U.S. patent application number 09/746566 was filed with the patent office on 2001-08-30 for solar cell and method of fabricating the same.
Invention is credited to Kubota, Yuichi, Nishi, Kazuo.
Application Number | 20010017153 09/746566 |
Document ID | / |
Family ID | 18480011 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017153 |
Kind Code |
A1 |
Kubota, Yuichi ; et
al. |
August 30, 2001 |
Solar cell and method of fabricating the same
Abstract
It is achieved to provide a solar cell in which stability at a
connection portion between a circuit substrate of an electric
instrument and a rear electrode, and reliability against
electrostatic damage are improved, and also to provide a method of
fabricating the same. A rear electrode is formed of a material
containing carbon as a main ingredient. In formation of the rear
electrode, a thermosetting conductive carbon paste is used and the
formation is made by a printing method. Further, when the
resistance values of the transparent electrode layer and the rear
electrode layer are made the same level and are balanced, the
resistance against electrostatic damage can be remarkably
improved.
Inventors: |
Kubota, Yuichi; (Chiba,
JP) ; Nishi, Kazuo; (Yamanashi, JP) |
Correspondence
Address: |
SCOTT C. HARRIS
Fish & Richardson P.C.
Suite 500
4350 La Jolla Village Drive
San Diego
CA
92122
US
|
Family ID: |
18480011 |
Appl. No.: |
09/746566 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
136/256 ;
136/252; 257/E27.125; 257/E31.042; 257/E31.126; 438/98 |
Current CPC
Class: |
H01L 31/046 20141201;
H01L 31/022466 20130101; H01L 31/03921 20130101; H01L 31/0465
20141201; H01L 31/022425 20130101; H01L 31/02008 20130101; Y02E
10/50 20130101 |
Class at
Publication: |
136/256 ;
136/252; 438/98 |
International
Class: |
H01L 021/00; H01L
031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 1999 |
JP |
11-363714 |
Claims
What is claimed is:
1. A solar cell comprising a transparent electrode layer, a
photoelectric conversion layer, and a rear electrode layer, which
are provided on a translucent substrate, wherein the rear electrode
layer is a carbon electrode containing a conductive coating film
obtained by drying and hardening a paste which contains as main
ingredients fine particle carbon black and graphite carbon black
containing conductive fine particles of ITO, SnO.sub.2, ZnO, Ag,
Cu, Ni, or Mo, and further contains a binder resin, a solvent, and
an additive.
2. A solar cell according to claim 1, wherein the transparent
electrode layer has a sheet resistance of 120 to 150
.OMEGA./.quadrature. and the rear electrode layer has a sheet
resistance of 30 to 80 .OMEGA./.quadrature..
3. A solar cell according to any one of claim 1, wherein the rear
electrode layer is in contact with an n-type microcrystalline
semiconductor layer of the photoelectric conversion layer, and the
n-type microcrystalline semiconductor layer has a thickness of 30
to 80 nm.
4. A solar cell comprising a transparent electrode layer, a
photoelectric conversion layer, a rear electrode layer, and an
output terminal, which are provided on a translucent substrate,
wherein the rear electrode layer is a carbon electrode containing a
conductive coating film obtained by drying and hardening a paste
which contains as main ingredients fine particle carbon black and
graphite carbon black containing conductive fine particles of ITO,
SnO.sub.2, ZnO, Ag, Cu, Ni, or Mo, and further contains a binder
resin, a solvent, and an additive, and wherein the output terminal
is formed of the same material as the rear electrode layer.
5. A solar cell according to claim 4, wherein the transparent
electrode layer has a sheet resistance of 120 to 150
.OMEGA./.quadrature. and the rear electrode layer has a sheet
resistance of 30 to 80 .OMEGA./.quadrature..
6. A solar cell according to any one of claim 4, wherein the rear
electrode layer is in contact with an n-type microcrystalline
semiconductor layer of the photoelectric conversion layer, and the
n-type microcrystalline semiconductor layer has a thickness of 30
to 80 nm.
7. A solar cell comprising a transparent electrode layer, a
photoelectric conversion layer, and a rear electrode layer, which
are provided on a translucent substrate, wherein the rear electrode
layer is a carbon electrode containing a conductive film obtained
by drying and hardening a paste which contains as main ingredients
fine particle carbon black and graphite carbon black, and further
contains a binder resin.
8. A solar cell according to claim 7, wherein the transparent
electrode layer has a sheet resistance of 120 to 150
.OMEGA./.quadrature. and the rear electrode layer has a sheet
resistance of 30 to 80 .OMEGA./.quadrature..
9. A solar cell according to any one of claim 7, wherein the rear
electrode layer is in contact with an n-type microcrystalline
semiconductor layer of the photoelectric conversion layer, and the
n-type microcrystalline semiconductor layer has a thickness of 30
to 80 nm.
10. A solar cell comprising a transparent electrode layer, a
photoelectric conversion layer, and a rear electrode layer, which
are provided on a translucent substrate, wherein the rear electrode
layer is a carbon electrode containing a conductive film obtained
by drying and hardening a paste which contains as main ingredients
fine particle carbon black and graphite carbon black, and further
contains a binder resin. wherein the output terminal is formed of
the same material as the rear electrode layer.
