U.S. patent application number 12/007154 was filed with the patent office on 2011-01-06 for process for making multi-crystalline silicon thin-film solar cells.
This patent application is currently assigned to ATOMIC ENERGY COUNCIL - INSTITUTE OF NUCLEAR ENERGY RESEARCH. Invention is credited to Chin-Chen Chiang, Yu-Hsiang Huang, Chien-Te Ku, Shan-Ming Lan, Wei-Yang Ma, Tsun-Neng Yang.
Application Number | 20110003425 12/007154 |
Document ID | / |
Family ID | 43384938 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110003425 |
Kind Code |
A1 |
Yang; Tsun-Neng ; et
al. |
January 6, 2011 |
Process for making multi-crystalline silicon thin-film solar
cells
Abstract
Dichlorosilane and diborane are deposited on the titanium-based
alloy film to grow a p.sup.+ type back surface field film. The
temperature is raised to grow a p.sup.- type light-soaking film on
the p.sup.+ type back surface field film. Phosphine is deposited on
the p.sup.- type light-soaking film to form an n.sup.+ type
emitter. Thus, an n.sup.+-p.sup.--p.sup.+ laminate is provided on
the titanium-based alloy film. SiCNO:Ar plasma is used to passivate
the n.sup.+-p.sup.--p.sup.+ laminate, thus forming an
anti-reflection film of SiCN/SiO2 on the n.sup.+ type emitter. The
n.sup.+-p.sup.--p.sup.+ laminate is etched in a patterned mask
process. A p.sup.- type ohmic contact is formed on the
titanium-based alloy film. The anti-reflection film is etched in a
patterned mask process. The n.sup.+ type emitter is coated with a
titanium/palladium/silver alloy film that is annealed in hydrogen.
An n.sup.- type ohmic contact is formed on the n.sup.+ type
emitter.
Inventors: |
Yang; Tsun-Neng; (Taipei
City, TW) ; Lan; Shan-Ming; (Daxi Town, TW) ;
Chiang; Chin-Chen; (Daxi Town, TW) ; Ma;
Wei-Yang; (Banqiao City, TW) ; Ku; Chien-Te;
(Pingzhen City, TW) ; Huang; Yu-Hsiang; (Pingzhen
City, TW) |
Correspondence
Address: |
Jackson Intellectual Property Group PLLC
106 Starvale Lane
Shipman
VA
22971
US
|
Assignee: |
ATOMIC ENERGY COUNCIL - INSTITUTE
OF NUCLEAR ENERGY RESEARCH
Taoyuan
TW
|
Family ID: |
43384938 |
Appl. No.: |
12/007154 |
Filed: |
January 7, 2008 |
Current U.S.
Class: |
438/72 ;
257/E31.119 |
Current CPC
Class: |
H01L 31/03921 20130101;
H01L 31/182 20130101; H01L 31/1804 20130101; Y02E 10/546 20130101;
Y02P 70/50 20151101; Y02E 10/547 20130101; H01L 31/1864 20130101;
H01L 31/03682 20130101; H01L 31/202 20130101; H01L 31/02168
20130101; Y02E 10/548 20130101; H01L 31/075 20130101; Y02P 70/521
20151101 |
Class at
Publication: |
438/72 ;
257/E31.119 |
International
Class: |
H01L 31/18 20060101
H01L031/18 |
Claims
1. A process for making a tandem solar cell comprising the steps
of: providing a ceramic substrate; providing a titanium-based alloy
film on the ceramic substrate; providing an n.sup.+-p.sup.--p.sup.+
laminate on the titanium-based alloy film by the steps of: using an
atmospheric pressure chemical vapor deposition apparatus to deposit
dichlorosilane and diborane on the titanium-based alloy film, thus
causing the epitaxial growth of a p.sup.+ type back surface field
film on the titanium-based alloy film; raising the temperature in
the atmospheric pressure chemical vapor deposition apparatus, thus
causing the epitaxial growth of a p.sup.- type light-soaking film
on the p.sup.+ type back surface field film; and conducting n.sup.+
type deposition of phosphine on the p.sup.- type light-soaking
film, thus forming an n.sup.+ type emitter on the p.sup.- type
light-soaking film; using a plasma-enhanced chemical vapor
deposition apparatus to provide SiCNO:Ar plasma to passivate the
n.sup.+-p.sup.--p.sup.+ laminate, thus forming an anti-reflection
film of SiCN/SiO.sub.2 on the n.sup.+ type emitter; using potassium
hydroxide solution to etch a portion of the n.sup.+-p.sup.--p.sup.+
laminate in a patterned mask process; forming a p.sup.- type ohmic
contact on a portion of the titanium-based alloy film exposed from
the n.sup.+-p.sup.--p.sup.+ laminate; etching portions of the
anti-reflection film in a patterned mask process; providing a
titanium/palladium/silver alloy film on portions of the n.sup.+
type emitter exposed from the anti-reflection film; annealing the
titanium/palladium/silver alloy film in hydrogen; and forming an
n.sup.- type ohmic contact on the n.sup.+ type emitter.
