JPH08162658A - Solar cell - Google Patents

Abstract

PURPOSE: To effectively pickup all solar lights in the morning, the daytime and the evening and to efficiently make photoelectric conversion by setting the internal resistance of a solar cell in the region opposed to an incident region lower than that of the region of the periphery. CONSTITUTION: An optical system 200 of an incident light guide member is provided above a solar cell 100, a solar light is converged by the system 200, and incident to the cell 100. The cell 100 has a p-type board 10, and three n<+> type layers 12a, 12b, 12c are formed by thermal diffusion of n-type impurity on the surface of the board 100. The internal resistance of the region opposed in the direction incident with the light is lower than that of the periphery. Accordingly, even if a large current is generated, a voltage drop, a heat generation can be relatively reduced, and the life time of the carrier generated is maintained long, and high photoelectric conversion efficiency can be obtained for the strong light in the daytime and the weak light in the morning or evening.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell that receives sunlight through an incident light guide member that defines an incident area, and particularly has characteristics that correspond to changes in morning, noon and evening light. Regarding

[0002]

2. Description of the Related Art Conventionally, various kinds of solar cells have been known, and relatively inexpensive and small ones have been developed with the progress of semiconductor technology and are widely used as various kinds of power sources. In this solar cell, how to efficiently collect light and how to efficiently convert the incident light obtained by collecting the light into electric power is an important issue.

In order to efficiently collect sunlight, it is preferable that the solar cell always faces the sun. That is, if the solar cell can always receive sunlight from the front, the amount of incident light per area of the solar cell can be maximized. For this purpose, it is possible to change the direction of the solar cell and drive the solar cell following the direction of the sun. However, in order to keep track of the sun accurately throughout the four seasons, a fairly large-scale drive device is required, which is actually a difficult problem.

On the other hand, for example, in the device disclosed in Japanese Utility Model Application Laid-Open No. 57-93159, a sun light incident from each direction is refracted by a predetermined amount according to the incident angle by using a lens of a special shape, and the sun The solar cell is designed to have a substantially constant incident angle regardless of the change in height. Therefore, according to this conventional example, the incident angle of sunlight on the solar cell can be made to approach a fairly constant value.

[0005]

However, comparing the morning and evening sunlight with the day sunlight, not only the incident angle but also the amount of light and the distribution of wavelengths contained in the sunlight are different.
In other words, morning and evening sunlight has a smaller amount of light than daylight, and much of the light on the short wavelength side is scattered because it obliquely passes through the air layer. It contains a lot of.

On the other hand, considering the characteristics of the solar cell, it is difficult to efficiently perform light-power conversion on both daylight and morning and evening light. That is, when strong daylight is received in fine weather, the number of generated carriers (holes and electrons) increases and the carrier density (current density) increases. Therefore, the conversion efficiency is greatly affected by the electrical resistance (internal resistance of the solar cell) until the carrier is taken out from the electrode. Therefore, it is conceivable to increase the impurity concentration in the substrate of the solar cell and reduce the internal resistance. On the other hand, when the amount of carriers generated in the morning and evening is small, the carrier lifetime, which is how long the carriers generated can exist, becomes important. The carrier lifetime is shortened when there are many crystal defects, and thus the impurity concentration is preferably low. Therefore, it is required to set the impurity concentration to a low level.

Further, an antireflection film is often provided on the surface of the solar cell in order to effectively take in incident light. The thickness of the antireflection film to be set depends on the wavelength of light. different. As described above, morning and evening light contains more light on the long wavelength side than daylight, so it is difficult to effectively incorporate both.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a solar cell capable of efficiently taking in all sunlight in the morning, noon, and evening and performing efficient light-power conversion. To do.

[0009]

DISCLOSURE OF THE INVENTION The present invention is a solar cell that receives sunlight through an incident light guide member that defines an incident area, and the internal resistance of the solar cell in the area facing the incident area. Is set to be lower than the internal resistance of the area around it.

Further, the present invention is a solar cell that receives sunlight through an incident light guide member that defines an incident area, and the film thickness of the antireflection film of the solar cell in the area facing the incident area. Is set thinner than the film thickness of the antireflection film in the surrounding area.

[0011]

As described above, according to the present invention, the internal resistance in the region facing the direction in which sunlight is incident is made smaller than that in the peripheral portion. Therefore, in this confronting area, even if a large current is generated, voltage drop, heat generation, etc. can be made relatively small. Therefore, strong light in the daytime is received by this portion, and high light-power conversion efficiency can be obtained. On the other hand, the peripheral portion has a relatively small internal resistance. Therefore, the lifetime of the generated carriers (electrons and holes) can be maintained to be long, and high light-power conversion efficiency can be obtained even with weak light such as morning and evening.