11. A solar cell according to claim 10, wherein the transparent
electrode layer has a sheet resistance of 120 to 150
.OMEGA./.quadrature. and the rear electrode layer has a sheet
resistance of 30 to 80 .OMEGA./.quadrature..
12. A solar cell according to any one of claim 10, wherein the rear
electrode layer is in contact with an n-type microcrystalline
semiconductor layer of the photoelectric conversion layer, and the
n-type microcrystalline semiconductor layer has a thickness of 30
to 80 nm.
13. A method of fabricating a solar cell, comprising: a first step
of forming a transparent electrode layer on a translucent
substrate; a second step of forming a photoelectric conversion
layer on the transparent electrode layer; a third step of forming a
first opening and a second opening reaching the substrate in the
transparent electrode layer and the photoelectric conversion layer;
a fourth step of forming an insulating layer covering the first
opening and an upper end portion of the opening; a fifth step of
forming a conductive layer covering the photoelectric conversion
layer, the insulating layer, the second opening and an upper end
portion of the second opening; and a sixth step of forming an
insulating sealing resin layer on the photoelectric conversion
layer and the conductive layer, wherein the conductive layer is a
carbon electrode containing a conductive coating film obtained by
drying and hardening a paste which contains as main ingredients
fine particle carbon black and graphite carbon black containing
conductive fine particles of ITO, SnO.sub.2, ZnO, Ag, Cu, Ni, or
Mo, and further contains a binder resin, a solvent, and an
additive.
14. A method of fabricating a solar cell, comprising: a first step
of forming a transparent electrode layer on a translucent
substrate; a second step of forming a photoelectric conversion
layer on the transparent electrode layer; a third step of forming a
first conductive layer using a predetermined pattern on the
photoelectric conversion layer; a fourth step of forming a first
opening and a second opening reaching the substrate in the
transparent electrode layer and the photoelectric conversion layer;
a fifth step of forming an insulating layer covering the first
opening and an upper end portion of the opening; a sixth step of
forming a second conductive layer covering the photoelectric
conversion layer, the insulating layer, the second opening and an
upper end portion of the second opening; and a seventh step of
forming a sealing resin layer on the photoelectric conversion layer
and the conductive layer, wherein the conductive layer is a carbon
electrode containing a conductive coating film obtained by drying
and hardening a paste which contains as main ingredients fine
particle carbon black and graphite carbon black containing
conductive fine particles of ITO, SnO.sub.2, ZnO, Ag, Cu, Ni, or
Mo, and further contains a binder resin, a solvent, and an
additive.
15. A method of fabricating a solar cell, comprising: a first step
of forming a transparent electrode layer on a translucent
substrate; a second step of forming a photoelectric conversion
layer on the transparent electrode layer; a third step of forming a
first opening and a second opening reaching the substrate in the
transparent electrode layer and the photoelectric conversion layer;
a fourth step of forming an insulating layer covering the first
opening and an upper end portion of the opening; a fifth step of
forming a conductive layer covering the photoelectric conversion
layer, the insulating layer, the second opening and an upper end
portion of the second opening; and a sixth step of forming an
insulating sealing resin layer on the photoelectric conversion
layer and the conductive layer, wherein the conductive layer is a
carbon electrode containing a conductive coating film obtained by
drying and hardening a paste which contains as main ingredients
fine particle carbon black and graphite carbon black, and further
contains a binder resin.
16. A method of fabricating a solar cell, comprising: a first step
of forming a transparent electrode layer on a translucent
substrate; a second step of forming a photoelectric conversion
layer on the transparent electrode layer; a third step of forming a
first conductive layer using a predetermined pattern on the
photoelectric conversion layer; a fourth step of forming a first
opening and a second opening reaching the substrate in the
transparent electrode layer and the photoelectric conversion layer;
a fifth step of forming an insulating layer covering the first
opening and an upper end portion of the opening; a sixth step of
forming a second conductive layer covering the photoelectric
conversion layer, the insulating layer, the second opening and an
upper end portion of the second opening; and a seventh step of
forming a sealing resin layer on the photoelectric conversion layer
and the conductive layer, wherein the conductive layer is a carbon
electrode containing a conductive coating film obtained by drying
and hardening a paste which contains as main ingredients fine
particle carbon black and graphite carbon, and further contains a
binder resin.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a structure of a solar cell
well suited for a power source of electric instrument with low
power consumption, such as a calculator and a watch, and also
relates to a method of fabricating the same.
[0003] 2. Description of the Related Art
[0004] Solar cells are becoming popular not only for a sunlight
electrical generating system, which is installed outdoors, but also
for a power source of electric instrument with low power
consumption, such as a calculator, a radio, and a watch. In such a
consumer use, for example, like a wrist watch, in the case where
importance is attached to not only the function but also to its
external design, a mounting method of the solar cell is also
devised. The solar cell is directly used as a face of the watch, or
is installed under a semitranslucent face of watch to make it
unnoticeable.
