U.S. patent application number 11/331181 was filed with the patent office on 2006-07-13 for active layer for solar cell and the manufacturing method making the same.
This patent application is currently assigned to Chung-Hua Li. Invention is credited to Jian-Ging Chen, Chung-Hua Li.
Application Number | 20060151025 11/331181 |
Document ID | / |
Family ID | 36652031 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151025 |
Kind Code |
A1 |
Li; Chung-Hua ; et
al. |
July 13, 2006 |
Active layer for solar cell and the manufacturing method making the
same
Abstract
A method for manufacturing an active layer of a solar cell is
disclosed, the active layer manufactured including multiple micro
cavities in sub-micrometer scale, which can increase the
photoelectric conversion rate of a solar cell. The method comprises
following steps: providing a substrate having multiple layers of
nanospheres which are formed by the aggregated nanospheres; forming
at least one silicon active layer to fill the inter-gap between the
nanospheres and part of the surface of the substrate; and removing
the nanospheres to form an active layer having plural micro
cavities on the surface of the substrate. The present invention
also provides a solar cell comprising: a substrate, an active
layer, a transparent top-passivation, at least one front contact
pad, and at least one back contact pad. The active layer locates on
a surface of the substrate and has plural micro cavities whose
diameter is less than one micrometer.
Inventors: |
Li; Chung-Hua; (Taipei City,
TW) ; Chen; Jian-Ging; (Donggang Township,
TW) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
US
|
Assignee: |
Li; Chung-Hua
Taipei City
TW
|
Family ID: |
36652031 |
Appl. No.: |
11/331181 |
Filed: |
January 13, 2006 |
Current U.S.
Class: |
136/256 ;
257/E31.013; 438/98 |
Current CPC
Class: |
Y02E 10/547 20130101;
Y02P 70/50 20151101; H01L 31/1804 20130101; Y10S 438/96 20130101;
Y10S 977/893 20130101; H01L 31/0284 20130101; Y10S 977/78 20130101;
Y10S 977/784 20130101; Y02P 70/521 20151101 |
Class at
Publication: |
136/256 ;
438/098 |
International
Class: |
H01L 21/00 20060101
H01L021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2005 |
TW |
094100969 |
Claims
1. A method for forming an active layer having plural micro
cavities, comprising following steps: (A) providing a substrate
having multiple layers of nanospheres, wherein the multiple layers
are formed by the aggregated nanospheres; (B) forming at least one
silicon active layer to fill the inter-gap between the nanospheres
and part of the surface of the substrate; and (C) removing the
nanospheres to form the active layer having plural micro cavities
on the surface of the substrate.
2. The method as claimed in claim 1, wherein the substrate having
multiple layers of nanospheres is prepared through following steps:
(A1) providing a substrate, and a molding-solution comprising
nanospheres and a surfactant; (A2) laying the substrate in the
molding-solution to let the molding-solution cover at least part of
a surface of the substrate; and (A3) adding a volatile solution or
a volatile solvent to the molding-solution to remove the
surfactant, and form the multiple layers of nanospheres on the
surface of the substrate.
3. The method as claimed in claim 1, further comprising step (B1)
annealing the silicon active layer after the silicon active layer
is formed in step (B).
4. The method as claimed in claim 1, wherein the substrate is made
of single crystal silicon, poly silicon, amorphous silicon, gallium
arsenide, indium phosphide, gallium indium phosphide, or copper
indium selenide.
5. The method as claimed in claim 1, wherein the nanospheres are
made of silicon oxide.
6. The method as claimed in claim 1, wherein the silicon active
layer is formed to fill the inter-gap between the nanospheres and
part of the surface of the substrate through metal organic chemical
vapor deposition.
7. The method as claimed in claim 1, wherein the silicon active
layer is a single crystal silicon layer.
8. The method as claimed in claim 1, wherein the nanospheres are
removed by hydrofluoric acid.
9. The method as claimed in claim 1, further comprising step (D)
forming at least one thin doping layer on the active layer after
the active layer having plural micro cavities is formed in step
(C).
10. The method as claimed in claim 9, wherein the thin doping layer
is formed on the surface of the silicon active layer by vapor
deposition.
11. The method as claimed in claim 9, wherein the substrate is
P-type silicon substrate, and the thin doping layer is made of
phosphine.
12. The method as claimed in claim 9, wherein the substrate is
N-type silicon substrate, and the thin doping layer is made of
magnesium.
