JP3206341B2 - Solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell for receiving sunlight through an incident light guide member defining an incident area, and more particularly to a solar cell having characteristics corresponding to changes in morning, noon, and evening light. About.

[0002]

2. Description of the Related Art Conventionally, various types of solar cells have been known, and with the advance of semiconductor technology, relatively inexpensive and small-sized cells have been developed and widely used as various power sources. In this solar cell, it is an important issue how to efficiently condense light and how to efficiently convert incident light obtained by condensing light into electric power.

[0003] 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. To this end, it is conceivable that the direction of the solar cell can be changed and the solar cell is driven to follow the direction of the sun. However, in order to always accurately track the sun throughout the four seasons, a considerably large-scale driving device is required, and there is a problem that it is difficult in practice.

On the other hand, for example, in the apparatus described in Japanese Utility Model Laid-Open No. 57-93159, sunlight entering from each direction is refracted by a predetermined amount according to the incident angle by using a lens having a special shape. Irrespective of the change in the height, a substantially constant incident angle is obtained for the solar cell. Therefore, according to this conventional example, the incident angle of sunlight on the solar cell can be made quite close to a constant value.

[0005]

However, when comparing morning and evening sunlight with daylight, not only the angle of incidence but also the amount of light and the distribution of wavelengths contained in sunlight are different.
In other words, the morning and evening sunlight has a smaller amount of light than the daytime light, and since it passes through the air layer diagonally, much of the light on the short wavelength side is scattered. Are included.

On the other hand, considering the characteristics of the solar cell, it is difficult to efficiently convert both daylight and morning and evening light to light-to-power conversion. In other words, when strong daylight is received during fine weather, generated carriers (holes and electrons) increase, 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 extracted 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 generated carriers in the morning and evening is small, the carrier lifetime which is how long the generated carriers can exist becomes important. Since the carrier lifetime becomes shorter when there are many crystal defects, the impurity concentration is preferably low. Therefore, it is required that the impurity concentration be set lower.

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, since morning and evening light contains more light on the long wavelength side than daytime light, it is difficult to effectively incorporate both.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a solar cell capable of effectively taking in all of morning, noon, and evening sunlight and performing efficient light-to-power conversion. I do.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a solar cell for receiving sunlight through an incident light guide member defining an incident area, wherein the internal resistance of the solar cell in an area facing the incident area is described. Is set lower than the internal resistance of the surrounding area.

The present invention also relates to a solar cell for receiving sunlight through an incident light guide member for defining an incident area, wherein the thickness of the antireflection film of the solar cell in the area facing the incident area. Is set to be thinner than the thickness of the antireflection film in the peripheral region.

[0011]

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

Further, according to the present invention, the thickness of the antireflection film in a region facing the direction in which sunlight enters is made thinner than the peripheral portion. Therefore, it is possible to prevent the reflection of light having a relatively short wavelength in the region facing the reflection region and the reflection of light having a relatively long wavelength in the periphery.
The morning and evening sunlight has a relatively long wavelength and is incident on the periphery 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, the morning and evening light can be effectively received at the peripheral portion, and the daytime light can be effectively received at the central confronting region, so that the light-power conversion efficiency of the entire solar cell can be increased.

[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. An optical system 200 as an incident light guide member is provided above a solar cell 100, and sunlight is collected by the optical system 200. The light enters the solar cell 100.

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

To receive as much light as possible, the solar cell 100 is set so that daytime sunlight can be received straight from above. The optical system 200 is set so as to condense the light incident straight from above onto the n + layer 12b at the center of the solar cell 100. For this reason, the light obliquely incident is inevitably focused on the peripheral portion of the solar cell 100. In this embodiment, since the n + layers 12a and 12c are arranged in the peripheral portion of the solar cell 100, the light incident on the optical system 200 from an oblique direction is condensed and irradiated on the n + layers 12a and 12c. . Thus, according to the present embodiment, daytime sunlight is collected on the n + layer 12b, and sunlight in the morning and evening is concentrated on the n + layers 12a and 12b.
The light is focused on c.

In the present embodiment, the impurity concentration of the n + layer 12b at the center 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 area where 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 that of the peripheral n + layers 12a and 12c.

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

On the other hand, the sunlight of the morning and evening
2a and 12c, which contain a large amount of long wavelength light with a small amount of irradiation and low energy. Then, 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 effect of the large internal resistance is not so large. Since the impurity concentration is low, the number of crystal defects is small, the recombination of carriers can be suppressed, and the lifetime of carriers can be extended. As a result, 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 the present embodiment, when the intense light in the daytime is incident, the central portion of the n region having a high impurity concentration is n.
By using the + layer 12b, for weak light in the morning and evening, the switching to use the n + layers 12a and 12c having a low impurity concentration in the peripheral portion can be automatically performed. Thus, efficient photoelectric conversion can always be obtained.

FIG. 2 shows the configuration of the solar cell 100 of the present embodiment. In general, the solar cell 100 is a crystalline S
In many cases, i-solar cells are used. In this case, a single crystal Si wafer having 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.

