U.S. patent application number 14/495048 was filed with the patent office on 2016-03-24 for solar cell structure and method for fabricating the same.
The applicant listed for this patent is Huey-Liang Hwang. Invention is credited to Cheng-Siang HU, Huey-Liang HWANG, Chao-Chang LI, Jian-Yang LIN.
Application Number | 20160087115 14/495048 |
Document ID | / |
Family ID | 55487485 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160087115 |
Kind Code |
A1 |
HWANG; Huey-Liang ; et
al. |
March 24, 2016 |
SOLAR CELL STRUCTURE AND METHOD FOR FABRICATING THE SAME
Abstract
A solar cell structure with a microsphere-roughened
antireflection structure comprises a P-type metal contact
electrode, a P-type semiconductor layer, a P-type monocrystalline
substrate, an N-type semiconductor layer, an N-type metal contact
electrode, and a microsphere-roughened antireflection layer. The
N-type semiconductor layer and the P-type semiconductor layer are
respectively arranged on an upper surface and a lower surface of
the P-type monocrystalline substrate. The P-type metal contact
electrode is arranged below the P-type semiconductor layer. The
N-type metal contact electrode has a specified pattern and is
connected with the N-type semiconductor layer. The
microsphere-roughened antireflection layer is arranged on an upper
surface of the N-type semiconductor layer without covering the
N-type metal contact electrode. The microsphere-roughened
antireflection layer reduces the reflection of sunlight and
increases the transmittance of sunlight to enhance the efficiency
of solar cells.
Inventors: |
HWANG; Huey-Liang; (Hsinchu,
TW) ; LIN; Jian-Yang; (Douliu City, TW) ; HU;
Cheng-Siang; (Douliu City, TW) ; LI; Chao-Chang;
(Douliu City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hwang; Huey-Liang |
Hsinchu |
|
TW |
|
|
Family ID: |
55487485 |
Appl. No.: |
14/495048 |
Filed: |
September 24, 2014 |
Current U.S.
Class: |
136/256 ;
204/192.26; 438/72 |
Current CPC
Class: |
Y02E 10/547 20130101;
H01L 31/02168 20130101; Y02P 70/521 20151101; H01L 31/068 20130101;
H01L 31/02366 20130101; H01L 31/1804 20130101; H01L 31/02167
20130101; H01L 31/02363 20130101; Y02P 70/50 20151101 |
International
Class: |
H01L 31/0216 20060101
H01L031/0216; H01L 31/0236 20060101 H01L031/0236; H01L 31/18
20060101 H01L031/18 |
Claims
1-3. (canceled)
4. A method for fabricating a solar cell structure with a
microsphere-roughened antireflection structure, the solar cell
structure with the microsphere-roughened antireflection structure
comprising: a P-type monocrystalline substrate; a N-type
semiconductor layer and a P-type semiconductor that are
respectively arranged on an upper surface and a lower surface of
the P-type monocrystalline substrate; a P-type metal contact
electrode arranged below the P-type semiconductor layer; a N-type
metal contact electrode having a specified pattern and connected
with the N-type semiconductor layer; a microsphere-roughened
antireflection layer arranged on an upper surface of the N-type
semiconductor layer without covering the N-type metal contact
electrode; and a surface passivation layer arranged on the upper
surface of the N-type semiconductor layer, wherein the N-type metal
contact electrode passes through the surface passivation layer to
connect with the N-type semiconductor layer, wherein the surface
passivation layer is fabricated on the upper surface of the N-type
semiconductor layer beforehand; next, the N-type metal contact
electrode having the specified pattern is fabricated on an upper
surface of the surface passivation layer; next, a baking process is
undertaken to make the N-type metal contact electrode pass through
the surface passivation layer to connect with the N-type
semiconductor layer; next, the microsphere-roughened antireflection
layer is fabricated on the upper surface of the surface passivation
layer, without covering the N-type metal contact electrode.
