JP2002198550A - Photoelectric conversion device - Google Patents

Abstract

(57) [Problem] To provide a low-cost and highly reliable photoelectric conversion device. SOLUTION: On a substrate 1 having one electrode layer, a large number of granular crystal semiconductors 2 having one conductivity type are arranged and joined to the substrate 1, and an insulator 3 is filled between the granular crystal semiconductors 2 to fill the same. A photoelectric conversion device in which a semiconductor layer 4 having the opposite conductivity type is provided on the granular crystal semiconductor 2 and the other electrode is connected to the semiconductor layer 4 having the opposite conductivity type. By using a material having an expansion coefficient of 30 to 60 × 10 ⁻⁷ / ° C. and a softening point of 500 ° C. or less, a good insulator 3 in which defects such as cracks and voids are prevented is formed. Provide a highly reliable photoelectric conversion device.

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, and more particularly to a photoelectric conversion device using a granular crystal semiconductor used for photovoltaic power generation.

[0002]

2. Description of the Related Art FIGS. 3 to 5 show a conventional photoelectric conversion device using a granular crystal semiconductor. For example, as shown in FIG. 3, an opening is formed in the first aluminum foil 10, and p is formed in the opening.
A silicon ball 2 having an n-type skin 9 on the shape is bonded, the n-type skin 9 on the back side of the ball 2 is removed, and an oxide insulating layer 3 is formed on the back side of the first aluminum foil 10. There has been disclosed a photoelectric conversion device in which the oxide insulating layer 3 on the back side of the silicon sphere 2 is removed and the silicon sphere 1 and the second aluminum foil 8 are joined (for example, see Japanese Patent Application Laid-Open No. 61-124179). .

As shown in FIG. 4, a low melting point metal layer 11 is formed on a substrate 1 and a first melting point metal layer 11 is formed on the low melting point metal layer 11.
A photoelectric conversion device in which a conductive-type granular crystal semiconductor 2 is provided, and a second conductive-type amorphous semiconductor layer 7 is formed on the granular crystal semiconductor 2 between the low-melting-point metal layer 11 and the insulating layer 3. Is disclosed (for example, Japanese Patent No. 264180).
No. 0).

Further, as shown in FIG. 5, a high melting point metal layer 12, a low melting point metal layer 11, and semiconductor fine crystal grains are deposited on a substrate 1, and the semiconductor fine crystal grains are melted and saturated. There is disclosed a method of forming a polycrystalline thin film 13 by gradually cooling a semiconductor by liquid phase epitaxy (for example, see Japanese Patent Publication No. 8-34177).

[0005]

However, in the photoelectric conversion device as shown in FIG. 3, an opening is formed in the first aluminum foil 10, and the silicon sphere 2 is pushed into the opening to insert the silicon sphere into the first aluminum foil. Since it is necessary to bond to the aluminum foil 10, uniformity of the diameter of the silicon ball 2 is required, and there is a problem that the cost is high. In addition, since the processing temperature at the time of joining is 577 ° C. or lower, which is the eutectic temperature of aluminum and silicon, there is a problem that the joining becomes unstable.

Further, according to the photoelectric conversion device as shown in FIG. 4, since the amorphous semiconductor layer 7 of the second conductivity type is provided on the granular semiconductor 2 of the first conductivity type, it is necessary to form a stable pn junction. Requires that the surface of the granular crystal semiconductor 2 be sufficiently etched and cleaned before the formation of the amorphous conductive layer 7. Further, the film thickness must be reduced due to the large light absorption of the amorphous semiconductor layer 7. If the film thickness of the amorphous semiconductor layer 7 is small, tolerance for defects is reduced, and the cleaning process and the manufacturing environment are reduced. Has to be strictly controlled, resulting in a problem of high cost.

Further, according to the photoelectric conversion device as shown in FIG. 5, since the low-melting-point metal layer 11 is mixed into the liquid-phase epitaxial polycrystalline layer 13 of the first conductivity type, the performance deteriorates and there is no insulator. Therefore, there is a problem that a leak occurs between the lower electrode 12 and the lower electrode 12.

[0008] The present invention has been made in view of the above-mentioned problems in the prior art, and an object thereof is to provide a low-cost photoelectric conversion device.

