JPH09181343A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the thickness of thickness silicon layers and to improve a voltage-current characteristic especially in low illuminance by providing a back electrode layer on one main face side of a substrate constituted of crystal silicon and sequentially stacking first and second amorphous silicon layers with specified thickness, and light-receiving electrode layer on the other main face. SOLUTION: The back electrode layer 8 is provided on one main face side of the substrate 1 constituted of p-type or n-type crystal silicon, and the i-type first amorphous silicon layer 2, the p-type or n-type second amorphous silicon layer 3 and the light-receiving electrode layer 4 are sequentially stacked on the other main face of the substrate 1. The thickness of the first amorphous silicon layer 2 is set to be less than 400Å, and the thickness of the second amorphous silicon layer 3 is set to be less than 100Å. Especially, the thickness of the second amorphous silicon layer 3 is set to be optimum one for suppressing the absorption of light. Thus, the voltage-current characteristic becomes satisfactory especially in low illuminance, and the photoelectric conversion device S of the solar battery superior in high efficiency and the optical sensor superior in the characteristic can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device used for photosensors, solar cells, and the like, and more particularly to a photoelectric conversion device in which an amorphous silicon layer is laminated on crystalline silicon.

[0002]

2. Description of the Related Art Conventionally, much research has been done on a heterojunction photoelectric conversion device in which amorphous silicon is laminated on a substrate made of crystalline silicon (polycrystalline silicon or single crystalline silicon) to obtain high conversion efficiency. Has been done in.

For example, as shown in FIG. 6, a metal film 52 made of gold-antimony is provided on one main surface (rear surface) of a crystalline silicon substrate 51, and the other main surface (light receiving surface) of this crystal silicon 51 is provided. An amorphous silicon carbide film 53 is provided, and a transparent conductive film 54 is formed on the silicon carbide film 53.
A photoelectric conversion device J provided with is known (for example, Jpn.
J. Appl. Phys. 23 (1984) 515.).

In a photoelectric conversion device in which an i-type amorphous silicon layer, an n-type microcrystalline silicon layer, and a transparent electrode layer are sequentially stacked on a crystalline silicon substrate, an n-type amorphous silicon layer is used. It is also known that the layers are laminated to a thickness of 100 Å or more and the impurity concentration is extremely high (for example, 12TH EUROPEAN PHOTOVOLTAIC SOLAR ENERGY CONF.
11-15 APRIL 1994. 705-708).

However, in such a heterojunction photoelectric conversion device, in order to improve the diode characteristics, the impurity-doped layer (p-type or n-type layer) is thick (for example, 200 Å or more), and the impurity is further increased. Due to the high concentration, a large proportion of incident light is absorbed in this layer before it reaches the region where it can be converted into photocurrent. Therefore, there is a problem that improvement in conversion efficiency cannot be expected.

Therefore, various problems of the conventional photoelectric conversion device are solved, and the thickness of the amorphous silicon layer to be laminated on the crystalline silicon is optimized so that the voltage-especially at low illuminance.
It is an object to provide a photoelectric conversion device having excellent current characteristics.

[0007]

A photoelectric conversion device which achieves the above object is provided with a back electrode layer on one main surface side of a substrate made of p-type or n-type crystalline silicon and on the other main surface of the substrate. In addition, an i-type first amorphous silicon layer having a thickness of 400 Å or less, a second amorphous silicon layer of p-type or n-type having a thickness of 100 Å or less, and a light-receiving surface electrode layer are sequentially laminated. It will be done.

Here, in order to improve the conversion efficiency particularly in the low illuminance region, the thickness of the first amorphous silicon layer is more preferably 50 to 200Å, and the second amorphous silicon layer is more preferable. The thickness is more preferably 40 to 90Å. That is, by optimizing the first amorphous silicon layer in this way, there is no hindrance to the extraction of photocurrent (if the first amorphous silicon layer is too thick, the photo-generated carriers generated on the crystalline silicon side are exposed to light). It becomes difficult to take out as a current), and the second amorphous silicon layer suppresses absorption of light, and an appropriate diode characteristic is obtained.

