JPH09205221A - Solar cell - Google Patents

Abstract

(57) Abstract: Reflected light of a surface electrode provided on the surface of a P-type silicon substrate can be efficiently incident on the P-type substrate. An N-type impurity diffusion layer 11a is provided on a surface portion of a P-type silicon substrate 11 having an uneven surface portion, and a pair of stripe-shaped recesses is formed on the surface portion. An electrode installation recess 11c is provided. A surface electrode 12 is provided in each electrode installation recess 11c so as not to project from the uneven surface portion. The surface of the P-type silicon substrate 11 is covered with a glass plate 15 adhered by an adhesive layer 14.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solar cell that receives sunlight to generate electricity.

[0002]

2. Description of the Related Art FIG. 8 shows an example of a solar cell that receives sunlight to generate electricity. This solar cell 40 has a P-type silicon substrate 41, and an N-type impurity diffusion layer 41a is provided on the surface portion thereof. The P-type silicon substrate 41 is
Due to the PN junction with the N-type impurity diffusion layer 41a, the surface is irradiated with sunlight to generate power. The surface of the P-type silicon substrate 41 provided with the N-type impurity diffusion layer 41a is flat, and the surface electrode 42 is provided on the surface.

The surface electrode 42 is formed of a metal in a comb shape, and has a linear portion 42a provided on a side portion of the N-type impurity diffusion layer 41a and a plurality of lateral portions extending laterally in an orthogonal state from the linear portion 42a. And an orthogonal portion 42b of. Each of the orthogonal portions 42b of the surface electrode 42 has a width dimension reduced so that the interval is relatively large, and extends from the side portion where the linear portion 42a is provided to the other side portion on the surface of the P-type silicon substrate 41. ing. Except for the straight line portion 42a, the front surface electrode 42 is provided with an adhesive layer 44,
Glass plates 45 are laminated.

On the back surface of the P-type silicon substrate 41, P
The type impurity diffusion layer 41b is provided, and the back surface electrode 46 is provided on the entire back surface of the P type impurity diffusion layer 41b.

In such a solar cell 40, the glass plate 4
The sunlight entering from No. 5 enters the P-type silicon substrate 41 to generate power, and a voltage is generated between the front surface electrode 42 and the back surface electrode 46.

Since the surface electrode 42 provided on the surface of the P-type silicon substrate 41 is usually made of metal, the P-type solar light incident on the glass plate 45 and radiated to the orthogonal portions 42b is irradiated. The light is reflected without entering the silicon substrate 41. For this reason, each orthogonal portion 42b of the surface electrode 42 has a widthwise dimension reduced to N so that many electrons are collected in the N-type impurity diffusion layer 41a.
The area occupied by the surface of the type impurity diffusion layer 41a is made as small as possible, and the electrical resistance is made small so as to be thick. Generally, each orthogonal portion 4 of the surface electrode 42
As for the thickness of 2b, the thickness of the P-type silicon substrate 41 is 50 to 2
While it is 00 μm, it is 5 to 10 μm.

FIG. 9 shows a solar cell in which the irradiated sunlight is made to enter the silicon substrate more efficiently. In this solar cell 50, an N-type impurity diffusion layer 51a is provided on the surface portion of a P-type silicon substrate 51, whereby a PN junction is formed. In addition, on the back surface of the P-type silicon substrate 51, the P-type impurity diffusion layer 51b is formed.
And the back electrode 56 is provided on the P-type impurity diffusion layer 51b. The surface of the N-type impurity diffusion layer 51a provided on the surface of the P-type silicon substrate 51 has a concavo-convex shape in which concave and convex portions each having a quadrangular pyramid shape are alternately formed in the vertical and horizontal directions.

