JPH0793453B2 - Method for manufacturing silicon solar cell element - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates has a pair of main electrodes on the back <br/> surface opposite to the light receiving surface, manufacturing method of a silicon solar cell element formed by Faiasuru the one main electrode Regarding

[0002]

2. Description of the Related Art In order for solar power generation, which currently has a high power generation cost, to spread as a practical power source, it is necessary to improve the conversion efficiency of solar cells and reduce the manufacturing cost. Recently, backside contact solar cell devices (Backside Contact Silicon Solar Cell) are expected to improve the conversion efficiency of solar cells and reduce their manufacturing costs.
lls) has been announced, and efforts are currently underway to reduce the manufacturing cost of this device. The 5th International Conference on Solar Cell Science and Technology (1990), Technical Digest, 50th
Page 8 discusses silicon solar cell devices suitable for manufacturing using screen printing techniques.

[0003]

The solar cell element in the prior art described above has an element structure which can be manufactured by a simple process in which the number of steps is greatly reduced, and the number of steps is greatly reduced by using a low-cost screen printing technique. Although the element structure can be manufactured by a simple process that is reduced, there are still insufficient points in reducing the manufacturing cost. That is, there is a problem that a lot of man-hours are required to separate the junction between the n + layer and the p + layer on the back surface.

An object of the present invention is to solve the above problems, reduce the steps for manufacturing a silicon solar cell element, and increase the conversion efficiency.

[0005]

The above-mentioned objects are p-type or
On the back surface, which is the side opposite to the light-receiving surface of the n-type silicon substrate, the front surface
An n-type conductive layer having a concentration of 1 × 10 ¹⁹ / cm ³ or less is expanded with phosphorus.
And the oxide film on the surface of the n-type conductive layer.
And the aluminum pace on the surface of the oxide film.
Screen printed on the electrode pattern and baked to remove the oxide film and
And an aluminum silicon alloy layer penetrating the n-type conductive layer
A first electrode composed of a
The process of forming the re-grown layer and the silver coating on the surface of the oxide film.
Screen printed on the electrode pattern, baked and oxidized
A second electrode that penetrates the film and makes ohmic contact with the n-type conductive layer.
And forming a pole .

[0006]

[0007]

[0008]

[0009]

[Function] When aluminum and a silicon substrate coated with a silicon oxide film are subjected to an alloy reaction, as a fact of experiment, the silicon oxide film is penetrated by a fire through, and aluminum and silicon show a eutectic alloy phase. A first main electrode made of an alloy layer and a first layer, which is a p + -type silicon regrowth layer in which aluminum is dissolved in solid solution, are simultaneously formed on the silicon surface outside the first main electrode.

The p-type silicon substrate is covered with an n-type conductive layer, and the n-type conductive layer is covered with a silicon oxide film.
The silicon oxide film and the n-type conductive layer are penetrated through, and a first main electrode made of an aluminum-silicon alloy layer, an n-type conductive layer outside the first main electrode, and p + which is a solid solution of aluminum on the p-type silicon substrate surface are formed. Type silicon regrowth layer first
Layers occur simultaneously. As a result, the first main electrode composed of the aluminum-silicon alloy layer forming the metal electrode is
Contacting the first layer, which is the + type silicon regrowth layer, while
Since the first layer, which is the p + layer, is connected to the n-type conductive layer by a pn junction and is in ohmic contact with the p-type silicon substrate, the metal electrode exhibits a pn junction to the n-type conductive layer. As a result, the p-type silicon substrate exhibits ohmic contact.

When the silicon substrate is n-type, with respect to the silicon substrate, a first layer which is a p + type silicon regrowth layer which constitutes a pn junction and an aluminum silicon alloy layer which constitutes a metal electrode in contact with the first layer are formed. Since the metal electrode layer is not in direct contact with the n-type silicon substrate, it exhibits good pn junction characteristics with the silicon substrate.

Since the pn junction can be formed at a position deeper than the other main surface by using the n-type silicon substrate, the efficiency of collecting photogenerated charges is increased and the conversion efficiency is increased.

