JP3258680B2 - Photovoltaic device - 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 for converting light energy into electric energy.

[0002]

2. Description of the Related Art One of the characteristics for evaluating the characteristics of a photovoltaic device is a conversion efficiency which indicates a conversion ratio from light energy to electric energy.

Conventionally, as a method for improving the conversion efficiency, a method of absorbing incident light as much as possible by increasing a film thickness of a semiconductor layer which plays a central role in photoelectric conversion, or a method of originally converting light into light. Since it is necessary to use at least one electrode as a transparent electrode because it is a device to be used, it is necessary to reduce the electrical resistance by making the material of the transparent electrode high quality, and to take out the optical carrier. That reduce the loss of

[0004] However, these methods cannot be fundamentally solved because each of them is a matter to be designed in consideration of many factors.

On the other hand, a method which is particularly effective for improving the conversion efficiency and has been practiced is a method of providing irregularities on a supporting substrate used in a photovoltaic device.

FIG. 3 is a diagram showing a conventional element structure of a photovoltaic device having irregularities on a supporting substrate. In the figure, (31) is a translucent substrate made of glass or the like, (32) is a surface-side transparent electrode made of indium tin oxide or the like provided with unevenness on one surface of one electrode of the photovoltaic device, (33) ) Is a photoelectric conversion layer for converting light energy into electric energy, and (34) is a back electrode made of metal or the like.

The conventional photoelectric conversion layer (33) uses a well-known amorphous silicon film, and its layer structure is a p-type amorphous silicon film.
(33p), i-type amorphous silicon (33i) and n-type amorphous silicon (33n).

[0008] The operation mechanism of such a photovoltaic device is as follows.

Light (35) is applied to the photovoltaic device by the light transmitting substrate (3).
When incident from the side of 1), the light (35) passes through the front-surface-side transparent electrode (32) and enters the photoelectric conversion layer (33). At this time, the light (35) is scattered by irregularities on the surface (32a) of the front-side transparent electrode (32), even if it is light that has been incident perpendicular to the surface of the translucent substrate (31) until then. This scattering causes the traveling direction to be bent.

As a result, the light (35) is transmitted to the photoelectric conversion layer (3).
3), the light passes obliquely, and the substantial optical path length becomes longer. This acts to increase the amount of light (35) absorbed in the photoelectric conversion layer (33), and can improve conversion efficiency. In particular, such an effect is effective for increasing the absorption efficiency of long wavelength light.

Regarding such technical contents, for example, Technica
l Digest of the International PVSEC-5, Kyoto, Japan,
1990, pp 261-264.

However, the surface (32a) of the front transparent electrode (32)
Although the method of making the surface irregularities surely improves the conversion efficiency, it does not yet provide sufficient light absorption. This is because long-wavelength light cannot be sufficiently absorbed by one pass of light from the translucent substrate (31) to the photoelectric conversion layer (33).

In order to solve such a problem, the light (35) reaching the back electrode (34) is reflected by the back electrode (34), passes through the photoelectric conversion layer (33) again, and then is incident. It is necessary to increase the effective optical path length by causing the reflected light to be reflected many times between the front surface side transparent electrode (32) and the back surface electrode (34).

[0014]

In order to efficiently perform such a large number of reflections, it is conceivable that the surface of the back electrode (34) is also provided with an uneven shape for scattering light.

However, even if irregularities are formed on the surface of the front side transparent electrode (32) as shown in FIG. 3, the degree of the irregularities becomes gradually less due to the photoelectric conversion layer (33) formed later and the like. Until (34), the shape is not sufficiently uneven.

On the other hand, an extremely large uneven shape is provided on the surface of the front side transparent electrode (32) so that the unevenness can maintain a sufficient degree of unevenness even after the photoelectric conversion layer (33) and the like are formed. However, p-type amorphous silicon (33p) and n-type amorphous silicon (33n) used in the photoelectric conversion layer (33) can be considered.
All have a thickness of at most several hundreds of degrees, so if the degree of unevenness of the surface-side transparent electrode (32) as the base is too large, these films will not be in a film state but in an island state. As a result, the function as the photoelectric conversion layer (33) is rapidly reduced.