Further, according to the present invention, the thickness of the antireflection film in the area facing the direction in which sunlight is incident is made thinner than that in the peripheral portion. Therefore, it is possible to prevent reflection of light having a relatively short wavelength in the facing region and to prevent reflection of light having a relatively long wavelength in the peripheral region.
Then, the morning and evening sunlight has a relatively long wavelength and is incident on the peripheral portion of the solar cell, while the daylight has a relatively short wavelength and is incident on a region facing the incident direction of the solar cell. Therefore, it is possible to effectively receive morning and evening light in the peripheral portion and effectively receive daylight light in the central confronting region, thereby increasing the light-power conversion efficiency of the entire solar cell.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the embodiment, in which an optical system 200, which is an incident light guide member, is provided above the solar cell 100, and sunlight is condensed by the optical system 200. It is incident on the solar cell 100.

The solar cell 100 is a p-type substrate 1 in which p-type impurities (for example, B (boron)) are diffused in a Si single crystal.
0, and three n + layers 12a, 12b, 12c are formed on the surface of the p-type substrate 10 by thermal diffusion of n-type impurities (for example, P (phosphorus)). Then, on each of the n + layers 12a, 12b, 12c, surface electrodes 14a, 14b, 14c that act as negative electrodes of the solar cell 100 are formed, respectively. Further, on the back surface side of the p-type substrate 10, a back surface electrode 18 acting as a positive electrode is formed via the p + layer 16. The back surface electrode 18 may be formed by depositing Al, and the p + layer 16 may be formed by thermal diffusion of this Al.

In order to receive as much light as possible, the solar cell 100 is set so that it can receive daytime sunlight straight from above. Then, the optical system 200 is set so as to focus the light incident straight from above on the n + layer 12b at the center of the solar cell 100. Therefore, the light that is obliquely incident is inevitably focused on the peripheral portion of the solar cell 100. In the present embodiment, since the n + layers 12a and 12c are arranged in the peripheral portion of the solar cell 100, the light that is obliquely incident on the optical system 200 is focused and irradiated on the n + layers 12a and 12c. . In this way, according to the present embodiment, daytime sunlight is condensed on the n + layer 12b, and morning and evening sunlight is collected on the n + layers 12a and 12a.
It is focused on c.

In this embodiment, the impurity concentration of the n + layer 12b in the central portion where daytime sunlight is incident is set to 10 ¹⁹ to 10 ^21.
/ Cm ³ , and the impurity concentration of the n + layers 12a and 12c in the peripheral portion where the morning and evening sunlight is incident is 10 ¹⁸ to 10 ¹⁹ / cm ^3.
The impurity concentration of the central n + layer 12b is set higher than the impurity concentration of the peripheral n + layers 12a and 12c.

The daylight contains a large amount of light having a short wavelength of light energy and has a large amount of light. Therefore, n + layer 1
In 2b, a relatively large current is generated.
Since the impurity concentration of the + layer 12b is relatively high, the internal resistance is low, and the power consumption here can be suppressed low.

On the other hand, the sunlight in the morning and evening is the n + layer 1 in the peripheral portion.
Although it is incident on 2a and 12c, it contains a large amount of long wavelength light with a small irradiation amount and a small energy. Therefore, n
The carriers (electrons and holes) generated in the + layers 12a and 12c are relatively small. Therefore, even if the impurity concentration is low, the large internal resistance has little effect. Since the impurity concentration is low, crystal defects are small, carrier recombination can be suppressed, and the carrier lifetime can be lengthened. Thereby, the surface electrodes 14a, 14
Electrons can be efficiently extracted from c, and the light-power conversion efficiency can be increased.

As described above, according to this embodiment, when the strong light is incident in the daytime, n having a high impurity concentration in the central portion is used.
By using the + layer 12b and for weak light in the morning and evening, it is possible to automatically perform switching to use the n + layers 12a and 12c having a low impurity concentration in the peripheral portion. Therefore, efficient photoelectric conversion can be obtained at all times.

FIG. 2 shows the structure of the solar cell 100 of this embodiment. Although it depends on the degree of light concentration, the type of the solar cell, the use, etc., the solar cell 100 generally has a crystalline system S.
i solar cells are often used. In this case, a single crystal Si wafer with a diameter of 3 to 6 inches or 50 to
A 100 mm square polycrystalline substrate is used. Therefore, the width (dTOTAL) of the solar cell 100 is 10 to 100 mm.
The degree is preferred.

Further, the higher the degree of condensing in the optical system 200, the higher the amount of light received by the solar cell 100, so that the cost can be reduced. However, the degree of light collection is 10
When it exceeds 0 times, the amount of incident light becomes too large and the cell temperature rises greatly, which leads to deterioration of the solar cell 100. Therefore, it is practical that the light collection degree is about 30 to 100 times.

