U.S. patent application number 14/048285 was filed with the patent office on 2014-11-20 for preparation of cigs absorber layers using coated semiconductor nanoparticle and nanowire networks.
This patent application is currently assigned to Sun Harmonics Ltd. The applicant listed for this patent is Sun Harmonics Ltd. Invention is credited to Bo Gao, Paifeng Luo, Yuhang Ren.
Application Number | 20140342496 14/048285 |
Document ID | / |
Family ID | 51896089 |
Filed Date | 2014-11-20 |
United States Patent
Application |
20140342496 |
Kind Code |
A1 |
Ren; Yuhang ; et
al. |
November 20, 2014 |
PREPARATION OF CIGS ABSORBER LAYERS USING COATED SEMICONDUCTOR
NANOPARTICLE AND NANOWIRE NETWORKS
Abstract
We disclose a method of preparing CIGS absorber layers using
coated semiconductor nanoparticle and nanowire networks. The
nanoparticles and nanowires containing one or more elements from
group IB and/or IIIA and/or VIA are prepared from metal salts such
as metal chloride and acetate at room temperature without inert gas
protection. A uniform and non-aggregation CIGS precursor layer is
fabricated with the formation of nanoparticle and nanowire networks
utilizing ultrasonic spraying technique. High quality CIGS film is
obtained by cleaning the residue salts and carbon agents at an
increased temperature and selenizing the pretreated precursor
layer.
Inventors: |
Ren; Yuhang; (Hangzhou,
CN) ; Luo; Paifeng; (Hangzhou, CN) ; Gao;
Bo; (Hangzhou, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sun Harmonics Ltd |
Hangzhou |
|
CH |
|
|
Assignee: |
Sun Harmonics Ltd
Hangzhou
CH
|
Family ID: |
51896089 |
Appl. No.: |
14/048285 |
Filed: |
December 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13893756 |
May 14, 2013 |
|
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14048285 |
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Current U.S.
Class: |
438/95 |
Current CPC
Class: |
H01L 31/18 20130101;
Y02E 10/544 20130101; Y02E 10/541 20130101; H01L 31/0322 20130101;
Y02P 70/521 20151101; C09D 11/02 20130101; Y02P 70/50 20151101;
H01L 31/0749 20130101 |
Class at
Publication: |
438/95 |
International
Class: |
H01L 31/18 20060101
H01L031/18; H01L 31/032 20060101 H01L031/032 |
Claims
1. A method of preparing a CIGS absorber layer by using a metal
salt, a thickening agent, and a binding agent to form uniform
nanoparticle and nanowire networks and to finish a high quality
CIGS film after selenization comprising the steps of: a) producing
CIGS nanoparticles and nanowires based on using a metal salt at
room temperature without inert gas protection; b) coating a CIGS
precursor layer on a Mo glass substrate; c) generating uniform
nanoparticle and nanowire networks by initial heat treatment; d)
obtaining a clean CIGS precursor layer by cleaning residue salts
and carbon agents at an increased temperature above 200.degree. C.;
and e) fabricating high quality CIGS film after selenizing the
pretreated precursor layer at a temperature above 400.degree.
C.
2. A method as defined in claim 1, wherein the metal salt used to
produce said nanoparticles and nanowires is at least one of a metal
chloride and a metal acetate.
3. A method as defined in claim 1, wherein said glass substrate is
coated by ultrasonic spraying of said nanoparticles and nanowires
solution.
4. A method of preparing a CIGS-based solar cell comprising the
steps of: synthesizing the soluble CuInGaS.sub.2
nanoparticles/wires precursor at room temperature under non-vacuum
condition; preparing a CIGS-based ink, adding CIGS powder into
specific solvent and adding additives to form monodispersed CIGS
ink; ultrasonic spraying CIGS ink on Mo glass substrate, using
ultrasonic spray to reduce the aggregation effect of CIGS
nanoparticles/wires and obtaining uniform CIGS precursor films;
heat treating of the CIGS precursor films to melt soluble CIGS
nanopowder and change it to a clear solution, and cooling the
solution to dry to a uniform and black color CIGS precursor film;
selenizing the heat treated CIGS precursor films, using Se powder
as the Se-source and, creating high quality CIGS films after
selenizing the precursor films in a double zone furnace for one
approximately hour; and preparing a CIGS device by chemical bath
deposition and sputtering and evaporating step.