On the surface of the N-type impurity diffusion layer 51a, a pair of electrode mounting bases 5 extending in stripes along the width direction.
1c are provided in parallel at appropriate intervals. Note that FIG. 9 illustrates an example of a solar cell, and the electrode installation base portions 51c need not be a pair and need not extend over the entire width direction. Each electrode installation base 51c
As shown in FIG. 10, is formed flat at a level slightly higher than the level of the top of each convex portion on the surface of the P-type silicon substrate 51 having an uneven shape. The long plate-shaped surface electrode 52 is provided over substantially the entire length of each electrode installation base 51c in a state of being in contact with the N-type impurity diffusion layer 51a.

A glass plate 55 is laminated on the surface of the P-type silicon substrate 51 via an adhesive layer 54, and each surface electrode 52 is also covered with the adhesive layer 54 and the glass plate 55. Has become.

The surface of the long plate-like surface electrode 52 is formed in a predetermined uneven shape, and each electrode installation base 5 is formed.
The P-type silicon substrate (wafer) 51 on which 1c is formed is formed as follows. As shown in FIG. 11, a photoresist 20 having a thickness of about 10 μm is uniformly applied to the P-type silicon substrate 51 having the N-type impurity diffusion layer 51a on the surface thereof, and the photoresist 2 is formed.
0 is patterned into a stripe shape corresponding to the shape of the surface electrode 52. The patterning of the photoresist 20 is performed by bringing a glass mask provided with a stripe pattern into close contact with the photoresist 20 and exposing and developing the glass mask. As a result, in the photoresist 20, stripe-shaped recesses 21 are formed on the electrode mounting base 51c.

Next, an electrode material is uniformly vapor-deposited on the surface of the P-type silicon substrate 51 having the photoresist 20 having the predetermined stripe-shaped recess 21 formed therein. The electrode material enters the recess 21 of the photoresist 20,
The surface electrode 52 is formed. Then, the P-type silicon substrate 5
The photoresist 20 is removed from the surface of No. 1 by a solvent. As a result, the electrode material deposited on the photoresist 20 is removed together with the resist, and only the electrode material in the stripe-shaped recess 21 of the photoresist 20 remains, and the surface electrode 52 is formed.

[0012]

The metal surface electrode 52 thus formed also reflects the sunlight applied to the surface of the surface electrode 52 without causing it to enter the P-type silicon substrate 51. Moreover, as shown in FIG. 10, since the surface of each surface electrode 52 is at a higher level than that of the P-type silicon substrate 51, the sunlight radiated to the surface of each surface electrode 52 and reflected is There is a problem that the efficiency of incident light from the surface of the P-type silicon substrate 51 adjacent to the electrode mounting base 51c to the inside is extremely low.

Surface electrode 52 occupying on the electrode mounting base 51
By reducing the area of the P type silicon substrate 51.
The amount of sunlight entering the inside increases, but in this case, in order to reduce the electric resistance of the surface electrode 52, the thickness must be increased to increase the cross-sectional area. However, if the thickness of the surface electrode 52 is increased in this way,
The surface of the surface electrode 52 is in a state of largely protruding from the surface of the P-type silicon substrate 51. As a result, in order to form the surface electrode 52, the photoresist 20 provided on the P-type silicon substrate 51 must be thickly laminated, and therefore a large amount of photoresist must be used.

The electrode mounting base 51c, on which the surface electrode 52 is provided, is usually at the same level as the convex portion of the uneven surface of the P-type silicon substrate 51. To form the surface electrode 52, the photoresist 20 is applied to the P-type silicon substrate 51.
When the amount of 0 is small, as shown by the chain double-dashed line in FIG.
Due to the unevenness of the surface of the mold type silicon substrate 51, the surface of the photoresist 20 becomes wavy, and the electrode installation base 5
There is a possibility that the photoresist 20 on 1c may become thin.
As described above, a large amount of photoresist 20 is required to stack the photoresist 20 having a predetermined thickness on the electrode mounting base 51c.

