JP2001313399A - Photoelectric conversion device - Google Patents

Abstract

(57) [Problem] A photoelectric conversion device using a conventional crystalline semiconductor particle has high cost and low conversion efficiency. SOLUTION: A large number of crystalline semiconductor particles of a first conductivity type are arranged on a substrate, and a semiconductor layer of a second conductivity type is formed on the crystalline semiconductor particles. In a photoelectric conversion device with an insulator interposed between
The semiconductor layer of the second conductivity type was formed of a crystalline semiconductor layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photoelectric conversion device used for photovoltaic power generation, and more particularly to a photoelectric conversion device using crystalline semiconductor particles.

[0002]

2. Description of the Related Art The emergence of low-cost next-generation solar cells using silicon-saving materials is strongly desired. FIG. 2 shows a conventional photoelectric conversion device using granular or spherical silicon crystal particles advantageous for resource saving (see, for example, Japanese Patent No. 2641800). In this photoelectric conversion device, a low-melting-point metal layer 7 is formed on a substrate 1, and first-conductivity-type crystalline semiconductor particles 3 are disposed on the low-melting-point metal layer 7. There is disclosed a photoelectric conversion device in which an amorphous semiconductor layer 6 of the second conductivity type is formed between the amorphous semiconductor layer 6 and the low melting point metal layer 7 via an insulating layer 2.

According to Japanese Patent Laid-Open No. 61-124179, as shown in FIG. 3, an opening 10a is formed in an upper aluminum foil 10, and an opening 10a is formed in the opening 10a on the surface of a p-type core 9a. A silicon ball 9 having a silicon ball 9b is disposed, the n-type skin portion 9b on the back side of the silicon ball 9 is removed, the insulating layer 2 is formed on the back side of the upper aluminum foil 10, and the p-type on the back side of the silicon ball 9 is formed. A photoelectric conversion device in which the insulating layer 2 on the nucleus 9a is removed and the lower aluminum foil 8 and the p-type nucleus 9a of the silicon sphere 9 are joined is disclosed.

Further, according to Japanese Patent Publication No. 8-34177, as shown in FIG.
3, a method of forming a polycrystalline thin film 13 by melting and saturating the semiconductor fine crystal grains 13 and then gradually cooling the semiconductor microcrystal grains 13 to cause liquid phase epitaxial growth of the semiconductor. In FIG. 4, reference numeral 11 denotes Sn.
12 is a high melting point metal film such as Mo,
Reference numeral 14 denotes a second conductivity type monocrystalline or amorphous semiconductor layer;
5 is a transparent conductive film.

[0005]

However, according to Japanese Patent No. 2641800, since an amorphous semiconductor layer is used as the second conductivity type semiconductor layer 6, the amorphous semiconductor layer 6 has a large light absorption. Due to this, when the semiconductor layer 6 is formed along the surface of the particle 3, a film thickness distribution depending on the position occurs. Particle 3
It is difficult to form a pn junction along the outline of the pn junction. Even if the poor coverage is compensated for by forming the semiconductor layer 6 after the particles 3 and the insulating layer 2 are polished and exposed to a flat surface, the number of polishing steps and cleaning steps for removing polishing debris increases, and When the height of the particles 3 varies, the pn junction area varies, and sufficient characteristics cannot be obtained. As a result, there is a problem that the cost is high and the conversion efficiency is low.

[0006] Further, Japanese Patent Application Laid-Open No. 61-12417 shown in FIG.
In the photoelectric conversion device as disclosed in Japanese Patent Application Laid-Open No. 9-209, it is necessary to manufacture a silicon sphere 9 having an n-type skin portion 9b on a p-type central core 9a, and an opening 1 in an aluminum foil 10.
Since the silicon spheres 9 need to be formed and then bonded by pushing the silicon spheres 9 into the openings 10a, uniformity is required for the sphere diameter of the silicon spheres 9, resulting in a high cost.

According to Japanese Patent Publication No. 8-34177, the components of the low melting point metal film 11 are mixed into the polycrystalline thin film 13 to deteriorate the characteristics, and since there is no insulator, the upper electrode 15 and the lower electrode 12 There is a problem that a short circuit is easily generated between them.

The present invention has been made in view of the above-mentioned problems in the prior art, and an object of the present invention is to provide a photoelectric conversion device having excellent characteristics at low cost.

[0009]

Means for Solving the Problems To achieve the above object, a photoelectric conversion device according to the present invention comprises arranging a large number of first-conductivity-type crystalline semiconductor particles on a substrate; In a photoelectric conversion device in which a semiconductor layer of the second conductivity type is formed and an insulator is interposed between the semiconductor layer of the second conductivity type and the substrate, the semiconductor layer of the second conductivity type is a crystalline semiconductor layer. It is characterized by being formed by.