5. A method as defined in claim 4, wherein said step of
synthesizing CIGS nanoparticles/wires comprises the steps of: (a)
providing a solution comprising Cu, In and Ga ions, the ratio of
Cu, In and Ga being in the following proportions: Cu 0.9.about.1;
In 0.6.about.0.8 and Ga 0.4.about.0.2; (b) providing a thickening
solution; (c) providing a sulfurated precipitant; (d) providing an
effective coupling agent; (e) adding the solution comprising Cu, In
and Ga ions into said thickening solution and stirring the mixture
to form a homogeneous solution; and (f) sequentially adding
appropriate amounts of sulfurated precipitant and coupling agent
into above homogeneous solution and stirring the mixture to form
CuInGaS.sub.2 nanoparticles/nanowires in a well dispersed
solution.
6. A method as defined in claim 4, wherein said step of preparing
the CIGS-based ink comprises the steps of: (a) separating the CIGS
nanoparticles/wires by centrifuging method; (b) washing and drying
the centrifuged CIGS nanoparticles/wires under vacuum pump and low
temperature; (c) providing the high volatilizing solvent with low
boiling point; (d) providing a small amount of additives, such as
dispersants and thickening agents; and (e) weighing an appropriate
amount of CIGS solid powder, adding into the organic solvent and
some additives, stirring for overnight to form a uniform ink.
7. A method as defined in claim 4, wherein said step of ultrasonic
spraying CIGS ink on Mo glass substrate comprises the steps of: (a)
providing a Mo-coated glass substrate; (b) providing monodisperse
CIGS ink; and (c) automatically ultrasonically spraying the CIGS
ink onto the Mo-glass a plurality of times under 300.degree. C.
8. A method as defined in claim 7, wherein said CIGS ink is sprayed
less than five times onto the Mo-glass.
9. A method as defined in claim 4, wherein said selenizing step
comprises the steps of: (a) providing pre-treated CIGS precursor
films; and (b) selenizing the hot-treated precursor films at a
temperature above 500.degree. C. for approximately 60 minutes in a
selenization furnace using Selenium powder as the Se-source to
obtain high-quality CIGS absorb layer.
10. A method as defined in claim 4, wherein said step of preparing
said CIGS device comprises the steps of: (a) depositing a buffer
layer of CdS employing CBD method; (b) sputtering a window layer of
i-ZnO and a conductive AZO layer; and (c) evaporating Ni/Al
top-electrode to form a CIGS PV device with structure of
glass/Mo/CIGS/CdS/i-ZnO/AZO/Ni--Al.
11. A method as defined in claim 4, wherein said step of
synthesizing CIGS nanoparticles/wires based solution comprises the
steps of: (a) synthesizing a CuInGa precursor solution A by: Adding
CuCl.sub.2.2H.sub.2O, InCl.sub.3 and GaCl.sub.3 into Methanol,
stirring for up to 30 min and a green color solution is obtained;
(b) synthesizing a thickening solution B by: Adding EC into
Terpinol, stirring overnight and heating up to a temperature of
200.degree. C. until it is completely dissolved; (c) mixing
solution A and thickening agent solution B, and stirring for up to
5 hours; and (d) gradually adding Thiourea and 3-MPA into the
mixture of solution A and B to obtain a white nanoparticles-based
solution.
