Title of Invention

A METHOD OF MANUFACTURING A TANDEM TYPE THIN FILM PHOTOELECTRIC CONVERSION DEVICE

Abstract A method of manufacturing a tandem-type thin film photoelectric conversion device includes the steps of forming at least one photoelectric conversion unit (3) on a substrate (1) in a deposition apparatus, taking out the substrate (1) having the photoelectric conversion unit (3) from the deposition apparatus to the air, introducing the substrate (1) into a deposition apparatus and carrying out plasma exposure processing on the substrate (1) in an atmosphere of a gas mixture containing an impurity for determining the conductivity type of the same conductivity type as that of the uppermost conductivity type layer (33) and hydrogen, forming a conductivity type intermediate layer (5) by additionally supplying semiconductor raw gas to the deposition apparatus, and then forming a subsequent photoelectric conversion unit
Full Text Description
A METHOD OF MANUFACTURING A TANDEM TYPE THIN FILM PHOTOELECTRIC
CONVERSION DEVICE
Technical Field
The present invention relates to a method of manufacturing
a tandem-type thin film photoelectric conversion device and,
more particularly, to a method of manufacturing which can
suppress reduction in performance of a photoelectric conversion
device, enhance the flexibility of manufacturing steps and
improve manufacturing efficiency. In the specification, terms
"crystalline" and "microcrystalline" are used also for a state
partially including amorphous regions, as generally used in
the field of the art.
Background Art
In recent years, semiconductor thin film photoelectric
conversion devices as represented by a solar cell have been
diversified, and crystalline silicon thin film solar cells have
been developed in addition to conventional amorphous silicon
thin film solar cells. Furthermore, a tandem (hybrid)-type
thin film solar cell having a stack thereof have come into
practical use.
In general, a silicon thin film photoelectric conversion
device includes a first electrode, one or more semiconductor
thin film photoelectric conversion units and a second electrode
stacked in sequence on a substrate at least a surface portion
of which is insulated. Further, one photoelectric conversion
unit includes an i-type layer sandwiched between a p-type layer
and an n-type layer.
A major portion of the thickness of the thin film
photoelectric conversion unit is occupied by the i-type layer
of a substantially intrinsic semiconductor layer and
photoelectric conversion occurs mainly in the i-type layer.
Accordingly, it is preferable that the i-type layer as a
photoelectric conversion layer has a greater thickness for the
purpose of light absorption, though increase of the thickness
increases costs and time for deposition of the i-type layer.
The p-type and n-type conductive layers serve to produce
a diffusion potential within the photoelectric conversion unit,
and magnitude of the diffusion potential affects the value of
open-circuit voltage which is one of important properties of
the thin film photoelectric conversion device. However, these
conductive layers are inactive layers which do not directly
contribute to photoelectric conversion. That is, light
absorbed by these inactive layers is a loss, which does not
contribute to electric power generation. Consequently, it is
preferable to minimize the thickness of the p-type and n-type
conductive layers as far as they provide a sufficient diffusion
potential.
For this reason, regardless of whether p-type and n-type
conductivity type layers included in a photoelectric conversion
unit or a photoelectric conversion device is amorphous or
crystalline, one whose i-type photoelectric conversion layer
which occupies a major portion of the conductivity type layer
is amorphous is called an amorphous unit or an amorphous
photoelectric conversion device, and one whose i-type layer
is crystalline is called a crystalline unit or a crystalline
photoelectric conversion device.
Currently, a wide variety of materials and forming
technologies have been developed for achieving quality required
for conductivity type layers included in a photoelectric
conversion device. As a material for a conductivity type layer
of a silicon photoelectric conversion device, amorphous silicon
or its alloy material or crystalline silicon or its alloy
material is generally used. Generally, an amorphous silicon
material having a wider band gap than that of a photoelectric
conversion layer (i-type layer) or a microcrystalline silicon
material having a high impurity activation rate is used for
a conductivity type layer, with the intention to attain a high
photoelectric conversion characteristic while reducing
electric and optical losses as small as possible.
A conductive layer of a silicon photoelectric conversion
unit is generally formed by a method substantially the same
as that for a photoelectric conversion layer (i-type layer)
such as a plasma CVD method. The conductive layer is formed
from reaction gas which is a mixture of a raw gas containing
atoms of silicon and doping gas containing atoms of a
conductivity-type determining impurity. In recent years, a
modified process of general plasma CVD method has been attempted
in order to form the conductivity type layer.
For example, JP-A-06-232429 discloses a plasma doping
method in which an i-type layer is once formed by a plasma CVD
method and then plasma processing is carried out in an atmosphere
containing a mixture of doping gas and a dilution gas such as
hydrogen whereby an area near a surface of the i-type layer
is changed to a conductivity type layer. Alternatively,
JP-A-10-074969 discloses a method for improving crystallinity