In the above-mentioned photoelectric conversion device, it is preferable that the thickness of the crystalline semiconductor layer is 50 nm to 700 nm.

In the above-mentioned photoelectric conversion device, it is preferable that the crystalline semiconductor layer is formed along the surface of the crystalline semiconductor particles.

Further, in the above-mentioned photoelectric conversion device, it is desirable to provide a transparent conductive layer on the crystalline semiconductor layer.

According to the photoelectric conversion device of the present invention, crystalline semiconductor particles of the first conductivity type are arranged on the substrate, and a crystalline semiconductor layer of the second conductivity type is formed on the crystalline semiconductor particles. By forming an insulator between the crystalline semiconductor layer of the second conductivity type and the substrate, the prior art is disclosed in Japanese Patent No. 2641800, Japanese Patent Application Laid-Open No. 61-124179, and Japanese Patent Publication No. 8-34.
As compared with the photoelectric conversion device disclosed in, for example, Japanese Patent Application Laid-Open No. 177, 177, it is possible to manufacture the device at lower cost and to realize excellent characteristics. In other words, it is only necessary to produce particles having a single conductivity type with low particle size accuracy, so that low-cost production is possible, the degree of freedom in the thickness of the semiconductor layer is large, and the separation of the positive electrode and the negative electrode by the insulator is ensured. Therefore, excellent characteristics can be realized.
The excellent properties indicate that the coatability is sufficient, there is no short circuit between the crystalline semiconductor particles and the conductive film, and the conversion efficiency is high.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. In FIG. 1, 1 is a substrate, 2 is an insulating layer,
3 is a crystalline semiconductor particle of the first conductivity type, 4 is a crystalline semiconductor layer, and 5 is a transparent conductive film.

As the substrate 1, metal, ceramic, resin or the like is used. Since the substrate 1 also serves as a lower electrode, it has only to have conductivity as a characteristic. When the material is metal, the substrate 1 has a single-layer structure or a multilayer structure with another metal. When the substrate 1 is an insulator such as ceramic or resin, it is necessary to form a conductive layer on the surface thereof.

The insulating layer 2 is provided for separating the positive electrode and the negative electrode. For example, it is formed using a glass slurry containing SiO ₂ , Al ₂ O ₃ , PbO, ZnO or the like as an optional component.
The thickness of the insulating layer 2 is 2 / the average particle size of the crystalline semiconductor particles 3.
It is preferably 3 or less and 1 μm or more. If the thickness of the insulating layer 2 is 2/3 or more of that of the crystalline semiconductor particles 3, the area where the pn junction is formed becomes small, and it is not preferable because carriers cannot be efficiently collected. Further, when the thickness of the insulating layer 2 is 1 μm or less, insulation between the substrate 1 and the crystalline semiconductor layer 4 becomes insufficient, and the substrate 1 and the crystalline semiconductor layer 4 partially come into contact with each other, causing a short circuit. Not preferred because it causes.

The crystalline semiconductor particles 3 of the first conductivity type are S
i and Ge contain p-type B, Al, Ga, or the like, or n-type P, As, or the like, in a small amount. The shape of the semiconductor particles 2 includes a polygonal shape, a curved shape, and the like. For example, when the semiconductor particles 3 are pushed into the insulator layer 2 described below and brought into contact with the substrate 1, the insulator layer 2 is formed. One with a curved surface to push away efficiently,
Particularly, those having a spherical shape are preferable. The particle size distribution may be uniform or non-uniform, but if uniform, a process for adjusting the particle size is required. In order to obtain a lower cost, the non-uniform case is advantageous. The particle 3 has a particle size of 10 to 500 μm.
When the thickness is less than 10 μm, the insulating layer 2 adheres to the pressing jig when pressing and the surface of the semiconductor particles 3 is contaminated. It is no different from quantity,
The advantage of applying particles in the sense of saving semiconductor materials is lost.