5. The method for fabricating a solar cell structure with a
microsphere-roughened antireflection structure according to claim
4, wherein fabricating the N-type semiconductor layer on the P-type
monocrystalline substrate includes the following steps of: using a
spin-coating machine to spin-coat a phosphorus diffusion solution
on the P-type monocrystalline substrate uniformly, wherein the
spin-coating machine is set to respectively rotate at two different
stages; during the first stage, the spin-coating machine rotates at
a speed of 1000 rpm for 15 seconds; during the second stage, the
spin-coating machine rotates at a speed of 3000 rpm for 20 seconds;
placing the P-type monocrystalline substrate in a high-temperature
furnace tube filled with nitrogen to be baked at a temperature of
200.degree. C. for 15 minutes to dry organic materials of the
phosphorus diffusion solution; placing the P-type monocrystalline
substrate in a fast-annealing furnace; evacuating the
fast-annealing furnace to a pressure of below 100 millitorr;
filling the fast-annealing furnace with nitrogen which is
maintained at a pressure of 4-6 torr; and annealing the P-type
monocrystalline substrate at a temperature of 950.degree. C. for
about 60 seconds to complete fabrication of the N-type
semiconductor layer.
6. The method for fabricating a solar cell structure with a
microsphere-roughened antireflection structure according to claim
4, wherein before the N-type semiconductor layer is fabricated on
the P-type monocrystalline substrate, a surface of the P-type
monocrystalline substrate for the N-type semiconductor layer to be
fabricated thereon is etched to become a serrated surface.
7. The method for fabricating a solar cell structure with a
microsphere-roughened antireflection structure according to claim
4, wherein fabricating the P-type semiconductor layer on the P-type
monocrystalline substrate includes the following steps of: using a
spin-coating machine to spin-coat a boron diffusion solution on the
P-type monocrystalline substrate uniformly, wherein the
spin-coating machine is set to respectively rotate at two different
stages; during the first stage, the spin-coating machine rotates at
a speed of 2000 rpm for 10 seconds; during the second stage, the
spin-coating machine rotates at a speed of 3000 rpm for 20 seconds;
placing the P-type monocrystalline substrate in a high-temperature
furnace tube filled with nitrogen to be baked at a temperature of
200.degree. C. for 15 minutes to dry organic materials of the boron
diffusion solution; placing the P-type monocrystalline substrate in
a fast-annealing furnace; evacuating the fast-annealing furnace to
a pressure of below 100 millitorr; filling the fast-annealing
furnace with nitrogen which is maintained at a pressure of 4-6
torr; annealing the P-type monocrystalline substrate at a
temperature of 950.degree. C. for about 60 seconds to complete
fabrication of the P-type semiconductor layer.
8. The method for fabricating a solar cell structure with a
microsphere-roughened antireflection structure according to claim
4, wherein the surface passivation layer is fabricated by using a
sputtering system to deposit a hafnium dioxide (HfO.sub.2) film,
and wherein the sputtering system is filled with 95% of argon and
5% of oxygen that are controlled at a pressure of 5 millitorr; a
radio frequency power for the sputtering system is controlled to
100-300 W for 4 minutes to obtain the surface passivation layer
having a thickness of about 80 nm.
9. The method for fabricating a solar cell structure with a
microsphere-roughened antireflection structure according to claim
4, wherein the N-type metal contact electrode is fabricated by
using a thermal evaporation system to deposit aluminum having a
thickness of about 150 nm on the upper surface of the surface
passivation layer, whereafter a baking process is undertaken to
make the N-type metal contact electrode diffuse through the surface
passivation layer to connect with the N-type semiconductor
layer.
10. The method for fabricating a solar cell structure with a
microsphere-roughened antireflection structure according to claim
4, wherein fabricating the microsphere-roughened antireflection
layer includes the following steps: using a spin-coating machine to
spin-coat a solution of silicon dioxide (SiO.sub.2) particles on
the upper surface of the surface passivation layer, wherein the
spin-coating machine is set to respectively rotate at two different
stages; during the first stage, the spin-coating machine rotates at
a speed of 1000 rpm for 10 seconds; during the second stage, the
spin-coating machine rotates at a speed of 1000-5000 rpm for 20-40
seconds; placing the coated structure in a high-temperature
annealing furnace to be processed at a temperature of 300.degree.
C. for 10 minutes to enhance cohesion of crystalline structures
inside the silicon dioxide particles.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a solar cell structure,
particularly to a surface structure of a crystalline silicon solar
cell.