[0005] In most of solar cells in the consumer use, glass,
stainless, organic resin material or the like is used for a
substrate, and a photoelectric conversion layer is formed thereon
with a thin film of amorphous semiconductor, microcrystalline
semiconductor, or chalcopalide-based (or II-VI group) compound
semiconductor. Especially, the solar cell using an organic resin
material for the substrate is thin and lightweight, and has an
excellent shock resistance so that it is not cracked even if it is
dropped. Accordingly, it is suitable for the solar cell to be
mounted to a portable product, such as a card type calculator, a
wrist watch, and a remote-control device of an indoor electric
instrument such as a television.
[0006] In the solar cell fabricated by using the organic resin
material for the substrate, there is a well known technique for
forming a photoelectric conversion layer with a non-monocrystalline
semiconductor material, such as amorphous silicon or
microcrystalline silicon, fabricated by a plasma CVD method. As
means for increasing the productivity of such a solar cell and
decreasing the manufacturing costs, there is known a roll-to-roll
method in which a long organic resin film substrate wound into a
roll shape or a metal film substrate of a stainless alloy etc., is
fed out from one side of substrate holding means provided in a
plasma CVD apparatus, a sputtering apparatus, or another
manufacturing apparatus, the substrate is made to continuously (or
stepwise) move in a treatment space of coating formation or the
like, and it is rewound by substrate holding means provided at the
other side.
[0007] In addition, there is known a method in which a rear
electrode opposite to a transparent electrode provided at an
incident side of light is formed by printing a paste containing a
powder of conductive material with a binder of organic resin
material, instead of a metal film by a sputtering method, a vacuum
evaporation method, etc. Japanese Patent No. 2698401 discloses a
technique in which a rear electrode of a solar cell is formed by a
printing method using a conductive paste containing a conductive
material of molybdenum powder with a binder of phenolic resin.
[0008] As a method of connecting a circuit substrate of a
calculator, a watch, a remote-control device of an indoor electric
instrument, or the like to an output terminal of a solar cell, in
addition to soldering or a method of thermocompression bonding of a
flexible printed substrate by an anisotropic conductive adhesive, a
pressure contact system using a spring terminal is adopted.
Although this method can prevent damage by heat from being applied
to the solar cell, if the output terminal is formed of a metal
material, similarly to the rear electrode, there has been a problem
of aging of contact resistance due to surface oxidation or the
like. Thus, contrivance has been made such that a carbon electrode
is intentionally provided at this portion.
[0009] Since a conductive carbon electrode film obtained by
applying a carbon paste by a printing method, drying and hardening,
is not oxidized, the aging of the contact resistance to a spring
terminal is small. Therefore, it is regarded as a suitable
material. However, there has been a problem in that the contact
resistance to a semiconductor layer is high, and peeling and warp
of a substrate, etc. would occur.
[0010] On the other hand, as another problem, like a consumer use
electric instrument, in the case where importance is mainly
attached to photoelectric conversion characteristics under low
illumination in an indoor environment or the like, a minute short
circuit region is formed between a transparent electrode and a rear
electrode by electro-static damage, and output voltage is lowered.
As a result, the reliability of a product has been remarkably
deteriorated.
SUMMARY OF THE INVENTION
[0011] The present invention is a technique for solving the
foregoing problems, and an object thereof is to provide a solar
cell in which stability at a connection portion between a circuit
substrate of an electric instrument and a rear electrode, and
reliability against electro-static damage are improved, and also to
provide a method of fabricating the same.
[0012] In order to achieve the object, according to the present
invention, in a solar cell using an organic resin material for a
substrate, a rear electrode is formed of a material containing
carbon as a main ingredient. In formation of the rear electrode, a
thermosetting conductive carbon paste is used and the formation is
made by a printing method.
[0013] A conventional conductive film formed by mixing and
dispersing a powder of conductive material on a flexible substrate
using a binder of organic thermoplastic resin is weak to an organic
solvent, and at the time of formation of an insulating sealing
resin layer formed thereon, expansion and dissolving of the resin
component by the solvent occurs. Therefore, it has not been capable
of being used. Besides, in an environment resistance test of the
conductive film itself, a matrix component of the resin easily
receives the influence of the change of temperature and humidity,
and softened resin is apt to intervene between contacted conductive
fine powders, and as a result, series resistance is increased.
Consequently, it has not been capable of withstanding the
environment resistance test.