[0017]

The feature of the photovoltaic device of the present invention is that a transparent electrode on a front surface side is provided on a transparent substrate.
It is made of a photoelectric conversion layer, a back transparent electrode, and a conductive material.
In the photovoltaic device the light reflecting layer is formed by sequentially laminated that, Shi free of light scattering material to the back surface side transparent electrode in
In front of the transparent electrode containing the light scattering substance
The light reflecting layer is formed by being adhered .

[0018]

The light scattering material is contained in the transparent electrode on the back surface formed on the photoelectric conversion layer, so that light that has passed without being absorbed by the photoelectric conversion layer is positively absorbed by the light scattering material. The light can be scattered and light can be efficiently caused to travel again in the photoelectric conversion layer.

In particular, since this scattering causes light to be scattered in an unspecified direction, the scattered light can travel obliquely in the photoelectric conversion layer as described above, and absorption of long-wavelength light is effectively achieved. I can do it.

Further, since a light reflecting layer is formed on the back surface side transparent electrode containing the light scattering material on the film forming surface side, light not scattered by the light scattering material is reflected by the light reflecting layer. The light is reflected and travels again toward the photoelectric conversion layer. In addition, this light reflective layer is made of conductive material
Since it is a material, it also functions as a back electrode.

In particular, the light that has passed through the inside of the photoelectric conversion layer and has reached the transparent electrode on the back side is mainly long-wavelength light that is hardly absorbed in the photoelectric conversion layer in the first place. Light scattering due to the unevenness of the transparent electrode is insufficient, and a sufficiently long optical path length can be ensured in the photoelectric conversion layer by the scattering of the light scattering material in the rear transparent electrode of the present invention. 1

[0022]

FIG. 1 is an element structure diagram of an embodiment of the photovoltaic device of the present invention.

In the figure, (1) is a transparent substrate made of glass, quartz, etc., and (2) is a transparent surface side made of tin oxide, indium tin oxide, etc. formed on the transparent substrate (1). Electrode (film thickness 5
(000 ° to 2 μm), the surface is provided with an uneven shape. (3) is a photoelectric conversion layer made of amorphous silicon,
p-type amorphous silicon carbide (film thickness 50 to 200)
Å) (3p), i-type amorphous silicon (film thickness 2000 Å to 1 μm)
m) (3i), and n-type amorphous silicon (film thickness of 50Å to 5
00Å) (3n). (4) is a first back side transparent electrode (thickness: about 5000 °) made of tin oxide, indium tin oxide, zinc oxide or the like. (5) is a light scattering material which is a feature of the present invention, and silver was used in this example.
FIG. 2 is an enlarged view showing the state of containing the light scattering substance (5).
The silver of this example is hemispherical and is scattered in the film plane. The diameter of this hemisphere is about 400 nm, and the distance between the islands is about 1500 nm between the centers of the hemisphere. (6) is a second back side transparent electrode (having a film thickness of about 1 μm) made of the same material as the first back side transparent electrode.
m) and (7) are light reflection layers made of silver or the like.

Therefore, the light-scattering substance in this embodiment is in a state of being sandwiched between the two rear-surface-side transparent electrodes (4) and (6).

In this embodiment, in addition to the first and second back side transparent electrodes (4) and (6), the light reflecting layer (7) is also made of a conductive material, and thus the light reflecting layer (7) is used. Also function as a back electrode .

Materials other than the light scattering material (5) are conventionally known materials. Hereinafter, a method for forming the first back-side transparent electrode (4) to the second back-side transparent electrode (6) will be described in detail.