13. The method as claimed in claim 9, further comprising step (E)
annealing the thin doping layer, the active layer, and the
substrate after the thin doping layer is formed on the active layer
in step (D).
14. An electrode for a solar cell, comprising: a substrate; and an
active layer locating on a surface of the substrate and having
plural micro cavities, wherein the diameter of the micro cavity is
less than one micrometer.
15. The electrode as claimed in claim 14, wherein the substrate is
made of single crystal silicon, poly silicon, amorphous silicon,
gallium arsenide, indium phosphide, gallium indium phosphide, or
copper indium selenide.
16. The electrode as claimed in claim 14, wherein the active layer
is a single crystal silicon layer.
17. The electrode as claimed in claim 14, wherein the substrate is
a P-type silicon substrate, and the active layer is a gallium
arsenide layer.
18. The electrode as claimed in claim 14, wherein the substrate is
a N-type silicon substrate, and the active layer is a cadmium
selenide layer.
19. A solar cell, comprising: a substrate; an active layer locating
on a surface of the substrate and having plural micro cavities,
wherein the diameter of the micro cavity is less than one
micrometer; a transparent top-passivation locating on a surface of
the active layer; at least one front contact pad electrically
connected to the active layer; and at least one back contact pad
electrically connected to the substrate; wherein the front contact
pad and the back contact pad are electrically connected to an
external circuit.
20. The solar cell as claimed in claim 19, further comprising a
bottom-passivation locating between the substrate and the back
contact pad.
21. The solar cell as claimed in claim 19, wherein the active layer
is a single crystal silicon layer.
22. The solar cell as claimed in claim 19, wherein the substrate is
a P-type silicon substrate, and the active layer is a gallium
arsenide layer.
23. The solar cell as claimed in claim 19, wherein the substrate is
a N-type silicon substrate, and the active layer is a cadmium
selenide.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for manufacturing
an active layer of a solar cell, and, more particularly, to a
method for manufacturing an active layer including multiple micro
cavities in sub-micrometer scale which can increase the
photoelectric conversion rate of a solar cell.
[0003] 2. Description of Related Art
[0004] The conventional energy for human society such as uranium,
natural gas, and petroleum will be used up in future decades. The
scientists therefore pay lots efforts to develop alternative energy
such as solar energy, wind energy, wave energy, and earth heat.
[0005] However, the application of wind energy, wave energy, or the
earth heat is limited by the geometrical regions such as the
neighborhood of volcano, or that of sea shore. Moreover, most
equipment required for the application of wind energy, wave energy,
and earth heat is huge. Hence, the solar energy with high
convenience attracts scientists' attention.
[0006] So far, many materials are used in the solar cells. Without
surprise, the photoelectric conversion rates of various materials
differ a lot. Generally speaking, current solar cells can be
categorized into three major styles, i.e. silicon series solar
cells, III-V series solar cells, and II-VI series. The silicon
series solar cells include solar cells made of single crystal
silicon, poly silicon, and amorphous silicon matrix. The III-V
series solar cells include solar cells made of gallium arsenide
matrix, indium phosphide matrix, and gallium indium phosphide
matrix. The II-VI solar cells include the solar cells made of
cadmium selenide matrix, and or copper indium selenide matrix. The
maximum photo electro conversion rates of the solar cells are:
single crystal silicon 24.7%, poly silicon 19.8%, amorphous silicon
14.5%, gallium arsenide 25.7%, and copper indium selenide 18.8%,
individually. In fact, the photoelectric conversion rate for the
solar cells in laboratory can be about 30%. However, the
photoelectric conversion rate for the commercial solar cells is
lower than 20%. Hence, the photoelectric conversion rate for the
commercial solar cells still needs to be improved. Currently, the
commercial solar cells are mainly made of single crystal silicon or
poly silicon since the cost for mass production is relative low and
the photoelectric conversion rate is acceptable.
[0007] However, the price of the solar cells is still high since
more than half of the cost of the solar cells is the cost of the
silicon matrix. Hence, scientists try to find the new materials for
solar cells and improve the manufacturing process to reduce the
cost. So far, the most effective option for reducing the cost and
increasing the photoelectric conversion rate is to increase the
photo-absorption area of the solar cells (e.g. using nanorod as
materials for photoreaction) or to increase the number of the
projected photons (e.g. applying an antireflection layer). But the
manufacturing process for the solar cells containing nanorod is
very complicated. Many metal catalysts are required to facilitate
the formation of nanorods. Therefore, the cost increases since many
metal catalysts are required. Furthermore, the metal catalysts also
act as impurities in the solar cells to interfere the migration of
electrons in the solar cells. Of course, the photoelectric
conversion rate decreases. On the other hand, the formation of
anti-reflection layer needs complicated photomasks to shape the
surface into a pyramid-form. Then deposition is introduced to form
anti-reflection layer. All this complicate process increase the
cost of solar cells a lot, lower down the yield, and is not
suitable for mass production.