of a conductivity type layer in which a conductivity type
microcrystalline layer is once formed by a plasma CVD method
and then plasma processing is carried out in a hydrogen
atmosphere. In both of the methods, film deposition by the
plasma CVD method and subsequent plasma processing are carried
out as continuous processes in a decompression reaction chamber .
Thus, a good junction interface and a high quality conductivity
type layer can be formed.
In order to enhance a conversion efficiency of a thin
film photoelectric conversion device, it is known that two or
more photoelectric conversion units are stacked to form a
tandem-type thin film photoelectric conversion device . In this
case, a front unit including a photoelectric conversion layer
having a large band gap (such as of an amorphous silicon or
an Si-C alloy) is disposed closer to the light incident side
of the photoelectric conversion device, and a rear unit including
a photoelectric conversion layer having a small band gap (such
as of an Si-Ge alloy) is disposedbehind the front unit in sequence .
Thus, photoelectric conversion can be performed over a wide
wavelength range of incident light, and the conversion
efficiency of the entire photoelectric conversion device can
be improved. Among such tandem-type thin film photoelectric
conversion devices, one including both of an amorphous
photoelectric conversion unit and a crystalline photoelectric
conversion unit is occasionally called a hybrid thin film solar
cell in particular.
For example, a wavelength of light that can be
photoelectrically converted by an i-type amorphous silicon
ranges to about 800 nm maximum on the long wavelength side,
while an i-type crystalline silicon can photoelectrically
convert light having a longer wavelength ranging to about 1100
nm. Here, an amorphous silicon photoelectric conversion layer
having large light absorption is enough to light absorption
in the thickness of about 0.3 (J-m or less even in the case of
a single layer . However, in order to sufficiently absorb light
of a longer wavelength also, a crystalline silicon photoelectric
conversion layer having a small light absorption coefficient
is preferably about 2 to 3 urn thick or above in the case of
a single layer. In other words, a crystalline photoelectric
conversion layer generally desirably has a large thickness about
ten times of that of an amorphous photoelectric conversion layer .
In the tandem-type thin film photoelectric conversion
device, respective photoelectric conversion units are desired
to be formed under respective optimum conditions. Therefore,
the respective photoelectric conversion units may be formed '
discontinuously by separate deposition apparatuses.
Furthermore, in order to enhance flexibility of manufacturing
processes of the tandem-type thin film photoelectric conversion
device and to improve production efficiency, the respective
photoelectric conversion units may be desired to be formed
discontinuously by separate deposition apparatuses.
However, the inventors experienced that, when a first
photoelectric conversion unit was formed, then a substrate
including the unit was once taken out to the air from a deposition
apparatus, and a second photoelectric unit was stacked
thereafter, characteristics of the resulting tandem-type thin
film photoelectric conversion device deteriorate as compared
to that of a tandem-type thin film photoelectric conversion
device wherein all units were continuously formed without taking
a substrate out to the air.
Disclosure of the Invention
In view of the circumstances of the conventional arts,
the invention is aimed at to minimize the reduction in
photoelectric conversion efficiency of a tandem-type thin film
photoelectric conversion device due to exposure to the air when
a substrate having one or more photoelectric conversion units
is once taken out to the air from a deposition apparatus in
mid-course of formation of a plurality of the units involved
in the photoelectric conversion unit.
A method of manufacturing a tandem-type thin film
photoelectric conversion device according to the invention
includes the steps of forming at least one photoelectric
conversion unit on a substrate in a deposition apparatus, taking
out the substrate having the photoelectric conversion unit to
the air from the deposition apparatus, introducing the substrate
into a deposition apparatus and carrying out plasma exposure
processing on the substrate in an atmosphere of a gas mixture
containing an impurity element for determining the conductivity
type of the same type as that of the uppermost conductivity
type layer of the photoelectric conversion unit on the substrate
and hydrogen, forming a conductivity type intermediate layer
by additionally supplying a semiconductor raw gas to the
deposition apparatus, and then forming a subsequent
photoelectric conversion unit.
In any photoelectric conversion unit included in the
tandem-type thin film photoelectric conversion device, a
one-conductivity type layer, a photoelectric conversion layer
of substantially intrinsic semiconductor and an
opposite-conductivity type layer are stacked in sequence. The
tandem-type thin film photoelectric conversion device
preferably includes at least one amorphous silicon thin film
photoelectric conversion unit and at least one crystalline
silicon thin film photoelectric conversion unit.
Preferably, a non-doped intermediate layer having a
thickness of 5 nm or less is formed subsequently to the formation
of the at least one photoelectric conversion unit on the
substrate and the substrate is then taking out to the air.
The plasma exposure processing is preferably carried out
for 60 seconds or less using high frequency discharging at a
frequency of 13.56 MHz or higher in the mixed atmosphere