[0014] Therefore, a resin binder in view of the following points is
used for the conductive film of the thermosetting conductive carbon
paste of the present invention. First, conductive fine particles
are highly filled to raise conductivity of the film, and at the
same time, the molecular structure of a matrix resin component of
the film and a crosslinking agent are optimized to obtain the
conductive electrode film having high heat resistance and humidity
resistance and the matrix resin of sufficiently high crosslinking
strength. Even when the upper portion of this electrode film is
covered with, for example, an insulating ink film, it has such
solvent resistance that it sufficiently withstands the contained
solvent. Besides, with respect to the conductive contact at the
interface between the conductive fine particle and a transparent
thin film conductive film as well, the resin matrix is not swelled
and dissolved, and can be firmly fixed. Further, against the
increase of temperature and humidity as well, since the heat
resistance and humidity resistance of the resin matrix is improved,
the change of mechanical properties is small. As an example of a
method of obtaining a conductive coating film including such resin
matrix, a saturated polyester resin having the highest possible
residual hydroxyl group content is used, and in order to keep the
pot life of a curing agent having high reactivity with this
functional group, that is, a conductive ink more stably in a period
including the time of screen printing, such resin blending
composition is designed that glass transition temperature (Tg)
becomes at least 70.degree. C. or more by high density thermal
crosslinking using the curing agent, such as multi-functional block
isocyanate compound which is made inactive under room temperature
by a block agent and easily dissociates isocyanate especially at
low temperature, or melamine resin. More specifically, the
thermosetting conductive paste is formed such that its main
component is a conductive coating matrix resin typified by
saturated polyester resin in which a dispersion property enabling
conductive carbon fine particles to be highly filled, a printing
property, and conductive coating formation performance thereafter
are excellent, consideration is sufficiently paid to monomer
blending at the time of condensation polymerization of dicarboxylic
acid and diol, an OH value content is high, and Tg is higher than
that of the resin, and a resin binder is a combination with block
isocyanate which easily dissociates highly reactive isocyanate
groups by low temperature heating.
[0015] When the fine granular conductive carbon particles are
obtained by mixing artificial graphite of an average particle
diameter of 0.1 to several tens of .mu.Mm into the carbon particles
at a mixing ratio of {fraction (1/3)} to {fraction (3/1)} in weight
ratio and by further making the particles fine by a ball mill or
the like, it is effective in decrease of the electric resistance of
a carbon conductive coating film.
[0016] The organic resin material is generally apt to be charged,
and the electrostatic withstand voltage of a solar cell formed
thereon becomes deteriorated. In order to improve the electrostatic
withstand voltage between terminals, the resistance of the
transparent electrode and the rear electrode is rather made high so
that the electric field is not concentrated on the element portion.
The sheet resistance of the conductive film using the thermosetting
conductive carbon paste and formed by the printing method is 30 to
80 .OMEGA./.quadrature., and it is possible to make the resistance
just coincident with the value of the transparent electrode formed
of ITO.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In the accompanying drawings:
[0018] FIGS. 1A to 1C are sectional views for explaining a
fabricating process of a solar cell;
[0019] FIG. 2 is a sectional view showing a state where the solar
cell is completed;
[0020] FIGS. 3A to 3C are sectional views for explaining a
fabricating process of a solar cell;
[0021] FIG. 4 is a sectional view showing a state where the solar
cell is completed;
[0022] FIG. 5 is a plan view of a solar cell for a watch;
[0023] FIGS. 6A to 6C are partial sectional views of the solar cell
for the watch; and
[0024] FIG. 7 is a view for explaining connection between an output
terminal of a solar cell and a circuit substrate of an electric
instrument.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] (Embodiment 1)
[0026] An embodiment of the present invention will be described
with reference to FIGS. 1A to 1C and FIG. 2. A method of
fabricating an integrated solar cell in which an organic resin
material is used for a substrate and a plurality of unit cells are
connected in series with each other on the same substrate, is
disclosed in Japanese Patent Application Laid-open No. Hei
5-183177, and also in this embodiment, the solar cell is fabricated
using the method of the publication.
[0027] In FIG. 1A, a translucent organic resin material, such as
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
or polyethersulfone (PES), is used for a substrate 101. Of course,
other commercially available soda-lime glass or alkali-free glass
can also be used.
[0028] A sheet-like substrate of a suitable size may be used, or as
described before, on the assumption that the process is carried out
by the roll-to-roll method, a substrate wound into a roll shape may
be used. In the case where the roll-to-roll method is applied, it
is appropriate that an organic resin film substrate having a
thickness of 60 to 100 .mu.m is used.
[0029] The solar cell fabricated in this embodiment has such a
structure that light is received by a surface of a substrate
opposite to a surface on which a photoelectric conversion layer is
formed, and first, a transparent electrode layer 102 is formed on
the substrate 101. The transparent electrode 102 is formed of
indium tin oxide alloy (ITO), zinc oxide (ZnO), tin oxide
(SnO.sub.2), ITO--ZnO alloy, or the like to a thickness of 40 to
200 nm (preferably 50 to 100 nm). However, since the continuously
usable maximum temperature of the foregoing organic resin material
is 200.degree. C. or less, a sputtering method, a vacuum
evaporation method or the like is used for the formation of the
transparent electrode layer 102, and the formation is carried out
while the substrate temperature at the film formation is limited
within the range from room temperature to about 150.degree. C.
Detailed forming conditions may be suitably determined by an
operator to obtain a sheet resistance of 20 to 200
.OMEGA./.quadrature. for the above film thickness.
