JPH0793450B2 - Corrugated solar cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to corrugated solar electricity, and more particularly to a solar cell using a corrugated substrate having a long optical path length and high photoelectric conversion efficiency.

[Conventional technology]

The corrugated substrate used in the conventional corrugated solar cell is, for example, IEE, Transaction on Electron Devices, Vol. 37,
Issue 2, (1990) pp. 344-347 [IEEE, TRANSAC
TION ON ELECTRON DEVICES, VOL.37, NO.2, (1990) pp.34
As described in [4-347], the optical path length of the light incident on the corrugated substrate is partly short, which causes a problem that the photo-generated current decreases.

[Problems to be Solved by the Invention]

As described above, the corrugated substrate used in the conventional corrugated solar cell has a problem that the photo-generated current is low because there is a portion where the optical path length of incident light is short.

An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a corrugated solar cell having a structure in which a photo-generated current is increased by using a corrugated substrate having a long optical path length of incident light. It is in.

[Means for Solving the Problems]

In order to achieve the above-mentioned object of the present invention, by limiting the depth of the V-groove of the corrugated substrate to be formed to a specific depth with respect to the thickness of the wafer, the optical path length of all incident light is increased. It is possible to increase the photo-generated current.

According to the present invention, in a corrugated substrate that constitutes a corrugated solar cell in which V-grooves are formed on the front surface and the back surface of a wafer, light that is incident substantially perpendicularly to the surface of the substrate is reflected by the V-groove slope on the back surface of the substrate. After that, a corrugated solar cell using a corrugated substrate having a V-groove structure having a shape that passes through the substrate for a long time without being emitted from the V-groove slope on which the incident light is incident can be increased. Is.

Further, according to the present invention, in a corrugated substrate that constitutes a corrugated solar cell in which V-grooves are formed on the front surface and the back surface of a wafer, light that is incident on the surface of the substrate almost perpendicularly is reflected by the V-groove slope on the back surface of the substrate. A corrugated solar cell capable of increasing the photo-generated current by using a corrugated substrate having a V-groove structure having a shape that passes through the substrate for a long time without being provided.

The specific shape of the corrugated substrate that constitutes the corrugated solar cell of the present invention is as follows: the angle between the V-groove slope of the corrugated substrate and the incident light is α, and the angle between the optical path after incidence and the perpendicular of the V-groove slope. in case of a beta, the relationship between the thickness w and the thickness d of the substrate of the wafer, w ≦ d (sinα + tanβcosα + 2cos 2 α / sinα) ... (1) or, w ≦ d (sinα-tanβcosα + 2cos 2 α / sinα) It is a corrugated solar cell using a corrugated substrate satisfying the condition of (2).

The present invention relates to a corrugated solar cell having a flat portion on at least a front surface or a back surface of a corrugated substrate. When the value obtained by adding the thickness is used as the thickness w of the wafer for forming the corrugated substrate, the above formula (1) or It is a corrugated solar cell characterized by using a corrugated substrate having the relationship of formula (2).

Further, in the present invention, in a corrugated solar cell having a flat portion in the concave portion on the back surface of the corrugated substrate, the height of the triangle formed by the flat portion of the concave portion of the corrugated substrate and the extension line of the V groove slope is subtracted. When the value is used as the thickness w of the wafer for forming the corrugated substrate, the above formula (1) or (2) is defined between the thickness w of the wafer and the thickness d of the corrugated substrate. It is a corrugated solar cell characterized by using a corrugated substrate having the above relationship.

[Action]

The performance of the corrugated substrate that constitutes the corrugated solar cell of the present invention will be described with reference to the drawings.

In the conventional corrugated solar cell substrate, even if a reflecting mirror is formed on the back surface of the corrugated substrate, a part of the incident light 2 will be inside the corrugated substrate as shown in FIG. After traveling about 4 times as large as d, the vehicle goes out of the substrate. Further, during this period, the backside reflection of the substrate causes reflection loss twice, and the surface reflection also causes reflection loss twice, so that the photo-generated current in the corrugated substrate is significantly reduced. On the other hand, in the corrugated substrate of the present invention, for example, as shown in FIG. 1, the incident light 2 incident on the surface of the substrate is reflected by the back surface of the substrate and then emitted from the incident surface to the outside of the substrate. Instead, it travels over a long distance in the substrate. By this,
It is possible to greatly increase the current generated in the corrugated substrate.