2. The process according to claim 1, wherein the thickness of the
ceramic substrate is 0.1 to 1.0 mm.
3. The process according to claim 1, wherein the step of providing
the titanium-based alloy film comprising the steps of: providing a
titanium film on the ceramic substrate; and depositing
dichlorosilane on the titanium film in an atmospheric pressure
chemical vapor deposition apparatus so that the dichlorosilane and
the titanium film exchange silicon atoms and titanium atoms to form
the titanium/silicon alloy film.
4. The process according to claim 3, wherein the thickness of the
titanium film is 500 to 5000 angstroms.
5. The process according to claim 1, wherein the step of providing
the titanium-based alloy film comprising the steps of: providing a
titanium film and an amorphous silicon film on the ceramic
substrate; and heating the titanium film and the amorphous silicon
film in a high-temperature annealing apparatus so that they
exchange titanium atoms and silicon atoms, thus forming the
titanium/silicon alloy film.
6. The process according to claim 5, wherein the step of providing
the titanium film and the amorphous silicon film comprises the
steps of providing the titanium film on the ceramic substrate in an
e-gun evaporation system; and providing the amorphous silicon film
on the titanium film in a plasma-enhanced chemical vapor deposition
apparatus.
7. The process according to claim 5, wherein the step of providing
the titanium film and the amorphous silicon film comprises the
steps of: providing the amorphous silicon film on the ceramic
substrate in a plasma-enhanced chemical vapor deposition apparatus;
and providing the titanium film on the amorphous silicon film in an
e-gun evaporation system.
8. The process according to claim 5, wherein ratio of the thickness
of the amorphous silicon film to the thickness of the titanium film
is 2:1.
9. The process according to claim 8, wherein the thickness of the
amorphous silicon film is 1000 to 10000 angstroms, and the
thickness of the titanium film is 500 to 5000 angstroms.
10. The process according to claim 1, wherein the step of providing
the titanium-based alloy film comprising the step of using the
atmospheric pressure chemical vapor deposition apparatus to deposit
dichlorosilane and titanium tetrachloride on the ceramic
substrate.
11. The process according to claim 1, wherein the titanium-based
alloy film is made of a material selected from a group consisting
of TiSi.sub.2, TiN, TiC, TiB.sub.2 and TiC.sub.xN.sub.y.
12. The process according to claim 1, wherein the thickness of the
titanium-based alloy film is 1000 to 5000 angstroms.
13. The process according to claim 1, wherein the grain size of the
titanium-based alloy film is in the order of a micrometer.
14. The process according to claim 5, wherein the titanium-based
alloy film is used both as a back contact and a seed film.
15. The process according to claim 1, wherein the sheet resistance
of the titanium-based alloy film is smaller than 0.5
ohm/cm.sup.2.
16. The process according to claim 1, wherein the thickness of the
p.sup.+ type back surface field film is no larger than 1
micrometer.
17. The process according to claim 1, wherein the thickness of the
p.sup.- type light-soaking film is 1 to 15 micrometers, and the
grain size of the p.sup.- type light-soaking film is larger than 10
micrometers.
18. The process according to claim 1, wherein the thickness of the
n.sup.+ type emitter is smaller than 1000 angstroms.