Further, when the glass plate 55 is bonded to the P-type silicon substrate 51 by the adhesive layer 54, the surface electrode 5
2 is projected from the surface of the P-type silicon substrate 51, the surface of each surface electrode 52 and the glass plate 55 are
The gap between and becomes smaller and the adhesive layer 54 becomes thinner. FIG.
As shown in 0, the adhesive layer 54 is thickest between the lowest level portion of the concave portion of the P-type silicon substrate 51 and the glass plate 55, and the thickness thereof is T _1. The agent layer 54 is thinnest between the surface electrode 52 and the glass plate 55, and its thickness is T ₄ . The thinnest thickness T ₄ of the adhesive layer 54 is the P-type silicon substrate 51.
Is significantly smaller than the thickness T ₂ of the adhesive layer 54 between the glass plate 55 and the highest level portion of the convex portion. For this reason, the adhesive does not cure sufficiently in the thinned portion of the adhesive layer 54,
Depending on the environment of use, the glass plate 55 may peel off at that portion.

The present invention is intended to solve such a problem, and an object thereof is to allow solar light to efficiently enter the semiconductor substrate, and thus to significantly improve power generation efficiency. To provide. Another object of the present invention is to provide a solar cell which is small in size, can be easily manufactured, and can prevent the glass plate adhered to the semiconductor substrate from peeling off.

[0017]

According to a first aspect of the present invention, there is provided a solar cell having a semiconductor substrate that generates electric power when sunlight is incident from a surface portion of the semiconductor substrate, the surface of the semiconductor substrate on which sunlight is incident. The part has an uneven shape, and the surface part is provided with an electrode installation concave part that is recessed in a stripe shape, and the electrode installation concave part is provided with a surface electrode so as not to protrude from the uneven surface part. It is characterized by being.

In the solar cell according to a second aspect of the present invention, the surface of the surface electrode is formed on the inner surface of the recess so that the irradiated sunlight is efficiently incident on the inner surface of the stripe-shaped electrode installation recess. It has an inclined surface inclined so as to face each other.

In the solar cell according to a third aspect of the present invention, the electrode installation concave portion is formed at the same time when the surface of the semiconductor substrate is formed in an uneven shape.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a perspective view showing an example of an embodiment of a solar cell of the present invention. The solar cell 10 is a silicon solar cell using a P-type silicon substrate 11 as a semiconductor substrate. The P-type silicon substrate 11 is provided with an N-type impurity diffusion layer 11a on the surface portion where sunlight is irradiated, and thus a PN junction is formed inside thereof. A P-type impurity diffusion layer 11b is provided on the back surface of the P-type silicon substrate 11.

On the surface of the P-type silicon substrate 11 provided with the N-type impurity diffusion layer 11a, quadrangular pyramidal concave portions and quadrangular pyramidal convex portions are formed alternately in the vertical and horizontal directions. It is uneven.

FIG. 2 is an enlarged sectional view of the surface portion of the silicon solar cell 10. As shown in FIGS. 1 and 2, on the surface of the P-type silicon substrate 11 provided with the N-type impurity diffusion layer 11a, a pair of stripe-shaped electrode installation recesses 11c extending in the width direction are appropriate. They are provided in parallel with each other at regular intervals. It should be noted that FIG. 1 shows a part of the solar cell, and the electrode installation concave portions 11c do not have to be a pair and do not necessarily have to be provided over the entire surface of the solar cell. The same applies to other examples. The lower surface of each electrode installation concave portion 11c is formed flat at a level almost equal to the lowest portion of each concave portion on the surface of the uneven P-type silicon substrate 11. The inner side surfaces of the electrode installation recesses 11c facing each other are in the same inclined state as the unevenness on the surface of the P-type silicon substrate 11.

On each electrode installation recess 11c, a long plate-shaped surface electrode 12 is provided over substantially the entire length of each electrode installation recess 11c in contact with the N-type impurity diffusion layer 11a.

Each surface electrode 12 is made of, for example, metal.
It is configured in a rectangular parallelepiped shape having a vertically long cross section in which the dimension in the thickness direction is larger than the dimension in the width direction, and the upper surface thereof is flat. The upper surface of each electrode 12 is set to a level lower than the highest portion of each convex portion on the surface of the P-type silicon substrate 11 having an uneven shape.

