FIELD OF THE INVENTION
The invention relates to preparation of CIGS and CZTS quaternary sputtering
targets by hot iso-static pressing (HIP) or uni-axial cold pressing or cold iso-static
pressing (CIP) of various composition CIGS and CZTS powders synthesized by
microwave technique followed by sintering at appropriate temperature. More
particularly, the invention relates to a method to prepare copper indium Gallium
sulphide/selenide (CIGS) and copper zinc tin sulphide/selenide (CZTS) powder by
heating commercially available salts of Cu, In, Ga, S, Se, Zn and Sn in liquid
media by microwave irradiation.
BACKGROUND OF THE INVENTION
Sputtering, a process of depositing wide variety of materials on to
substrates of various shapes and sizes from a solid target material is an
industrially proven technology. The process is reliable and can be up-scaled
from R&D stage to commercial production. Hence, sputtering is one of
the processes utilized commercially for preparing relatively high
efficiency thin film solar cells of copper-indium-gallium-sulphide/selenide
(CIGS) and copper-zinc-tin-sulphide/selenide (CZTS). The solar characteristics of
the sputtered thin films apart from other processing parameters also depend
on the quality and composition of the solid sputter target. Therefore
improvements relating to material composition, quality and cost of sputter
target are of great interest. If the compound sputter targets are utilized
for sputtering CIGS or CZTS thin films, the characteristics of the thin films
are influenced by those of the compound target. On the other hand quality of
the sputter target is influenced by the starting powders and their sintering
conditions.

Generally the compound sputtering targets are prepared by hot iso-static
pressing (HIP) or uni-axial cold pressing or cold iso-static pressing (CIP) of alloy
powders synthesized by solid-state reaction routes. Some of the prior art
disclosing the process for preparation of CIGS and CZTS sputter targets powders
from solid state and other methods are summarized below.
CN 102051584A discloses the manufacturing method of CIGS solar photoelectric
quaternary sputtering target. The powders for preparing CIGS taget are prepared
by hot melting, curing and grinding of copper/indium and copper/gallium alloy
with selenium powder. Finally the target is prepared by hot melting and pressing
of CIGS powder.
EP 2182083B1 discloses the preparation of CIGS target from powder prepared by
solid state route involving thermal and mechanical methods. The CIGS target
having 71-78 atomic% of Cu and 22-29 atomic% of Ga is disclosed.
US 2012/0205242 Al and EP 2500447A1 discloses the preparation of quaternary
CIGS alloy sputtering target. CIGS alloy power is prepared by heating Cu, In, Ga
and Se in vacuumed quartz ampule. The synthesized powder is converted to
CIGS target by hot pressing.
EP 2540643A2 also discloses the preparation of CIGS target from powders
prepared by solid state reaction routes. In-addition to solid state routs other
methods have also been disclosed for preparation of CIGS sputter targets
summary of them is as follows.

EP 2420590A1 discloses the preparation Cu-Ga sputtering target. The target
preparation involves a first step of gas atomizing and refining a molten metal of
a Ga-containing Cu-based alloy (Cu-Ga alloy); a second step of depositing the
refined Cu-Ga on a collector, and obtaining a Cu-Ga alloy perform; and a third
step of densifying the Cu-Ga alloy perform by a densification means, and
obtaining a Cu-Ga alloy densified product.
US 20130255525 Al discloses the preparation CZTS powders from wet chemistry
route from elemental Cu, Zn, S and Se and then formation CZTS target by
thermal processing and sintering route.
Accordingly, prior art for the preparation of CIGS and CZTS targets involve
powder prepared from solid state synthesis or wet chemistry methods. Even
though the disclosed methods are capable of producing the raw powders for
preparing the solid sputter targets, disadvantages for example, precise
composition variations/ control and purity of the powders including time required
to prepare the powders persist. Hence a method that can produce powders with
precise composition, purity and is less time consuming is preferred for preparing
the CIGS and CZTS targets.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method to prepare copper
indium gallium sulphide/selenide CIGS and copper zinc tin sulphide/selenide
(CZTS powder by heating commercially available salts of Cu, In, Ga, S Se, Zn and
Sn in liquid media by microwave irradiation.