[0030] In view of decreasing the resistance of the transparent
electrode layer, an ITO film is suitable. However, when a
semiconductor layer is formed thereon, if the ITO film is exposed
to a plasma atmosphere containing hydrogen, it is reduced and
becomes opaque. In order to prevent this, it is appropriate that a
SnO.sub.2 film or a ZnO film is formed on the ITO film. The ZnO
(ZnO:Ga) film containing gallium (Ga) of 1 to 10 wt % has high
transmittance and is a material suitable to be laminated on the ITO
film. As an example of the combination, when the ITO film is formed
to a thickness of 50 to 60 nm and the ZnO:Ga film with a thickness
of 25 nm is formed thereon, it is possible to prevent transparency
from being lost, and an excellent light transmitting property can
be obtained. In this laminate film, a sheet resistance of 120 to
150 .OMEGA./.quadrature. can be obtained.
[0031] A non-monocrystalline semiconductor film formed by using a
plasma CVD method is used for a photoelectric conversion layer 103.
Typically, it is a hydrogenated amorphous silicon (a-Si:H) film
formed using SiH.sub.4 gas as a raw material, and in addition to
this, it may be formed of a hydrogenated amorphous silicon
germanium (a-SiGe:H) film, a hydrogenated amorphous silicon carbon
(a-SiC:H) film, a hydrogenated microcrystalline silicon
(.mu.c-Si:H) film, or the like. Although the photoelectric
conversion layer is formed of a p-i-n junction, p-type and n-type
layers in which valence electron control is made, may be formed by
using a-Si:H or .mu.c-Si:H added with an impurity element such as
boron or phosphorus. Especially, for the purpose of lowering light
absorption loss or forming excellent ohmic contact with the
transparent electrode or the rear electrode, .mu.c-Si:H is
suitable.
[0032] FIG. 1A shows a state where the photoelectric conversion
layer 103 is made of a laminate of a p-type layer 103a, an i-type
layer 103b, and an n-type layer 103c from the side of the
transparent electrode layer 102, and the thicknesses of the
respective layers are 10 to 20 nm for the p-type layer, 200 to 1000
nm for the i-type layer, and 20 to 60 nm for the n-type layer. When
the p-i-n junction is formed of such non-monocrystalline silicon
material, an open circuit voltage of about 0.4 to 1 V can be
obtained. If this p-i-n junction is made one unit and a plurality
of such units are laminated to form a stack type structure, the
open circuit voltage can also be raised.
[0033] As shown in FIG. 1B, in order to form a plurality of unit
cells on the same substrate, openings M.sub.0 to M.sub.n and
C.sub.1 to C.sub.n reaching the transparent electrode layer 102
from the photoelectric conversion layer 103 are formed by a laser
working method. The openings M.sub.0 to M.sub.n are openings for
insulation and separation and are provided to form the unit cells.
The openings C.sub.1 to C.sub.n are openings for forming connection
between the transparent electrode and the rear electrode. Although
the kind of a laser used for the laser working method is not
restricted, a Nd-YAG laser, an excimer laser, or the like is used.
At all events, by performing the laser working in the state where
the transparent electrode layer 102 and the photoelectric
conversion layer 103 are laminated, it is possible to prevent the
transparent electrode layer from peeling off the substrate at the
working.
[0034] In this way, the transparent electrode layer 102 is divided
into T.sub.1 to T.sub.n, and the photoelectric conversion layer 103
is divided into K.sub.1 to K.sub.n. Then, as shown in FIG. 1C,
insulating resin layers Z.sub.0 to Z.sub.n. filling the openings
M.sub.0 to M.sub.n and further covering the upper end portions are
formed.
[0035] For the purpose of forming the insulating resin layers
Z.sub.0 to Z.sub.n by a screen printing method, the following
insulating resin material was prepared.
[0036] phenoxy resin (manufactured by UCC Inc.: PKHH Mn=15,400), 20
pts.
[0037] cyclohexane, 40 pts.
[0038] isophorone, 30 pts.
[0039] high resistance carbon black (manufactured by Degussa Inc.:
average particle diameter of 25 nm), 4 pts.
[0040] aerosil (manufactured by Degussa Inc.: average particle
diameter of 15 nm), 10 pts.
[0041] dispersing agent (oleic acid), 3 pts.
[0042] antifoaming agent (manufactured by Toshiba Silicone Co.,
Ltd.: TSA-720), 1 part by weight
[0043] leveling agent (manufactured by Sin-etsu Silicone Co., Ltd.:
KS-66), 1 pts.
[0044] First, among the above raw materials, phenoxy resin was
completely dissolved in a mixture solvent of
cyclohexane/isophorone, and was dispersed for 48 hours by a ball
mill made of zirconia, together with carbon black, aerosil and
dispersing agent. Next, the antifoaming agent and leveling agent
were added and were further mixed for two hours. Next, thermal
crosslinking reactive component resins described below were added
thereto.
[0045] n-butylated melamine resin (manufactured by Mitsui Toatsu
Chemical Co., Ltd.: U-VAN 21R: weight average molecular weight of
about 7000), 5 pts.
[0046] hardening accelerator (manufactured by Mitsui Toatsu
Chemical Co., Ltd.: Catalyst 6000), 0.03 pts.
[0047] These were further mixed and dispersed for 20 minutes to
obtain an insulating resin composite for a passivation film.
[0048] The obtained insulating resin composite ink was used, and
the insulating film was formed by using the screen printing method.