A glass plate 15 is provided via an adhesive layer 14 on the uneven surface of the P-type silicon substrate 11 provided with the N-type impurity diffusion layer 11a. Therefore, the uneven surface of the P-type silicon substrate 11 and each surface electrode 12 are covered with the adhesive layer 14 and the glass plate 15.

A back surface electrode 16 is provided on the back surface of the P-type silicon substrate 11 via a silicon oxide film 11d. The silicon oxide film 11d is in a state where a part of the P-type impurity diffusion layer 11b of the P-type silicon substrate 11 and a part of the back surface electrode 16 are in direct contact with each other.

A silicon solar cell 10 having such a structure
The sunlight incident on the glass plate 15 is incident on the P-type silicon substrate 11 through the N-type impurity diffusion layer 11a by irradiating the surface of the N-type impurity diffusion layer 11a. However, the sunlight applied to the surface of each metal surface electrode 12 is reflected by each surface electrode 12, and thus is not directly incident on the P-type silicon substrate 11. However, as shown in FIG. 3, the surface of each surface electrode 12 is flat and is at a lower level than the highest portion of the convex portion of the surface of the P-type silicon substrate 11 which is uneven. Therefore, the sunlight diffusely reflected by the corners on the surface of each surface electrode 12 is efficiently incident on the inclined inner side surface (the inclined surface of the P-type silicon substrate 11) of the electrode installation recess 11c. Therefore, the amount of sunlight reflected on the surface of each surface electrode 12 and entering the P-type silicon substrate 11 increases, and the output of the silicon solar cell 10 increases.

Further, as shown in FIG. 3, the thickness of the adhesive layer 14 in the silicon solar cell 10 becomes maximum at the lowest level portion of the concave portion on the surface of the P-type silicon substrate 11, and the thickness thereof is reduced. T ₁ while P
It becomes minimum in the highest level portion of the convex portion on the surface of the mold silicon substrate 11, and its thickness becomes T ₂ .
Since the upper surface of each surface electrode 12 is at a lower level than the highest part of the convex portion on the surface of the P-type silicon substrate 11, the adhesive layer 14 coated on each surface electrode 12 is formed.
Has a thickness T ₃ greater than the minimum thickness T ₂ . Therefore, if the minimum thickness T ₂ of the adhesive layer 14 that prevents the adhesive layer 14 from peeling from the P-type silicon substrate 11 is set by an environmental test or the like, each surface electrode 12 has a minimum thickness T 2. It will be covered by the adhesive layer 14 which is thicker than ₂ . As a result, in order to prevent the peeling of the glass plate 15 and protect each surface electrode 12, the thickness of the adhesive layer 14 covering each surface electrode 12 does not need to be particularly increased, The adhesive layer 14 can be made thin throughout. As a result, the silicon solar cell 10 can be made smaller and lighter.

The surface electrode 12 of the silicon solar cell 10 having such a structure is manufactured as follows. First, FIG.
As shown in (a), a P-type silicon substrate (wafer) 1
A silicon oxide film 11e is formed on the surface of 1. And
As shown in FIG. 4B, a photoresist 20 is laminated on the silicon oxide film 11e. Next, as shown in FIGS. 4C and 4D, a planar shape corresponding to the uneven shape of the surface of the P-type silicon substrate 11 and the electrode mounting recesses 1 are formed.
The photoresist 20 is patterned into a planar shape corresponding to 1c. In this case, as shown in FIG.
The photoresist 20 is not patterned in stripes in the portion corresponding to the electrode installation recess 11c in which the surface electrode 12 is provided.

The patterning of the photoresist 20 is carried out by disposing a glass mask in which a predetermined shape is written in close contact with the photoresist 20, exposing the glass mask, and developing it. As a result, the photoresist 20 is patterned into a predetermined shape by removing unnecessary portions.