The crystalline semiconductor layer 4 of the second conductivity type comprises a catalyst C
For example, a VD method, a VHF-CVD method, a plasma CVD method, or the like is used to introduce a slight amount of an n-type phosphorus-based compound gas phase or a p-type boron-based compound gas phase into a silane compound gas phase. Note that the crystalline semiconductor layer 4 may be monocrystalline, polycrystalline, or microcrystalline. It is desirable that the crystalline semiconductor layer 4 is formed along the surface of the semiconductor particle 3 and the semiconductor junction is formed near the light incident surface and along the particle shape. By forming a junction along the surface of the semiconductor particles 3, carriers generated at any position inside the crystalline semiconductor particles 3 can be efficiently collected. When the semiconductor layer 4 is formed into an uneven shape, if the film thickness is too small, it becomes difficult to cover all the exposed portions of the particles along the particle surface. Conversely, if the film thickness is too large, the coverage is good, but the loss due to light absorption of the semiconductor layer 4 increases, and the conversion efficiency decreases. Since the crystalline semiconductor layer 4 absorbs less light than the amorphous semiconductor layer, the loss does not increase rapidly even when the thickness is increased. Film thickness is 50-700n
m is preferred. If the thickness is 50 nm or less, the coverage is deteriorated, and a leak occurs in which the semiconductor particles 3 and the transparent conductive film 5 come into direct contact with each other. Also,
A thickness of 700 nm or more is not preferable because conversion efficiency is reduced, tact is reduced, and material costs are increased, resulting in high costs.

The transparent conductive film 5 is formed of, for example, tin oxide or ITO by a sputtering method, a plasma CVD method, or the like. Note that, when the absorption of sunlight is large, the conversion efficiency is reduced. Therefore, the absorption of sunlight is preferably small. Further, the thickness of the transparent conductive film is more preferably from 10 to 300 nm.
A film thickness of 10 nm or less is not preferable because resistance increases and conversion efficiency decreases. A film thickness of 300 nm or more is not preferable because light absorption increases, conversion efficiency decreases, tact decreases, and material costs increase, resulting in high costs.

Further, a protective film may be provided on the transparent conductive film 5. As the protective film, silicon nitride, titanium oxide, or the like is formed by a sputtering method, a plasma CVD method, or the like. It is also possible to give roles such as a multiple reflection effect, an antireflection effect, and an improvement in weather resistance.

Further, it is desirable to form a high-concentration first conductivity type portion on the outer portion of the semiconductor particle 3 adjacent to the boundary between the substrate 1 and the semiconductor particle 2. As described above, by forming the first conductive type portion having a high concentration, the carriers formed by the semiconductor particles 3 can be efficiently separated, and the conversion efficiency can be improved. As a method of forming the first conductive type portion having a high concentration, the substrate 1 and the semiconductor particles 3 are brought into contact with each other and heated so that a part of the elements of the substrate 1 or the conductive film 6 formed on the substrate 1 becomes semiconductor particles. 3 and the like.

[0022]

Next, an embodiment of the photoelectric conversion device of the present invention will be described.

[Embodiment 1] First, an insulating layer 2 is formed on a substrate 1. Aluminum was used for the substrate 1. Insulating layer 2
Was formed to a thickness of 80 μm using a glass paste.
Next, one layer of polycrystalline p-type silicon particles 3 having an average diameter of 200 μm was densely arranged thereon. Next, heating was performed to a temperature higher than the softening point of the insulating layer 2, so that the silicon particles 3 were sunk into the insulating layer 2 and brought into contact with the substrate 1. Next, an n-type crystalline silicon layer 4 was formed on the silicon particles 3 and the insulating layer 2. Table 1 shows the results of examining the characteristics by changing the film thickness of the n-type crystalline silicon layer 4. A transparent conductive film 5 made of tin oxide is placed on the
It was formed to a thickness of 0 nm. A protective film made of silicon nitride was formed thereon to a thickness of 500 nm.

As a comparative example, a sample in which an n-type amorphous silicon layer was formed instead of the n-type crystalline silicon layer 4 was manufactured. Table 1 also summarizes the results obtained by changing the film thickness of the n-type amorphous silicon layer, and comparing the results.

The covering property was evaluated based on the frequency of leakage due to direct contact between the crystalline silicon particles and the transparent conductive film.
If the coverage of the n-type silicon is sufficient, the crystalline silicon particles do not come into direct contact with the transparent conductive film. Specifically, 10 sets of samples were prepared, and all leaks were evaluated as x, 9
３ indicates リ ー ク 3 leaks, ２〜 indicates 2-1 leaks, and ◎ indicates no leaks. The conversion efficiency was measured without leakage, and the average was obtained.