containing the gas containing the element for determining the
conductivity-type in an amount of 20 ppm or more based on the
hydrogen. The plasma exposure processing and the formation
of the conductivity-type intermediate layer are preferably
carried out in the same deposition apparatus and under
substantially the same pressure.
Accompanying
Brief Description of the Accompanying Drawings
Fig. 1 is a schematic cross section diagram showing a
tandem-type thin film photoelectric conversion device
manufactured by a method of manufacturing according to an
embodiment of the invention.
Fig. 2 is a schematic cross section diagram showing a
tandem-type thin film photoelectric conversion device
manufactured by a method of manufacturing according to another
embodiment of the invention.
Fig. 3 is a transmission electron microscopic (TEN)
photograph showing a cross section structure in the vicinity
of a boundary between an amorphous unit and a crystalline unit
in a hybrid-type thin film photoelectric conversion device
according to Example 1 of the invention.
Fig. 4 is a TEM photograph showing a cross section
structure in the vicinity of a boundary between an amorphous
unit and a crystalline unit in a hybrid-type thin film
photoelectric conversion device according to Reference
Example.
Best Mode for Carrying Out the Invention
Preferred embodiments of the invention will be described
below with reference to the drawings. In order to clarify and
simplify the drawings, dimension relationships of the thickness,
the length and the like are modified appropriately in the
drawings of this application, and they do not show the actual
dimension relationships. In the drawings, the same reference
numerals are given to the same components and equivalent parts
in the drawings.
Fig. 1 shows a schematic cross section diagram of a silicon
tandem-type thin film photoelectric conversion device
manufactured by a method according to an embodiment of the
invention. Namely, in the photoelectric conversion device,
a transparent electrode 2 made of a transparent conductive oxide
(TCO) film is formed on a transparent insulative substrate 1
made of glass or the like. On the transparent electrode 2,
a one-conductivity type layer 31, a intrinsic semiconductor
amorphous or crystalline photoelectric conversion layer 32 and
an opposite-conductivity type layer 33 included in a first
photoelectric conversion unit 3 are deposited in sequence
preferably by plasma CVD (or they may be deposited by other
chemical vapor deposition as a matter of course) . Preferably,
a P-type layer 31, a substantially intrinsic semiconductor
photoelectric conversion layer 32 and an n-type layer 33 are
deposited in this order.
After the first photoelectric conversion unit 3 is formed,
the substrate 1 is taken out from a plasma CVD apparatus to
the air whereby, the surface of the opposite-conductivity type
layer 33 is exposed to the air. Then, the substrate 1 is
introduced into another plasma CVD apparatus and undergoes
plasma exposure processing in a mixed atmosphere of doping gas
containing an element for determining the conductivity type
of the same type as that of the opposite-conductivity type layer
33 (such as phosphine) and hydrogen. As the doping gas, gas
containing phosphorus, oxygen and the like may be used for n-type
and, in particular, phosphorus is preferably contained. In
the case of p-type, doping gas containing boron, aluminum and
the like may be used and, in particular, boron (such as diborane)
is preferably contained.
Next, an intermediate layer 5 of the same opposite
conductivity type as that of the plasma-exposed
opposite-conductivity-type layer 33 is formed thereon. More
specifically, when the opposite conductivity type layer 33 is
of n-type, the intermediate layer 5 is also made to be n-type,
and when the opposite conductivity type layer 33 is of p-type,
the intermediate layer 5 is also made to be p-type. The
conductivity type intermediate layer 5 is preferably a fresh
additional layer, which can act such that a good np (or pn)
tunnel junction is formed between the intermediate layer 5 and
a subsequent photoelectric conversion unit 4. The opposite
conductivity type intermediate layer 5 is preferably deposited
by plasma CVD.
The conductivity type intermediate layer 5 may be formed
by adjusting deposition gas containing a new doping element
after plasma exposure processing. However, the conductive
intermediate layer 5 can be formed simply by performing plasma
exposure processing with doping gas and hydrogen and then
additionally supplying semiconductor raw gas to a reaction
chamber. Here, the semiconductor raw gas may be silane for
silicon, silane and methane for silicon carbide or silane and
germane for a silicon-germanium alloy.
A one-conductivity type layer 41, a substantially
intrinsic semiconductor amorphous or crystalline photoelectric
conversion layer 42 and an opposite conductivity type layer
43 included in a second photoelectric conversion unit 4 are
deposited in sequence on the opposite conductivity type
intermediate layer 5 preferably by plasma CVD. Finally, aback
electrode 10 is formed thereon.
The plasma exposure processing, the formation of the
opposite conductivity type intermediate layer 5 and the
formation of the one conductivity-type layer 41 in the second
photoelectric conversion unit 4 are preferably carried out in
the same decompression reaction chamber and are preferably
carried out under substantially the same pressure. After the .
completion of the plasma exposure processing, the intermediate
layer 5 can be formed continuously by additionally supplying
the semiconductor raw gas such as silane to the reaction chamber