19. The process according to claim 1, wherein the dangling bonds of
the silicon atoms on the surface of the n.sup.+ type emitter and at
the grain boundaries in the p.sup.- type light-soaking film and the
p.sup.- type light-soaking film and the p.sup.+ type back surface
field film are filled during the passivation.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a process for making
multi-crystalline silicon thin-film solar cells and, more
particularly, to a high-temperature process for making
multi-crystalline silicon thin-film solar cells based on
plasma-enhanced chemical vapor deposition.
[0003] 2. Related Prior Art
[0004] Silicon-based solar cells are generally made in
low-temperature processes based on plasma-enhanced chemical vapor
deposition ("PECVD"). An amorphous or microcrystalline silicon film
is coated on a substrate of glass, aluminum, silicon, stainless
steel or plastics. A back contact is made of aluminum, gold, silver
or transparent conductive oxide such as indium-tin oxide ("ITO")
and zinc oxide.
[0005] The primary advantage of the low-temperature processes is
the wide variety of materials that can be used to make the
substrates. However, they suffer drawbacks such as defective
silicon films, low photoelectrical conversion efficiencies and low
light-soaking stability. In the PECVD, while coating the
microcrystalline silicon film, a silicon material is highly diluted
in hydrogen according to the following notion:
[H.sub.2]/[SiH.sub.4]>15
[0006] That is, the concentration or flow rate of H.sub.2 is more
than 15 times as high as that of SiH.sub.4. The problems with the
PECVD include a low growth rate of the film, a long process and a
high cost.
[0007] Regarding the making of the multi-crystalline silicon solar
cells, there are various techniques such as solid phase
crystallization ("SPC") and aluminum-induced crystallization
("AIC").
[0008] The SPC is based on the PECVD. In the SPC, an amorphous
silicon film is deposited, intensively heated and annealed at a
high temperature. Thus, a multi-crystalline silicon film with a
grain size of 1 to 2 micrometers is made.
[0009] There are however problems with the low-temperature
processes for making multi-crystalline silicon solar cells based on
the PECVD. Firstly, many defects occur in the silicon films.
Secondly, the photoelectrical conversion efficiencies are low.
Thirdly, the light soaking stabilities are low. Fourthly, the
growth rates of the films are low. Sixthly, the processes are long.
Seventhly, the costs are high.
[0010] Referring to FIGS. 11 through 15, in the AIC, a substrate 71
is coated with an aluminum film 72. An amorphous silicon film 73 is
coated on the aluminum film 72 based on the PECVD and annealed at a
temperature of 575 degrees Celsius for a long time to form a seed
film 74. Then, it is subjected to an epitaxial process such as the
PECVD or an electron cyclotron resonance chemical deposition
("ECR-CVD") to make a multi-crystalline silicon film 75. The AIC
however involves many steps and takes a long time. The resultant
grain size is 0.1 to 10 micrometers.
[0011] A conventional silicon-based tandem solar cell includes an
upper laminate and a lower laminate. The upper laminate is an
amorphous silicon p-i-n laminate. The lower laminate is a
microcrystalline silicon p-i-n laminate. Thus, the infrared and
visible light of the sunlit can be converted into electricity.
However, the photoelectrical conversion efficiency of the
conventional silicon-based tandem solar cell deteriorates
quickly.
[0012] Concerning the process for making multi-crystalline silicon
solar cells based on the AIC, the processes are long for including
many steps and therefore expensive. As for the conventional
silicon-based tandem solar cell, the photoelectrical conversion
efficiency deteriorates quickly.
[0013] The present invention is therefore intended to obviate or at
least alleviate the problems encountered in prior art.
SUMMARY OF INVENTION
[0014] It is the primary objective of the present invention is to
provide a process for making a tandem solar cell.