As a result of the evaluation under such conditions, in order to obtain a preferable light-to-power conversion efficiency throughout the year, the total cell width dTOTAL is the cell width d of the central n + layer 12b.
It has been found that about 2 to 5 times as much as A is preferable.

FIG. 3 shows an example of the relationship between time and solar cell output in this embodiment. As described above, the n + layer 12b in the central portion is replaced with the n + layers 12a, 1 in the peripheral portion according to the present embodiment.
Solar cell 10 with higher impurity concentration than 2c
It is understood that 0 gives a larger output than usual in the morning and evening.

FIG. 4 shows still another configuration example. Light that is weaker toward the periphery enters the solar cell 100. Therefore, in the example of FIG. 4, the peripheral n + layers 12a and 12c are divided into a plurality of regions 12a-1 and 12a according to the distance from the center.
-2, 12a-3, 12c-1, 12c-2, 12c-
Divided into three. Then, these areas 12a-1, 1
2a-2, 12a-3, 12c-1, 12c-2, 12
Regarding c-3, the impurity concentration is set to decrease as the distance from the center increases. As a result, a more optimal impurity concentration can be set according to the incident sunlight, and more efficient light-power conversion can be performed.

FIG. 7 shows still another embodiment, in which the p + layer 16 is divided into a plurality of parts. That is, the p + layer 16b having a relatively large area located below the central n + layer 12b.
And the p + layers 16a-1, 16a-2, 16a- having a relatively small area located below the peripheral n + layers 12a, 12c.
3, 16c-1, 16c-2, 16c-3 are provided. Therefore, the n + layers 12a and 12c in the peripheral portion, the p-type substrate 10 and the p + layers 16a-1 and 16a- below the n + layers 12a and 12c are provided.
2, 16a-3, 16c-1, 16c-2, 16c-3
The solar cell composed of 1 has a large internal resistance, and the solar cell formed by the central n + layer 12b and the p-type substrate 10 and the p + layer 12b therebelow has a low internal resistance. Therefore, with this configuration, similar to the above-described embodiment, it is possible to achieve suitable light-power conversion depending on the type of incident sunlight.

In the above example, the p + layer 16 is divided and the contact area is changed in the central portion and the peripheral portion. However, the impurity concentration of the p + layer 16 may be changed, and the contact area may be changed. Both the impurity concentrations may be changed.

Next, FIG. 5 shows the structure of a solar cell 100 according to another embodiment of the present invention. In this example, a plurality of n
The antireflection film 20 is provided above the + layers 12a, 12b, 12c.
a, 20b, 20c are formed. The antireflection films 20a, 20b, 20c have different film thicknesses, so that antireflection according to the center wavelength of the incident light can be achieved, and the incident light can be effectively protected from the internal light. The light-to-power conversion efficiency can be increased.

Here, the antireflection film 20 is made of Si.
It is formed by depositing O ₂ , SiN _x or the like by CVD or vapor deposition. Then, the antireflection film 20 is made of Si.
When formed of O ₂ , the thickness of the antireflection film 20b above the central n + layer 12b is about 100 to 110 nm, and the antireflection film 20a above the peripheral n + layers 12a and 12c.
The film thickness of 20c is set to about 120 to 150 nm.

As described above, the probability that sunlight in the morning and evening will be incident on the peripheral portion is high, and the wavelength of this incident light is relatively long. Therefore, as in this embodiment, the antireflection film 2
By changing the film thickness of 0, solar light with a short wavelength in the central part and long wavelength in the peripheral part is efficiently taken in, and the solar cell 10
The overall light-to-power conversion efficiency can be increased.

FIG. 6 shows the relationship between the wavelength and the reflectance of the antireflection film 20 having a film thickness of 110 nm and 140 nm. In this way, the antireflection film 20a having a thickness of 140 nm,
20c has a low reflectance on the long wavelength side of 600 nm or more, and the antireflection film 20b having a film thickness of 110 nm has a reflectance of 6 nm.
It can be seen that the reflectance on the short wavelength side of 00 nm or less is low.

8 and 9 show examples of the configuration of the optical system 200. The optical system 200 of FIG. 8 uses a condenser using a linear Fresnel lens, and this configuration forms an elongated rectangular focal plane. The solar cell 100 of the present embodiment is formed to be larger than this focal plane, and the central n + layer 12b is arranged on the focal plane.

FIG. 9 shows an example using a parabolic mirror concentrator, and FIG. 9 (A) shows a rotation (or a circle) and FIG. 9 (B).
Uses a cylindrical collector. These light collectors can be used as the optical system 200 as well.