The first back-side transparent electrode (4) may be formed by any forming method such as a sputtering method, a vapor deposition method, and a CVD method. In particular, the photoelectric conversion layer (3) serving as a base material may be damaged. Anything is acceptable. In the embodiment, indium tin oxide having a thickness of 10 to 10000 °, preferably 1000 ° or less, formed by a sputtering method was used.

The range of the film thickness may be a certain thickness because the material is originally a light-transmitting material. However, if the film is thicker than necessary, the problem of light loss also occurs. Accordingly, the above range is preferable from the viewpoint of the reproducibility of the film thickness and the light loss. Silver used as the light scattering substance (5) is a material having a high reflectance as a material characteristic, and was formed by a sputtering method in the embodiment. Table 1 shows the forming conditions.

[0029]

[Table 1]

The feature of the forming conditions is that the substrate temperature at the time of sputtering is high, whereby the silver thin film is deposited, the silver thin film is aggregated by the heat energy from the substrate to be hemispherical, and the first thin film is formed. On the surface of the back side transparent electrode (4).

Next, the second back side transparent electrode (6) is
Then, silver is formed as a light reflection layer (7) at a low temperature of about 150 ° C. or less so as to be in a film state.

In the structure of this embodiment, silver is contained between the first back-side transparent electrode (4) and the second back-side transparent electrode (6). was used but, Toru
The function as a bright electrode is that these two electrodes are combined to form one back side transparent electrode. Therefore, it goes without saying that the photovoltaic device of the present invention may be a single transparent electrode on the back surface side as long as it contains a light scattering substance.

The light reflecting layer (7) is to reflect light that has reached the light reflecting layer (7) without being scattered by the light scattering substance to the photoelectric conversion layer (3) again by reflection , and Since it is intended to function as a back electrode, silver having high reflectivity was used in a thin film state.

Therefore, in the photovoltaic device of the present invention, the incident light (8) is bent on the surface of the front-side transparent electrode (2), passes through the photoelectric conversion layer (3), and a part of the light is reflected on the reflection layer. The other part of the light is efficiently scattered by the light scattering material (5).

An important parameter when implementing the photovoltaic device of the present invention is the size of the light scattering material. That is, in order to effectively use light that could not be fully utilized in the past, it is necessary that the size of the light scattering material be in a relationship compatible with the wavelength of the light to be used.

For example, since the first and second back side transparent electrodes (4) and (6) made of indium tin oxide used in this embodiment have a refractive index of usually about 2, light passing therethrough Behaves as if it is effectively about half the length of light. Therefore, if the wavelength of light to be effectively used in the photovoltaic device of the present invention is set to be 600 to 800 nm, it is preferable to use a light scattering substance having half the size.

Therefore, it is preferable that the size is about 400 nm as shown in the embodiment.

Therefore, in the photovoltaic device of the present invention, it is preferable to design the size of the light scattering material in accordance with the wavelength of light to be effectively used. However, in a normal photovoltaic device, since it is desired to use light containing various wavelengths for power generation as much as possible, the present invention may be implemented by including various sizes of light scattering materials.

In this case, preferably 200 to 100
0 nm, and the optimal size is preferably 300 to 500 nm.

Table 2 shows typical characteristics of the photovoltaic device of the present invention in comparison with a conventional example. The conventional photovoltaic device has the same structure as that of the embodiment except that only the light scattering substance is omitted.

[0041]

[Table 2]

The table shows typical characteristics of the photovoltaic device, such as open-circuit voltage, short-circuit current, curvature factor (FF), and conversion efficiency.

As is clear from the numerical values in the table, in the embodiment, as compared with the conventional example, the difference in the open-circuit voltage and the curvature factor is small, but the short-circuit current is from 17.4 to 18.3 mA / c.
An increase of about 5% to m ² has been realized, and as a result, the conversion efficiency can be improved by about 5% from 11.2% to 11.8%.

From this, it can be seen that light that could not be used effectively before has sufficiently contributed to power generation by employing the photovoltaic device of the present invention.