[0015] To achieve the primary objective, a titanium-based alloy
film is provided on a ceramic substrate. Dichlorosilane and
diborane are deposited on the titanium-based alloy film to grow a
p.sup.+ type back surface field film. The temperature is raised to
grow a p.sup.- type light-soaking film on the p.sup.+ type back
surface field film. Phosphine is deposited on the p.sup.- type
light-soaking film to form an n.sup.+ type emitter. Thus, an
n.sup.+-p.sup.--p.sup.+ laminate is provided on the titanium-based
alloy film. SiCNO:Ar plasma is used to passivate the
n.sup.+-p.sup.--p.sup.+ laminate, thus forming an anti-reflection
film of SiCN/SiO2 on the n.sup.+ type emitter. The
n.sup.+-p.sup.--p.sup.+ laminate is etched in a patterned mask
process. A p.sup.- type ohmic contact is formed on the
titanium-based alloy film. The anti-reflection film is etched in a
patterned mask process. The n.sup.+ type emitter is coated with a
titanium/palladium/silver alloy film that is annealed in hydrogen.
An n.sup.- type ohmic contact is formed on the n.sup.+ type
emitter.
[0016] Other objectives, advantages and features of the present
invention will become apparent from the following description
referring to the attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0017] The present invention will be described via the detailed
illustration of the preferred embodiment referring to the
drawings.
[0018] FIG. 1 is a flowchart of a process for making
multi-crystalline silicon thin-film solar cells according to the
preferred embodiment of the present invention.
[0019] FIG. 2 is a side view of a ceramic substrate for use in the
process shown in FIG. 1.
[0020] FIG. 3 is a side view of a titanium-based alloy film coated
on the ceramic substrate in the process shown in FIG. 2.
[0021] FIG. 4 is an atmospheric chemical vapor deposition apparatus
for processing the laminate shown in FIG. 3.
[0022] FIG. 5 is a side view of an amorphous silicon film coated on
the titanium-based alloy film shown in FIG. 4.
[0023] FIG. 6 is a side view of a p.sup.+ type multi-crystalline
silicon back surface field converted from the amorphous silicon
film and the titanium-based alloy film shown in FIG. 5.
[0024] FIG. 7 is a side view of an n-i-p multi-crystalline silicon
laminate coated on the laminate shown in FIG. 6.
[0025] FIG. 8 is a side view of a plasma-enhanced chemical vapor
deposition apparatus for providing SiCNO:Ar plasma to coat an
anti-reflection film on the n-i-p multi-crystalline silicon
laminate shown in FIG. 7.
[0026] FIG. 9 is a side view of a p.sup.- type ohm contact provided
on the laminate shown in FIG. 6.
[0027] FIG. 10 is a side view of an n.sup.- type ohm contact
connected to the anti-reflection film shown in FIG. 9.
[0028] FIG. 11 is a side view of a substrate for use in a
conventional process for making a multi-crystalline silicon
film.
[0029] FIG. 12 is a side view of an aluminum film coated on the
substrate shown in FIG. 11.
[0030] FIG. 13 is a side view of an amorphous silicon film coated
on the aluminum film shown in FIG. 12.
[0031] FIG. 14 is a side view of the substrate coated with a seed
film converted from the amorphous silicon film and the aluminum
film of FIG. 13.
[0032] FIG. 15 is a side view of a multi-crystalline silicon film
coated on the seed film shown in FIG. 14.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0033] Referring to FIG. 1, there is shown a process for making
multi-crystalline silicon thin-film solar cells according to the
preferred embodiment of the present invention.
[0034] Referring to FIGS. 1 and 2, at 11, a ceramic substrate 21 is
provided. The ceramic substrate 21 is made of aluminum oxide. The
thickness of the substrate 21 is 0.1 to 1.0 mm.
[0035] The ceramic substrate 21 is coated with a titanium-based
alloy film 24 (FIG. 6). The titanium/silicon alloy film 24 may be
made of TiSi.sub.2, TiN, TiC, TiB.sub.2 or TiC.sub.xN.sub.y. The
titanium-based alloy film 24 can be provided in three
subroutines.
[0036] In the first subroutine, at 12 (FIGS. 1 and 3), a titanium
film 22 is coated on the ceramic substrate 21 in an e-gun
evaporation system at 250 degrees Celsius. The thickness of the
titanium film 22 is 1000 to 5000 angstroms.