[0008] Therefore, it is desirable to provide a solar cell with
improved photoelectric conversion rate and method for manufacturing
the same to mitigate the aforementioned problems.
SUMMARY OF THE INVENTION
[0009] The present invention provides a method for forming an
active layer having plural micro cavities. The method comprises
following steps: providing a substrate having multiple layers of
nanospheres, wherein the multiple layers are formed by the
aggregated nanospheres; forming at least one silicon active layer
to fill the inter-gap between the nanospheres and part of the
surface of the substrate; and removing the nanospheres to form an
active layer having plural micro cavities on the surface of the
substrate.
[0010] The present invention also provides an electrode for a solar
cell. The electrode for a solar cell of the present invention,
comprises: a substrate; and an active layer locating on a surface
of the substrate and having plural micro cavities, wherein the
diameter of the micro cavity is less than one micrometer.
[0011] The present invention also provides a solar cell. The solar
cell of the present invention comprises: a substrate, an active
layer, a transparent top-passivation, at least one front contact
pad, and at least one back contact pad. The active layer locates on
a surface of the substrate. The active layer also has plural micro
cavities. Moreover, the diameter of the micro cavity is less than
one micrometer. The transparent top-passivation locates on a
surface of the active layer. The front contact pad is electrically
connected to the active layer, while the back contact pad is
electrically connected to the substrate. Moreover, the front
contact pad and the back contact pad are electrically connected to
an external circuit.
[0012] The micro cavities of the active layer can greatly increase
the surface area for the reaction for the incident photons. Hence,
the photoelectric conversion rate can be increased. In addition,
since the photoelectric conversion rate of the solar cell of the
present invention is higher than that of the conventional solar
cells, the anti-reflection layer (AR layer) is not necessary for
the solar cells of the present invention. Hence, the solar cells of
the present invention can be produced through simpler processes,
and the cost for manufacturing the solar cells can thus be
reduced.
[0013] The nanospheres used in the method of the present invention
can be any nanosphere. Preferably, the nanospheres are silicon
oxide nanospheres, ceramic nanospheres, polymethyl methacrylate
(PMMA) nanospheres, titanium oxide nanospheres, or polystyrene
nanospheres. The method of the present invention can optionally
further include step (B1) annealing the silicon active layer after
the silicon active layer is formed in step (B). The temperature of
annealing is not limited. Preferably, the temperature of annealing
silicon active layer is in a range from 700 to 900.degree. C. The
substrate of the present invention can be any substrate.
Preferably, the substrate is P-type silicon substrate or N-type
silicon substrate. Preferably, the substrate of the present
invention can be made of single crystal silicon, poly silicon,
amorphous silicon, gallium arsenide, indium phosphide, gallium
indium phosphide, or copper indium selenide. The formation of the
active layer on the substrate can be achieved through any adequate
process. Preferably, the formation of the silicon active layer on
the substrate is achieved through sputtering or metal organic
chemical vapor deposition (MOCVD). The silicon active layer of the
present invention can be made of any silicon. Preferably, the
silicon active layer is made of single crystal silicon, poly
silicon, or amorphous silicon. The nanospheres in the silicon
active layer of the present invention can be removed through any
solution. Preferably, the nanospheres in the silicon active layer
of the present invention are removed by hydrofluoric acid, formic
acid, butanone, or toluene. The method of the present invention can
optionally further comprises step (D) forming at least one thin
doping layer on the active layer after the active layer having
plural micro cavities is formed in step (C). The formation of the
thin doping layer on the active layer can be achieved by any
process. Preferably, the formation of the thin doping layer on the
active layer is achieved by vapor deposition or sputtering. The
combination of the substrate and the thin doping layer is not
limited. Preferably, as the substrate is N-type silicon substrate,
and the thin doping layer is made of boron, gallium, magnesium, or
as the substrate is P-type silicon substrate, and the thin doping
layer is made of phosphine, asinine, sulfur, or oxygen. The method
of the present invention can optionally further comprises step (E)
annealing the thin doping layer, the active layer, and the
substrate after the thin doping layer is formed on the active layer
in step (D). The temperature for annealing thin doping layer is not
limited. Preferably, the temperature for annealing thin doping
layer is in a range from 700 to 900.degree. C.
