Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-07-26
2003-04-22
Whitehead, Jr., Carl (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
Reexamination Certificate
active
06552405
ABSTRACT:
This application is based on applications Nos. 2000-227638 and 2000-258025 filed in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric conversion device, in particular, to a photoelectric device using numerous crystalline semiconductor particles. The photoelectric conversion device according to this invention is utilized suitably in solar cells.
2. Description of the Related Art
Advent of a next-generation, low-cost solar cell that allows the quantity of silicon material to be small has been eagerly awaited.
Photoelectric devices using crystalline semiconductor particles that have been proposed so far are shown in
FIGS. 8-13
.
FIG. 8
shows a structure disclosed in U.S. Pat. No. 4,514,580. In
FIG. 8
, a steel substrate
41
is surrounded by an aluminum film
42
to which crushed silicon particles
43
are joined. The aluminum film
42
in the areas where the silicon particles
43
are not present has an insulator layer
44
formed thereon. The upper portions of the silicon particles
43
are formed with n type silicon portions
45
thereon. A transparent conductive layer
46
is formed over the entire surfaces.
FIG. 9
shows a structure disclosed in Japanese Patent No. 2522024. In this structure, a substrate
47
is formed with a diffusion-preventive layer
48
on which a rear face electrode
49
comprising a doping impurity for p type is formed. N type silicon particles
52
are densely deposited on the rear face electrode
49
. The silicon particles
52
and the rear face electrode
49
are brought into contact and heated for alloying the silicon particles
52
and the material of the rear face electrode
49
. Then, they are cooled, thereby forming p type regions
50
partially within the n type silicon particles. An insulator layer
51
is formed on the areas where the silicon particles
52
are not present, and a transparent conductive layer
53
is formed over the entire surface.
FIG. 10
shows a structure disclosed in Japanese Patent No. 2641800. In this structure, a tin layer
55
having a low melting point is formed on a stainless substrate
54
. First conductive-type crystalline semiconductor particles
56
are deposited on the tin layer
55
. An insulating layer
57
is formed on the areas where the crystalline semiconductor particles
56
are not present. After the upper portions of the crystalline semiconductor particles are ground, a second conductive-type amorphous semiconductor layer
58
is formed thereon. A metal electrode shaped as a strip is denoted by
59
.
The structure in
FIG. 11
is one disclosed in Japanese Patent Laid-Open Publication No. S61-124179. According to this structure, a first aluminum foil
62
is provided with openings into which silicon balls
63
having n type silicon surface portions
64
on the surfaces of p type silicon portions are inserted. The n type surface portions
64
in the rear faces of the silicon balls
63
are then removed. On a second aluminum foil
60
coated with an oxide layer
61
, a part of the oxide layer
61
located at the rear faces of the silicon balls
63
is removed, thereby joining the silicon balls
63
to the second aluminum foil
60
.
FIG. 12
discloses a method in which a high-melting point metal layer
66
, a low melting-point metal layer
67
, and semiconductor microcrystalline particles
68
are deposited on a substrate
65
. The semiconductor microcrystalline particles
68
are fused, saturated and gradually cooled so that the semiconductor is grown by liquid phase epitaxial growth, thereby forming a liquid phase epitaxial polycrystalline thin film
71
(Refer to Japanese Patent Publication No.H8-34177).
In addition, FIG.
13
. discloses a method in which a PN-junction is formed by forming a n type layer
73
that is formed by making an element, which is a n type impurity, diffused on both the front and rear surfaces of a p type substrate
72
. In this method, a conductive diffusion region
74
to be connected to inside the p type layer
72
is formed by making the PN-junction penetrate the rear surface. A glass-type isolator
75
is formed around the conductive diffusion regions and baked so as to separate the PN-junction (Refer to, for example, Japanese Patent Publication No. S61-59678, and Japanese Patent Laid-Open Publication No. H10-233518).
However, in the photoelectric conversion device according to the U.S. Pat. No. 4,514,580 shown in
FIG. 8
, when the crushed silicon particles
43
are deposited on fused aluminum liquid heated up to its melting point 660° C. so as to be bonded thereto, the fused liquid flows out permitting only a small part of the silicon particles
43
to be bonded, the fused liquid climbs the surfaces of the silicon particles
43
causing short circuit, or the fused liquid scatters. Such phenomena make control of the junction characteristics difficult.
In the photoelectric conversion device in
FIG. 9
disclosed in Japanese Patent No. 2522024, because of the PN-junction present below the incident light, loss is large when generated carriers are collected.
According to the photoelectric conversion device shown in
FIG. 10
disclosed in Japanese Patent No. 2641800, the tin layer
55
on the stainless substrate
54
is fused so as to be joined to the first conductivity-type crystalline semiconductor particles
56
. However, the extremely low melting point of tin has the problem of low reliability. In addition, since the second conductivity-type amorphous conductive layer
58
is formed on the first conductivity-type crystalline semiconductor particles
56
, the surfaces of the crystalline semiconductor particles
56
need to be sufficiently etched and cleaned before the formation of the amorphous conductive layer
58
in order to form a secure PN-junction. Also, the film thickness has to be thin taking the large light absorption of the amorphous conductive layer
58
into account. However, the amorphous conductive layer
58
with such a small thickness has only small tolerance to defects necessitating stricter management of the cleaning process and the production environment, which leads to high-cost production.
According to the photoelectric conversion device in
FIG. 11
disclosed in Japanese Patent Laid-Open Publication No. S61-124179, when silicon balls having n type surface portions
64
covering the p type cores
63
are joined to the second aluminum foil
60
so as to form an aluminum-silicon alloy layer, aluminum diffuses into the n type surface portions
64
causing the n type surface portions
64
to be destroyed. Also, because the first aluminum foil
62
′ has to be provided with openings into which the silicon balls are pressed so as to be joined thereto, evenness is required for the particle diameters of the silicon balls, which causes the cost to increase. In addition, because the temperature applied during the joining is below 577° C., which is the eutectic temperature of aluminum and silicon, the junction is unstable.
The photoelectric conversion device shown in
FIG. 12
has problems that the low melting-point metal
67
mixes into the first conductivity-type liquid phase epitaxial polycrystalline layer
69
deteriorating the performance, and that the absence of insulator causes leakage to occur between the layer and the lower electrode
66
.
In the case of using crystalline semiconductor particles in the photoelectric conversion device shown in
FIG. 13
, it is difficult in terms of manufacture to form the conductive diffusion region
74
such that it is connected to the internal layer by penetrating the PN-junction. In such a case, the PN-junction itself is fused and destroyed when the substrate and the crystalline semiconductor particles are joined together.
The present invention has been devised in consideration of the problems described above, and the object thereof is to provide a low-cost photoelectric conversion device having good conversion efficiency.
BRIEF SUMMARY OF THE INVENTION
A photoelectric conversion device accordin
Arimune Hisao
Kyoda Takeshi
Sugawara Shin
Hogan & Hartson LLP
Jr. Carl Whitehead
Kyocera Corporation
Vesperman William C.
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