immediately without stopping plasma discharging resulting from
the application of high frequency electric power. In some
cases, the one-conductivity type layer 41 can be further formed.
In such a method, though the steps of plasma exposure processing
and formation of the intermediate layer 5 are added, the addition
of time and facility required for these steps can be kept at
minimum.
With the method of manufacturing a tandem-type thin film
photoelectric conversion device, even when the surface of the
opposite-conductivity-type layer 33 of the first photoelectric
conversion unit 3 is deteriorated due to the air-exposure, the
surface can be cleaned or re formed by plasma exposure processing.
Here, a similar effect can be expected from plasma exposure
processing only in a hydrogen atmosphere without doping gas.
However, plasma exposure processing with hydrogen only may
adversely affect the quality of a silicon film in the vicinity
of the surface to be processed. Therefore, it is believed that
plasma exposure processing is preferably carried out with mixed
gas of doping gas and hydrogen.
In fact, when plasma exposure processing was carried out
with hydrogen only, the photoelectric conversion
characteristic was slightly lower than that of the case where
the first and second units 3 and 4 are formed continuously without
exposure to the air. Furthermore, the reproducibility was not
veryhigh. On the other hand, whenplasma processing was carried
out in an atmosphere of hydrogen mixed with doping gas like
the invention, almost the same photoelectric conversion
characteristic was obtained as that of the continuous f ormation
without exposure to the air.
The reason why these effects are brought about is
considered that the plasma exposure with hydrogen only results
in increase in resistance due to a phenomenon that a part of
impurity atoms in the conductivity type layer 33 in the vicinity
of the air-exposed surface is inactivated or leaves from the
layer. On the other hand, it is considered that, when plasma
processing is carried out with doping gas being mixed, such
increase in resistance can be prevented, whereby the
conductivity of the conductivity type layer 33 can be maintained.
Alternatively, it is also considered that mixing of doping gas
can reduce the increase in resistance because of decrease in
carrier mobility of the conductivity type layer 33 due to the
occurrence of defects or irregularity in the film structure
resulting from a plasma damage, which is often a problem in
hydrogen plasma processing.
The hydrogen plasma processing with doping gas being mixed
is carried out preferably within two minutes, more preferably
within one minute, through high-frequency discharging at a
frequency equal to or higher than 13.56 MHz. Discharging at
a lower frequency than the frequency or a longer processing
time than the time may increase a side effect such as a plasma
damage near the surface to be processed.
Since an increase in costs of a high frequency power supply
can be prevented by setting a discharging frequency in the plasma
processing to be the same as the frequency employed in the
subsequent forming steps for semiconductor layers, a frequency
equal to or higher than 13.56 MHz is preferably used. This
is because the fact that plasma discharging at such a high
frequency is preferably used for forming a high performance
thin film photoelectric conversion unit is widely recognized
in experimental and industrial points of view. In view of a
productivity, the plasma processing time is preferably as short
as possible. In order to make certain of the effect of addition
of the doping gas, the concentration of the doping gas is
preferably 20 ppm or more based on hydrogen.
When it becomes possible to form a plurality of
photoelectric conversion units in separate plasma CVD
apparatuses in this way, optimum facility specifications and
forming conditions for achieving best characteristics required
for the respective units can be set independently. Thus,
improvement in the characteristic of the tandem-type thin film
photoelectric conversion apparatus as a whole can be expected.
Furthermore, since a plurality of production lines can be used
for the respective units, the production efficiency and the
flexibility for changes and additions of the lines can be
increased. Still further, as a plurality of manufacturing
apparatuses are used, maintenance thereof can be carried out
one by one smoothly.
Fig. 2 shows a schematic cross section diagram of a
tandem-type thin film photoelectric conversion device
manufactured by a method of manufacturing according to another
embodiment of the invention. The apparatus in Fig. 2 is similar
to that of Fig. 1 but differs in that an additional non-doped
intermediate layer 6 is formed subsequent to the deposition
of the opposite conductivity type layer 33 included in the first
photoelectric conversion unit 3. The non-doped intermediate
layer 6 is preferably in the thickness of 5 nm or less, which
may cause a tunnel effect. The non-doped intermediate layer
6 may be produced preferably by plasma CVD but may be produced
by other different kinds of formation methods.
After the non-doped intermediate layer 6 is formed, the
substrate 1 is taken out from the plasma CVD apparatus to the
air, and the outermost surface of the non-doped intermediate
layer is exposed to the air. According to the review by the
inventors, the surface tends to be porous when impurity atoms
(such as phosphorus for an n-type layer, especially) are doped
therein like a conductivity-type layer. As the doping
concentration increases, the tendency increases. Therefore,
the exposure of the porous surface of the conductivity-type
layer 33 according to the embodiment in Fig. 1 into the air
