JP2614561B2 - Photovoltaic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device having a semiconductor junction formed by an amorphous semiconductor and a single crystal semiconductor or a polycrystalline semiconductor.

[0002]

2. Description of the Related Art In recent years, devices using thin film semiconductors as photovoltaic devices have been actively developed.

[0003] Since this semiconductor is used in a thin film state, the crystalline state basically uses an amorphous or polycrystalline material. This does not require an ordered array of crystal structures such as a single crystal, so that the area can be easily increased and the basic conditions of a photovoltaic element such as a solar cell can be sufficiently satisfied.

However, these semiconductors, on the other hand,
Since the crystal structure is not ordered, it contains a large amount of dangling bonds in the crystal structure, and cannot be said to be a high quality material as compared with a single crystal semiconductor.

In order to solve these problems, there has recently been proposed a photovoltaic element in which a photoactive layer is formed from an amorphous semiconductor and a crystalline semiconductor.

FIG. 3A is a diagram showing a first conventional example of a photovoltaic element constituted by a single crystal semiconductor and an amorphous semiconductor, which is currently proposed. Also in the figure
(b) is a band profile diagram of the photovoltaic element. The same reference numerals in the figures denote the same materials.

[0007] The band profile diagrams of the conventional example and the device of the present invention used in the present specification are diagrammatically considered in consideration of the characteristics and the like of the device, and are not proved but are explained. This is adopted for ease of use.

In the figure, (31) is a transparent electrode on the light incident side of the present photovoltaic element, (32) is an amorphous semiconductor made of p-type amorphous silicon, and (33) is an n-type single crystal semiconductor. Specifically, the back electrode is made of single crystal silicon, and (34) is a back electrode made of metal.
This photovoltaic element consists of an amorphous semiconductor (32) and a single crystal semiconductor.
One semiconductor junction is formed with (33).

Further, as shown in FIG.
The surface on the light incident side of 3) is processed to have an uneven shape (c) in order to reduce loss due to reflection of incident light on the surface.

[0010] As such a processing method, the surface of a single crystal semiconductor is initially treated with 0.25 mol of sodium hydroxide (liquid temperature of 8%).
(5 ° C.) and exposure to isopropyl alcohol to easily form a desired uneven shape.

In the following, the other conventional example and the element of the present invention are also subjected to unevenness processing by the same method.

According to the profile shown in FIG. 1B, this photovoltaic element has an internal electric field (A) formed of p-type amorphous silicon (32) and n-type single-crystal silicon (33). The incident light is separated into electrons and holes due to (bending of a large band) and is taken out.

The photogenerated carriers in such a portion can be efficiently extracted to the outside by the two factors of the traveling due to the drift due to the internal electric field (a) and the traveling due to the diffusion. In particular, the carrier travels in such a portion largely due to the former drift.

However, in the portion (b) of FIG. 1B, that is, the portion corresponding to the bulk of single crystal silicon, there is no bending of the band and there is almost no internal electric field. Therefore, in such a portion, the photogenerated carriers do not travel due to the drift but only travel due to the diffusion, and thus sufficient external extraction of the photogenerated carriers cannot be achieved.

In particular, in the case of diffusion, the photogenerated carriers travel in such a manner that both electrons and holes travel uniformly in both the direction of the transparent electrode (31) and the direction of the back electrode (34). Therefore, recombination of photogenerated carriers frequently occurs in the back electrode.

Therefore, as a conventional measure in such a case,
A second conventional photovoltaic element having a BSF (back surface field) structure as shown in FIG. 4 has been tried. The same reference numerals in the drawing denote the same materials as in FIG.

The feature of this device is that the back electrode (3) is formed by the diffusion of photogenerated carriers from the bulk (b) described above.
In order to prevent recombination in 4), between the single crystal silicon (33) and the back electrode (34), the single crystal silicon (33) and the n-type amorphous semiconductor (35 ), Specifically, that amorphous silicon is interposed.