BACKGROUND OF THE INVENTION
[0002] In monocrystalline silicon, atoms are periodically arranged
according to a specified rule. In fabricating monocrystalline
silicon, silicon metal having a purity of 99.999999999% (totally 11
digits of "9" used to express the purity) is fused in a quartz
crucible. Next, a seed crystal is inserted into the liquid silicon,
rotated at a speed of 2-20 rpm and slowly pulled up at a speed of
0.3-10 mm per minute to form a monocrystalline silicon ingot having
a diameter of 4-8 inches. The abovementioned process is the
so-called Czochralski method. The monocrystalline silicon-based
solar cell has high efficiency and high reliability and has been
widely used nowadays.
[0003] The fossil fuel power plants and nuclear power plants
dominate power generation in Taiwan. Therefore, Taiwan relies on
the imported coal and nuclear fuel very much. Recently, the price
of petroleum is growing higher and higher. Further, the safety of
nuclear power is worried by people because the nuclear power plants
have been too old to operate safely in Taiwan. In order to reduce
the dependence on imported coal and nuclear power generation,
Taiwan pays much attention to renewable energies now.
[0004] Taiwan is a subtropical country having abundant sunshine.
Further, Taiwan has mature semiconductor industry and plays a
significant role in the global solar cell production. Therefore,
Taiwan is very suitable to develop solar energy.
[0005] The current solar cell fabrication process includes the
following steps: using the RCA process to clean the surface of the
substrate; patterning the surface of the substrate; using an acidic
solution to clean the patterned surface; using a diffusion process
to fabricate a P-type or N-type semiconductor layer on the surface
of the substrate; etching the edges of the substrate having
experienced the abovementioned diffusion process; removing the
oxide on the surface of the substrate; fabricating an
antireflection layer on the surface of the substrate; and
fabricating metal electrodes on the substrate. Whether a P-type or
N-type semiconductor layer is fabricated in the abovementioned
diffusion process depends on the conductivity type of the
substrate. However, a P-type doped silicon substrate is normally
used as the substrate, and a high-temperature diffusion process is
used to fabricate an N-type doped semiconductor layer.
[0006] From the abovementioned description, it is leaned that a
solar cell fabrication process includes many different fabrication
processes. It is very important for solar cells to increase the
efficiency and decrease fabrication cost in the fabrication
process. It is particularly critical to enhance the antireflection
performance. The antireflection function is usually achieved via
etching the surface with an acidic solution or fabricating an
antireflection layer on the surface, which needs many fabrication
processes and increases the fabrication cost. Metal electrodes are
fabricated after the antireflection layer is completed. However,
the fabrication of the metal electrodes would decrease the
performance of the antireflection layer, which should decrease
light utilization and efficiency of the solar cell.
SUMMARY OF THE INVENTION
[0007] Considering the problems discussed above, the present
invention fabricates a microsphere-roughened antireflection
structure after the metal electrodes have been done to avoid
degrading the antireflection function and promote the efficiency of
the crystalline silicon solar cell.
[0008] The present invention proposes a solar cell structure
comprising a P-type metal contact electrode; a P-type semiconductor
layer; a P-type monocrystalline substrate; an N-type semiconductor
layer; an N-type metal contact electrode; and a
microsphere-roughened antireflection layer, wherein the N-type
semiconductor layer and the P-type semiconductor layer are
respectively arranged on an upper surface and a lower surface of
the P-type monocrystalline substrate. The P-type metal contact
electrode is disposed below the P-type semiconductor layer, and the
N-type metal contact electrode has a specified pattern and is
connected with the N-type semiconductor layer. The
microsphere-roughened antireflection layer is arranged on an upper
surface of the N-type semiconductor layer, which is not cover the
N-type metal contact electrode.
[0009] In one embodiment, the solar cell structure of the present
invention further comprises a surface passivation layer disposed on
the upper surface of the N-type semiconductor layer. The N-type
metal contact electrode passes through the surface passivation
layer to connect with the N-type semiconductor layer. In
fabrication, the surface passivation layer is fabricated on the
upper surface of the N-type semiconductor layer beforehand; next,
the N-type metal contact electrode having a specified pattern is
fabricated on an upper surface of the surface passivation layer;
next, a baking process is undertaken to let the N-type metal
contact electrode pass through the surface passivation layer to
connect with the N-type semiconductor layer; then, the
microsphere-roughened antireflection layer is fabricated on the
upper surface of the surface passivation layer without covering the
N-type metal contact electrode.