FIG. 10 shows a solar tracking system. In the present invention, efficient light-power conversion can be efficiently performed in response to obliquely incident morning and evening light. However, the conversion efficiency can still be increased by directing it toward the sun. Therefore, by using the tracking system as shown in FIG. 10 and using the solar cell of the above-described embodiment as the solar cell of this system, the conversion efficiency can be further increased. In this example, a linear Fresnel lens similar to that shown in FIG. 8 is used as the optical system 200, and the solar cell 100 is arranged at this focal plane portion. Then, the optical system 200 and the solar cell 100 are
It is rotatable in the azimuth direction. In this example, the worm gear 3 is rotated by rotating the time angle tracking shaft 302.
The optical system 200 and the like are rotated in the azimuth direction via 04.

Further, the optical system 200 and the solar cell 100 are pivotally fixed at one end (upper side in the drawing) and movable at the other end (lower side in the drawing). That is, by rotating the declination tracking shaft 306, the hour angle tracking shaft 30 is moved through the worm gear 308.
Move 2 in the elevation direction. Therefore, it is possible to move in the elevation direction as a whole.

Therefore, the movement of the sun on one day is tracked by the rotation in each direction, and the change in the height of the sun depending on the season is tracked by the rotation in the elevation angle direction. Even with such tracking, weak light such as morning and evening is likely to be incident on the peripheral portion of the solar cell, and according to the present invention,
Efficient light for weak light entering these peripheral parts
Power conversion can be performed.

FIG. 11 shows a structural example of the surface electrode 14. In this example, the solar cell 100 is circular,
Electrode pieces 14a are radially provided on the surface portion.
The electrode pieces 14a are connected to the surrounding ring-shaped electrode pieces 14b. In addition, the electrode piece 14a is formed in a triangular shape whose width increases toward the peripheral portion. With this configuration, the contact area with the n + layer 12 can be made sufficient while maintaining a large incident area of sunlight, and the power loss in the recovery of generated power can be minimized.

In each of the above-mentioned embodiments, only the parts necessary for the description are shown in the figures, and the other parts are omitted as appropriate.

Further, a more effective solar cell can be obtained by combining the respective embodiments described above, such as adjusting the film thickness of the antireflection film and adjusting the impurity concentration of the n + layer.

Further, as the optical system 200, as long as it is possible to substantially limit the incident range of sunlight, those other than those described above can be adopted, and for example, the solar cell may be surrounded by a reflector.

[0040]

As described above, according to the present invention,
The internal resistance in the area facing the direction of sunlight is smaller than that in the surrounding area. Therefore, in this confronting area, even if a large current is generated, voltage drop, heat generation, etc. can be made relatively small. Therefore, strong light in the daytime is received by this portion, and high light-power conversion efficiency can be obtained. On the other hand, the peripheral portion has a relatively small internal resistance. Therefore, the lifetime of the generated carriers (electrons and holes) is maintained to be long, and high light is generated even with weak light such as morning and evening.
Power conversion efficiency can be obtained.

Further, according to the present invention, the thickness of the antireflection film in the area facing the direction in which sunlight is incident is made thinner than that in the peripheral portion. Therefore, it is possible to prevent reflection of light having a relatively short wavelength in the facing region and to prevent reflection of light having a relatively long wavelength in the peripheral region.
Then, the morning and evening sunlight has a relatively long wavelength and is incident on the peripheral portion of the solar cell, while the daylight has a relatively short wavelength and is incident on a region facing the incident direction of the solar cell. Therefore, it is possible to effectively receive morning and evening light in the peripheral portion and effectively receive daylight light in the central confronting region, thereby increasing the light-power conversion efficiency of the entire solar cell.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment.

FIG. 2 is a diagram showing a configuration of a solar cell of an example.

FIG. 3 is a diagram showing an output for each time of the embodiment.

FIG. 4 is a diagram showing the configuration of another embodiment of the solar cell.

FIG. 5 is a diagram showing the configuration of still another embodiment of the solar cell.

FIG. 6 is a diagram showing the relationship between the wavelength and the reflectance according to the thickness of the antireflection film.

FIG. 7 is a diagram showing the configuration of still another embodiment of the solar cell.

FIG. 8 is a diagram showing a configuration of an example of an optical system.

FIG. 9 is a diagram showing the configuration of another example of the optical system.

FIG. 10 is a diagram showing a configuration of an example of a solar light tracking system.

FIG. 11 is a diagram showing a configuration example of a surface electrode of a solar cell.

[Explanation of symbols]

10 p-type substrate, 12a, 12b, 12c n + layer, 1
4a, 14b, 14c surface electrode, 16 p + layer, 18
Back electrode, 100 solar cells, 200 optics.

Claims (2)

[Claims] 1. A solar cell that receives sunlight through an incident light guide member that defines an incident area, wherein the internal resistance of the solar cell in the area facing the incident area is the internal resistance of the surrounding area. A solar cell characterized by being set lower than 2. A solar cell that receives sunlight through an incident light guide member that defines an incident area, wherein the film thickness of the antireflection film of the solar cell in the area facing the incident area is set to A solar cell characterized by being set thinner than the film thickness of the antireflection film in the region.