After application, thermal hardening was conducted in an oven for
20 minutes at 160.degree. C. to obtain the insulating resin layers
Z.sub.0 to Z.sub.n.
[0049] Next, for the purpose of forming rear electrode layers
E.sub.0 to E.sub.n as shown in FIG. 2 by the screen printing
method, the following were prepared for ink to be used. In addition
to the following, conductive fine particles such as ITO, SnO.sub.2,
ZnO, Ag, Cu, Ni, or Mo may be added to increase the
conductivity.
[0050] graphite powder CPB-5000 (manufactured by Chuetsu Graphite
Industry Co., Ltd.), 9 pts.
[0051] high conductive black #3950 (16 nm) manufactured by
Mitsubishi Chemical Corp., 6 pts.
[0052] oleic acid (dispersing agent) of 0.5 pts.
[0053] isophorone (solvent), 20 pts.
[0054] These were put into a ball mill to crush them for 24 hours,
and obtain finer particles. Next, 75 pts. of 20 wt %
.gamma.-butyrolactone lacquer of saturated polyester resin having
the following contents were put into them.
[0055] VYLON 220 (OH value of about 55 KOHmg/g) manufactured by
Toyobo Co., Ltd., 7 pts.
[0056] VYLON 200 (OH value of about 5 KOHmg/g) manufactured by
Toyobo Co., Ltd., 5 pts.
[0057] VYLON 630 (OH value of about 42 KOHmg/g) manufactured by
Toyobo Co., Ltd., 3 pts.
[0058] .gamma.-butyrolactone (solvent), 60 pts.
[0059] Then, an antifoaming agent and a leveling agent having the
following contents were added thereto.
[0060] antifoaming agent (manufactured by Toshiba Silicone Co.,
Ltd.: TSA-720), 2 pts.
[0061] leveling agent (manufactured by Sin-etsu Silicone Co., Ltd.:
KS-66) of 0.5 pts.
[0062] Further, a paste obtained after dispersing and mixing by the
ball mill for 24 hours was further dispersed by a three-roll mill
to obtain a conductive carbon paste.
[0063] This paste was added with 5 pts. of ethyl acetoacetate block
body (solid content 80 wt %, NCO content 10 wt %) Coronate 2513
(manufactured by Nippon Polyurethane Kogyo Co., Ltd.) which was
obtained by blocking isocynate group of
hexamethylenediisocynate-based polyisocynate of aliphatic
polyfunctional isocynate by ethyl acetoacetate and by diluting it
with a solvent of cellosolve acetate and xylene at one to one,
mixing was sufficiently manufactured by disper, and defoaming was
sufficiently made to obtain a conductive carbon paste.
[0064] Then, the obtained conductive carbon paste was printed into
a predetermined pattern by the screen printing method, and after
leveling and drying, it was firmly hardened at 150.degree. C. for
30 minutes to form the rear electrode layers E.sub.0 to E.sub.n as
shown in FIG. 2.
[0065] If doing so, although the rear electrode layers come in
contact with the n-type layer 103c of the photoelectric conversion
layer, in order to make this contact ohmic contact and further to
lower the contact resistance, it is necessary that the n-type layer
103c is formed of .mu.c-Si:H, and its thickness is made 30 to 80
nm.
[0066] The respective rear electrodes E.sub.1 to E.sub.n are formed
so as to be connected with the transparent electrode layers T.sub.1
to T.sub.n at the openings C.sub.1 to C.sub.n. The same material as
the rear electrode is filled in the openings C.sub.1 to C.sub.n,
and in this way, the rear electrode E.sub.n-1 is electrically
connected to the transparent electrode T.sub.n.
[0067] Finally, in order to form a sealing resin layer 104 by the
printing method, as a sealing resin raw material, the following was
prepared.
[0068] epoxy resin (manufactured by Yuka-Shell Epoxy K.K.: Epikote
1009, molecular weight of about 3750), 20 pts.
[0069] .gamma.-butyrolactone, 40 pts.
[0070] isophorone, 30 pts.
[0071] antifoaming agent (manufactured by Toshiba Silicone Co.,
Ltd.: TSA-720), 3 pts.
[0072] leveling agent (manufactured by Shin-etsu Silicone Co., Lt.:
KS-66), 1 pts.
[0073] First, among the above raw materials, epoxy resin was
completely dissolved in a mixture solvent of
y-butyrolactone/isophorone, and was dispersed for 48 hours by a
ball mill made of zirconia. Next, the antifoaming agent and the
leveling agent were added and further mixed for 2 hours, and a
thermal crosslinking reactive component described below was
added.
[0074] butylated melamine resin (manufactured by Mitsui Chemical
Corp.: U-VAN 20SE-60: molecular weight of about 3500 to 4000), 5
pts.
[0075] These were further mixed and dispersed for 20 minutes to
obtain a transparent composite for an insulating surface protecting
sealing film.
[0076] The ink of the obtained composite for the insulating surface
protecting sealing film was used, and the sealing resin layer 104
was formed by using the screen printing method, and was thermally
hardened at 150.degree. C. for 30 minutes. In the sealing resin
layer 104, opening portions 105 and 106 were respectively formed on
the rear electrodes E.sub.0 and E.sub.n, with the result that they
were connected to an external circuit substrate at these
portions.