12. A method as defined in claim 4, wherein said step of preparing
the CIGS-based ink comprises the steps of: (a) separating the CIGS
nanoparticles/wires by methanol using centrifuging method up to
five times; (b) drying the centrifuged powder under vacuum pump
under 100.degree. C. for less than ten hours to obtain white color
dried powder; (c) weighing the CIGS dried powder, adding MEK as the
solvent and PEG as the thickening agent and SHMP as the dispersant,
then mixing together and stirring overnight to form CIGS ink.
13. A method as defined in claim 4, wherein the procedure of
ultrasonic spraying CIGS ink comprises the steps of: (a) providing
a clean Mo-coated glass substrate, using acetone, ethanol and DI
water to wash the Mo-glass successively, finally using N2 to blow
to dry; (b) providing monodispersed CIGS ink and storing in a
container, extracting ink for ultrasonic spraying under following
conditions or parameters: running power of ultrasonic generator:
P=less than 15 W; temperature of the Mo-glass substrate: Ts=under
300.degree. C.; spraying rate: V=greater than 1 ml/min; pressure of
gas flow: P=greater than 5 Psi; distance between the nozzle and the
Mo-glass substrate: less than 150 mm; number of sprays: n=less than
5 times; whereby CIGS ink is ultrasonically sprayed onto the
Mo-glass under 300.degree. C. for less than five times, aggregation
effect is reduced to obtain uniform and non-aggregated CIGS
precursor films.
14. A method as defined in claim 4, wherein said heat treatments
step comprises: (a) heating the CIGS nanoparticles/nanowires coated
substrate up to 350.degree. C. to fuse all the particles to become
a clear solution; (b) heating the sample up to 450.degree. C.
gradually solidify the solution and the color changes from clear to
red, and finally becomes deep black and the networks are formed
through the decomposed nanowires; and (c) increasing the
temperature up to 500.degree. C. and holding the temperature for
half an hour to remove all the organic solvents and additives to
finally cause the color to change to deep black.
15. A method as defined in claim 4, wherein said step of
selenization comprises the steps of: (a) using selenium powder as
the solid-state Se-source and placing same in a graphite box, and
then into a quartz tube of a selenization furnace at a low
temperature zone; and (b) placing the sample in a high temperature
zone of the selenization furnace, and then using a mixture of Ar or
N as the protection gas and Selenizing the hot-treated precursor
films above 500.degree. C. for 30-70 mins in a selenization furnace
to form a high-quality CIGS absorber layer.
16. A method as defined in claim 4, wherein said step of
fabricating comprises the steps of: (a) preparing a CdS buffer
layer through a chemical bath deposition (CBD) method; (b) using
CdSO.sub.4 and Thiourea, adding NH.sub.3H.sub.2O and DI water,
stirring and dissolving completely; (c) placing the sample into a
solution and heating up to 100.degree. C. for up to 30 mins and
removing the sample and using DI water flushing for removing the
aggregated CdS particles and drying in an oven below 100.degree. C.
for 60-180 minutes; (d) sputtering i-ZnO and AZO window layers, (e)
the sputtering depositing parameters of ZnO being as follows:
sputtering power: P=100-200 W; sputtering pressure: P=0.5-10 mTorr;
Ar/O.sub.2=5:1-2:1 gas flow=10-100 sccm; sputtering time: T=up to
20 minutes; (f) sputtering depositing parameters of AZO being as
follows: sputtering power: P=100-200 W; sputte 00 sccm; sputtering
time: T=up to 30 minutes; (g) evaporating Ni--Al electrode: and (h)
loading Ni wire and Al wire, placing the sample with mask covered
on a heating stainless steel plate and sequencially evaporating Ni
and Al wires under high vacuum background to create a CIGS device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method synthesizing CIGS
nanoparticle/wires based on metal salts.
[0003] 2. Description of the Prior Art
[0004] A CIGS thin film is prepared by the formation of
semiconductor nanoparticle and nanowire networks and selenization
for a light absorption layer of photovoltaic devices.