[0037] At 13a (FIGS. 1 and 4), dichlorosilane is deposited on the
titanium film 22 in an atmospheric pressure chemical vapor
deposition ("APCVD") apparatus 4, at 800 to 1100 degrees Celsius.
The dichlorosilane and the titanium film 22 exchange silicon atoms
and titanium atoms to form the titanium/silicon alloy film 24. The
grain size of the titanium/silicon alloy film 24 is larger than 1
micrometer. The sheet resistance of the titanium/silicon ally film
24 is lower than ohm/cm.sup.2.
[0038] In the second subroutine, at 12 (FIGS. 1 and 3), a titanium
film 22 is coated on the ceramic substrate 21 in an e-gun
evaporation system at 250 degrees Celsius. The thickness of the
titanium film 22 is 1000 to 5000 angstroms. At 13b (FIGS. 1 and 5),
an amorphous silicon film 23 is coated on the titanium film 22 in a
plasma-enhanced chemical vapor deposition ("PECVD") apparatus.
Alternatively, the amorphous silicon film 23 may be coated on the
ceramic substrate 21 before the titanium film 22 is coated on the
amorphous silicon film 23. In either case, the ratio of the
thickness of the amorphous silicon film 23 to the thickness of the
titanium film 22 is 2:1.
[0039] The titanium film 22 and the amorphous silicon film 23 are
heated in a high-temperature annealing apparatus 5 at 700 to 900
degrees Celsius so that they exchange titanium atoms and silicon
atoms, thus forming the titanium/silicon alloy film 24. Then, the
temperature in the APCVD apparatus 5 is raised to a value-higher
than 1000 degrees Celsius for the epitaxial growth of the grains.
The size of the grains of the titanium/silicon alloy film 24 is
larger than 1 micrometer. The sheet resistance of the
titanium/silicon alloy film 24 is lower than ohm/cm.sup.2.
[0040] In the third subroutine, dichlorosilane and titanium
tetrachloride are made to react with each other to form the
titanium/silicon alloy film 24 in the APCVD apparatus 4.
[0041] Referring to FIGS. 1 and 7, at 15, dichlorosilane and
diborane are made to exchange silicon atoms and boron atoms in the
APCVD apparatus 4 at 900 to 1000 degrees Celsius, thus forming a
type multi-crystalline silicon back surface field film 25.
[0042] The temperature in the APCVD apparatus 4 is raised to a
value higher than 1000 degrees Celsius. More dichlorosilane and
diborane are made to exchange silicon atoms and boron atoms, thus
forming a p.sup.- type multi-crystalline silicon light-soaking film
26 on the p.sup.+ type multi-crystalline silicon back surface field
film 25, which is used as a seed layer. The epitaxial growth of the
p.sup.- type multi-crystalline silicon light-soaking film 26 is 0.5
micrometer/minute and lasts for 30 minutes. The thickness of the
p.sup.- type multi-crystalline silicon light-soaking film 26 is 1
to 15 micrometers. The size of the grains 261 of the p.sup.- type
multi-crystalline silicon light-soaking film 26 is larger than 10
micrometers. The concentration of the boron atoms in the p.sup.-
type multi-crystalline silicon light-soaking film 26 is 10.sup.16
to 10.sup.17 #/cm.sup.3.
[0043] At 800 to 1000 degrees Celsius, phosphine is deposited on
the p.sup.- type multi-crystalline silicon light-soaking film 26,
thus executing the n.sup.+ type deposition of the phosphor atoms of
the phosphine on the p.sup.- type multi-crystalline silicon
light-soaking film 26. That is, an n.sup.+ type multi-crystalline
silicon emitter 27 is form on the p.sup.- type multi-crystalline
silicon light-soaking film 26. The thickness of the n.sup.+ type
multi-crystalline silicon emitter 27 is smaller than 1000
angstroms. The concentration of the boron atoms in the n.sup.+ type
multi-crystalline silicon emitter 27 is 10.sup.18 to 10.sup.19
#/cm.sup.3. The n.sup.+ type multi-crystalline silicon emitter 27,
the p.sup.- type multi-crystalline silicon light-soaking film 26
and the p.sup.+ type multi-crystalline silicon back surface field
film 25 together form a n.sup.+-p.sup.--p.sup.+ laminate 1.