Next, after the incident light 2 on the surface of the corrugated substrate is reflected by the back surface of the substrate, the thickness d of the corrugated substrate that can travel in the substrate for a long distance and the thickness w of the wafer to be used are The relationship will be described with reference to FIG. In the figure, the length of the slope of the V groove is d ₂ , the angle between the slope and the incident light is α, the angle between the optical path after incidence and the perpendicular of the slope of the V groove is β,
Assuming that the distance between the bottom of the front V-groove and the bottom of the back V-groove of the corrugated substrate is d ₄ , assuming that the incident light 2 does not return to the incident surface once after being reflected by the rear surface, the following relationship is obtained. It holds.

_{w = d 4 + 2d 2 cosα} d 4 = dsinγ / cosβ d 4 / tanγ = d 2 sinα From this, the thickness d of the substrate, the leads to the relationship between the thickness w of the wafer w ≦ d (sinα + tanβcosα + 2cos 2 α / sinα ) ... (1) Therefore, by making the thickness w of the wafer equal to or smaller than the right side of the above equation (1), the incident light 2 travels in the corrugated substrate over a long distance, increasing the photo-generated current. Can be made.

Next, the substrate structure for further suppressing the reflection loss of the incident light 2 due to the back surface reflection of the corrugated substrate will be described with reference to FIG. Wafer thickness w, substrate thickness d, V groove slope length d ₂ , angle α between the slope and incident light, angle β between the optical path after incidence and the V groove slope normal, surface V groove If the distance d ₄ between the bottom of the V-shaped groove and the bottom of the V-shaped groove on the back surface is defined as shown in FIG.
Also, the condition not reflected by the V-groove slope on the back surface of the substrate immediately below the incident surface is expressed by the following equation (2).

w ≦ d (sin α−tan β cos α + ² cos ² α / sin α) (2) Therefore, by making the thickness w of the wafer equal to or smaller than the right side of the above equation (2), the loss due to back surface reflection is reduced. It can be kept low to increase the photogenerated current.

The characteristic of the corrugated substrate described above is that the thickness d of the substrate is smaller than the thickness w of the wafer. In fact, when applied to a solar cell, the effect of increasing the photo-generated current becomes remarkable when the thickness d of the substrate is less than about 1/2 of the thickness w of the wafer, and the output voltage is improved. It was observed.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in more detail with reference to the drawings.

(Example 1) FIG. 2 is a schematic view showing an example of the configuration of a corrugated substrate of the corrugated solar cell of the present invention. Single crystal Si with (100) surface is used for wafers processed into corrugated substrates.
And using the oxide film as an etching mask, anisotropic etching was performed to form a V groove. In the case of the V groove formed by this method, the angle α formed between the incident light and the V groove slope is about 35.3.
It was °. In addition, the refractive index n of single crystal Si is such that the wavelength of light is 0.
It was about 3.6 at 9 μm. Therefore, the angle β formed by the optical path after incidence and the vertical line of the V-groove slope is β = sin ^-1 (sin (90 ° -α) / n) ≈ 13.1 °. This relationship of the above (1) The thickness of the thickness d and the wafer is substituted substrates equation w becomes w ≦ d (sinα + tanβcosα + 2cos 2 α / sinα) ... (1) w ≦ 3.07d. Therefore, the thickness w of the wafer is 150 μm and the thickness d of the substrate is 50 μm. As a result, the light incident on the corrugated substrate of the present invention is reflected on the V-groove slope on the back surface of the substrate immediately below the incident light, and then travels within the substrate for a long distance without being emitted from the incident surface to the outside of the substrate. It was possible to significantly increase the photo-generated current.

(Embodiment 2) As shown in FIG. 3, in this embodiment, in order to prevent the incident light 2 incident on any position of the incident surface from being reflected by the V-groove slope on the back surface of the substrate directly below the incident light. The relationship between the thickness w of the wafer and the thickness d of the corrugated substrate will be described. Substituting α≈35.3 ° and β≈13.1 ° obtained in Example 1 into the above equation (2), the relationship between the substrate thickness d and the wafer thickness w is: w ≦ d (sinα−tanβcosα + 2cos ² α / sin α) (2) W ≦ 2.69d. Therefore, the wafer thickness is 130 μm and the substrate thickness is 5 μm.
It was set to 0 μm. As a result, the light incident on the corrugated substrate of the present invention can be traveled over a long distance in the substrate without being reflected by the V-groove slope on the back surface of the substrate immediately below the incident light, and the photo-generated current is significantly increased. I was able to do it.