may likely accelerate the oxidization of and/or the adhesion
of a foreign substance to the porous surface as compared to
the case of a flat surface.
On the other hand, as compared to the conductivity-type
layer, the surface of the non-doped intermediate layer 6 may
not likely be deteriorated or contaminated when the non-doped
intermediate layer is exposed to the air. The non-doped
intermediate layer 6 does not inhibit current flow because it
causes a tunnel effect when its thickness is 5 nm or less,
therefore, the non-doped intermediate layer 6 is less apt to
be a factor that causes decrease in the electric characteristic
as an photoelectric conversion device.
After the surface of the non-doped intermediate layer
6 is exposed to the air, hydrogen plasma exposure processing
with doping gas being mixed is carried out on the non-doped
intermediate layer 6 also in the case in Fig. 2 like the case
in Fig. 1. Subsequently, the opposite-conductivity type
intermediate layer 5 and the second photoelectric conversion
unit 4 are formed by plasma CVD.
The opposite-conductivity type intermediate layer 5 is
formed in both of the embodiments in Figs. 1 and 2. Since the
opposite-conductivity type intermediate layer 5 can also act
to support the function of the opposite-conductivity type layer
33 of the first photoelectric conversion unit 3, the opposite
conductivity type intermediate layer 5 may be considered as
a part of the opposite conductivity type layer 33. Since the
one-conductivity type layer 41 of the second photoelectric
conversion unit 4 is formed continuously on the opposite
conductivity type intermediate layer 5without exposing the
opposite conductivity type intermediate layer 5 to the air,
it is expected that a good np (or pn) tunnel junction, which
is desirable for achieving a high photoelectric conversion
characteristic in the tandem-type photoelectric conversion
device, is formed.
The photoelectric conversion devices according to these
embodiments may have a so-called super-straight structure
having the back electrode 10 on the two photoelectric conversion
units 3 and 4 including semiconductor layers in the pin order
stacked on the glass substrate 1. Alternatively, the
photoelectric conversion devices may have a so-called
sub-straight structure having the transparent electrode 10 on
a multiple of the units 3 and 4 formed on an arbitrary substrate
1, for example. Furthermore, the invention is not limited to
two-stack type tandem-type structure in which the two
photoelectric conversion units 3 and 4 are stacked and may be
applicable to a tandem-type structure in which three or more
photoelectric conversion units are stacked.
As an example of a method of manufacturing a tandem-type
thin film photoelectric conversion device according to the
embodiments in Figs . 1 and 2 , a method of manufacturing a hybrid
thin film solar cell having a two-stack type super straight
structure including the amorphous silicon unit 3 and the
crystalline silicon unit 4 will be described below with reference
to a reference example and comparative examples.
Example 1 corresponds to a method of manufacturing a thin
film solar cell in Fig. 2. First of all, a transparent electrode
layer 2 containing tin oxide as a main component was formed
on a transparent glass substrate 1. Then, the laminate
including the substrate 1 and the electrode layer 2 was
introduced in a first plasma CVD apparatus, and a p-type
amorphous silicon carbide layer 31, an i-type amorphous silicon
photoelectric conversion layer 32 and an n-type
microcrystalline silicon layer 33 included in an amorphous
silicon unit 3 were formed in the thickness of 8 nm, 300 nm
and 10 nm, respectively, at a predetermined substrate
temperature. After the formation of the; n-type layer 33,
introduction of phosphine as doping gas was shut off in the
same reaction chamber, and a non-doped intermediate layer 6
was formed in the thickness of 4 nm.
After that, the laminate was transferred to an unload
chamber of the first plasma CVD apparatus, and the laminate
was taken out to the air after the camber was promptly filled
with nitrogen gas. The laminate was left in the air for about
40 hours and then was introduced into a second plasma CVD
apparatus.
In the second plasma CVD apparatus, plasma exposure
processing was carried out at a predetermined substrate
temperature for 20 seconds in an atmosphere; in which hydrogen
and phosphine gas were mixed. The concentration of the
phosphinegas to hydrogen at that time was 200 ppm. Subsequently,
silane gas was additionally introduced into the same chamber
under substantially the same pressure condition while plasma
discharging by application of high frequency electric power
was continued whereby an n-type microcrystalline silicon
intermediate layer 5 was deposited in the thickness of 20 nm
in a mixed atmosphere of silane, hydrogen and phosphine.
After that, high frequency electric power was shut off
once. Then, in the same chamber under substantially the same
pressure condition, introduction of phosphine gas was stopped
and diborane gas was introduced into the chamber. Then, it
was held for about 30 seconds until silane, hydrogen and diborane
became stable as a mixed gas atmosphere. Then, high frequency
power was applied thereto to cause plasma discharging to deposit
a p-type microcrystalline silicon layer 41 included in the
crystalline silicon unit in the thickness of 16 nm. Table 1
shows detail conditions in the second plasma CVD apparatus for
the steps so far.
As is apparent from Table 1, plasma exposure processing
in an atmosphere of a gas mixture containing phosphine and
hydrogen, the formation of the n-type intermediate layer 5 and
the formation of the p-type layer 41 were continuously carried