[0009]

According to a first aspect of the present invention, there is provided a photoelectric conversion device comprising a substrate having one electrode layer and a plurality of granular semiconductors having one conductivity type disposed on a substrate having one electrode layer. A semiconductor layer having an opposite conductivity type is provided on the grain crystal semiconductor by filling an insulator between the grain crystal semiconductors, and the other electrode is connected to the semiconductor layer having the opposite conductivity type. In the provided photoelectric conversion device,
The insulator is formed using a material having a coefficient of thermal expansion of 30 to 60 × 10 ⁻⁷ / ° C. and a softening point of 500 ° C. or less.

According to the photoelectric conversion device of the present invention, a large number of granular crystal semiconductors are arranged on a substrate, heated and joined by a molten alloy portion of both, and an insulator is filled between the plurality of granular crystal semiconductors. In the structure described above, the entire surface of the substrate on which the insulator is exposed is covered without defects, and cracks are prevented from occurring in the insulator and the granular crystal semiconductor.
No. 641800, Japanese Patent Publication No. 8-34177, Japanese Patent Publication No. 61-59678, Japanese Unexamined Patent Publication No. Hei 10-23351.
As compared with the photoelectric conversion device disclosed in Japanese Patent Application Publication No. 8 (1994) -208, the manufacturing margin is large, and low-cost manufacturing is possible. That is, it is only necessary to manufacture the granular crystal semiconductor with lower particle size accuracy, and the positive electrode and the negative electrode can be reliably separated by the insulator, so that low-cost manufacturing is possible.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIGS. 1 and 2 are views showing an embodiment of the photoelectric conversion device according to claim 1. 1 and 2
, 1 is a substrate, 2 is a granular crystal semiconductor, 3 is an insulator made of a glass material, 4 is a semiconductor layer, 5 is a protective layer, 6 is a conductive layer (the other electrode), and 15 is a substrate 1 and a granular crystal semiconductor. It is a joint.

The substrate 1 is made of metal, ceramic, resin or the like. Since the substrate 1 also serves as a lower electrode, any material having a conductive property of aluminum may be used.
When the whole is made of aluminum, it has a single layer as shown in FIG. 1, and when the substrate 1 does not contain aluminum, it has a multiple layer with a conductive layer 1 ′ made of aluminum as shown in FIG. When the substrate 1 is an insulator such as ceramic or resin, it is necessary to form a conductive layer 1 'made of aluminum shown in FIG. 2 on the surface thereof.

The central part of the granular crystal semiconductor 2 is Si, Ge.
B, Al, Ga, etc. exhibiting a p-type or an n-type
It contains a small amount of P, As, or the like. And the base
In a state where the plate 1 and the granular crystal semiconductor 2 are in contact with each other,
Exceeds 577 ° C., which is the eutectic temperature of Al and Si
The alloy part 15 is formed by firing at a temperature.
The alloy part 15 is in contact with Al, which is the material of the substrate 1, and the substrate 1.
Is melted together with the material of the granular crystal semiconductor 2
It is a molten alloy part. In addition, there is no contact with the alloy part 15
In the region of the first conductivity type, aluminum
Um diffuses and p ⁺Forming a layer. However,
If a conductive diffusion region is simply formed, Al and Si
577 ° C. or less, which is the eutectic temperature of
Is weak from the substrate 1 because the bonding between the
The crystal semiconductor 2 is detached, and the structure as a solar cell can be maintained.
Will not be able to.

The grain size distribution of the granular crystal semiconductor 2 may be uniform or non-uniform, but if uniform, a process for adjusting the grain size is required. Is more advantageous. Further, since the granular crystal semiconductor 2 has a convex curved surface, dependence on the light ray angle of light is reduced.

The diameter of the particles 2 is preferably 10 to 500 μm, and if the diameter is less than 10 μm, leakage occurs with the upper semiconductor layer 4 because the granular crystal semiconductor 2 is completely melted at the time of bonding with the substrate 1. On the other hand, when the thickness exceeds 500 μm, the amount of the semiconductor material used in the conventional flat plate photoelectric conversion device is not changed, and the advantage of applying particles in terms of saving the semiconductor material is lost. Note that the granular crystal semiconductor 2 has an n-type P, As, or the like, or a p-type B,
It may contain a small amount of Al, Ga, or the like.