Another object of the invention is to propose a method to prepare copper indium
gallium sulphide/selenide CIGS and copper zinc tin sulphide/selenide (CZTS
powder by heating commercially available salts of Cu, In, Ga, S Se, Zn and Sn in
liquid media by microwave irradiation in which the produced CIGS and CZTS
powders are converted to quaternary sputtering targets by hot iso-static
pressing (HIP) or uni-axial cold pressing or cold iso-static pressing subsequent to
sintering.
SUMMARY OF THE INVENTION
Accordingly, the invention provides a method to prepare various compositions of
CIGS (CulnxGa1-xS/Se2) and CZTS (Cu2-aZNbSnc(S/Se)4+d nano powders in liquid
media from salts of Cu, In, Ga, S, Se, Zn and Sn by microwave irradiation. The
present invention further provides a method to convert various compositions of
CIGS and CZTS powders into quaternary sputtering targets by hot iso-static
pressing (HIP) or uni-axial cold pressing or cold iso-static pressing (CIP) followed
by sintering into quaternary sputtering targets.
According to the invention, various compositions of CIGS (CulnxGa1-xS/Se2) and
CZTS (Cu2-aZNbSnc(S/Se)4+d nano powders in liquid media are synthesized from
salts of Cu, In, Ga, S, Se, Zn and Sn by microwave irradiation. The various
compositions of CIGS and CZTS powders are thereafter converted into
quaternary sputtering targets by hot iso-static pressing (HIP) or uni-axial cold
pressing or cold iso-static pressing (CIP) followed by sintering into quaternary
sputtering targets.

The conversion of microwave assisted synthesis produces specific sized nano
(10-100 nm) and micron (0.5-1 μm) size powders with specific composition of
CIGS (CulnxGa1-xS/Se2) and CZTS (Cu2-aZNbSnc(S/Se)4+d wherein 0<=a<=l,
0<=b<=l, 0<=c<=l and -I<=d<=l) powders to produce better green
compacts and their subsequent conversion to quaternary sputtering targets by
hot iso-static pressing (HIP) or uni-axial cold pressing or cold iso-static pressing
(CIP) followed by sintering.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows the process chart for preparation of quaternary sputtering
target of CIGS and CZTS compositions by microwave synthesis according to the
invention.
Figure 2 - shows the XRD of CIGS and CZTS powder synthesized by microwave
method from salts of Cu, In, Ga, S, Se, Zn and Sn in liquid media.
Figure 3 - shows the UV-ViS-NIR spectrum of CIGS(~1.1 eV) and CZTS (-1.26
eV) powder.
Figure 4 - shows the Raman spectrum of CZTS powder.

DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention provides a method to prepare copper
indium Gallium sulphide/selenide(CIGS) and copper zinc tin sulphide/selenide
(CZTS) powder by heating commercially available salts of Cu, In, Ga, S, Se, Zn
and Sn in liquid media by microwave irradiation. The embodiment of heating
precursors by microwave irradiation can be explained as follows. Microwave
irradiation is a fast, reliable and efficient technique for thermally driven chemical
reactions used to produce various in-organic nano-powders. Microwave energy is
considered as a heat source that leads to faster chemical reactions, better
product yield and purity than conventional heating methods. Further, microwave
synthesis, due to its volumetric heating, is unique in its ability to be scaled up
without suffering from thermal gradient effects. It can potentially be scaled up to
produce nano materials by either large microwave systems or by microwave flow
reactors [1-2]. Microwave dielectric heating apart from improving the material
formation rate, also enhances the quality and size distributions. The reaction
rates are influenced by the microwave field and by the choice of precursors. The
final quality of the generated materials depends on the reactant choice, applied
power, reaction time, and temperature.
The precursors appropriate for preparing CIGS can include, but are not limited to
any commercially available Cu, In and Ga acetylacetonate's and Se powder that
can be reacted in oleylamine or other suitable solvent. The precursors