[0005] Chalcopyrite CuInGaSe.sub.2 (CIGS) is a direct band gap
semiconductor and has an exceptionally high absorption coefficient
of more than 10.sup.5/cm for 1.5 eV and higher energy photons.
According to the recent report from the ZSW, a solar cell based on
CIGS has reached a power conversion efficiency of 20.3%, which is
comparable with the energy conversion efficiency of crystalline Si
solar cells. Decent conversion efficiency and high chemical
stability of CIGS make itself a promising p-type material for thin
film photovoltaic devices.
[0006] Vacuum and non-vacuum technologies are the two main methods
of preparing CIGS thin films. Vacuum-based processes including
co-evaporation and sputtering, which have been successfully applied
in commercial production lines. However, the high cost and
complexity of vacuum-based fabrication process become barriers to
affordable commercial modules.
[0007] An efficient non-vacuum printing process has the potential
to overcome this barrier. The low cost technique is inherently
suitable for large-scale applications and may benefit from
established industries of coatings, paints, inks, electronic
ceramics and colloidal systems. In particular, deposition at
atmospheric environment offers an opportunity for the deposition of
absorber materials at large scale with high throughput. This
provides a potential cost advantage over conventional fabrication
process that involves expensive vacuum equipment.
[0008] Kapur et al (U.S. Pat. No. 6,268,014) describe a method for
fabricating a CIGS solar cell based upon the solution-based
deposition of a source material comprised of mechanically milled,
oxide-containing, sub-micron sized particles, while Eberspacher and
Pauls (U.S. Pat. No. 6,268,014); Published U.S. Patent Application
No. 2002/0006470) describe the forming of mixed metal oxide,
sub-micron sized particles by pyrolizing droplets of a solution,
then ultrasonically spraying the resulting particles onto a
substrate. However, the high-temperature hydrogen reduction step is
potentially explosive and requires substantial time and energy.
Meanwhile, highly toxic H.sub.2Se gas atmosphere is requested in
the selenization process. Byoung Koun Min in Published U.S. Patent
Application No. 2012/0080091 A1 also involves the reduction
process.
[0009] Fuqiang Huang in Published U.S. Patent Application No.
2011/0008927 A1 gets a 14.6% high efficiency employing a non-vacuum
liquid-phase chemical technique.
[0010] David B. Mitzi. in Published U.S. Patent Application No.
2009/01454 also gets above 10% efficiency CIGS thin film solar
cells using hydrazine as the solvent source.
[0011] Nanosolar Inc. in Published U.S. Patent Application No.
2008/0149176 has used binary copper selenide and indium/gallium
selenides nanoparticles as starting materials to fabricate 14% thin
film CIGS solar cells. Single metallic nanoparticles are the
simplest form one could design. The structure of nanoparticles used
by Nanosolar has a core-shell structure. Copper nanoparticles serve
as the cores which are coated with IIIA-VIA shells such as indium
selenide, gallium selenide etc. These selenide nanoparticles are
dispersed in organic solution which may contain various ingredients
including solvents, surfactants, binders, emulsifiers, thickening
agents, film conditioners, anti-oxidants, flow and leveling agents,
plasticizers and preservatives. By using the similar core shell
strategy, Yoon et al. synthesized CuSe/InSe nanoparticles which
yield only .about.1% efficiency.
[0012] However, those methods mentioned here require toxic
reagents, need inert gas protection, require complex processes and
are not easy to scale up to mass production. Thus, there is a need
in the art, for a non-oxide, nanoparticle based precursor material
that overcomes the above disadvantages.
SUMMARY OF THE INVENTION
[0013] In order to solve these problems, the subject invention
presents a facile way to synthesize soluble CIGS
nanoparticles/wires at room temperature under non-vacuum condition
and the reaction can finish in 5 minutes. We employ ultrasonic
spray to effectively reduce the aggregation and obtain uniform CIGS
precursor films. After heat treatment and selenization, high
quality CIGS thin films are prepared. Finally, the effective solar
cells based on the non-vacuum method in accordance with the
invention are also achieved.
