in an island shape in a mesa structure on one main surface which is a light-receiving surface of an n-type conductive silicon substrate.
-Type conductive first p + layer, a titanium oxide film for preventing light reflection formed on the first p + layer, and formed through the titanium oxide film and the first p + layer The first main electrode of the pair of main electrodes of the aluminum-silicon alloy and the first main electrode and the first p + layer are in contact with each other.
P + formed so as to be in contact with the silicon substrate at the pn junction
Type second conductive p-type second layer of regrown silicon and one second main electrode formed by firing a silver paste mixed with aluminum particles in contact with the one first main electrode; Formed on the other main surface, which is the back surface located on the side opposite to the main surface, of the p + -type conductive third p + layer separated in an island shape with a mesa structure, and penetrating the third p + layer. N + type conductivity formed so as to be in contact with the other first main electrode of the pair of gold-silicon alloy main electrodes and the other first main electrode and the third p + layer, and to be in contact with the n type silicon substrate. Formed by baking a silver paste in which a first n + layer of reproducible silicon and a gold-antimony grain in contact with the third p + layer and the other first main electrode and the first n + layer are mixed. And the other second main electrode. 3. A pair of gold-silicon alloy main electrodes formed by penetrating an n + -type conductive third n + layer separated and formed in an island shape with a mesa structure on the other main surface serving as the back surface. One of the first main electrodes, the one of the first main electrodes, and the third
A second n + layer of n + type conductive silicon regrowth formed so as to be in contact with the n + layer of the above and to be in contact with the p type silicon substrate at a pn junction, and a gold-antimony grain which is in contact with the one first main electrode. The solar cell element according to claim 1, wherein the solar cell element is configured by adding one of the second main electrodes formed by firing a mixed silver paste. 4. A pair of main electrodes of an aluminum-silicon alloy formed by penetrating a p + type conductive third p + layer separated and formed in an island shape in a mesa structure on the other main surface serving as the back surface. One of the first main electrodes and a p + -type conductive silicon regrowth layer formed so as to contact the one first main electrode and the third p + layer and contact the n-type silicon substrate at the pn junction. 2 p + layer and one second main electrode formed by baking a silver paste mixed with aluminum particles in contact with the one first main electrode. The solar cell element according to claim 2.