[0026]

[Table 1]

As can be seen from the above results, when the crystalline silicon layer is used, both the conversion efficiency and the coverage can be achieved as compared with the case where the amorphous silicon layer is used. A conversion efficiency of 6% or more and a covering property of ○ or more are practically necessary.
When an amorphous silicon layer is used, the coverage is improved.
In the range of 0 nm or more, all conversion efficiencies are 5% or less, which is not practical. This is probably because the amorphous silicon layer has a higher light absorption rate than the crystalline silicon layer, and therefore, the transmittance decreases as the film thickness increases. On the other hand, when a crystalline silicon layer is used, coverage and conversion efficiency can be compatible. Further, since it has a stable crystal structure as compared with amorphous, it can be expected that it is superior in terms of life and reliability. The film thickness is preferably from 50 nm to 700 nm. When the thickness of the crystalline silicon layer is less than 50 nm, the coverage is not sufficient, and when the thickness exceeds 700 nm, the conversion efficiency deteriorates, which is not preferable. [Embodiment 2] Next, the difference due to the shape of the pn junction is evaluated. Sample No. Samples having different pn junction shapes were prepared as Comparative Examples 1 to 7. The comparative example was produced as follows. An insulating layer 2 is formed on a substrate 1. Aluminum was used for the substrate 1. The insulating layer 2 was formed to a thickness of 200 μm using a glass paste. Next, one layer of polycrystalline p-type silicon particles 3 having an average particle diameter of 200 μm was densely arranged thereon. Next, the substrate was heated to a temperature higher than the softening point of the insulating layer 2 so that the silicon particles 3 were sunk into the insulating layer 2 and brought into contact with the substrate 1.
Next, polishing was performed so that the silicon particles 3 and the insulating layer 2 were exposed on a plane. Next, n is placed on the silicon particles 3 and the insulating layer 2.
Form crystal silicon layer 4 was formed. n-type crystalline silicon layer 4
Table 3 shows the results of evaluation by changing the film thickness of. A transparent conductive film 5 made of tin oxide was formed thereon to a thickness of 500 nm. A protective film made of silicon nitride is formed thereon to a thickness of 500 nm.
Formed to a thickness of

[0028]

[Table 2]

From the above results, when the pn junction is formed in a plane, the coverage is good, but the conversion efficiency is low.
Not practical. On the other hand, in the case where the pn junction is formed along the particle surface, excellent characteristics in both coverage and conversion efficiency can be obtained when the n-type silicon layer is in the range of 50 to 700 nm.

[0030]

As described above, according to the photoelectric conversion device of the present invention, a large number of crystalline semiconductor particles of the first conductivity type are arranged on a substrate, and a semiconductor of a second conductivity type is placed on the crystalline semiconductor particles. Forming a layer, in the photoelectric conversion device in which an insulator is interposed between the semiconductor layer of the second conductivity type and the substrate, since the semiconductor layer of the second conductivity type is formed of a crystalline semiconductor layer, High characteristics can be obtained by making the coating property and the conversion efficiency compatible. Further, there is no need to form an n-type skin on the p-type central core and to require high uniformity in the particle size, so that an inexpensive photoelectric conversion device can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a photoelectric conversion device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a conventional photoelectric conversion device.

FIG. 3 is a cross-sectional view showing another conventional photoelectric conversion device.

FIG. 4 is a cross-sectional view showing another conventional photoelectric conversion device.

[Explanation of symbols]

 1 ... substrate 2 ... insulating layer 3 ... crystalline semiconductor particles 4 ... crystalline semiconductor layer 5 ... transparent conductive film 6 ... Amorphous semiconductor layer 7 Low-melting metal layer 8 Lower aluminum foil 9 Silicon sphere having n-type skin on p-type 10 Upper aluminum foil 11 ... Low melting point metal film 12 ... High melting point metal film 13 ... Liquid phase epitaxial polycrystalline layer of first conductivity type 14 ... Polycrystalline or amorphous layer of second conductivity type

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F051 AA03 AA16 BA14 CB12 CB29 DA03 DA20 EA18 FA04 GA02 GA03

Claims (4)

[Claims] A first conductive type crystalline semiconductor particle disposed on a substrate; a second conductive type semiconductor layer formed on the crystalline semiconductor particle; In a photoelectric conversion device with an insulator interposed between the substrate and
A photoelectric conversion device, wherein the semiconductor layer of the second conductivity type is formed of a crystalline semiconductor layer. 2. The method according to claim 1, wherein said crystalline semiconductor layer has a thickness of 50 nm to 50 nm.
The photoelectric conversion device according to claim 1, wherein the thickness is 700 nm. 3. The photoelectric conversion device according to claim 1, wherein the crystalline semiconductor layer is formed along a surface of the crystalline semiconductor particles. 4. The photoelectric conversion device according to claim 1, wherein a transparent conductive layer is provided on the crystalline semiconductor layer.