[0014] The present invention allows the drawbacks of the known
non-vacuum techniques to be eliminated. For this purpose, the
invention provides a method for preparing CIGS absorber layers by
using a metal salt, thickening and binding agents to form uniform
nanoparticle and nanowire networks and to provide a finished high
quality CIGS film after selenization, in which:
[0015] a) CIGS nanoparticles and nanowires are produced based on
using a metal salt such as metal chloride and acetate at room
temperature without inert gas protection;
[0016] b) A CIGS precursor layer is coated on a Mo glass substrate
by ultrasonic spraying of the CIGS nanoparticle and nanowire
solution;
[0017] c) Uniform nanoparticle and nanowire networks are generated
by initial heat treatment;
[0018] d) A clean CIGS precursor layer is obtained by cleaning the
residue salts and carbon agents at an increased temperature above
200.degree. C.;
[0019] e) High quality CIGS film is fabricated after selenizing the
pretreated precursor layer at a temperature above 400.degree.
C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] According to the following description and drawings of this
invention, the objects and features of the present invention will
become apparent, which respectively show:
[0021] FIG. 1 is a diagram of the fabrication process of CIGS PV
device;
[0022] FIG. 2 is a diagram of the synthesis process of CIGS
nanoparticles/wires;
[0023] FIG. 3 is a detailed schematic diagram of the process of
preparing CIGS solar cells based on non-vacuum method;
[0024] FIG. 4 is the TEM and the picture of CIGS
nanoparticles/wires;
[0025] FIG. 5 is the TEM of decomposed CIGS nanowires;
[0026] FIG. 6 is a diagram of the selenization temperature
profile;
[0027] FIG. 7 is cross-sectional TEM of CIGS films; and
[0028] FIG. 8 is the structure diagram and picture of CIGS
device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] FIG. 1 shows the fabrication process of CIGS photo-voltaic
("PV") device.
[0030] CIGS nanoparticles/wires have been synthesized using the
low-cost solution route under atmospheric conditions in accordance
with the present invention. The approach is simpler and less costly
than any other non-vacuum methods with the following
advantages:
[0031] (1) Normal atmosphere fabrication. No need to have inert gas
protection;
[0032] (2) Short reaction time. The whole synthesis process may
only take up to 5 minutes;
[0033] (3) Formation of amorphous and soluble nanoparticles/wires.
The nanoparticles can be deposited on various substrates and turn
into uniform thin films at low temperature (<350.degree.
C.);
[0034] (4) Low cost and easy to scale-up. The amorphous CIGS
nanoparticles fabricated in our invention melt under low
temperature (even below 180.degree. C.) and crystallize to various
sizes of nanoparticles with increasing temperature (above
200.degree. C.). We observe such dynamical changes by the color of
CIGS nanoparticle solutions: with increasing temperature, the color
changes from white to red, then to yellow, finally black. We
deposit the nanoparticle-based precursor on the Moly-coated
substrate to form a smooth precursor layer. After typical
selenization and typical device fabricating process, we obtain a
high quality CIGS film and effective solar cells.
[0035] In accordance with the present invention, there is provided
a method for preparing effective CIGS-based solar cells, comprising
the following steps:
[0036] (1) Synthesizing the soluble CuInGaS2 nanoparticles/wires
precursor at room temperature under non-vacuum condition. The
process of synthesizing CIGS nanoparticles/wires, as shown in FIG.
2, includes the following steps:
[0037] (a) Providing a solution comprising Cu, In and Ga ions at
26, 28, 30, respectively, in a solvent at 32, the ratios of Cu, In
and Ga ions being in the following proportions: Cu 0.9.about.1; In
0.6.about.0.8 and Ga 0.4.about.0.2 to form the CIG solution at
34;
[0038] (b) Providing a thickening solution at 36;
[0039] (c) Providing a sulfurated precipitant at 38;
[0040] (d) Providing a highly effective coupling agent at 40;
[0041] (e) Adding the solution comprising Cu, In and Ga ions into
the thickening solution and stirring the mixture to form
homogeneous solution;
[0042] (f) Sequentially adding appropriate amount of sulfurated
precipitant and coupling agent into above homogeneous solution and
stirring the mixture to form a CuInGaS2 nanoparticles/nanowires
well dispersed solution at 42.