[0014] The electrode for a solar cell of the present invention can
have an actively layer having plural micro cavities with any
diameters. Preferably, the diameter of the micro cavity is less
than one micrometer. More preferably, the diameter of the micro
cavity is in a range from 150 nm to 450 nm. The substrate of the
electrode for a solar cell of the present invention is not limited.
Preferably, the substrate is made of single crystal silicon, poly
silicon, amorphous silicon, gallium arsenide, indium phosphide,
gallium indium phosphide, or copper indium selenide. More
preferably, the substrate is P-type silicon substrate or N-type
silicon substrate. The combination of the substrate and the active
layer of the electrode for a solar cell of the present invention is
not limited. Preferably, as the substrate is P-type silicon
substrate, the active layer is made of N-type materials doped with
VA or VIA elements, or as the substrate is N-type silicon
substrate, the active layer is made of P-type materials doped with
IIA or IIIA elements.
[0015] The solar cell of the present invention can optionally
further comprises a bottom-passivation locating between the
substrate and the back contact pad. The substrate of the present
invention is not limited. Preferably, the substrate is made of
single crystal silicon, poly silicon, amorphous silicon, gallium
arsenide, indium phosphide, gallium indium phosphide, or copper
indium selenide. More preferably, the substrate is P-type silicon
substrate or N-type silicon substrate. The combination of the
substrate and the active layer is not limited. Preferably, as the
substrate is P-type silicon substrate, the active layer is made of
N-type materials doped with VA or VIA elements, or as the substrate
is N-type silicon substrate, the active layer is made of P-type
materials doped with IIA or IIIA elements. Preferably, the diameter
of the micro cavity in the active layer of the solar cell of the
present invention is less than one micrometer. More preferably, the
diameter of the micro cavity is in a range from 150 nm to 450 nm.
The active layer of the solar cell of the present invention can be
any silicon. Preferably, the silicon of the active layer is single
crystal silicon, poly silicon, or amorphous silicon. Preferably, as
the substrate is P-type silicon substrate, the active layer is made
of N-type materials doped with VA or VIA elements, or as the
substrate is N-type silicon substrate, the active layer is made of
P-type materials doped with IIA or IIIA elements
[0016] Other objects, advantages, and novel features of the
invention will become more apparent from the following detailed
description when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1a and 1b are figures showing the method of forming a
substrate having multiple layers of nanospheres;
[0018] FIG. 2 is a figure showing the method of forming an active
layer having plural micro cavities according to the first preferred
embodiment of the present invention;
[0019] FIG. 3 is a cross-sectional view of the electrode for a
solar cell according to the second preferred embodiment of the
present invention;
[0020] FIG. 4 is a cross-sectional view of the solar cell according
to the third preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] Since the manufacturing of the active layer with plural
micro cavities of the present invention needs to use a mold plate
having multiple layers of nanospheres on its surface. The mold
plate having multiple layers of nanospheres can be prepared through
the following process, as shown in the FIG. 1a and FIG. 1b.
[0022] At first, a molding-solution 12 and a P-type substrate 11
are provided. The molding-solution 12 used here comprises plural
nanospheres and a surfactant. The P-type substrate 11 is put and
immersed in the molding solution 12 in a container 13. Several
minutes later, the nanospheres 14 aggregate on the surface of the
P-type substrate 11 and assemble to form multiple layers of
nanospheres on the surface of the substrate 11 automatically. The
material of the nanospheres used here is silicon oxide (SiOx). The
average diameter of the nanospheres used in the present embodiment
is in a range from 150 nm to 450 nm.
[0023] However, the material of the nanospheres used in the
invention is not limited to silicon oxide (SiOx). It is noticed
that the material of the nanospheres is not limited. Preferably,
the nanospheres can be made of poly methyl methacrylate (PMMA),
polystyrene (PS), or titanium oxide (TiOx).
[0024] Besides, the average diameter can be less than one
micrometer. Actually, the average diameter can be adjusted
according to the species of the nanospheres and the actual demand
of the application. After the multiple layers of nanospheres 14 are
formed on the P-type substrate 11, a volatile acetone solution 15
is poured into the container 13. Owing to the volatile solvent such
as acetone, the molding solution 12 evaporates out. The P-type
substrate 11 with multiple layers of nanospheres 14 on its surface
is taken out of the container 13 for further application.