The surface concentration of the n-type conductive layer is 1 × 10 ¹⁹ / cm.
^{Since it is 3} or less, formation of a compound of aluminum and phosphorus is not observed in the reaction between the n-type conductive layer and aluminum,
Therefore, the first layer, which is a p + type silicon regrowth layer, and n
The pn junction characteristic with the type conductive layer was not short-circuited and showed good characteristics. In addition, n covered with a silicon oxide film
Good pn junction characteristics are exhibited also for the type conductive layer and the n type silicon substrate covered with this n type conductive layer.

[0014]

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

First Embodiment FIG. 1 is a perspective view showing the structure of the first embodiment of the present invention.

FIG. 2 is a sectional view showing the construction of the first embodiment of the present invention.

First, the structure of this embodiment will be described.

In the figure, reference numeral 1 denotes a silicon solar cell element of the present embodiment, one main surface 11 serving as a light receiving surface of a p-type conductive silicon substrate, the other main surface 11 opposite to the other main surface 11. P + -type conductive first layer 13 formed on the main surface 12 of n, and conductive n + -type on the side opposite to the first layer 13 adjacent to the first layer 13 and having a surface concentration of 1 × 10 ¹⁹ /
p adjacent to the second layer 14 and the first layer 13 of ³ cm ³ or less
And a first main electrode 15 made of an aluminum-silicon alloy layer. One main surface 11 and the other main surface 12 are textured surfaces having fine irregularities, and oxide films 2 and 3 are formed thereon. Reference numeral 4 is a TiO ₂ film formed on the oxide film 2. First electrode 1 made of aluminum-silicon alloy layer
5 is on the other main surface 12 together with the p + layer 13,
It has a shape in which comb teeth are intermeshed with the n + layer 14, makes contact with the n + layer 14 at the pn junction through the first layer 13, makes ohmic contact with the p-type silicon substrate, and forms the oxide film 3 It is insulated from the I Ri n + layer 14. Reference numeral 51 denotes a second electrode, which is on the other main surface and is in contact with the n + layer 14, and is insulated from the p + layer 13 by the oxide film 3. The first electrode 15 made of an aluminum silicon alloy layer is
Since it is a p-type impurity source of the first layer 13, it can be formed at the same time as the first layer 13 without performing alignment for contacting with the first layer 13, so that the manufacturing cost can be reduced. it can. 1 × 10 ¹⁹ / cm of the second layer 12
The surface concentration of ³ or less has a function of reducing recombination of electron-hole pairs generated in the second layer 12 and improving an electromotive voltage and a photo-generated current.

Generally, in a silicon solar cell, charges of electrons and holes generated by sunlight are separated by a pn junction, holes are accumulated in a p-type region and electrons are accumulated in an n-type region. Generate voltage.

When the p-type silicon substrate has the above structure, holes are accumulated in the p-type silicon substrate and the p + layer, electrons are accumulated in the n-type conductive layer, and an electromotive voltage is generated by the charge double layer. When the p + layer and the n-type conductive layer show good pn junction characteristics, holes in the p-type silicon substrate and the p + layer are extracted through the aluminum-silicon alloy electrode without leaking to the n-type conductive layer. The electrons in the n-type conductive layer are p
It is extracted through the electrode provided on the n-type conductive layer without leaking to the p-type silicon substrate and the p + layer.

Further, when the above-mentioned structure is formed on the n-type silicon substrate, holes are accumulated in the p + layer, electrons are accumulated in the n-type silicon substrate and the n-type conductive layer, and an electromotive voltage is generated by the charge double layer. To do. When the p + layer and the n-type silicon substrate and the n-type conductive layer exhibit good pn junction characteristics, holes in the p + layer are extracted through the aluminum-silicon alloy electrode without leaking to the n-type conductive layer. The electrons of the n-type silicon substrate and the n-type conductive layer do not leak to the p + layer,
It is drawn out through the electrode provided on the n-type conductive layer. Next, a method for manufacturing the solar cell element of this embodiment will be described.

1) p-type, specific resistance 1 Ωcm, thickness 200 μ
A silicon substrate of m, crystal orientation (1, 0, 0) is etched by about 20 μm with an alkaline etching solution containing a few% of KOH to remove a strained layer generated when a wafer is processed from an ingot on both sides of the substrate. , Make the surface a textured surface with fine irregularities.

