JP3193287B2 - Solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell, and more particularly to a crystalline silicon solar cell having high photoelectric conversion efficiency.

[0002]

2. Description of the Related Art Conventionally, in this type of crystalline silicon solar cell, in order to enhance photoelectric conversion efficiency, a back surface (substrate back surface) opposite to a light incident surface (light receiving surface) of a silicon semiconductor substrate is provided. In the part where the majority carrier is taken out,
Between the back surface of the substrate and the back electrode provided on the back surface of the substrate, a silicon oxide film layer and a plurality of portions of the silicon oxide film layer are penetrated to have the same conductivity type as the semiconductor substrate and a higher dopant concentration. A structure in which a crystalline silicon semiconductor layer (also referred to as a “microcrystalline silicon film”) is provided (see Japanese Patent Application Laid-Open No. 4-192569).

The structure of such a conventional solar cell is shown in FIG.
As shown in FIG. 1, an N-type silicon semiconductor layer 12 is formed on the light-receiving surface side of a P-type silicon semiconductor substrate 11. N
The silicon semiconductor layer 12 is covered with a silicon oxide film layer 13, and the silicon oxide film layer 13 is covered with an antireflection film layer 14.

[0004] The grid electrode 15 is formed of the antireflection film layer 1.
4 is connected to the N-type silicon semiconductor layer 12 through the silicon oxide film layer 13, and a current is taken out through the grid electrode 15.

The back surface of the P-type silicon semiconductor substrate 11 is covered with a silicon oxide film layer 16, and a P ⁺ type (high concentration P-type) microcrystalline silicon semiconductor layer 18 covers the silicon oxide film layer 16. And is connected to the back surface of the P-type silicon semiconductor substrate 11 through a plurality of portions of the silicon oxide film layer 16. Further, the P ⁺ type microcrystalline silicon semiconductor layer 18 is covered with a back electrode 19. The current on the back surface is extracted from the P-type silicon semiconductor substrate 11 via the P ⁺ -type microcrystalline silicon semiconductor layer 18.

In this structure, surface defects of the P-type silicon semiconductor substrate 11 are inactivated by the silicon oxide film layer 16 on the rear surface of the substrate, and recombination of carriers is suppressed. Further, an internal electric field is formed between the P ⁺ -type microcrystalline silicon semiconductor layer 18 and the P-type silicon semiconductor substrate 11, and the minority carriers out of the carriers generated by the internal electric field near the rear surface of the substrate enter the semiconductor substrate. After being pushed back, the majority carriers are led out to the electrode side (hereinafter, referred to as “back surface field effect”), thereby increasing the photoelectric conversion efficiency.

[0007]

As a method of forming the solar cell having the conventional structure, a silicon oxide film layer 16 is formed on the back surface of a silicon substrate by using a thermal oxidation method or a chemical vapor deposition method (CVD method). Thereafter, a plurality of openings are formed in the silicon oxide film by photoetching, and then the plasma C
A method of forming the microcrystalline silicon semiconductor layer 18 by a VD method is general.

However, when a microcrystalline silicon semiconductor layer (microcrystalline silicon film) is deposited on a silicon oxide film, the quality of the microcrystalline silicon semiconductor layer deteriorates, and a sufficient back surface field effect cannot be obtained. However, there is a disadvantage that the improvement of the photoelectric conversion efficiency is limited.

The deterioration of the film quality of the microcrystalline silicon semiconductor layer is caused by exposing the silicon oxide film to plasma during the deposition of the microcrystalline silicon film, so that a part of oxygen atoms in the silicon oxide film is reduced in the microcrystalline silicon film. It is because it is taken into.

The present invention has been made in view of such circumstances, and provides a solar cell having a high back surface field effect and a high photoelectric conversion efficiency by forming a microcrystalline silicon semiconductor layer without deterioration in film quality. It is intended to be.

[0011]

According to the present invention, a silicon semiconductor substrate of a first conductivity type is formed, and a silicon semiconductor layer of a second conductivity type is formed on a light incident side surface of the silicon semiconductor substrate of the first conductivity type. A silicon oxide film layer formed on the opposite surface of the silicon semiconductor substrate of the first conductivity type on the light incident side; an insulating film layer formed on the silicon oxide film layer; A first-conductivity-type microcrystalline silicon semiconductor layer formed through a part of the insulating film layer and the silicon oxide film layer and in contact with the opposite surface of the first-conductivity-type silicon semiconductor substrate on the light incident side. A solar cell characterized by the following.