Further, since the photovoltaic device of the present invention can improve light absorption more than before, a sufficient function can be obtained even if the thickness of the photoelectric conversion layer is made thinner than usual.

This means that the steps for forming the photoelectric conversion layer can be shortened, and the productivity as a photovoltaic device is improved.

Although silver was used as the light-scattering substance in this embodiment, the present invention is not limited to this, and a material having a different refractive index from the material of the back-side transparent electrode, in this embodiment, indium tin oxide. Anything may be used.

That is, as long as light scattering occurs in the rear-surface-side transparent electrode, the function and effect of the present invention are exhibited in principle. Specifically, as the combination of the back side transparent electrode and the light scattering substance, a combination of tin oxide and copper, a zinc oxide and silicon oxide, or the like can be considered.

In the embodiment, the method of forming a light-scattering substance utilizes the coagulation action by heating the substrate during the formation of silver. However, the method of manufacturing the photovoltaic device of the present invention is not limited to this. For example, conventionally known photolithography
The light scattering substance may be formed in an island shape by etching by a lithography technique.

Further, the formation of the light-scattering substance and the formation of the back-side transparent electrode are performed not only in separate steps as in the embodiment, but also, for example, while forming indium tin oxide which is the back-side transparent electrode while forming silver. May be deposited. Even in such a case, if the coagulation action of silver is utilized, the substrate temperature during these depositions may be maintained at a high temperature.

If such a method is used, the light scattering substance can be widely distributed in the rear transparent electrode, and the light scattering effect is further enhanced.

In addition, the photovoltaic device of the present invention is not limited to a semiconductor having amorphous silicon as a base material, but is applicable to a semiconductor comprising amorphous silicon germanium, an amorphous selenium-based semiconductor, and a polycrystalline semiconductor. It is needless to say that the same effect can be obtained.

[0053]

According to the photovoltaic device of the present invention, a light scattering substance is contained in the back transparent electrode formed on the photoelectric conversion layer to scatter light which could not be sufficiently utilized conventionally. This gives the photoelectric conversion layer a number of opportunities for light absorption.

Therefore, according to the present invention, the characteristics as the photovoltaic device, particularly, the short-circuit current is increased, and the conversion efficiency is increased.

Further, by designing the size of the light scattering material in accordance with the wavelength of light to be used, the effect can be further enhanced.

Further, due to the effect of the use of the light-scattering substance, a sufficient output can be obtained even if the thickness of the photoelectric conversion layer is made thinner than in the prior art, so that the productivity of the device can be improved. . As a result, there is also an effect of reducing photodeterioration which is a problem when a photoelectric conversion layer using amorphous silicon as a base material is used.

[Brief description of the drawings]

FIG. 1 is a sectional view of an element structure for explaining a photovoltaic device of the present invention.

FIG. 2 is an enlarged structural sectional view of a part of the photovoltaic device.

FIG. 3 is a sectional view of an element structure for explaining a conventional photovoltaic device.

[Explanation of symbols]

(1) Translucent substrate (2) Front transparent electrode (3) Photoelectric conversion layer (4) First back transparent electrode (5) Light scattering material (6) Second back side Transparent electrode (7)… Light reflection layer (8)… Light

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Iwata 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-1-106472 (JP, A) JP-A-2-106077 (JP, A) JP-A-2-105558 (JP, A) JP-A-61-218178 (JP, A) JP-A-62-209872 (JP, A) JP-A-1-139458 (JP, A) , U)

Claims (1)

(57) [Claims] 1. A photovoltaic device in which a front-side transparent electrode, a photoelectric conversion layer, a back-side transparent electrode, and a light-reflecting layer made of a conductive material are sequentially laminated on a light-transmitting substrate. Including a light scattering substance in the side transparent electrode ,
In addition, the light is applied to the back transparent electrode containing this light scattering substance.
A photovoltaic device comprising a reflection layer formed thereon .