[0043] (2) Preparing the CIGS-based ink, adding CIGS powder into
specific solvent and adding some additives to form monodispersed
CIGS ink. The process of preparing CIGS-based ink includes the
following steps:
[0044] (a) Separating the CIGS nanoparticles/wires by centrifuging
method;
[0045] (b) Washing and drying the centrifuged CIGS
nanoparticles/wires under vacuum pump and low temperature;
[0046] (c) Providing the high volatilizing solvent with a low
boiling point;
[0047] (d) Providing a small amount of additives, such as
dispersants and thickening agents;
[0048] (e) Weighing an appropriate amount of CIGS solid powder,
adding into the special organic solvent and some additives,
stirring for overnight to form uniform ink.
[0049] (3) Ultrasonic spraying CIGS ink on Mo glass substrate,
using ultrasonic spray to reduce the aggregation effect of CIGS
nanoparticles/wires and obtaining uniform CIGS precursor films. The
process of ultrasonic spraying CIGS-based ink on Mo glass substrate
includes the following steps illustrated in FIG. 3:
[0050] (a) Providing a Mo-coated glass substrate at 44;
[0051] (b) Providing monodisperse CIGS ink at 46;
[0052] (c) Automatically ultrasonic spraying the CIGS ink onto the
Mo-glass under 300.degree. C. a plurality of times (e.g. 3 times)
at 48. Using ultrasonic spray technology can effectively reduce the
aggregation effect and easily provide uniform and non-aggregated
CIGS precursor films.
[0053] (4) Heating treatment of the CIGS precursor films at 50, the
soluble CIGS nanopowder will melt again and change to clear
solution, as the temperature improve, the uniform and black color
CIGS precursor films are obtained after the solution drying.
[0054] (5) Selenizing the heat treated CIGS precursor films at 52
to a temperature above 500.degree. C., using Se powder as the
Se-source and, high quality CIGS films will be achieved after
selenizing the precursor films in a furnace (e.g. double zone
furnace) for approximately one hour. The process of selenization
includes the following steps:
[0055] (a) Providing pre-treated CIGS precursor films at 54;
[0056] (b) Selenizing the hot-treated precursor films at a
temperature above 500.degree. C. for approximately 60 mins in the
selenization furnace using Selenium powder as the Se-source, so we
can get high-quality CIGS absorb layer.
[0057] (6) Preparing CIGS device uses typical chemical bath
deposition and sputtering and evaporating route. The whole process
of fabricating CIGS PV device includes the following detailed
steps:
[0058] (a) Depositing buffer layer CdS employing chemical bath
deposition ("CBD") method;
[0059] (b) Sputtering window layer i-ZnO and conductive AZO
layer;
[0060] (c) Evaporating Ni/Al top-electrode, at 56, the standard
CIGS PV device with structure of glass/Mo/CIGS/CdS/i-ZnO/AZO/Ni--Al
is obtained in our invention. The detailed schematic diagram of
whole process of preparing CIGS solar cells based on non-vacuum
method is shown in FIG. 3.
[0061] The typical synthesis of CIGS nanoparticles wires-based
solution is shown as following:
[0062] First, synthesis of CuInGa precursor solution A by: Adding
CuCl.sub.2H.sub.2O b(e.g. 0.68 g), InCl.sub.3 (e.g. 0.74 g) and
GaCl.sub.3 (e.g. 0.35 g) into 5 mL Methanol, stirring for up to 30
min and a green color solution is obtained.