[0025] The preparation of the active layer having plural micro
cavities of the present embodiment is achieved through the
following steps. With reference to FIG. 2, a silicon active layer
21 is formed on the multiple layers of nanospheres through metal
organic chemical vapor deposition (MOCVD). As shown in FIG. 2, the
formed silicon active layer 21 covers the multiple layers of
nanospheres 14 and part of the surface of the P-type substrate 11.
The P-type substrate 11 and the formed silicon active layer 21 are
then annealed at a temperature in a range from 700 to 900.degree.
C. The annealing process will help the single crystal silicon of
the silicon active layer 21 rearranges in order. Later, the
annealed silicon active layer 21 and the P-type substrate 11 are
immersed in a hydrofluoric acid solution (not shown) to remove the
nanospheres 14 in the silicon active layer 21. Thus, an active
layer 21 having plural micro cavities 22 can be made. Even though
the etching solution for removing the nanospheres 14 is
hydrofluoric acid solution in the present embodiment, the etching
solution for removing the nanospheres 14 is not limited, and it can
be other solutions according to the materials of the nanospheres.
For example, the etching solution for removing the nanospheres 14
can be formic acid if the nanospheres are PMMA nanospheres.
Likewise, the etching solution for removing the nanospheres 14 can
be butanone or toluene if the nanospheres are polystyrene (PS)
nanospheres.
[0026] Then, a thin doping layer of gallium 23 is formed on the
silicon active layer 21 having plural micro cavities 22 through
vapor deposition. The formed thin doping layer 23 is then annealed
to let the gallium diffuse into the silicon active layer 21. Hence,
the silicon active layer 21 is transferred into a N-type silicon
layer with plural micro cavities.
[0027] FIG. 3 shows an electrode of a solar cell according to the
second preferred embodiment of the invention, where the electrode
includes the active layer of the first preferred embodiment of the
present invention. In the present embodiment, the substrate 31 is a
transparent indium tin oxide glass. The active layer 32 on the
surface of the substrate 31 has plural micro cavities 321. The
diameters of the micro cavities 321 are in a range from 150 nm to
450 nm. However, the material of the active layer can be a silicon,
or doped silicon. In the present embodiment, the active layer is
made of N-type single crystal silicon through the method described
in the first preferred embodiment of the present invention. In
addition, if the substrate 31 of an electrode of a solar cell is a
P-type silicon substrate, the active layer 32 is gallium arsenide.
On the other hand, if the substrate 31 of an electrode of a solar
cell is a N-type silicon substrate, the active layer 32 is cadmium
selenide.
[0028] FIG. 4 is a cross-sectional view of the solar cell of the
present invention according to the third preferred embodiment of
the present invention. The solar cell 40 of the third preferred
embodiment of the present invention is adapted to an external
circuit (not shown). The solar cell 40 converts the photo energy
into electrical energy and output the converted electrical energy
to the external circuit (not shown). The solar cells includes the
electrode (i.e. the P-type silicon substrate 41, the active layer
42 made of N-type single crystal silicon, and the micro cavities
421 in the active layer 42), a transparent top-passivation 43
locating on the surface of the active layer 42, two front contact
pads 44, a back contact pad 46, and a bottom-passivation 45
locating between the P-type substrate 41 and the back contact pad
46. In the present embodiment, the transparent top-passivation 43
is glass. The bottom-passivation 45 is made of silicon oxide.
Besides, the two front contact pads 44 of the present embodiment
are made of silver, and are electrically connected to the active
layer 42. The back contact pad 46 of the present embodiment is made
of silver and is electrically connected to the P-type silicon
substrate 41.
[0029] As the photons of the incident light passed the transparent
top-passivation 43 and enter the solar cell 40, the photons impact
the active layer 42 and the P-type-silicon substrate 41 back and
forth. Therefore, multiple electrons and multiple holes generate in
a form of hole-electro pair. Then, the holes locating in the N-type
single crystal silicon of the active layer 42 move toward the
P-type silicon substrate 41. The electrons locating in the P-type
silicon substrate 41 move toward the active layer 42 made of N-type
single silicon. Therefore, the moving holes and the moving
electrons pass through the front contact pad or the back contact
pad to enter an external circuit (not shown) to form an electrical
current. At this point, the photoelectric conversion can be
achieved in the solar cell of the present embodiment through the
interaction illustrated above.
[0030] Although the present invention has been explained in
relation to its preferred embodiment, it is to be understood that
many other possible modifications and variations can be made
without departing from the spirit and scope of the invention as
hereinafter claimed.
* * * * *