[0044] Referring to FIGS. 1 and 8, at 16, SiCNO:Ar plasma is
provided in a PECVD apparatus 6. Silane, nitrous oxide and methane
are used as the raw materials of the SiCNO:Ar plasma while argon is
used as a carrier. The SiCNO:Ar plasma passivates the
n.sup.+-p.sup.--p.sup.+ laminate 1. Hence, the dangling bonds of
the silicon atoms on the surface 271 of the n.sup.+ type
multi-crystalline silicon emitter 27 are filled. The dangling bonds
of the silicon atoms at the grain boundaries 262 between the grains
261 of the p.sup.- type multi-crystalline silicon light-soaking
film 26 are also filled. The dangling bonds of the silicon atoms in
the p.sup.+ type multi-crystalline silicon back surface field film
25 are also filled. Moreover, an anti-reflection film 28 of
SiCN/SiO.sub.2 is coated on the n.sup.+ type multi-crystalline
silicon emitter 27.
[0045] Referring to FIGS. 1 and 9, at 17, potassium hydroxide
solution is used to etch the multi-crystalline silicon laminate in
a patterned mask process. The substrate 21 and the titanium/silicon
alloy film 24 are not etched at all. A p.sup.- type ohmic contact
29 is made on the titanium/silicon alloy film 24.
[0046] Referring to FIGS. 1 and 10, at 18, the anti-reflection film
28 are etched in a patterned mask process so that ortions of the
n.sup.+ type multi-crystalline silicon emitter 27 are exposed from
the anti-reflection film 28. A titanium/palladium/silver alloy film
30 is provided in the exposed portions of the n.sup.+ type
multi-crystalline silicon emitter 27 and annealed in the
high-temperature annealing apparatus 5. Finally, an n.sup.- type
ohmic contact 31 is provided on the titanium/palladium/silver alloy
film 30.
[0047] As discussed above, the multi-crystalline silicon laminate 1
includes the ceramic substrate 21 and the titanium/silicon alloy
film 24 used as the seed layer. The APCVD apparatus 6 is used in
the high-temperature process for the exchange of the silicon atoms
and the boron atoms, thus forming the p.sup.+ type
multi-crystalline silicon back surface field film 25 and the
p.sup.- type multi-crystalline silicon light-soaking film 26. Then,
the phosphor atoms and the silicon atoms are exchanged so that the
n.sup.+ type multi-crystalline silicon emitter 28 is made. The
SiCNO:Ar plasma is used to passivate the laminate 1. The patterned
mask process is used to make the p.sup.- type ohmic contact 29 on
the titanium/silicon alloy film 24. The patterned mask process is
used to coat the titanium/palladium/silver alloy film 30 on the
n.sup.+ type multi-crystalline silicon emitter 27 and provide the
n.sup.- type ohmic contact 31 on the n.sup.+ type multi-crystalline
silicon emitter 27.
[0048] Solar cells made in the process according to the present
invention exhibits several advantages. The ceramic substrate 21 is
inexpensive, refractory and chemically stable, and can be
integrated with materials for construction.
[0049] The titanium/silicon alloy film 24 is environmentally
friendly, abundant and inexpensive. The titanium/silicon alloy film
24 ensures the integrity of the multi-crystalline silicon laminate
1 since its thermal expansion coefficient is matched with that of
the ceramic substrate 21 and the p.sup.+ type multi-crystalline
silicon back surface field film 25.
[0050] The solar cells provide a high photoelectrical conversion
efficiency and excellent light-soaking stability because the PEVCD
apparatus 6 is used in the high-temperature process to passivate
the multi-crystalline silicon films that would otherwise involve
high mobility and a large diffusion length, and take long for
recombination.
[0051] Moreover, the process of the present invention provides a
high epitaxial growth rate and a high crystal quality.
[0052] The present invention has been described via the detailed
illustration of the preferred embodiment. Those skilled in the art
can derive variations from the preferred embodiment without
departing from the scope of the present invention. Therefore, the
preferred embodiment shall not limit the scope of the present
invention defined in the claims.
* * * * *