[0063] Second, synthesis of a thickening solution B by: Adding EC
(e.g. 0.3 g) into Terpinol (e.g 10 mL), stirring overnight and
heating to a temperature up to 200.degree. C. until it is
completely dissolved.
[0064] Then mixing solution A and thickening agent solution B,
stirring for up to 5 hours.
[0065] Finally, gradually adding Thiourea (e.g. 0.3 g) and 3-MPA
(e.g. 2 mL) ("3-Mercaptopropionic Acid") into the mixture of
solution A and B and a white nanoparticles-based solution is
obtained. The transmission electron microscope ("TEM") and the
picture of CIGS nanoparticles/wires are shown in FIG. 4.
[0066] The procedures of preparing CIGS ink are described.
[0067] First, separating the CIGS nanoparticles/wires by methanol
using centrifuging method up to five times;
[0068] Second, drying the centrifuged powder under vacuum pump
under 100.degree. C. (e.g. 60.degree. C.) for less than 10 hours
(e.g. 8 hours), dried powder with a white color is obtained;
[0069] Then, weighing the CIGS dried powder (e.g. 3.0 g), adding
solvent methyl ethyl ketone ("MEK") (e.g. 70 mL) as the solvent and
PEG (e.g. 30 mL) as the thickening agent and SHMP (e.g. 10 drops)
as the dispersant, then mixing together and stirring for overnight
to prepare the CIGS ink.
[0070] The procedures of ultrasonic spraying CIGS ink are
described.
[0071] First, providing a clean Mo-coated glass substrate, using
acetone, ethanol and DI water to wash the Mo-glass successively,
finally using N2 to blow to dry.
[0072] Second, providing monodispersed CIGS ink (e.g. 100 mL) and
storing in a bottle, extracting 30 mL ink into a syringe inside
which is then ready to spray.
[0073] Then, set up the spraying parameters:
[0074] Run power of ultrasonic generator: P=less than 15 W (e.g. 5
W);
[0075] Temperature of the Mo-glass substrate: Ts=under 300.degree.
C. (e.g. 100.degree. C.);
[0076] Spraying rate: V=greater than 1 ml/min. (e.g. 3
ml/min.);
[0077] Pressure of gas flow: P=greater than 5 Psi (e.g. 15
Psi);
[0078] Distance between the nozzle and the Mo-glass substrate:
D=less than 150 mm (e.g. 90 mm);
[0079] Times of spray: n=less than 5 times (e.g. 3).
[0080] Automatically ultrasonic spraying the CIGS ink onto the
Mo-glass under 300.degree. C. (e.g. 100.degree. C.) for less than 5
times (e.g. three times). Using ultrasonic spray technology can
effectively reduce the aggregation effect and easy to obtain
uniform and non-aggregated CIGS precursor films.
[0081] The procedures of heating treatment are described. The
process of heat treatment includes the following steps:
[0082] First, heating the CIGS nanoparticles/nanowires coated
substrate up to 350.degree. C. (e.g. 150-200.degree. C.). All the
particles are fused and become a clear solution. FIG. 5 shown the
nanowires begin to decompose under 150.degree. C.;
[0083] Second, heating the sample up to 450.degree. C. (e.g.
250-300.degree. C.). The solution gradually solidified and the
color changes from clear to red, finally becoming a deep black.
Meanwhile referring to FIG. 5, the networks (on right side of FIG.
5) are formed through the decomposed nanowires (on left side of
FIG. 5).
[0084] Next the temperature is increased up to 500.degree. C. (e.g.
350.degree. C.) and held for half an hour, which will remove all
the organic solvents and additives, finally the color changes to a
deep black.
[0085] The procedures of selenization process are described.
[0086] First, using Selenium powder (e.g. 2.0 g) as the solid-state
Se-source and placing it in the graphite box, then placing it into
the quartz tube of a selenization furnace at a low temperature
zone. The temperature profile of Se-source is shown in FIG. 6;
[0087] Second, a sample is placed in the high temperature zone of
selenization furnace, then using mixture of Ar or N as the
protection gas and Selenizing the hot-treated precursor films above
500.degree. C. (e.g. 550.degree. C.) for 30-70 mins (e.g. 60 mins)
in the selenization furnace. FIG. 6 shows the selenization
temperature profile.