[0077] In the manner as described above, a unit cell made of the
transparent electrode T.sub.n, the photoelectric conversion layer
K.sub.n, and the rear electrode layer E.sub.n is formed on the
substrate 101, and the adjacent rear electrode E.sub.n-1 is
connected to the transparent electrode T.sub.n through the opening
C.sub.n, with the result that a solar cell of the n
series-connected unit cells can be fabricated. The rear electrode
E.sub.0 becomes a lead-out electrode of the transparent electrode
T.sub.1 in the unit cell U.sub.1.
[0078] In the solar cell fabricated in this embodiment, the sheet
resistance of the transparent electrode layer is 120 to 150
.OMEGA./.quadrature., and that of the rear electrode layer is 30 to
80 .OMEGA./.quadrature.. These values are high as compared with an
aluminum film suitably used for a rear electrode material of a
solar cell having a sheet resistance of 1 .OMEGA./.quadrature. or
less. However, like this, when the resistance values of the
transparent electrode layer and the rear electrode layer are made
the same level and are balanced, the resistance against
electrostatic damage can be remarkably improved.
[0079] (Embodiment 2)
[0080] Another embodiment of the present invention will be
described with reference to FIGS. 3A to 3C and FIG. 4. In FIG. 3A,
a substrate 301, a transparent electrode layer 302, and a
photoelectric conversion layer 303 are formed in the same manner as
the embodiment 1. Then, rear electrodes (XE) are formed on the
photoelectric conversion layer 303 by the screen printing method
like Embodiment 1.
[0081] Then, as shown in FIG. 3B, openings XM.sub.0 to XM.sub.n and
XC.sub.1 to XC.sub.n reaching the transparent electrode layer 302
from the photoelectric conversion layer 303 are formed by a laser
working method. The openings XM.sub.0 to XM.sub.n are openings for
insulation and separation and for forming unit cells, and the
openings XC.sub.1 to XC.sub.n are for forming connection between
the transparent electrode and the rear electrode.
[0082] At the laser working, there is a case where a residue
remains at the periphery of the opening. This residue is a spray of
a material to be worked, and since the spray heated up to a high
temperature by laser light is attached to the surface of the
photoelectric conversion layer 303 to damage the film, it is
originally undesirable. In order to prevent this, the rear
electrode is formed in accordance with the pattern of the openings,
and then, the laser working is carried out, with the result that
damage to at least the photoelectric conversion layer 303 can be
prevented.
[0083] After the transparent electrode layer 302 is divided into
XT.sub.1 to XT.sub.n, and the photoelectric conversion layer 303 is
divided into XK.sub.1 to XK.sub.n, insulating resin layers XZ.sub.0
to XZ.sub.n filling the openings XM.sub.0 to XM.sub.n and covering
the upper end portions are formed by the screen printing method as
shown in FIG. 3C.
[0084] Next, as shown in FIG. 4, wiring lines XB.sub.0 to
XB.sub.n-1 filling the openings XC.sub.1 to XC.sub.n and connecting
with the transparent electrodes XT.sub.1 to XT.sub.n are formed by
the screen printing method. The wiring lines XB.sub.0 to XB.sub.n-1
are formed of the same material as the rear electrode, and a
thermosetting carbon paste is used. In this way, the rear electrode
XE.sub.n-1 is electrically connected to the transparent electrode
XT.sub.n.
[0085] Finally, a sealing resin layer 304 is formed by a printing
method. Opening portions 305 and 306 are respectively formed in the
sealing resin layer 304 on the wiring lines XB.sub.0 and XB.sub.n,
and connected to an external circuit. In this way, a unit cell made
of the transparent electrode XT.sub.n, the photoelectric conversion
layer XK.sub.n, and the rear electrode layer XE.sub.n is formed on
the substrate 301, and the adjacent rear electrode XE.sub.n-1 is
connected to the transparent electrode XT.sub.n through the opening
XC.sub.n, with the result that a solar cell of the n
series-connected unit cells can be fabricated. The rear electrode
XB.sub.0 is a lead-out electrode of the transparent electrode
XT.sub.1 of the unit cell XU.sub.1.
[0086] (Embodiment 3)
[0087] FIG. 5 is a top view of a case where a solar cell of this
embodiment is seen from a rear electrode side. FIG. 5 shows an
example of a solar cell arranged at the lower side (portion in
which a movement of a wrist watch is installed) of a
semitranslucent dial plate in the wrist watch. A substrate 501 is
an organic resin film having a thickness of 70 .mu.m, and although
any of the organic resin materials set forth in Embodiment 1 can be
applied, a PEN substrate is typically used. Although the shape of
the substrate 501 is not limited to a circle, an insertion port 507
of a pointer shaft is provided at the center.
[0088] In the solar cell, a transparent electrode layer, a
photoelectric conversion layer, a rear electrode layer, and a
sealing resin layer are laminated from the side of the substrate
501. These are formed in the same manner as Embodiment 1 or
Embodiment 2. Although four unit cells are concentrically arranged
on the substrate 501, the structure of series connection of the
solar cell is basically the same as the embodiment 1, or the
structure like the embodiment 2 may be adopted.