According to the present invention, since the insulating film layer is formed between the silicon oxide film layer and the first conductivity type microcrystalline silicon semiconductor layer, when forming the first conductivity type microcrystalline silicon semiconductor layer, Oxygen in the silicon oxide film is not taken into the first conductivity type microcrystalline silicon semiconductor layer,
Thereby, the photoelectric conversion efficiency of the solar cell can be improved.

In the present invention, the distinction between the first conductivity type and the second conductivity type is that if the first conductivity type is P-type, the second conductivity type is N.
If the first conductivity type is N-type, the second conductivity type means each P-type semiconductor.

Therefore, as the first conductivity type silicon semiconductor substrate in the present invention, any of P-type and N-type silicon semiconductor substrates can be used. Further, the present invention is not limited to a single crystal silicon semiconductor substrate, and a polycrystalline silicon semiconductor substrate can be used.

The thickness of the silicon semiconductor substrate is 100 μm to 60 μm because it is necessary to sufficiently absorb light.
It is preferable to use one having a thickness of about 0 μm.

In the present invention, the semiconductor used for the silicon semiconductor layer of the second conductivity type is N-type if the first conductivity type is P-type, and P-type if the first conductivity type is N-type. Semiconductors can be used. The thickness of the silicon semiconductor layer is preferably formed to be about 0.05 μm to 1 μm.

As the silicon oxide film layer in the present invention, an SiO ₂ film is usually preferably 10 nm to 100 nm.
m.

The insulating film layer of the present invention is provided to prevent oxygen in the silicon oxide film from being taken into the first conductivity type microcrystalline silicon semiconductor layer. Therefore, the insulating film used for the insulating film layer needs to be made of a material not containing oxygen as a main component. Further, it is preferable that the insulating film is formed of a transparent and hydrogen-containing material such as silicon oxynitride or silicon hydride. When the insulating film layer is formed of a transparent insulating film, light transmitted through the first conductive type silicon semiconductor substrate is reflected by the transparent insulating film and returned to the inside of the first conductive type silicon semiconductor substrate again, and photoelectric conversion is performed. (This is called the “light confinement effect”).

In the case where the insulating film layer is formed of an insulating film containing hydrogen, hydrogen is contained in the insulating film, so that hydrogen is defective at the interface between the silicon oxide film and the first conductivity type silicon semiconductor substrate. To improve the interface characteristics (this is referred to as “passivation effect”).

Therefore, when the insulating film used for the insulating film layer is formed of a transparent insulating film made of a material containing hydrogen such as silicon oxynitride, the above-mentioned “light confinement effect” and “passivation effect” are not obtained. Can be obtained simultaneously.

As the material used for the insulating film layer, any material can be used as long as it is transparent and contains hydrogen. However, in order to obtain a high photoelectric conversion efficiency, hydronitridation is required. It is most suitable to use silicon. When the thickness of this insulating film layer is 10 nm or less, the effect as an insulating film is reduced.
A thickness of at least nm is required, but if it is more than this, there is no particular limitation on the film thickness.

This insulating film layer can be formed by various methods such as a plasma CVD method, a normal pressure CVD method and a low pressure CVD method. For example, when an insulating film is formed by an RF plasma CVD method, SiH ₄ , Si
Gases such as H ₂ Cl ₂ , SiCl ₄ , NH ₃ , and N ₂ can be used. However, when a gas containing hydrogen atoms is used, hydrogen atoms are generated when an insulating film is formed, and these are taken into the film. Because the above-mentioned passivation effect is obtained,
It is preferable to use a gas containing a hydrogen element such as SiH ₄ , SiH ₂ Cl ₂ , and NH ₃ .