The p-type or n-type amorphous silicon layer does not have to be completely amorphous, and may be a so-called microcrystalline layer in which microcrystals are mixed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail with reference to the drawings. Photoelectric conversion device S shown in FIG.
Is a solar cell that can maintain high conversion efficiency even when the illumination light has various wavelengths of light such as fluorescent light and incandescent light. Its ideal basic structure is as shown below. Is.

As shown in FIG. 1, the photoelectric conversion device S has p
-Type or n-type crystalline silicon is provided with a back surface electrode layer 8 on the one main surface (back surface) 1b side of the substrate 1, and on the other main surface (light receiving surface) 1a of the substrate 1, the i-type first amorphous Silicon layer 2,
The second amorphous silicon layer 3 having a deposition area smaller than the area of the other main surface of the p-type or n-type substrate 1 and the light-receiving surface electrode layer 4 are sequentially laminated.

Specifically, on the light-receiving surface 1a side of the substrate 1 made of polycrystalline silicon having a p-type conductivity, the first amorphous material having the i-type conductivity is formed on almost the entire light-receiving surface 1a of the substrate 1. A silicon layer 2 is provided, and a peripheral portion is patterned and removed on the first amorphous silicon layer 2, and a deposition area is smaller than an area of the light receiving surface 1a of the substrate 1 and a second conductivity type is an n type. An amorphous silicon layer 3 is provided, and the second amorphous silicon layer 3 is made of ITO (indium tin oxide) whose peripheral portion is patterned, and is covered by the second amorphous silicon layer 3. A light-receiving surface electrode layer 4 having a small mounting area is provided, and a conductive paste, a conductive paste + solder,
Alternatively, an output extraction electrode 5 made of a metal film or the like is provided.

On the back surface 1b side of the substrate 1, an i-type third amorphous silicon layer 6 is provided on almost the entire back surface 1b of the substrate 1, and on the third amorphous silicon layer 6. A peripheral portion is patterned, a deposition area is narrower than the area of the back surface 1b of the substrate 1, and a fourth amorphous silicon layer 7 having a conductivity type of p is provided, and on the fourth amorphous silicon layer 7. Is provided with a back surface electrode layer 8 made of aluminum whose peripheral area is patterned and whose deposition area is narrower than that of the fourth amorphous silicon layer 7.

Next, a method of manufacturing the photoelectric conversion device S having the above configuration will be described. First, a film is formed on the light receiving surface 1a side of the substrate 1. That is, the first amorphous silicon layer 2, which is an i-type hydrogenated amorphous silicon layer, is formed on substantially the entire light receiving surface 1a of the substrate 1 by plasma CVD to a thickness of 400 Å or less, that is, about 20 to 400 Å. Form a film. Here, the thickness of the first amorphous silicon layer 2 is more preferably 50 to 200 Å. With this thickness, there is no hindrance to the extraction of photocurrent. Then, phosphine, which is an impurity doping gas, is added to the amorphous silicon forming gas at a predetermined ratio (impurity concentration of about 0.2%) on substantially the entire upper surface of the first amorphous silicon layer 2. ˜2 at.%) And mixed to form a film having a thickness of about 30 to 100 Å to form the n-type second amorphous silicon layer 3. Then, a light-receiving surface electrode layer 4 made of ITO is formed on the almost entire upper surface of the second amorphous silicon layer 3 by a sputtering method so as to have a thickness of about 700 to 1000Å.

On the back surface 1b side of the substrate 1, first, i-type hydrogenated amorphous silicon is formed to a thickness of about 0 to 200 ° on almost the entire back surface 1b of the substrate 1 in the same manner as described above. Then, an i-type third amorphous silicon layer 6 is formed. And this third
The amorphous silicon forming gas is mixed with a gas for impurity doping such as diborane gas at a predetermined ratio in a similar manner on substantially the entire upper surface of the amorphous silicon layer 6 to have a thickness of about 0.
The p-type fourth amorphous silicon layer 7 is formed to about 200 Å. Then, the back surface electrode layer 8 made of aluminum is formed on almost the entire upper surface of the fourth amorphous silicon layer 7 by a vapor deposition method or a sputtering method to have a thickness of about 3000 Å.