(Embodiment 3) In this embodiment, description will be made on a case where the corrugated substrate has some of the convex portions and the concave portions that are flat.

In Fig. 4, the corrugated substrate has a flat portion that is cut off by heights d ₅ and d ₆ on the convex portions on the front and back surfaces, respectively. In this case, the corrugated substrate of the present invention can be obtained by replacing the thickness w of the wafer processed into the corrugated substrate with a thickness obtained by adding d ₅ and d ₆ as shown in FIG.

In FIG. 5, there is a flat portion shallowed by a height d _{7 in the} concave portion on the back surface of the corrugated substrate. In this case, the thickness w of the wafer to be processed into the corrugated substrate is set as shown in FIG.
by replacing the thinned thickness by d _7, it is possible to obtain a corrugated-type substrate of the present invention.

In the above embodiments, the case of using a single crystal Si wafer is described, but a single crystal wafer using a material such as GaAa, Inp, Ge or the like or another compound semiconductor material may be used. Further, when the corrugated substrate is formed by isotropic etching, mechanical processing, laser processing or the like, not only single crystal but also polycrystalline or amorphous material may be used.

〔The invention's effect〕

As described in detail above, in the thin solar cell using the corrugated substrate of the present invention, the light incident on the corrugated substrate can be confined in the substrate for a longer distance. The generated photocurrent can be further increased, and a corrugated solar cell with high photoelectric conversion efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of the structure of a corrugated substrate of a corrugated solar cell of the present invention, and FIG. 2 is a schematic diagram showing the structure of a corrugated substrate exemplified in Example 1 of the present invention.
FIG. 3 is a schematic diagram showing the structure of the corrugated substrate exemplified in Embodiment 2 of the present invention, and FIGS. 4 and 5 are schematic diagrams showing the structure of the corrugated substrate exemplified in Embodiment 3 of the present invention. FIG. 6 is a schematic diagram showing the structure of a conventional corrugated substrate. 1 ... Corrugated substrate, 2 ... Incident light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-49679 (JP, A) JP-A-59-127878 (JP, A) JP-A-2-220479 (JP, A) JP-A 62- 237768 (JP, A)

Claims (3)

[Claims] 1. A corrugated solar cell using a corrugated substrate in which V-grooves are formed on the front and back surfaces of a wafer, wherein the corrugated substrate has an angle α between a slope of the V-groove on the surface and incident light, which is after incidence. When the angle between the optical path of V and the perpendicular of the slope of the V groove on the surface is β, the thickness w of the wafer is
And the relationship between the thickness d of the corrugated side substrate satisfies w ≦ d (sinα-tanβcosα + 2cos 2 α / sinα) become conditions, light substantially vertically incident on the surface of the corrugated board, the corrugated A corrugated solar cell, wherein the corrugated solar cell passes through the corrugated substrate for a long time without being reflected by a V-groove slope existing on the extension line of the incident light on the back surface of the substrate. 2. A corrugated solar cell having a flat portion on at least a front surface or a back surface of a corrugated substrate, wherein the corrugated substrate has a triangular shape composed of a flat portion of the projected portion of the corrugated substrate and an extension line of a V-groove slope. The value obtained by adding the height is used as the thickness w of the wafer for forming the corrugated substrate, and the value between the thickness w of the wafer and the thickness d of the corrugated side substrate is set forth in claim 1. A corrugated solar cell using a corrugated substrate having a relationship. 3. In a corrugated solar cell having a flat portion in the recess on the back surface of the corrugated substrate, the height of a triangle formed by the flat portion of the recess of the corrugated substrate and the extension line of the V groove slope is drawn. When the value is used as the thickness w of the wafer for forming the corrugated substrate, the corrugated type having the relationship according to claim 1 between the thickness w of the wafer and the thickness d of the corrugated substrate. A corrugated solar cell characterized by using a substrate.