In general, the quality of the formed insulating film greatly differs depending on the type of the CVD method used. Various flow rates of the source gas may be employed depending on the CVD apparatus. For example, SiH ₄ , NH ₃ , N ₂ may be used as the source gas.
Is used, the flow rate ratio of the source gas is NH ₃ / Si
It is desirable to set H ₄ to 1 to 2. Since N ₂ is used as a carrier gas, its flow rate may be set as appropriate.

For example, when an insulating film is formed by an RF plasma CVD method, the temperature of the semiconductor substrate is set to 350 ° C. or less when a gas containing hydrogen atoms is used as a flow gas when forming the insulating film. As the RF power, various types of power are set according to the size of the device. In terms of power density (power per unit area of the electrode), 200 mW /
It is desirable to set to about cm ² .

As the semiconductor used for the first conductivity type microcrystalline silicon semiconductor layer (microcrystalline silicon film) in the present invention, the same conductivity type microcrystalline silicon semiconductor as the silicon semiconductor used for the substrate is used. That is, a P-type microcrystalline silicon semiconductor is used if the silicon semiconductor substrate is a P-type, and an N-type microcrystalline silicon semiconductor is used if the silicon semiconductor substrate is an N-type. The microcrystalline silicon semiconductor layer is preferably deposited to a thickness of about 100 nm to 250 nm.

In the above structure, the first conductivity type silicon semiconductor substrate is in contact with the silicon oxide film layer and the first conductivity type microcrystalline silicon semiconductor layer on the opposite surface to the light incident side, and is provided with the first conductivity type silicon semiconductor substrate. Higher than silicon semiconductor substrate and first
It is preferable to further form a first conductivity type silicon semiconductor layer containing an impurity at a lower concentration than the conductivity type microcrystalline silicon semiconductor layer.

According to this structure, holes located far from the first-conductivity-type microcrystalline silicon semiconductor layer in the first-conductivity-type silicon semiconductor substrate can be efficiently removed by the first-conductivity-type microcrystalline silicon semiconductor layer.
Since it is possible to extract the conductive type into the microcrystalline silicon semiconductor layer, the photoelectric conversion efficiency of the solar cell can be further increased.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. Note that the present invention is not limited to this.

[First Embodiment] FIG. 1 is an explanatory view showing a sectional structure of a first embodiment of a solar cell according to the present invention. FIG.
, The same components as those shown in the configuration diagram of the conventional solar cell in FIG. 4 are denoted by the same reference numerals.

As shown in this figure, in the solar cell of the present invention shown as the first embodiment, an N-type silicon semiconductor layer 12 is formed on the light-receiving surface side of a P-type silicon semiconductor substrate 11. This N-type silicon semiconductor layer 12 is made of Si
It is covered with a silicon oxide film layer 13 made of O _2, and the silicon oxide film 13 is covered with an antireflection film layer 14.

The grid electrode 15 is formed of the anti-reflection coating layer 1.
4 is connected to the N-type silicon semiconductor layer 12 through the silicon oxide film layer 13, and a current is taken out through the grid electrode 15.

The back surface of the P-type silicon semiconductor substrate 11 has S
It is covered with a silicon oxide film layer 16 made of iO _2, and the silicon oxide film layer 16 is covered with a silicon oxynitride film layer 17.

The P ⁺ -type (high-concentration P-type) microcrystalline silicon semiconductor layer 18 covers the silicon oxynitride film layer 17 and includes a plurality of portions of the silicon oxynitride film layer 17 and the silicon oxide film layer 16. And is connected to the back surface of the P-type silicon semiconductor substrate 11.

Further, the P ⁺ type microcrystalline silicon semiconductor layer 1
8 is covered by a back electrode 19. The current on the back surface is extracted from the P-type silicon semiconductor substrate 11 via the P ⁺ -type microcrystalline silicon semiconductor layer 18.

FIG. 2 is a manufacturing flowchart showing the method of manufacturing the solar cell of the first embodiment. In the solar cell according to the first embodiment, first, after cleaning the single-crystal P-type silicon semiconductor substrate 11 (the step of cleaning the P-type silicon semiconductor substrate), anisotropic etching is performed so that the surface becomes uneven (different from the first embodiment). Step of anisotropic etching). A P-type silicon semiconductor substrate 11 having a thickness of about 600 μm was used. The P-type silicon semiconductor substrate 11 is not limited to a single-crystal P-type silicon semiconductor substrate, but may be a polycrystalline P-type silicon semiconductor substrate.