out in the same chamber under the same set pressure . Furthermore,
in Example 1, the discharging frequencies, the applied power
densities, the substrate temperatures and the gas flow rates
were set uniformly, so that a series of processes and deposition
steps can be carried out quickly through simple manipulations
of opening/closing of valves of a gas introducing lines and
turning on/off of plasma discharging.
A transient change may occur in the pressure in the chamber
with the introduction or shut-off of the doping gas or the
semiconductor raw gas. However, the flow rates of these gases
are lower than that of the continuously introduced hydrogen
gas by about two orders ormore of magnitude . Thus, the transient
change in pressure can be significantly small. Therefore, the
waiting time (time for stabilizing pressure and a gas mixture
ratio) before the deposition of the n-type intermediate layer
5 and the p-type layer 41 can be as short as about 30 seconds
in total. In other words, the addition of the plasma exposure
processing and the step of forming the n-type intermediate layer
5 hardly cause a time loss in the process for manufacturing
a solar cell.
After the formation of the p-type layer 41, a non-doped
i-type crystalline silicon photoelectric conversion layer 42
and an n-type microcrystalline silicon layer 43 included in
the crystalline silicon unit 4 were formed in the thickness
of 1.7 urn and 15 nm, respectively, in the second plasma CVD
apparatus. Then, the laminate was transferred to the unload
chamber of the second plasma CVD apparatus, and the chamber
was filled with nitrogen gas promptly. Then, the laminate was
taken out to the air.
Then, a zinc oxide film having a thickness of 30 nm, a
silver film having a thickness of 240 nm a titan film having
a thickness of 5 nm included in a back electrode 10 were formed
by sputtering. Through these film forming steps, the two-stack
type hybrid-type thin film solar cell as shown in Fig. 2 in
which the amorphous silicon unit 3 and the crystalline silicon
unit 4 are stacked was formed.
By using a solar simulator, light of AM 1.5 spectrum was
irradiated to the hybrid thin film solar cell of Example 1 at
energy density of 1 kW/m2 at 25°C, and the photoelectric
conversion efficiency was measured. Relative values of the
result are shown in Table 2 . Though Table 2 includes examples
other than Example 1, maximum values, minimum values and mean
values of photoelectric conversion efficiencies of 20 samples
(N=20) are shown for all cases. The values are standardized
by referring the mean value of Example 1 to be 100.
(Example 2)
Example 2 was different from Example 1 only in that the
thickness of the n-type microcrystalline silicon layer 33 in
the amorphous silicon unit 3 was increased from 10 nm to 12
nm, and thereafter the laminate was taken out from the first
plasma CVD apparatus to the air without, formation of the
non-doped intermediate layer 6. In other words, Example 2
corresponds to a method of manufacturing a hybrid thin film
solar cell in Fig. 1.
(Reference Example)
Reference Example was different from Example 2 only in
that the thickness of the n-type microcrystalline silicon layer
33 was increased to 30 nm and the crystalline silicon unit 4
was subsequently formed without exposure of the laminate to
the air and also without formation of the n-type intermediate
As shown in Table 2, it is understood that the decreases
in the average photoelectric conversion efficiency of the solar
cells according to both of Example 1 and Example 2 fall within
the range of less than 2% in comparison with the solar cell
according to Reference Example, which was formed without
exposure to the air, and the variations in conversion efficiency
of the solar cells according to Example 1 and 2 are almost the
same as that of Reference Example. It is also understood that
Example 1 in which the non-doped intermediate layer 6 was formed
has a slightly higher conversion efficiency than that of Example
2.
Fig. 3 is a transmission electron microscopic (TEM)
photograph showing a cross section of a part in the vicinity
of the boundary between the amorphous unit 3 and crystalline
unit 4 in Example 1. The transparent electrode 2 partially
appears at the bottom of the photograph. When an oxide film
or contaminated layer is formed on the non-doped intermediate
layer 6, which was exposed to the air, such a foreign substance
layer may be clearly observed on a TEM photograph. However,
on the TEM photograph in Fig. 3, a clear foreign substance layer
is not observed between the amorphous unit 3 and the crystalline
unit 4. Only the change from the amorphous state to the
crystalline state can be observed.
Similarly, Fig. 4 is a TEM photograph showing a cross
section of a part in the vicinity of the boundary between the
amorphous unit 3 and the crystalline unit 4 in Reference Example .
Since the laminate was not exposed to the air between the
formation of the amorphous silicon unit 3 and the crystalline
unit 4 in Reference Example, no foreign substance layer can
be observed between the amorphous unit 3 and the crystalline
unit 4 on the TEM photograph in Fig. 4 as a matter of course.
Only the change from the amorphous state to the crystalline
state can be observed.
From the similarity between the Fig. 3 and Fig. 4 as
described above, even when the surface of the non-doped
intermediate layer 6 was exposed to the air and thereby it was
oxidized or contaminated in Example 1, the plasma exposure
processing in the second plasma CVD apparatus might remove and
clean a foreign substance layer such as an oxidized film or
a contamination film. In other words, the plasma exposure
processing can provide the same effect as that of the case in