The insulator 3 is used to separate the positive electrode and the negative electrode.
The material has a thermal expansion coefficient of
30-60 × 10^-7Material whose softening point is 500 ° C or less at / ° C
Is used. The thermal expansion coefficient is 30 × 10^-7/ ℃ or less
Underneath, a substrate made of aluminum (the coefficient of thermal expansion of Al:
240 × 10^-7/ ° C) due to the large difference in thermal expansion coefficient
After the insulator 3 is formed, cracks occur on the insulator surface.
60 × 10 ^-7/ G over crystalline semiconductor
2 (for example, the coefficient of thermal expansion of Si: 26 × 10^-7/ ℃)
Because the difference in thermal expansion coefficient is large, the granular crystal semiconductor 2 and
Cracks occur in the insulator 3 in the vicinity. Also
At the softening point, it melts at the temperature at which the semiconductor layer is formed
Or it must not decompose and has a softening point of 500
C., the bonding temperature of the substrate 1 and the granular crystal semiconductor 2
At a certain temperature around 577 ° C, the material does not melt and
Covers the exposed surface of the substrate 1 due to defects such as
Cannot function as an insulator.
Therefore, the range of the softening point is the temperature at which the amorphous semiconductor layer is formed.
In consideration of 200-500 ° C., preferably amorphous and crystalline
Considering the temperature for forming a semiconductor layer composed of a mixed crystal of
0-500 degreeC is good. The material of the insulator 3 satisfies the above conditions.
Any material can be used, such as SiO_Two, B_TwoO_Three, Al_Two
O_Three, CaO, MgO, P_TwoO_Five, Li_TwoO, SnO, Pb
O, ZnO, BaO, TiO_TwoEtc. as an optional component
Glass material for low-temperature firing of a material alone or one of the above materials
Insulators, etc., that combine seeds or multiple kinds of fillers
You. This insulator 3 is formed on the substrate 1 at least by granular bonding.
When a large number of crystal semiconductors 2 are arranged and bonded to a substrate,
It may be formed or formed after joining. Also, the table after formation
The surface may be subjected to processing such as etching.

The semiconductor layer 4 is made of, for example, Si. A small amount of a gaseous phase of a phosphorus-based compound exhibiting an n-type or a gaseous phase of a boron-based compound exhibiting a p-type is introduced into the gaseous phase of a silane compound by a vapor phase growth method or the like. Formed. The film quality may be crystalline, amorphous, or a mixture of crystalline and amorphous,
Considering the light transmittance, it is preferable to use a mixture of crystalline or crystalline and amorphous. Regarding the light transmittance, a part of the incident light passes through the semiconductor layer 4 in a portion where the granular crystal semiconductor 2 is not provided, By being reflected on the lower substrate 1 and irradiating the granular crystal semiconductor 2, it is possible to efficiently irradiate the granular crystal semiconductor 2 with light energy applied to the entire photoelectric conversion device.

Regarding the conductivity, the concentration of the trace element in the layer may be high, for example, 1 × 10 ¹⁶ to 10 ²¹ atm / c.
m ³ or so.

Further, it is desirable that the semiconductor layer 4 is formed along the surface of the granular crystal semiconductor 2 and is formed along the convex curved surface shape of the granular crystal semiconductor 2. By forming the pn junction along the convex curved surface of the granular crystal semiconductor 2, the area of the pn junction can be widened, and the carriers generated inside the granular crystal semiconductor 2 can be efficiently collected.
In the case where a granular crystal semiconductor 2 containing a small amount of n-type P, As, or the like, or p-type B, Al, Ga, or the like is used, the semiconductor layer 4 may not be provided.
The following conductive layer 6 may be formed thereon.