Next, an N-type silicon semiconductor layer 12 is formed on the light-receiving surface of the P-type silicon semiconductor substrate 11 by diffusing phosphorus by vapor phase diffusion using phosphorus oxychloride (POCl ₃ ) (PN junction formation). Process). In this embodiment, N
The type silicon semiconductor layer 12 was formed with a thickness of about 0.3 μm.

Subsequently, the back surface of the P-type silicon semiconductor substrate 11 is etched to remove the N-type silicon semiconductor layer formed on the back surface (back surface etching step). In the case where the N-type silicon semiconductor layer 12 is formed by using a coating solution such as a silicon oxide film glass solution to which phosphorus is added and diffusing it to only the light receiving surface of the P-type silicon semiconductor substrate 11, It is not necessary to remove the N-type silicon semiconductor layer on the back surface.

Subsequently, a silicon oxide film layer 13 and a silicon oxide film layer 16 are formed by a thermal oxidation method (step of forming a silicon oxide film layer). In this embodiment, the silicon oxide film layer 1
Nos. 3 and 16 were formed to a thickness of about 20 nm. Next, an anti-reflection film layer 14 made of a silicon nitride film is formed by plasma CVD.
(An anti-reflection film layer forming step). A titanium oxide (TiO ₂ ) film, an alumina (Al ₂ O ₃ ) film, or the like can be used as the anti-reflection film layer 14.

Next, a silicon oxynitride film layer 17 is formed on the silicon oxide film layer 16 (step of forming a backside silicon oxynitride film layer). This silicon hydronitride film layer 17
Is formed by RF plasma CVD, using SiH ₄ , NH ₃ , and N ₂ as source gases at a flow rate of 10
SCCM, 15 SCCM, 50 SCCM, reaction pressure 0.75 To
rr, the substrate temperature was 350 ° C., the RF power was 100 W, and the film was deposited to a thickness of 200 nm.

For the formation of the silicon oxynitride film layer 17,
In addition to the plasma CVD method, there are methods such as a normal pressure CVD method and a low pressure CVD method, and any of these methods may be used, but a gas containing a hydrogen element such as SiH ₄ , SiH ₂ Cl ₂ , NH _{3 as} a source gas is used. It is preferable to use

Next, after processing the silicon oxynitride film layer 17 and the silicon oxide film layer 16 on the rear surface side by photo-etching, P ^{+ is formed} by plasma CVD.
A type microcrystalline silicon semiconductor layer 18 is formed to cover the silicon oxynitride film layer 17 and the P-type silicon semiconductor substrate 11 (step of forming a P ⁺ type microcrystalline silicon semiconductor layer). In this embodiment, the P ⁺ type microcrystalline silicon semiconductor layer 18
It was formed with a thickness of about 00 nm. Then, the back electrode 19 is formed by evaporating a metal such as aluminum or silver by a vacuum evaporation method so as to cover the P ⁺ -type microcrystalline silicon semiconductor layer 18.

Next, after processing the silicon oxide film layer 13 and the antireflection film 14 on the light receiving surface side by using a photoetching method, a metal is deposited in the order of titanium, palladium, and silver. Finally, by performing lift-off, the grid electrode 15 is formed (a step of forming front and back electrodes).

Table 1 is a table comparing the characteristics of the solar cell of the first embodiment of the present invention and the conventional solar cell shown in FIG. The measurement of solar cell characteristics is performed using a solar simulator (A
M1.5 global, 100 mW / cm ² ) and the temperature of the solar cell was set to 25 ° C.

The difference between the two is that the silicon oxynitride film layer 17 exists between the silicon oxide film layer 16 and the P ⁺ -type microcrystalline silicon semiconductor layer 18 in the solar cell according to the first embodiment of the present invention. That is the point.

[0045]

[Table 1] As is clear from Table 1, the efficiency of the solar cell is improved by the present invention.