2) An n-type layer having a phosphorus concentration distribution of 1 × 10 ¹⁹ / cm ³ or less is formed on both surfaces of the silicon substrate by phosphorus diffusion. Diffusion of phosphorus oxychloride (POCl ₃ ) at 850 ° C
Perform 0 minutes, depth 0.5μm on both sides of silicon substrate
To form the n + layer. At this time, the phosphorus concentration distribution in the n + layer has a surface concentration of 1 × 10 ²⁰ / c due to experimental facts.
A high-concentration layer called a phosphorus pile-up layer having a depth of about 0.1 μm at a density of m ³ or more and a concentration of 1 × 10 ¹⁹ / cm ³ or less.

3) In order to remove this high-concentration phosphorus pile-up layer, after removing the phosphorus glass with hydrofluoric acid, the high-concentration phosphorus pile-up layer is oxidized in a steam atmosphere at 1000 ° C. for 30 minutes, The oxide film 3 is formed.

4) An acid resistant mask material is printed on the other surface of the substrate by screen printing.

5) The oxide film on one surface was removed with hydrofluoric acid,
Further, the resist is removed with a solvent.

6) One surface is etched by about 2 μm with an alkaline etching solution containing KOH of several%, and the n + layer formed on the one surface is removed.

7) 1000 ° C. in a dry oxygen gas atmosphere,
10 min, 200 Å oxide film 3 on the main surface of the hand by oxidizing
To form.

8) Approximately 7% aluminum with a particle size of approximately 5 μm
A paste containing 5% is screen-printed on the oxide film 3 to a thickness of about 10 μm and baked at 800 ° C. for 1 minute in a synthetic air atmosphere. By this firing, the aluminum particles in the paste react with the oxide film 3 and penetrate it, and then the n + layer 1
4, and penetrates through this, and p further reacts with another silicon substrate to form the aluminum silicon alloy layer 15 and the p + layer 1
And 3 are formed.

9) To form the second electrode 51, a paste containing 75% of silver particles is printed between the first electrode 15 and baked at 750 ° C. for 1 minute in a synthetic air atmosphere.

By this firing, the glass in the paste reacts with the oxide film 3 and penetrates it, and the silver particles in the paste are n.
A second electrode 51 is formed in ohmic contact with the + layer 14.

10) A TiO ₂ antireflection film 4 is formed on the surface of the oxide film by atmospheric pressure CVD method by 550Å.

When the solar cell element thus manufactured was measured for the minority carrier lifetime of the p-type silicon substrate by the light-receiving surface laser diode microwave method, no decrease was observed. It is considered that this is because the impurity source of the p + layer is aluminum.

Also in the above alloy reaction with an aluminum paste made of small aluminum particles or a paste obtained by mixing small aluminum particles in a silver paste, a good pn junction is formed between the metal electrode and the n-type conductive layer. It was confirmed that good ohmic characteristics were exhibited between the characteristics and the p-type silicon substrate.

Second Embodiment FIG. 3 is a perspective view showing the structure of the second embodiment of the present invention.

FIG. 4 is a sectional view showing the structure of the second embodiment of the present invention.

First, the structure of this embodiment will be described.

This embodiment uses an n-type silicon substrate whose conductivity characteristics are opposite to those of the p-type silicon substrate of the first embodiment. Since the first layer 13 is connected not only to the n + layer 14 that is the second layer but also to the n-type silicon substrate by the pn junction, the pn junction is located deeper than the other main surface. Can be formed. Therefore, there is an effect that the collection efficiency of the photo-generated charges of the n-type silicon substrate is increased.

Next, a method for manufacturing the solar cell element of this embodiment will be described.

The method of manufacturing the solar cell element of this embodiment is the same as that of the first embodiment except that the p-type silicon substrate is replaced by an n-type silicon substrate.

Third Embodiment FIG. 5 is a perspective view showing the structure of the third embodiment of the present invention.

FIG. 6 is a sectional view showing the structure of the third embodiment of the present invention.

First, the configuration of this embodiment will be described.