Next, first, predetermined regions of the light-receiving surface electrode layer 4 and the back surface electrode layer 8 are covered with a resist and masked. And
Using a mixed acid that is a mixture of hydrofluoric acid, nitric acid, and water,
The peripheral portions of the amorphous silicon layer 3, the light-receiving surface electrode layer 4, the fourth amorphous silicon layer 7, and the back surface electrode layer 8 are etched. Here, the first amorphous silicon layer 2 and the third amorphous silicon layer 6 are hardly etched. Here, in order to adjust the etching rate, the amount of nitric acid in the mixed acid is increased to lower the etching rate, or the amount of water is increased to lower the etching rate. Even if dilute hydrofluoric acid (2%) is used, the first amorphous silicon layer 2 and the second amorphous silicon layer 2
A difference in etching rate from the amorphous silicon 3 can be realized and a target structure can be formed. The same applies to the third amorphous silicon 6 and the fourth amorphous silicon 7.

Further, the light-receiving surface electrode layer 4 and the back surface electrode layer 8
Is etched with hydrochloric acid or hydrogen bromide, for example.

Then, screen printing, solder dip,
Alternatively, the extraction electrode 5 can be formed by a vapor deposition method or the like to manufacture the photoelectric conversion device S shown in FIG. When a large number of element regions are formed on the substrate 1, after the elements are formed as described above, cutting is performed by laser, dicing, diamond scribe or the like to separate the elements. .

Here, the substrate 1 may be single-crystal silicon, and the conductivity type of the substrate 1 may be n-type (in this case,
Instead of the n-type amorphous silicon layer provided on the light receiving surface side of the substrate 1, a p-type amorphous silicon layer may be provided. ).
Further, the second amorphous silicon layer 3 and the fourth amorphous silicon layer 7 do not have to be completely amorphous, and may be so-called microcrystalline layers. Alternatively, only the back surface electrode layer may be formed on the back surface side of the substrate 1. In addition, the light-receiving surface electrode layer 4
May be zinc oxide (ZnO) or the like. Further, the peripheral portions of the first amorphous silicon layer 2 and / or the third amorphous silicon layer 6 may be patterned and removed.

It is more preferable that a protective film is formed on the back electrode layer 8 in order to improve the reliability such as the moisture resistance of the photoelectric conversion device S as a whole. For example, a resin is formed as a protective film using a known printing method, and further, for example, a conductive resin is extracted using a known printing method, and an electrode portion is formed. In addition, a solder material may be formed thereon in order to improve the solderability at the time of mounting in a later step. This is because the conductive resin surface is oxidized by leaving it for a long time,
This is to prevent the possibility of adversely affecting the solderability during later mounting.

Next, the characteristics of the photoelectric conversion device S will be described. The voltage-current characteristics of the photoelectric conversion device S when the light-receiving area is about 0.5 cm ² are as shown by the solid line in FIG. 2, and the open-circuit voltage is about 0.4 V, indicating that the voltage-current characteristics are very good. there were. Further, the dark current at a forward bias of 0.3 V was also 2 × 10 ⁻⁶ A / cm ² or less. As described above, in the photoelectric conversion device S, the generation of dark current can be suppressed as much as possible by lengthening the length of the surface of the semiconductor junction, and the voltage-current characteristics at low illuminance can be significantly improved as compared with the related art. .

Next, a diagram showing the relationship between the thickness of the second amorphous silicon layer 3 and the short circuit current value under the measurement conditions of a light receiving area of about 0.42 cm ² , an illuminance of a fluorescent lamp of 250 lux and room temperature. As shown in FIG. As is apparent from this figure, the thinner the second amorphous silicon layer 3 is, the larger the short-circuit current value is.