Therefore, in the present embodiment, the first semiconductor junction between the amorphous semiconductor (32) and the single crystal semiconductor (33) is formed between the single crystal silicon (33) and the amorphous semiconductor (35). A second semiconductor junction is formed between them.

As a result, of the photo-generated carriers that are deeper when viewed from the incident side, holes are prevented from being diffused by the largely protruding portion (d) of the valence band of the amorphous semiconductor (35). On the other hand, electrons are hardly blocked by the extent of the protruding portion (e) to the conductive band even when the amorphous semiconductor (35) is used. 34) and can be extracted outside.

The photovoltaic element having the BSF structure is described in detail in, for example, "Solar Power Generation", pp. 396-398, 1980 (Moritakita Shuppan).

[0021]

The structure in which the n-type amorphous silicon (35) is provided as in the second prior art is a back electrode (34).
Is effective in reducing the recombination of photogenerated carriers at the same time, while n-type amorphous silicon (35) is interposed between the n-type single crystal silicon (33) and the back electrode (34) This means that a new interface is formed between the n-type single crystal silicon (33) and the n-type amorphous silicon (35).

Since this interface is formed by ones having different crystal structures, the interface is formed by an interface formed by ordinary single crystal semiconductors or an interface formed by amorphous semiconductors. In contrast, a large number of interface states are generated based on the mismatch of the crystal structure.

In addition, the film quality of an amorphous semiconductor is generally significantly deteriorated by doping with a conductivity type determining impurity. This is attributable to the conductivity-type-determining impurities in the case of a semiconductor junction using n-type amorphous silicon (35) as one of the amorphous semiconductors simultaneously containing the conductivity-type-determining impurities. This also results in an increase in the interface state, which increases the recombination of the photogenerated carriers.

Therefore, the method of preventing recombination of photogenerated carriers by the so-called BSF structure in which the n-type amorphous silicon (35) is provided has both advantages and disadvantages. This effect cannot be sufficiently achieved, and the effect is small compared to the complicated manufacturing process for providing the n-type amorphous silicon (35).

The same is true even between an amorphous semiconductor and a polycrystalline semiconductor.

[0026]

A feature of the photovoltaic element of the present invention is that a photovoltaic element arranged on the light incident side composed of an amorphous semiconductor having a reverse conductivity type and a crystalline semiconductor has a relation opposite to each other. And a second semiconductor junction disposed on the light transmission side, the second semiconductor junction comprising the crystalline semiconductor and an amorphous semiconductor having the same conductivity type as the crystalline semiconductor. An intrinsic amorphous semiconductor containing hydrogen is interposed between the amorphous semiconductor and the crystalline semiconductor of the second semiconductor junction.

[0027]

According to the present invention, an intrinsic amorphous semiconductor containing hydrogen is interposed between the crystalline semiconductor and the amorphous semiconductor having the same conductivity type to constitute the second semiconductor junction. This reduces recombination of photogenerated carriers at the interface at the second semiconductor junction, and increases the number of photogenerated carriers that can be extracted to the outside of the photovoltaic element.

That is, the recombination of photo-generated carriers can be suppressed by interposing an intrinsic amorphous semiconductor having a good film quality between the conductive crystalline semiconductor and the conductive amorphous semiconductor. It becomes possible.

Further, as the intrinsic amorphous semiconductor, 7 to
By using a material containing 30 atomic% or more of hydrogen, such a hydrogen is generated during the device formation by dangling bonds of interface states or in an interface state existing between grain boundaries in a polycrystalline semiconductor. Act to compensate for As a result, photogenerated carriers can be more efficiently taken out of the photovoltaic element.

[0030]

FIG. 1 (a) is a sectional view showing the structure of a photovoltaic device according to the present invention, and FIG. 1 (b) is a band profile diagram for explaining an internal electric field and the like of the photovoltaic device. is there.