Second Embodiment FIG. 3 is an explanatory view showing a sectional structure of a second embodiment of the solar cell according to the present invention. FIG.
In FIG. 1, the same components as those shown in the configuration diagram of the solar cell of the first embodiment in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in this figure, the solar cell of the present invention shown as the second embodiment has basically the same structure as the solar cell shown in the first embodiment, but the solar cell of the first embodiment The difference is that a high-concentration P-type silicon semiconductor layer 20 is formed on the back side of the P-type silicon semiconductor substrate 11.

Although the P-type silicon semiconductor layer 20 has a lower concentration than the P ⁺ -type microcrystalline silicon semiconductor layer 18,
It contains impurities at a higher concentration than the p-type silicon semiconductor substrate 11, and acts to spread the back surface field effect of the p ⁺ -type microcrystalline silicon semiconductor layer 18 toward the inside of the p-type silicon semiconductor substrate 11.

That is, in the solar cell according to the second embodiment, holes located far from the P ⁺ -type microcrystalline silicon semiconductor layer 18 inside the P-type silicon semiconductor substrate 11 are efficiently used for the P ⁺ -type microcrystalline silicon semiconductor layer 18. It can be extracted into the crystalline silicon semiconductor layer 18, thereby increasing the photoelectric conversion efficiency.

In the first and second embodiments, the solar cell having a P-type silicon substrate has been described. However, the present invention can be applied to a solar cell having an N-type silicon substrate. In that case, an N-type microcrystalline silicon semiconductor layer is used as the back surface electric field layer.

[0051]

As described above, according to the solar cell of the present invention, the insulating film layer is formed between the silicon oxide film layer on the back surface and the microcrystalline silicon semiconductor layer. Oxygen in the oxide film is not taken in, whereby deterioration of the film quality of the microcrystalline silicon semiconductor layer can be suppressed and photoelectric conversion efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a cross-sectional structure of a first embodiment of a solar cell according to the present invention.

FIG. 2 is a manufacturing flowchart showing a method for manufacturing the solar cell of the first embodiment.

FIG. 3 is an explanatory view showing a sectional structure of a second embodiment of the solar cell according to the present invention.

FIG. 4 is an explanatory view showing a cross-sectional structure of a conventional solar cell.

[Explanation of symbols]

REFERENCE SIGNS LIST 11 P-type silicon semiconductor substrate 12 N-type silicon semiconductor layer 13, 16 silicon oxide film layer 14 antireflection film layer 15 grid electrode 17 silicon oxynitride film layer 18 P ⁺ -type microcrystalline silicon semiconductor layer 19 back electrode 20 P-type silicon Semiconductor layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Komatsu 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Inside Sharp Corporation (72) Inventor Tasuke Shindo 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp (56) References JP-A-6-310740 (JP, A) JP-A-4-192569 (JP, A) JP-A-6-169096 (JP, A) JP-A-60-175464 (JP, A A) JP-A-5-235385 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (5)

(57) [Claims] 1. A solar cell comprising a silicon semiconductor substrate of a first conductivity type and a silicon semiconductor layer of a second conductivity type formed on a light incident side surface of the silicon semiconductor substrate of the first conductivity type. A silicon oxide film layer formed on the surface opposite to the light incident side of the conductive silicon semiconductor substrate; an insulating film layer formed on the silicon oxide film layer; and an insulating film layer and a silicon oxide film formed on the insulating film layer. A solar cell comprising a first conductivity type microcrystalline silicon semiconductor layer formed through a part of the film layer and in contact with a surface opposite to the light incident side of the first conductivity type silicon semiconductor substrate; . A first conductive type silicon semiconductor substrate formed on a surface opposite to the light incident side of the first conductive type silicon semiconductor substrate in contact with the silicon oxide film layer and the first conductive type microcrystalline silicon semiconductor layer; A first impurity containing an impurity having a higher concentration than the semiconductor substrate and a lower concentration than the microcrystalline silicon semiconductor layer of the first conductivity type;
2. The solar cell according to claim 1, further comprising a conductive silicon semiconductor layer. 3. The solar cell according to claim 1, wherein the insulating film layer comprises a transparent insulating film layer. 4. The solar cell according to claim 1, wherein said inter-insulating layer contains hydrogen. 5. The solar cell according to claim 1, wherein the inter-insulating layer is formed of a silicon oxynitride film layer.