When the photoresist 20 is patterned in this way, the silicon oxide film 11e on the surface of the P-type silicon substrate 11 is etched with an etching solution. In this case, the silicon oxide film 11e portion where the photoresist 20 is laminated is not removed by the etching solution, and only the portion that is not covered by the photoresist 20 is removed. Then, the photoresist 20
Is removed by, for example, a solvent, the silicon oxide film 11e is patterned into a shape similar to the shape of the patterned photoresist 20, as shown in FIGS. 4 (e) and 4 (f).

After that, the portion of the P-type silicon substrate 11 which is not covered with the silicon oxide film 11e is etched with an alkaline etching solution. In this case, the etching rate has anisotropy depending on the crystal orientation of the P-type silicon substrate 11, and as shown in FIGS.
On the surface of the P-type silicon substrate 11, quadrangular pyramid-shaped recesses and projections are etched in a continuous shape in the vertical and horizontal directions, and stripe-shaped electrode placement recesses 11c on which the surface electrodes 12 are provided are formed. . Then, the silicon oxide film 11e is removed.

In such a state, N-type impurities are diffused into the P-type silicon substrate 11, and the P-type silicon substrate 1
N-type impurity diffusion layer 11a is formed along the surface of No. 1.

Next, as shown in FIG. 5A, a photoresist 20 is laminated on the surface of the P-type silicon substrate 11 on which the N-type impurity diffusion layer 11a is formed. The photoresist 20 is laminated in such a thickness that the uneven surface of the P-type silicon substrate 11 is thinly covered. As a result, the photoresist 20 is thickly stacked on the electrode installation recess 11c.

Next, the photoresist 20 portion laminated in the electrode mounting recess 11c of the P-type silicon substrate 11 is patterned into a stripe shape corresponding to the surface electrode 12 to be formed. In the patterning in this case as well, a glass mask provided with a predetermined pattern is brought into close contact with the photoresist 20, the glass mask is exposed to light, and the photoresist 20 is exposed.
Is developed. As a result, FIG.
As shown in (b), a stripe-shaped recess 21 is formed in the photoresist 20 portion on the electrode installation recess 11c. The stripe-shaped recess 21 formed on the electrode installation recess 11c has the photoresist 20 thickly stacked on the electrode installation recess 11c.
It is formed deep from the surface of.

After that, a metal of an electrode material is vapor-deposited in the recess 21 at a predetermined height. Then, with a solvent, P
The photoresist 20 laminated on the mold silicon substrate 10 is removed. As a result, the striped surface electrode 12 extending in the vertical direction is formed on the electrode installation recess 11c. Surface electrode 12 formed on the electrode installation recess 11c
Is formed in the concave portion 21 provided in the photoresist 20 covering the surface of the P-type silicon substrate 11, so that it can be set at a lower level than the highest portion of the convex portion on the surface of the P-type silicon substrate 11. it can.

Each surface electrode 12 does not have to have a flat upper surface, and as shown in FIG. 6, a pair of inclined surfaces is formed so that the central portion in the width direction is sharply projected. It may have a shape having. Further, the structure may be such that only one side is inclined without providing a pair of inclined surfaces.

In this way, in the structure in which the surface of each surface electrode 12 has a pair of inclined surfaces such that the central portion in the width direction projects, the inclined surfaces face the inner side surfaces of the electrode installation recesses 11c. The sunlight entering the glass plate 15 and reflected by the inclined surfaces of the front surface electrodes 12 is efficiently reflected from the inner surface of the electrode installation recess 11c into the P-type silicon substrate 11. Incident. Therefore, the power generation efficiency with respect to sunlight of the silicon solar cell 10 is further improved.

In the case of forming the surface electrode 12 having the pair of inclined surfaces on the surface as described above, as shown in FIG. 7, when forming the electrode installation concave portion 11c, the central portion in the width direction is formed. Patterning is also performed on the surface of the P-type silicon substrate 11 before etching corresponding to the upper side so that the silicon oxide film 11e remains in a stripe shape having a relatively small width dimension. When etching is performed in such a state, due to the anisotropy of the etching rate of the crystal orientation of the P-type silicon substrate 11, a pair of inclined surfaces inclined in different directions are continuously provided on the lower surface of the electrode installation concave portion 11c. It is formed in an uneven shape.