In the figure, (1) is a transparent electrode made of indium tin oxide, tin oxide, zinc oxide or the like on the light incident side, and (2) is a p-type amorphous semiconductor made of amorphous silicon (film thickness). 30 ~
200 °), (3) is a single-crystal semiconductor (thickness: 0.1 μm to 100 μm) made of n-type single-crystal silicon, (4) is an amorphous semiconductor containing hydrogen, which is a feature of the present invention. (5) is an n-type amorphous semiconductor made of amorphous silicon (film thickness: 50 to 1 mm).
000 °) and (6) are back electrodes made of metals such as aluminum, silver and titanium.

In this device, a first semiconductor junction is formed by the p-type amorphous semiconductor (2) and the n-type single crystal semiconductor (3), and the n-type single crystal semiconductor (3) and the n-type amorphous semiconductor In the case of the semiconductor (5), a second semiconductor junction is formed via the amorphous semiconductor (4).

In this embodiment, the single-crystal semiconductor (3) is used as the material for forming the first and second semiconductor junctions. However, the operation and effect of the present invention are as follows. Even when polycrystalline silicon is used, it can be obtained in exactly the same manner.

Except for the amorphous semiconductor (4) containing hydrogen, it is a conventionally known film or bulk semiconductor material. Table 1 shows typical conditions for forming the used amorphous semiconductors (2), (4) and (5) by the plasma CVD method.

[0035]

[Table 1]

The hydrogen content of the amorphous silicon (4) containing hydrogen formed under the conditions shown in Table 1 is 7
-30 atomic%.

An amorphous semiconductor which is a feature of the present invention
(4) is not limited to the amorphous silicon used in this example, but may be amorphous silicon carbide, amorphous silicon germanium, or even amorphous silicon nitride. As a typical forming gas by the plasma CVD method when using such a film, silane (SiH ₄ ) gas and methane (CH ₄ ) gas are used in amorphous silicon carbide, and amorphous silicon germanium is used in amorphous silicon germanium. Silane (SiH ₄ ) gas and germane (GeH ₄ ) gas are used, and silane (SiH ₄ ) gas and ammonia (NH ₃ ) gas are used for amorphous silicon nitride.

The state of the internal electric field in the photovoltaic device will be described with reference to the band profile diagram of FIG.
First, the p-type amorphous semiconductor (2) and the single crystal semiconductor (3) on the light incident side
A large internal electric field (a) (bending of a large band in the figure) formed by the single crystal semiconductor (3) and the n-type amorphous semiconductor (5) with the intrinsic amorphous semiconductor (4) interposed There is a relatively small internal electric field (b) that is formed. This portion of the internal electric field (b) has the above-mentioned BSF structure.

According to the present invention, since the intrinsic amorphous semiconductor (4) is interposed, an interface generated in the case of direct contact between the single crystal semiconductor (3) and the n-type amorphous semiconductor (5) is obtained. The level is greatly reduced.

FIG. 2 is a photosensitivity spectrum diagram of the photovoltaic device (21) of the present invention.

When the present device is manufactured, the light incident surface of the single crystal semiconductor (3) is provided with a concave / convex shape for reducing light reflection by the same method as described above. In this example, the height of the uneven shape is 1 to 10 μm.

Incidentally, (22) in FIG. 2 is a conventional photovoltaic element, which is not provided with amorphous silicon (4) containing hydrogen as compared with the photovoltaic element of the present invention, and This is a structure in which the surface of the element has no irregularities. (23) does not include amorphous silicon (4), which is a feature of the present invention, although the surface of the element is provided with an uneven shape, and a single crystal semiconductor (3) and an n-type amorphous semiconductor (5) are used. This is a conventional photovoltaic element in direct contact.

According to the figure, the conventional photovoltaic element (22) and
In the case of (23), the photovoltaic element (23) shows larger photosensitivity characteristics in the wavelength region from 600 nm to 1200 nm due to the provision of the unevenness on the surface. However, in the photovoltaic element (21) of the present invention, the conventional photovoltaic element (23)
Compared to the above, the light sensitivity characteristics are further improved in the long wavelength light region.