which the laminate was not exposed into the air between the
formation step of the amorphous unit 3 and the formation step
of the crystalline unit 4.
(Comparative Example 1)
Comparative Example 1 was different from Example 1 only
in that plasma exposure processing on a surface of the laminate
was omitted in the second plasma CVD apparatus.
(Comparative Example 2)
Comparative Example 2 was different from Example 1 only
in that plasma exposure processing was carried out on a surface
of the laminate in an atmosphere of hydrogen gas only in the
second plasma CVD apparatus, and then silane gas and phosphine
gas were additionally introduced so that the n-type
microcrystalline silicon intermediate layer 5 was formed.
According to Table 2, the average conversion efficiency
in the case in which plasma exposure processing was not carried
out as in Comparative Example 1 is lower than that of Example
1 by 4% or above. On the other hand, though the conversion
efficiency improved slightly when plasma exposure process with
hydrogen only was carried out as in Comparative Example 2, a
large variation in the conversion efficiency was exhibited,
and the average efficiency was apparently lower than that of
Example 1.
(Example 3 and Comparative Example 3)
Example 3 and Comparative Example 3 were different from
Example 1 only in that the concentration of phosphine to hydrogen
was 20 ppm (example 3) and 4 ppm (Comparative Example 3) , which
are 1/10 and 1/50, respectively, of that of Example 1, in plasma
exposure processing carried out on the surface of the laminate
in the mixed atmosphere of phosphine and hydrogen. From Table
2, the conversion efficiency of Comparative Example 3 in which
4 ppm phosphine was added at plasma exposure processing is not
much different from that of Comparative Example 2 in which no
phosphine was added. However, the conversion efficiency of
Example 3 in which 20 ppm phosphine was added exhibits that
the phosphine in the concentration is sufficiently effective.
(Example 4 and Comparative Example 4)
Example 4 and Comparative Example 4 were different from
Example 1 only in that the processing time of plasma exposure
processing carried out on a surface of the laminate in an
atmosphere of a gas mixture of phosphine and hydrogen gas was
60 seconds (Example 4) and 180 seconds (Comparative Example
4), which are 3 times and 9 times, respectively, of those of
Example 1. From Table 2, the effects are not much different
even when the plasma exposure processing time is increased from
20 seconds in Example 1 to 60 seconds in Example 4. However,
the conversion efficiency adversely decreases when the
processing time was extended to 180 seconds in Comparative
example 4.
Industrial Applicability
As described above, according to the present invention,
when the substrate having one or more units is once taken out
from the deposition apparatus to the air in mid-course of the
formation of the plurality of photoelectric conversion units
included in the tandem-type thin film photoelectric conversion
device, the reduction in photoelectric conversion efficiency
of the completed apparatus due to the air exposure can be
minimized. Thus, the photoelectric conversion units can be
formed discontinuously by using separate deposition
apparatuses, and the flexibility and production efficiency of
steps of manufacturing a tandem-type thin film photoelectric
conversion device can be improved.
WE CLAIM :
1. A method of manufacturing a tandem-type thin film photoelectric
conversion device comprising the steps of: forming at least one photoelectric
conversion unit through sequentially stacking a first one-conductivity type layer, a
first photoelectric conversion layer of substantially intrinsic semiconductor and a first
opposite-conductivity type layer on a substrate in a deposition apparatus; taking out
the substrate having the photoelectric conversion unit from the deposition apparatus to
air, wherein a non-doped intermediate layer having a thickness of 5 nm or less is
formed subsequently to the step of forming the at least one photoelectric conversion
unit on the substrate and then the substrate is taken out to the air; introducing the
substrate into a deposition apparatus and carrying out plasma exposure processing on
the substrate in an atmosphere of a gas mixture containing an impurity element for
determining the conductivity type of the same conductivity type as that of the first
opposite-conductivity type layer and hydrogen; forming a conductivity type
intermediate layer by additionally supplying semiconductor raw gas to the deposition
apparatus; and then forming a subsequent photoelectric conversion unit through
sequentially stacking a second one-conductivity type layer, a second photoelectric
conversion layer of substantially intrinsic semiconductor and a second opposite-
conductivity type layer.
2. A method of manufacturing a tandem-type thin film photoelectric
conversion device as claimed in claim 1, wherein the tandem-type thin film
photoelectric conversion device comprises at least one amorphous silicon thin film
photoelectric conversion unit and at least one crystalline silicon thin film photoelectric
conversion unit.
3. A method of manufacturing a tandem-type thin film photoelectric
conversion device as claimed in claim 1, wherein the plasma exposure processing and
the formation of the conductivity-type intermediate layer are carried out in the same
deposition apparatus.
4. A method of manufacturing a tandem-type thin film photoelectric
conversion device as claimed in claim 1, wherein the plasma exposure processing and
the formation of the conductivity-type intermediate layer are carried out under
substantially the same pressure