On the semiconductor layer 4, a conductive layer (the other electrode layer)
6 may be formed. The conductive layer 6 is formed by a film forming method such as a sputtering method or a vapor phase growth method, or by coating and baking, and is composed of one or more oxides selected from SnO ₂ , In ₂ O ₃ , ITO, ZnO, TiO _{2 and the} like. Film, or Ti, P
One or more metal-based films selected from t, Au and the like are formed. If the thickness of the transparent conductive layer is selected, the effect as an antireflection film can be expected. The conductive layer 6 needs to be transparent, and a part of the incident light passes through the conductive layer 6 in a portion where the granular crystal semiconductor 2 is not present, and is reflected on the lower substrate 1 to irradiate the granular crystal semiconductor 2. By doing so, it becomes possible to efficiently irradiate the granular crystal semiconductor 2 with light energy applied to the entire photoelectric conversion device. Furthermore, it is desirable that the conductive layer 6 be formed along the surface of the semiconductor layer 4 or the granular crystal semiconductor 2 and formed along the convex curved surface shape of the granular crystal semiconductor 2. By forming along the convex curved surface of the granular crystal semiconductor 2, the area of the pn junction can be increased widely,
Carriers generated inside the granular crystal semiconductor 2 can be efficiently collected.

The protective layer 5 is formed on the semiconductor layer 4 or the conductive layer 6.
May be formed. Such a protective layer 5 is transparent
It is better to have the properties of an electric conductor, such as CVD or PVD.
For example, silicon oxide, cesium oxide, aluminum oxide, nitrogen
Silicon oxide, titanium oxide, SiO _Two-TiO_Two, Tantalum oxide
, Yttrium oxide, etc. in a single layer or in multiple layers
Or a combination of them on the semiconductor layer 4 or the conductive layer 6.
You. The protective layer 5 is transparent because it is in contact with the light incident surface.
And the semiconductor layer 4 or the conductive layer 6 and the outside
Must be dielectric to prevent leakage during
It is important. If the thickness of the protective layer 5 is optimized, the anti-reflection
It can also be expected to function as a barrier film.

In order to reduce the series resistance, a pattern electrode (the other electrode) such as a finger or a bus bar is provided at regular intervals on the semiconductor layer 4 or the conductive layer 6 to directly or indirectly connect with the semiconductor layer 4. It is also possible to connect and improve the conversion efficiency.

[0023]

Next, an embodiment of the photoelectric conversion device of the present invention will be described.
I do. [Example 1] Sample 1 manufactured as follows as an example
Was used. An aluminum layer 1 ′ is formed on a substrate 1 containing iron by 5
A thickness of 0 μm was formed, and an insulator 3 was formed thereon.
SiO for_Two, B_TwoO_Three, Al_TwoO_Three, CaO, MgO, P_Two
O _Five, Li_TwoO, SnO, PbO, ZnO, BaO, Ti
O_TwoGlass particles for low-temperature firing of the main material with optional components
A single element or a filter made of one or more of the above materials
Baked glass paste combined with glass
The thickness afterwards should be close to half the particle size of the silicon particles 2.
Was formed. On top of this, a p-type ceramic with a center diameter of 250 μm
The recon particles 2 are densely arranged and pressed into the insulator 3
It was brought into contact with the minium layer 1 '. Next, the melting of the insulator 3
For bonding silicon particles 2 to aluminum layer 1 '
At about 577 ° C. Insulator by above method
Silicon particles of the sample (n = 5) prepared by changing the material of No. 3
Cracks in element 2 and insulator 3 and melting state of insulator 3
Are shown in Table 1.

[0024]

[Table 1]

Comparative Example 1, Examples 1-4 and Comparative Example 2 show examples in which the thermal expansion coefficient of the insulator 3 is changed. In Comparative Example 1, although the insulator 3 was dissolved, cracks occurred on the entire surface of the insulator.
This is because the coefficient of thermal expansion of aluminum used for the substrate is less than 240 × 10 ⁻⁷ / ° C. (240 ° ^C./240° C.).
(× 10 ⁻⁷ / ° C.), it is considered that cracks occurred after the insulator was formed due to a large difference in thermal expansion coefficient between the two.
The generated cracks cause a problem in terms of reliability due to leakage. In Comparative Example 2, cracks occurred around the silicon particles 2. This is because the coefficient of thermal expansion exceeds 60 × 10 ⁻⁷ / ° C., and the coefficient of thermal expansion of silicon particles 2 (26 × 10 ⁻⁷ / ° C.)
/ ° C), it is considered that cracks occurred after the insulator was formed due to the large difference in thermal expansion coefficient between the two. On the other hand, in Examples 1 to 4, no crack was generated, and the glass particles were melted to form an insulator film. From the above, it has been found that the thermal expansion coefficient of the insulator 3 is preferably in the range of 30 to 60 × 10 ⁻⁷ / ° C.