The higher the degree of light 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, if the light concentration is 10
If it exceeds 0 times, the amount of incident light becomes too large, the temperature of the cell increases significantly, and the solar cell 100 is deteriorated. 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 favorable light-to-power conversion efficiency throughout the year, the width dTOTAL of the entire cell must be equal to the cell width d of the central n + layer 12b.
It is known that about 2 to 5 times of A is preferable.

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

FIG. 4 shows still another configuration example. Light that is weaker toward the solar cell 100 enters the solar cell 100. Therefore, in the example of FIG. 4, the surrounding 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−
It is divided into three. Then, these areas 12a-1, 1
2a-2, 12a-3, 12c-1, 12c-2, 12
As for c-3, the impurity concentration decreases as the distance from the center increases. As a result, a more optimal impurity concentration can be set in accordance with 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. That is, a relatively large area p + layer 16b located below the central n + layer 12b
And relatively small area p + layers 16a-1, 16a-2, 16a- located below the surrounding n + layers 12a, 12c.
3, 16c-1, 16c-2 and 16c-3 are provided. Therefore, the n + layers 12a and 12c in the peripheral portion, the p-type substrate 10 thereunder and the p + layers 16a-1 and 16a-
2, 16a-3, 16c-1, 16c-2, 16c-3
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 thereunder has a small internal resistance. Therefore, with this configuration, similar to the above-described embodiment, it is possible to achieve a suitable light-to-power conversion according to the type of incident sunlight.

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

Next, FIG. 5 shows a configuration 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, and 12c.
a, 20b and 20c are formed. The anti-reflection films 20a, 20b, and 20c have different thicknesses, so that anti-reflection according to the center wavelength of the incident light can be achieved, and the incident light can be effectively removed from the inside. And the light-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 anti-reflection film 20 is
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 thickness of the antireflection film 20a above the peripheral n + layers 12a and 12c.
In 20c, the film thickness is set to about 120 to 150 nm.

As described above, there is a high probability that morning and evening sunlight will be incident on the peripheral portion, and this incident light has a relatively long wavelength. Therefore, as in this embodiment, the anti-reflection film 2
By changing the thickness of the solar cell, the solar cell 10 can efficiently take in short-wavelength sunlight at the center and long wavelength at the periphery.
0 can increase the light-power conversion efficiency of the whole.

FIG. 6 shows the relationship between the wavelength and the reflectance of the antireflection film 20 having a thickness of 110 nm and 140 nm. Thus, 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.

FIGS. 8 and 9 show examples of the configuration of the optical system 200. FIG. The optical system 200 in FIG. 8 utilizes a light collector 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 in which a parabolic mirror concentrator is used. FIG. 9A shows a rotating (or circular) shape, and FIG.
Uses a cylindrical light collector. These light collectors can be similarly used as the optical system 200.

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

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

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

FIG. 11 shows a configuration example of the surface electrode 14. In this example, the solar cell 100 is circular,
Electrode pieces 14a are provided radially on the surface.
These electrode pieces 14a are connected to surrounding ring-shaped electrode pieces 14b. Further, 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 the incident area of sunlight is kept large, and the power loss in the recovery of generated power can be minimized.

In each of the embodiments described above, the drawings show only those parts necessary for the explanation, and other parts are omitted as appropriate.

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

Further, as the optical system 200, other than those described above can be adopted as long as the incident range of sunlight can be substantially limited. For example, a solar cell may be surrounded by a reflector.

[0040]

As described above, according to the present invention,
The internal resistance in a region facing the direction in which sunlight enters is made smaller than that in the peripheral portion. Therefore, even in a region where the large current is generated, a voltage drop, heat generation, and the like can be relatively reduced in the facing region. Therefore, strong light in the daytime is received by this portion, and high light-to-power conversion efficiency can be obtained. On the other hand, the peripheral portion has a relatively small internal resistance. Therefore, the lifetime of generated carriers (electrons and holes) is maintained long so that high light-
Power conversion efficiency can be obtained.

Further, according to the present invention, the thickness of the antireflection film in a region facing the direction in which sunlight enters is made thinner than the peripheral portion. Therefore, it is possible to prevent the reflection of light having a relatively short wavelength in the region facing the reflection region and the reflection of light having a relatively long wavelength in the periphery.
The morning and evening sunlight has a relatively long wavelength and is incident on the periphery 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, the morning and evening light can be effectively received at the peripheral portion, and the daytime light can be effectively received at the central confronting region, so that the light-power conversion efficiency of the entire solar cell can be increased.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of a solar cell according to an embodiment.

FIG. 3 is a diagram illustrating an output for each time according to the embodiment.

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

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

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

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

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

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

FIG. 10 is a diagram illustrating a configuration of an example of a solar 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)

(57) [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 an area facing the incident area is reduced by the internal resistance of a surrounding area. A solar cell characterized by being set lower than the above. 2. A solar cell that receives sunlight through an incident light guide member that defines an incident area, wherein the thickness of the antireflection film of the solar cell in an area facing the incident area is set to A solar cell characterized in that the thickness is set smaller than the thickness of the antireflection film in the region.