[0010] Thus, the surface passivation layer can provide very good
protection function, and the microsphere-roughened antireflection
layer can reduce sunlight reflection and increase the transmittance
of sunlight. In the present, the fabrication of the
microsphere-roughened antireflection layer is undertaken in the
last step to avoid degrading the performance of the
microsphere-roughened antireflection layer and promote the
efficiency of the solar cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a diagram schematically showing a solar cell
structure according to one embodiment of the present invention;
[0012] FIG. 2A is a diagram schematically showing a semi-finished
product of a solar cell structure according to one embodiment of
the present invention; and
[0013] FIG. 2B is a diagram schematically showing another
semi-finished product of a solar cell structure according to one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The technical contents of the present invention will be
demonstrated in detail with embodiments. However, it should be
understood: the embodiments are only to exemplify the present
invention but not to limit the scope of the present invention.
[0015] Refer to FIG. 1. The solar cell structure of the present
invention comprises a P-type metal contact electrode 10; a P-type
semiconductor layer 20; a P-type monocrystalline substrate 30; an
N-type semiconductor layer 40; an N-type metal contact electrode
50; a surface passivation layer 60; and a microsphere-roughened
antireflection layer 70. The N-type semiconductor layer 40 and the
P-type semiconductor layer 20 are respectively arranged on the
upper surface and the lower surface of the P-type monocrystalline
substrate 30. The P-type metal contact electrode 10 is disposed
below the P-type semiconductor layer 20. The surface passivation
layer 60 is disposed on the upper surface of the N-type
semiconductor layer 40. The N-type metal contact electrode 50 has a
specified pattern and passes through the surface passivation layer
60 to connect with the N-type semiconductor layer 40. The
microsphere-roughened antireflection layer 70 is arranged on a
portion of the upper surface of the surface passivation layer 60
which is free of the N-type metal contact electrode 50. I.e., the
microsphere-roughened antireflection layer 70 is arranged on the
upper surface of the surface passivation layer 60 without covering
the N-type metal contact electrode 50.
[0016] In one embodiment, the upper surface of the P-type
monocrystalline substrate 30, which contacts the N-type
semiconductor layer 40, is a serrated surface, so that the N-type
semiconductor layer 40, the surface passivation layer 60 and the
microsphere-roughened antireflection layer 70 that are formed
thereon also have a serrated shape, and whereby is enhanced the
antireflection effect and increased the efficiency of the solar
cell structure.
[0017] In the fabrication of the solar cell structure of the
present invention, provide a P-type monocrystalline substrate 30
firstly. Next, clean the P-type monocrystalline substrate 30 with
acetone for 10 minutes. Next, clean the P-type monocrystalline
substrate 30 with ethanol for 10 minutes. Next, clean the P-type
monocrystalline substrate 30 with deionized water (DI water) for 10
minutes. Next, dry the P-type monocrystalline substrate 30 at a
temperature of 100.degree. C. for 10 minutes.
[0018] In the fabrication of the N-type semiconductor layer 40 on
the P-type monocrystalline substrate 30, use a spin-coating machine
to spin-coat a phosphorus diffusion solution on the P-type
monocrystalline substrate 30 uniformly to let the P-type
monocrystalline substrate 30 coated with phosphorus. The
spin-coating machine is set to respectively rotate at two different
stages. During the first stage, the spin-coating machine rotates at
a speed of 1000 rpm for 15 seconds. During the second stage, the
spin-coating machine rotates at a speed of 3000 rpm for 20 seconds.
Next, place the P-type monocrystalline substrate 30 in a
high-temperature furnace tube filled with nitrogen, and bake the
P-type monocrystalline substrate 30 at a temperature of 200.degree.
C. for 15 minutes to dry the organic materials of the phosphorus
diffusion solution. Next, place the P-type monocrystalline
substrate 30 in a fast-annealing furnace. Next, evacuate the
fast-annealing furnace to a pressure of below 100 millitorr. Next,
fill the fast-annealing furnace with nitrogen and maintain the
pressure of nitrogen at 4-6 torr. Next, anneal the P-type
monocrystalline substrate 30 at a temperature of 950.degree. C. for
about 60 seconds. Thus is completed the fabrication of the N-type
semiconductor layer 40.