Next, in Examples 5 to 7 and Comparative Example 3, the insulator 3
Here is an example in which the softening point is changed. In Comparative Example 3, at a temperature around 577 ° C. for bonding the silicon particles 2 to the aluminum layer 19, the glass particles did not completely melt, and voids were generated. It is considered that this is because the softening point of the insulator exceeds 500 ° C. and is too high. On the other hand, Examples 5 to 7
Thus, the insulating film could be formed without melting the glass particles to generate voids, and no cracks were generated. From the above, the softening point of the insulator 3 is 500
It was found that the range of not more than ℃ was good.

In the eighth embodiment, an aluminum layer 1 ′ is formed to a thickness of 50 μm on a substrate 1 containing iron, and p-type silicon particles 2 having a center diameter of 250 μm are densely arranged on the aluminum layer 1 ′. The substrate 1 and the p-type silicon particles 2 are joined by heating at a temperature around 577 ° C., which is the eutectic temperature of Si, and then the gap between the silicon particles 2 is filled with glass particles having a thermal expansion coefficient and a softening point in the above range. An example is shown in which an insulator 3 is formed by burying the substrate 1 and firing at a temperature lower than the bonding temperature of the substrate 1 and the p-type silicon particles 2. The insulating film could be formed without melting the glass particles to generate voids, and no cracks were generated.

From the above, it was confirmed that the photoelectric conversion device of the present invention can form a good insulator in which defects such as cracks and voids can be prevented.

[0029]

As described above, according to the photoelectric conversion device of the first aspect, a large number of granular semiconductors exhibiting one conductivity type are arranged on a substrate having one electrode layer, and are joined to the substrate.
A photoelectric conversion device in which an insulator is filled between the granular crystal semiconductors, a semiconductor layer having an opposite conductivity type is provided on the granular crystal semiconductor, and the other electrode is connected to the semiconductor layer having the opposite conductivity type. In the above, since the insulator is formed of a material having a coefficient of thermal expansion of 30 to 60 × 10 ⁻⁷ / ° C. and a softening point of 500 ° C. or less, it is possible to prevent the occurrence of defects such as cracks and voids. A body can be formed, so that a highly reliable photoelectric conversion device can be provided.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing an example of another embodiment of the photoelectric conversion device of the present invention.

FIG. 3 is a cross-sectional view illustrating a photoelectric conversion device of Conventional Example 1.

FIG. 4 is a cross-sectional view illustrating a photoelectric conversion device of Conventional Example 2.

FIG. 5 is a cross-sectional view illustrating a photoelectric conversion device of Conventional Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 1 '... Conductive layer (one electrode) 2 ... Granular crystal semiconductor 3 ... Insulator 4 ... Semiconductor layer 5 ... Dielectric protective layer 6 ... ··· Transparent conductive film 7 ··· Amorphous semiconductor layer 8 ··· Second aluminum foil 9 ··· n-type skin 10 ··· First aluminum foil 11 ··· Low melting metal layer 12 ···・ High melting point metal layer 13 ・ ・ Liquid phase epitaxial polycrystalline layer of the first conductivity type 14 ・ ・ Polycrystalline or amorphous layer of the second conductivity type 15 ・ ・ Alloy part of substrate and granular crystal semiconductor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisao Arimune 1166, Haseno, Jabizo-cho, Yokaichi-shi, Shiga Prefecture F-term (reference) 5F051 AA03 AA20 FA06 GA02 GA03 HA20

Claims (1)

[Claims] 1. A large number of granular semiconductors having one conductivity type are arranged on a substrate having one electrode layer and joined to the substrate.
A photoelectric conversion device in which an insulator is filled between the granular crystal semiconductors, a semiconductor layer having an opposite conductivity type is provided on the granular crystal semiconductor, and the other electrode is connected to the semiconductor layer having the opposite conductivity type. 3. The photoelectric conversion device according to claim 1, wherein the insulator is formed using a material having a coefficient of thermal expansion of 30 to 60 × 10 ⁻⁷ / ° C. and a softening point of 500 ° C. or less.