One main surface 11 which becomes the light receiving surface in the first embodiment.
A third layer, n + layer 16 and a third layer in contact therewith
This is an example in which the main electrode 52 of FIG. In this embodiment, n +
Due to the layer 16 and the third main electrode 52 in contact therewith, the efficiency of collecting electron-hole charges near one main surface 11 is increased for a p-type silicon substrate having a short minority carrier lifetime, and the electromotive force and This has the effect of improving the photogenerated current.

Next, a method for manufacturing the solar cell element of this embodiment will be described.

In the manufacturing method of the first embodiment, the third main electrode 52 and the n + layer 14 formed on one main surface are K
Light is incident on the silver paste used for forming the second main electrode 51 before or after the second main electrode 51 is formed without being removed by etching with OH and further being not oxidized again. Printing is performed on the oxide film 2 formed on the main surface 11, and the oxide film 2 is formed through ohmic contact with the n + layer 16 under the same heat treatment condition.

As described above, according to this embodiment, the n + layer and the p + layer can be separated by the screen printing technique with the pn junction characteristic, and the p + layer and the electrode can be formed at the same time. In addition, the amount of expensive silver paste required for electrode formation can be reduced, and the conversion efficiency can be increased even for a p-type silicon substrate with a short minority carrier life, thereby improving conversion performance and economy. It will be possible.

[0048]

According to the present invention, the aluminum and the silicon substrate coated with the silicon oxide film are subjected to an alloy reaction to cause a first main electrode composed of an aluminum-silicon alloy layer and the outside of the first main electrode. A first layer, which is a p + type silicon regrowth layer in which aluminum is solid-dissolved on the silicon surface, is formed at the same time, and a paste containing aluminum is printed on the silicon oxide film to form a p + type silicon regrowth layer and an n layer. Can be separated while having the pn junction characteristic, so that the manufacturing process can be reduced.

By using the n-type silicon substrate, the pn junction can be formed at a position deeper than the other main surface, so that the efficiency of collecting photogenerated charges is increased and the efficiency of conversion is increased.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view showing the configuration of the first embodiment of the present invention.

FIG. 3 is a perspective view showing a configuration of a second exemplary embodiment of the present invention.

FIG. 4 is a sectional view showing a configuration of a second exemplary embodiment of the present invention.

FIG. 5 is a perspective view showing a configuration of a third exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view showing the configuration of a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon solar cell element 2 Oxide film 3 Oxide film 4 TiO ₂ film 11 One main surface which becomes a light-receiving surface 12 The other main surface 13 p + type conductive 1st layer 14 n + layer 15 1st main electrode 16 n + Layer 51 Second electrode 52 Third electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuaki Uchida 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi factory (72) Inventor Yasuhiro Kida 3-chome, Hitachi City, Ibaraki Prefecture No. 1 Incorporated Hitachi Ltd. in Hitachi factory (72) Inventor Kimio Hatsumi 3-1-1 1-1 Saiwaicho, Hitachi, Ibaraki Incorporated Hitachi Ltd. in Hitachi factory (72) Inventor Tadao Asahi Hitachi, Ibaraki Prefecture 3-1, 1-1 Sachimachi, Hitachi, Ltd. Hitachi factory (56) References JP-A-3-165578 (JP, A) JP-A-60-227483 (JP, A)

Claims (1)

[Claims] 1. A light-receiving surface of a p-type or n-type silicon substrate
On the opposite side, the back surface, the surface concentration is 1 × 10 ¹⁹ / cm ^{3 or} less
A step of forming a lower n-type conductive layer by phosphorus diffusion , a step of forming an oxide film on the surface of the n-type conductive layer, and an aluminum paste electrode pattern on the surface of the oxide film.
Calcined by SCREEN printing, the oxide film and the n-type
Ari mini um silicon alloy layer penetrating the conductive layer
P-type silicon having a solid solution of a first electrode and aluminum
The step of forming a regrowth layer, and the silver paste on the surface of the oxide film is screened to an electrode pattern.
Printed and fired to penetrate the oxide film and conduct the n-type conductivity.
Production of the silicon solar cell element and a step of forming a second electrode layers and ohmic contact, the
Way .