[0088] After selenization, we can get high-quality CIGS absorb
layer, as shown in FIG. 7.
[0089] The procedures of fabricating a CIGS are described.
[0090] First, preparing CdS buffer layer through chemical bath
deposition (CBD) method:
[0091] Using CdSO.sub.4 (e.g. 0.065 g) and Thiourea (e.g. 1.14 g),
adding 25 mL NH.sub.3H.sub.2O and DI water (e.g. 200 mL), stirring
and dissolving completely.
[0092] Then place the sample into the solution and heat up to
100.degree. C. (e.g. 75.degree. C.) for up to 30 mins (e.g. 15
mins). Taking the sample out and using DI water flushing and
removing the aggregated CdS particles. In the end, drying in the
oven below 100.degree. C. (e.g. 80.degree. C.) for 60-180 mins
(e.g. 120 mins).
[0093] Second, sputtering i-ZnO and AZO window layers:
[0094] The sputtering depositing parameters of ZnO is shown as
following: Sputtering power: P=100-200 W (e.g. 150 W); Sputtering
pressure: P=0.5-10 mTorr (e.g 4.5 mTorr); Ar/O.sub.2=5:1-2:1 (e.g.
3:1); Gas Flow=10-100 sccm (e.g. 25 sccm); Sputtering time: T=up to
20 mins (e.g. 5 mins);
[0095] The sputtering depositing parameters of AZO is as following
steps: Sputtering power: P=100-200 W (e.g. 150 W); Sputtering
pressure: P=3-15 mTorr (e.g 6.0 mTorr); Gas Flow=10-100 sccm (e.g.
25 sccm); Sputtering time: T=up to 30 mins (e.g. 20 mins).
[0096] Finally, evaporating Ni--Al electrode:
[0097] Loading Ni wire (e.g. 0.5 g) and Al wire (e.g. 4 g),
Sticking the sample with mask covered on the heating stainless
steel plate. Sequencely evaporating Ni and Al wires under high
vacuum background. FIG. 8 shows the structure diagram and picture
of CIGS device made in accordance with the invention.
[0098] The present invention allows the drawbacks of the known
non-vacuum techniques to be eliminated. For this purpose, the
invention provides a method for preparing CIGS absorber layers by
using a metal salt, thickening and binding agents to form uniform
nanoparticle and nanowire networks and to provide a finished high
quality CIGS film after selenization, in which:
[0099] a) CIGS nanoparticles and nanowires are produced based on
using a metal salt such as metal chloride and acetate at room
temperature without inert gas protection;
[0100] b) A CIGS precursor layer is coated on a Mo glass substrate
by ultrasonic spraying of the CIGS nanoparticle and nanowire
solution;
[0101] c) Uniform nanoparticle and nanowire networks are generated
by initial heat treatment;
[0102] d) A clean CIGS precursor layer is obtained by cleaning the
residue salts and carbon agents at an increased temperature above
200.degree. C.;
[0103] e) High quality CIGS film is fabricated after selenizing the
pretreated precursor layer at a temperature above 400.degree.
C.
[0104] In the process of synthesizing CIGS nanoparticles and
nanowires, the steps are performed under ambient condition and room
temperature. No inert protection gas and equipments are required in
our method and the reaction runs fast and all processes can be
finished in a few minutes. No toxic chemicals are involved.
[0105] The foregoing is considered as illustrative only of the
principles of the invention. Further, since numerous modifications
and changes will readily occur to those skilled in the art, it is
not desired to limit the invention to the exact construction and
operation shown and described, and accordingly, all suitable
modifications and equivalents may be resorted to, falling within
the scope of the invention.
* * * * *