In this way, when the electrode installation concave portion 11c having an uneven lower surface is formed, the photoresist 20 is formed as in the case of forming the surface electrode 12 having a flat surface.
Is laminated on the surface of the P-type silicon substrate 20, a recess 21 is formed on the electrode installation recess 11c, and a metal of an electrode material is vapor-deposited in the recess 21. In this case, since metal is vapor-deposited on the lower surface of the electrode installation recess 11c having a plurality of continuous inclined surfaces in a state corresponding to the shape of the lower surface of the electrode installation recess 11c, the surface of the surface electrode 12 to be formed. Is formed in a state where a pair of inclined surfaces are abutted against each other and a central portion in the width direction is projected upward. In this way, the surface electrode 12 having a pair of inclined surfaces is formed, and then the photoresist 20 is removed by the solvent.

[0042]

As described above, the solar cell of the present invention is provided with the recessed portion for installing an electrode on the uneven surface portion of the semiconductor substrate, and the surface electrode is provided in the recessed portion. The sunlight reflected by the electrodes is efficiently incident on the semiconductor substrate, and the power generation efficiency is significantly improved. The electrode installation concave portion is formed at the same time when the uneven surface of the semiconductor substrate is formed, and therefore the manufacturing is easy. Moreover,
Since the surface electrode does not protrude from the surface of the semiconductor substrate, when the surface of the semiconductor substrate is covered with the glass plate, the adhesive layer for adhering the glass plate does not need to be particularly thick to cover the surface electrode. Since the glass plate does not peel off and the adhesive layer does not need to be particularly thick, the solar cell is downsized.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an embodiment of a solar cell of the present invention.

FIG. 2 is a sectional view of a main part of the solar cell.

FIG. 3 is a cross-sectional view showing an enlarged main part for explaining the operation of the solar cell.

4A to 4H are cross-sectional views of a main part showing a step of forming a surface portion of a silicon substrate of the solar cell in a concavo-convex shape, respectively.

5 (a) and 5 (b) are cross-sectional views of a main part showing a step of providing a surface electrode on a silicon substrate of the solar cell, respectively.

FIG. 6 is a cross-sectional view of a main part showing another example of the embodiment of the solar cell of the present invention.

FIG. 7 is a cross-sectional view of a main part showing a step of forming a surface portion of a silicon substrate of the solar cell in an uneven shape.

FIG. 8 is a partially cutaway perspective view showing an example of a conventional solar cell.

FIG. 9 is a partially cutaway perspective view showing another example of a conventional solar cell.

FIG. 10 is a cross-sectional view showing an enlarged main part for explaining the operation of the solar cell.

FIG. 11 is an enlarged cross-sectional view of a main part in a manufacturing process of a surface electrode of the solar cell.

[Explanation of symbols]

 10 Solar Cell 11 P-type Silicon Substrate 11a N-type Impurity Diffusion Layer 11c Electrode Installation Recess 12 Surface Electrode 14 Adhesive Layer 15 Glass Plate

Claims (3)

[Claims] 1. A solar cell having a semiconductor substrate that generates power when sunlight is incident on the surface portion of the semiconductor substrate, wherein the surface portion of the semiconductor substrate on which the sunlight is incident has an uneven shape. , The electrode installation recessed portion that is recessed in a stripe shape is provided, and in the electrode installation recessed portion,
A solar cell, in which a surface electrode is provided so as not to project from the uneven surface portion. 2. The surface of the surface electrode is an inclined surface that is inclined so as to face the inner surface of the stripe-shaped electrode installation concave portion so that the irradiated sunlight can be efficiently incident on the inner surface. The solar cell according to claim 1, comprising: 3. The solar cell according to claim 1, wherein the electrode installation concave portion is formed at the same time when the surface of the semiconductor substrate is formed in an uneven shape.