[0019] Before the N-type semiconductor layer 40 is fabricated on
the P-type monocrystalline substrate 30, the upper surface of the
P-type monocrystalline substrate 30, which is going to contact the
N-type semiconductor layer 40, is etched to form a serrated
surface. Thereby, the N-type semiconductor layer 40, the surface
passivation layer 60 and the microsphere-roughened antireflection
layer 70 also have serrated surfaces.
[0020] In the fabrication of the P-type semiconductor layer 20 on
the P-type monocrystalline substrate 30, use a spin-coating machine
to spin-coat a boron diffusion solution on the P-type
monocrystalline substrate 30 uniformly to let the P-type
monocrystalline substrate 30 coated with boron. The spin-coating
machine is set to respectively rotate at two different stages.
During the first stage, the spin-coating machine rotates at a speed
of 2000 rpm for 10 seconds. During the second stage, the
spin-coating machine rotates at a speed of 3000 rpm for 20 seconds.
Next, place the P-type monocrystalline substrate 30 in a
high-temperature furnace tube filled with nitrogen, and bake the
P-type monocrystalline substrate 30 at a temperature of 200.degree.
C. for 15 minutes to dry the organic materials of the boron
diffusion solution. Next, place the P-type monocrystalline
substrate 30 in a fast-annealing furnace. Next, evacuate the
fast-annealing furnace to a pressure of below 100 millitorr. Next,
fill the fast-annealing furnace with nitrogen and maintain the
pressure of nitrogen at 4-6 torr. Next, anneal the P-type
monocrystalline substrate 30 at a temperature of 950.degree. C. for
about 60 seconds. Thus is completed the fabrication of the P-type
semiconductor layer 20.
[0021] In the fabrication of the surface passivation layer 60, a
sputtering system is used to deposit a hafnium dioxide (HfO.sub.2)
film, wherein the sputtering system is filled with 95% of argon and
5% of oxygen, and the pressure of a chamber of the sputtering
system is controlled to 5 millitorr, and the radio frequency power
for the sputtering system is controlled to 100-300 W for 4 minutes,
whereby is obtained a surface passivation layer 60 having a
thickness of about 80 nm.
[0022] Refer to FIG. 2A and FIG. 2B. In the fabrication of the
N-type metal contact electrode 50, a thermal evaporation system is
used to deposit aluminum having a thickness of about 150 nm on the
upper surface of the surface passivation layer 60 to function as
the N-type metal contact electrode 50, as shown in FIG. 2A. After
the deposition of the N-type metal contact electrode 50, a baking
process is undertaken to let the N-type metal contact electrode 50
diffuse through the surface passivation layer 60 to connect with
the N-type semiconductor layer 40, as shown in FIG. 2B.
[0023] Similarly, in the fabrication of the P-type metal contact
electrode 10, a thermal evaporation system is used to deposit
aluminum having a thickness of about 300 nm on the lower surface of
the P-type semiconductor layer 20 to function as the P-type metal
contact electrode 10.
[0024] In the fabrication of the microsphere-roughened
antireflection layer 70, a spin-coating machine is used to
spin-coat a solution of silicon dioxide (SiO.sub.2) particles which
is a material of the microsphere-roughened antireflection layer 70
on the upper surface of the surface passivation layer 60 contacting
the N-type metal contact electrode 50. The spin-coating machine is
set to respectively rotate at two different stages. During the
first stage, the spin-coating machine rotates at a speed of 1000
rpm for 10 seconds. During the second stage, the spin-coating
machine rotates at a speed of 1000-5000 rpm for 20-40 seconds.
Then, the structure coated with the SiO.sub.2 particles is placed
in a high-temperature annealing furnace at a temperature of
300.degree. C. for 10 minutes to enhance the cohesion of the
crystalline structures inside the silicon dioxide particles.
[0025] In conclusion, the present invention is characterized in
fabricating a surface passivation layer and a microsphere-roughened
antireflection layer in a solar cell to respectively provide a
protection effect and increase transmittance of sunlight. In the
present invention, the microsphere-roughened antireflection layer
is fabricated after the P-type metal contact electrode and the
N-type metal contact electrode have been done. Therefore, the
present invention is superior in the antireflection function and
able to promote the efficiency of solar cells.
* * * * *