A method of manufacturing a tandem-type thin film
photoelectric conversion device includes the steps of forming
at least one photoelectric conversion unit (3) on a substrate
(1) in a deposition apparatus, taking out the substrate (1)
having the photoelectric conversion unit (3) from the deposition
apparatus to the air, introducing the substrate (1) into a
deposition apparatus and carrying out plasma exposure
processing on the substrate (1) in an atmosphere of a gas mixture
containing an impurity for determining the conductivity type
of the same conductivity type as that of the uppermost
conductivity type layer (33) and hydrogen, forming a
conductivity type intermediate layer (5) by additionally
supplying semiconductor raw gas to the deposition apparatus,
and then forming a subsequent photoelectric conversion unit

Documents:

1384-kolnp-2004-abstract.pdf

1384-kolnp-2004-assignment.pdf

1384-kolnp-2004-claims.pdf

1384-KOLNP-2004-CORRESPONDENCE 1.1.pdf

1384-kolnp-2004-correspondence.pdf

1384-kolnp-2004-description (complete).pdf

1384-kolnp-2004-drawings.pdf

1384-kolnp-2004-examination report.pdf

1384-kolnp-2004-form 1.pdf

1384-kolnp-2004-form 13.pdf

1384-kolnp-2004-form 18.pdf

1384-KOLNP-2004-FORM 27.pdf

1384-kolnp-2004-form 3.pdf

1384-kolnp-2004-form 5.pdf

1384-KOLNP-2004-FORM-27.pdf

1384-kolnp-2004-gpa.pdf

1384-kolnp-2004-granted-abstract.pdf

1384-kolnp-2004-granted-assignment.pdf

1384-kolnp-2004-granted-claims.pdf

1384-kolnp-2004-granted-correspondence.pdf

1384-kolnp-2004-granted-description (complete).pdf

1384-kolnp-2004-granted-drawings.pdf

1384-kolnp-2004-granted-examination report.pdf

1384-kolnp-2004-granted-form 1.pdf

1384-kolnp-2004-granted-form 13.pdf

1384-kolnp-2004-granted-form 18.pdf

1384-kolnp-2004-granted-form 3.pdf

1384-kolnp-2004-granted-form 5.pdf

1384-kolnp-2004-granted-gpa.pdf

1384-kolnp-2004-granted-reply to examination report.pdf

1384-kolnp-2004-granted-specification.pdf

1384-kolnp-2004-reply to examination report.pdf

1384-kolnp-2004-specification.pdf


Patent Number 236194
Indian Patent Application Number 1384/KOLNP/2004
PG Journal Number 41/2009
Publication Date 09-Oct-2009
Grant Date 07-Oct-2009
Date of Filing 17-Sep-2004
Name of Patentee KANEKA CORPORATION
Applicant Address 2-4, NAKANOSHIMA 3-CHOME, KITA-KU, OSAKA-SHI, OSAKA
Inventors:
# Inventor's Name Inventor's Address
1 YOSHIMI MASASHI 6-6-4, IBUKIDAINISHI-MACHI, NISHI-KU, KOBE-SHI, HYOGO 651-2243
2 SUEZAKI TAKASHI 1-25-1 HIEITSUJI OTSU-SHI, SHIGA 520-0104
3 YAMAMOTO KENJI 2-W 1406, MIKATADAI 1-CHOME, NISHI-KU, KOBE-SHI, HYOGO 651-2277
PCT International Classification Number H01L 31/075
PCT International Application Number PCT/JP2003/04245
PCT International Filing date 2003-04-02
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2002-107133 2002-04-09 Japan