In particular, it should be noted here that the photovoltaic device (21) of the present invention has a light wavelength ranging from a short wavelength region to a long wavelength region of about 800 nm as compared with the conventional photovoltaic device (23). While keeping the sensitivity characteristics almost the same level,
In addition, the improvement of the photosensitivity characteristics with long wavelength light is observed.

These results indicate that, in the photovoltaic device of the present invention, light absorbed in a deep region as viewed from the light incident surface can be efficiently extracted as a carrier.

Incidentally, in the device structure of the embodiment used in the description of the photovoltaic device of the present invention, in addition to the above-described second semiconductor junction, those having different crystal structures may be used as junctions.
There is a first semiconductor junction. Specifically, a p-type amorphous semiconductor
This is a semiconductor junction composed of (2) and a single crystal semiconductor (3).

Although an interface level similar to that of the second semiconductor junction is generated in this junction, in such a portion,
Since the internal electric field (a) is very large, there is no need to consider the problem of preventing recombination due to the diffusion phenomenon of carriers, which was attempted by the present invention. This is because most of the carriers can be taken out to the outside.

However, in order to sufficiently reduce the recombination of photogenerated carriers at the interface level generated at the first semiconductor junction, the intrinsic amorphous semiconductor used in the present invention must be a p-type amorphous semiconductor. It is effective to interpose between (2) and the single crystal semiconductor (3).

In the present embodiment, the amorphous semiconductor is formed by a plasma CVD method. However, the present invention is not limited to this. For example, a sputtering method, a vapor deposition method, Exhibits exactly the same effect even when an amorphous semiconductor formed by a photo-CVD method is used.

In the embodiment, n is a single crystal semiconductor.
Although the type was used, the present invention is not limited to this.
Needless to say, it may be a type. In this case, the amorphous semiconductor (2) may be n-type, and the amorphous semiconductor (5) may be p-type.

[0051]

In the photovoltaic device of the present invention, a conventional problem arises because an intrinsic amorphous semiconductor containing hydrogen is interposed between a crystalline semiconductor and an amorphous semiconductor having the same conductivity type. It is possible to reduce the interface state between the crystalline semiconductor and the amorphous semiconductor, and it is possible to efficiently take out photogenerated carriers as a photovoltaic element from the outside.

Therefore, according to the present device, it is possible to improve the light sensitivity characteristic of long-wavelength light without lowering the light sensitivity of short-wavelength light. Thereby, the open-circuit voltage and the fill factor of the photovoltaic element are improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a device structure and a band profile diagram for explaining an example of a photovoltaic device of the present invention.

FIG. 2 is a light sensitivity spectrum characteristic diagram of the photovoltaic element.

FIG. 3 is a cross-sectional view of an element structure for explaining a first conventional example photovoltaic element and a band profile diagram.

FIG. 4 is a cross-sectional view of an element structure for explaining a second conventional example of a photovoltaic element, and a band profile diagram.

[Explanation of symbols]

(2) p-type amorphous semiconductor (3) n-type single crystal semiconductor (4) hydrogen-containing amorphous semiconductor (5) n-type amorphous semiconductor

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-130671 (JP, A) JP-A-1-280367 (JP, A) JP-A-60-218880 (JP, A)

Claims (1)

(57) [Claims] 1. A first semiconductor device comprising: an amorphous semiconductor having a reverse conductivity type; and a single-crystal semiconductor or a polycrystalline semiconductor (hereinafter, referred to as a crystalline semiconductor). Semiconductor junction, and the crystalline semiconductor,
A second semiconductor junction disposed on the light transmitting side, the second semiconductor junction comprising an amorphous semiconductor having the same conductivity type as the crystalline semiconductor; and the second semiconductor junction of the second semiconductor junction A photovoltaic element, wherein an intrinsic amorphous semiconductor containing hydrogen is interposed between the crystalline semiconductor and the crystalline semiconductor.