[0089] In FIG. 5, unit cells YU.sub.1 to YU.sub.4 are formed by an
opening YM.sub.0 formed in the transparent electrode layer and the
photoelectric conversion layer, and by openings YM.sub.1 to
YM.sub.4 in the inside of the opening YM.sub.0. The openings
YM.sub.0 to YM.sub.4 are filled with insulating resin layers
YZ.sub.0 to YZ.sub.4, and the insulating resin layers are formed so
that the upper end portions of the openings YM.sub.0 to YM.sub.4
are covered.
[0090] Rear electrodes YE.sub.1 to YE.sub.4 are formed on the
photoelectric conversion layer by the screen printing method using
a thermosetting conductive carbon paste, and are respectively
connected to transparent electrodes of the adjacent unit cell
through openings YC.sub.2 to YC.sub.4. A sealing resin layer 504 is
formed on the entire surface of the rear electrodes except for
connection portions 505 and 506 to the circuit substrate of the
wrist watch. An output electrode YE.sub.0 at the side of the
transparent electrode is formed at the connection portion 505 to
the circuit substrate and is connected to the transparent electrode
through an opening YC.sub.1. Besides, as shown in the drawing, it
is formed to be separate from the rear electrode YE.sub.1. The one
connection portion 506 is formed to serve also as the rear
electrode YE.sub.4.
[0091] FIG. 6A shows a section taken along A-A' of the periphery of
the connection portion 505 to the circuit substrate in FIG. 5. The
transparent electrode layer, the photoelectric conversion layer,
and the rear electrode layer are formed on the substrate 501. The
openings YM.sub.0 and YC.sub.1 are formed in the transparent
electrode layer and the photoelectric conversion layer by the laser
working method, and the insulating layer YZ.sub.0 is formed on the
opening YM.sub.0 to fill the opening and further to cover its upper
end portion. The output electrode YE.sub.0 at the side of the
transparent electrode is connected to the transparent electrode
YT.sub.1 of the unit cell YU.sub.1 through the opening YC.sub.1.
The sealing resin layer 504 is formed on the rear electrode
YE.sub.1 of the unit cell YU.sub.1.
[0092] Similarly, FIG. 6B shows a section taken along B-B' of the
periphery of the connection portion 506 to the external circuit,
and the transparent electrode YT.sub.4, the photoelectric
conversion layer YK.sub.4, and the rear electrode layer YE.sub.4
are formed on the substrate 501. The transparent electrode YT.sub.4
is formed at the inside of the end portion by the opening YM.sub.0,
and the insulating layer YZ.sub.0 fills the opening and further
covers its upper end portion. Although the sealing resin layer is
formed on the rear electrode layer YE.sub.4, it is not formed on
the connection portion 506.
[0093] FIG. 6C shows a section taken along C-C' of the connection
portion of the adjacent unit cells in FIG. 5. The transparent
electrodes YT.sub.3 and YT.sub.4 are formed on the substrate 501,
and are insulated and separated from each other by the opening
YM.sub.0 and the insulating layer YZ.sub.0 formed to cover the
opening and its upper end portion. Similarly, the photoelectric
conversion layers YK.sub.3 and YK.sub.4 are also separated. With
respect to the connection between the unit cells YU.sub.3 and
YU.sub.4, a conductive material is filled in the opening YC.sub.4,
and the rear electrode YE.sub.3 is connected to the transparent
electrode YT.sub.4.
[0094] In the manner as described above, it is possible to form the
solar cell in which the four unit cells YU.sub.1 to YU.sub.4 are
connected in series. In solar cells installed in various electric
instruments such as a calculator or a watch, with respect to
connection to a circuit of the electric instrument, there is an
adopted method of direct connection using a coil spring or a plate
spring, in addition to a connecting method using soldering or a
thermosetting adhesive. FIG. 7 is a view for explaining an example
of such a direct connection, and shows a state where connection
between a photoelectric conversion device 702 and a circuit
substrate is made through a connection spring. The structure of the
photoelectric conversion device 702 is simply shown, and the
drawing shows the state where a rear electrode 702b, an insulating
resin 702c, and a sealing resin 702d are formed on a substrate
702a. In addition, a stainless structural body 703, a support body
701 and the like are included. A connection spring 704 is in
contact with the rear electrode at an opening portion of the
sealing resin 702d, and electrical connection is formed to a
circuit substrate 706 through a terminal portion 705. The
connection structure of a contact by applying pressure using
mechanical force like this does not give severe damage to the solar
cell as compared with a connection method such as soldering or heat
sealing, and does not cause yield to be lowered in a manufacturing
process. When the rear electrode is formed of metal material, the
surface is oxidized by aging, with the result that contact
resistance is increased. However, in the case where the carbon
paste is used, such a problem does not occur.
[0095] According to the present invention, reliability at a
connecting portion between a solar cell installed in an electric
instrument, such as a watch, and a circuit substrate of the
electric instrument can be improved. Besides, electrostatic
withstand voltage can be improved, and the yield of a manufacturing
process can be improved.
* * * * *