FIG. 4 is a diagram showing the relationship between the thickness of the second amorphous silicon layer 3 and the short circuit current value. This result was measured under the same measurement conditions as above. As is clear from this figure, from the relationship between the bright current at a forward bias of 0.3 V and the thickness of the second silicon layer 3, the preferable thickness of the second silicon layer 3 is 40 to 90Å, and about 60 to 70Å. It seems that there is a peak in the vicinity. It is considered that the optimum thickness exists due to the balance between the degree of suppression of light absorption and the diode characteristics. The reason that the characteristics of the second amorphous silicon 3 are too thin and the characteristics are deteriorated is that the diode characteristics are deteriorated. More specifically, it is considered that the diffusion potential of the junction is insufficient.

As shown in FIG. 5, p-type or n-type
Of the rear surface electrode layer 34 on the rear surface of the substrate 31 of the polycrystalline silicon of the mold
And a p-type or n-type polycrystalline silicon substrate 31
The light receiving surface of the substrate 31 is patterned to have a peripheral edge portion, and the deposition area is narrower than the light receiving surface of the substrate 31. Photoelectric conversion having a structure in which a crystalline silicon layer 32 is stacked, and a peripheral portion is patterned on the amorphous silicon layer 32 to stack a light-receiving surface electrode layer 33 having a deposition area narrower than that of the amorphous silicon layer 32. It may be the device S3. Such a photoelectric conversion device S3
Also in the above, it was found that the first amorphous silicon layer 2 and the second amorphous silicon 3 have the same optimum range of thickness as in the above embodiment. Note that, in FIG. 5, the extraction electrode and the like of the substrate 31 are omitted. In addition, C3 in the figure indicates a portion where element isolation is performed by cutting with laser or dicing.

The etchant used at this time is an etchant (for example, mixed acid) in which the amorphous silicon layer 32 and the light-receiving surface electrode layer 33 are both etched, and is etched together. Side etching of the light-receiving surface electrode layer 33 may be performed using an etchant such as hydrochloric acid so that only 33 is etched.

[0026]

As described above, in the photoelectric conversion device of the present invention, the back electrode layer is provided on one main surface side of the substrate made of p-type or n-type crystalline silicon, and the other main surface of the substrate is provided. The i-type first amorphous silicon layer, the p-type or n-type second amorphous silicon layer, and the light-receiving surface electrode layer are sequentially stacked. Then, increase the thickness of the first amorphous silicon layer to 40
The thickness of the second amorphous silicon layer is set to 0 Å or less, and the thickness of the second amorphous silicon layer is set to 100 Å or less. It is possible to provide a photoelectric conversion device such as a solar cell having excellent characteristics and high efficiency and an optical sensor having excellent characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a photoelectric conversion device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing voltage-current characteristics of a photoelectric conversion device.

FIG. 3 is a diagram showing a relationship between a thickness of a second amorphous silicon layer and a short circuit current value.

FIG. 4 is a diagram showing a relationship between a thickness of a second amorphous silicon layer and a short circuit current value.

FIG. 5 is a cross-sectional view of a main part of a photoelectric conversion device according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view of a main part showing an example of a conventional photoelectric conversion device.

[Explanation of symbols]

 1 ... Substrate 2 ... 1st amorphous silicon layer 3 ... 2nd amorphous silicon layer 4 ... Light-receiving surface electrode layer 8 ... Back surface electrode layer S ... Photoelectric conversion device

Claims (1)

[Claims] 1. A back electrode layer is provided on one main surface side of a substrate made of p-type or n-type crystalline silicon, and an i-type first substrate having a thickness of 400 Å or less is provided on the other main surface of the substrate. A photoelectric conversion device comprising an amorphous silicon layer, a p-type or n-type second amorphous silicon layer having a thickness of 100 Å or less, and a light-receiving surface electrode layer, which are sequentially stacked.