appropriate for preparing CZTS can include any water soluble salt of Cu, Zn, Sn
and S (518/KOL/2013). Microwave systems can include any professional systems
from Antonpar or CEM or Milestone that is capable of performing closed vessel
reactions. Hot iso-static pressing (HIP) or uni-axial cold pressing or cold iso-static
pressing (CIP) equipment to compress the powders into desired shape in a
mould can include systems from PTI , Kobelco etc or any commercially available
systems. Sintering furnace for achieving the final solid target may include
commercially available furnaces with atmospheric or controlled atmosphere
capability.
Now having discussed various aspects of CIGS and CZTS synthesis by
microwave irradiation and its subsequent conversion to quaternary targets by
HIP, CIP or uni-axial cold pressing, embodiments on preparation of quaternary
sputtering target follows.
To prepare CIGS nanopowder stoichiometric amount of precursor powders were
weighed and mixed in oleylamine. Example for preparing Culn07Ga3Se2
composition, 0.2 mmol of copper (II) acetylacetonate (Cu(acac)2), 0.1 mmol of
Indium (III) acetylacetonate (In(acac)3), 0.1 mmol of gallium (III)
acetylacetonate (Ga(acac)3)were mixed with 0.4 mmol of selenium (Se) powder.
The entire powder mixture was mixed with oleylamine and then transferred into
Teflon or Quartz vessels for performing closed vessel reaction. The precursor
solution was heated to 180-210°C for 20-60 minutes in a 2.45 GHz Milestone Sri,
Micro-Synth microwave reactor. The power delivered by the microwave to heat

the solution can vary between 500-800 W depending upon the precursors,
quantity of the precursor solution and length of time of the reaction. After
completion of the reaction, the reacted solution was cooled to room temperature
and CIGS nanopowder from the reacted solution was extracted by centrifugation
at 1000-5000 rpm. Finally the centrifuged extract was dried in oven at 100-200°C
for 4-8 hrs and dried powder was transferred to storage vials.
To prepare of CZTS nanopower of composition Cu2ZnSnS4, 2.213 mmol of copper
(I) chloride (CuCI), 1.106 mmol of zinc chloride (ZnC12), 1.106 mmol of tin
chloride (SnC12) and 22.33 mmol of thiourea (CH4N2S) were used as starting
materials. The pre-cursor solution was prepared by adding the aforementioned
salts to a solution of DI water (30-50ml) and ammonium Hydroxide (5-30 ml).
The pre-cursor solution was transferred to Teflon or Quartz for performing closed
vessel reaction and the reaction was carried out for 60-90 minutes at 180-220°C.
After completion of the reaction, the reacted solution was cooled to room
temperature and CIGS nanopower from the reacted solution was extracted by
centrifugation at 1000-5000 rpm. Finally the centrifuged extract was dried in
oven at 100-200°C for 4-8 hrs and dried powder was transferred to storage vials.
The CIGS and CZTS powders are synthesized simultaneously in ten vessels (each
accommodating 85 ml solution) per batch. Required numbers of runs were
performed to prepare sufficient amount required for target preparation. Figure 2
illustrates the XRD pattern of CIGS and CZTS powders. All the peaks of CIGS and

CZTS match well with their standard JCPDS #35-1102 and #26-0575
respectively. XRD patterns were collected with Philips diffractometer using CuKa
radiation. Figure 3 illustrates the UV-VIS-NIR analysis of the CIGS and CZTS
powder. The band of the specific composition Culn0.7Gao3Se2 is 1.1 eV and
Cu2ZnSnS4 is 1.26 eV. Figure 4 illustrates the Raman spectrum showing the
representative peak of CZTS at 333 cm"1 confirming the CZTS phase.
To prepare the quaternary target, the dried powder (CIGS/CZTS) was processed
by high energy milling in planetary mill before CIP or HIP or cold iso-static
pressing to de-agglomerate the nanoparticles. The fine particles (10-100 nm or
0.5-1μm) were pressed at appropriate pressure by CIP or HIP or cold iso-static
pressing in circular mould of desired diameter and depth. The finer particles
result in better green compact in which it is possible to suppress the formation of
unevenness of the green compact. The green compacts were pre-sintered and
the pre-sintered compact were removed from mould and finally sintered at a
temperature of 200-700°C for roughly 1-10 hours in atmospheric and controlled
atmospheric furnace/oven. The average grain size of the sputtering target
achieved after final sintering is around 10-100 μm and the achieved density is
around 97-98%. The porosity control was achieved by applied pressure, initial
powder size and sintering cycle. Finally, the solid sintered target was machined
to achieve the require dimensions. Finally the solid sputter targets can be
bonded to backing plate as required.

b) NON - PATENT LITERATURE
1. Microwave Synthesis of Copper Indium Gallium (di) Selenide (CIGS)
Nanopowders for Thin Film Solar Applications, Raghunandan Seelaboyina,
Manoj Kumar, Alekhya Venkata Madiraju, Kshitij Taneja,
Anup Kumar Keshri, Sarang Mahajan and Kulvir Singh (2013), Journal of
Renewable and Sustainable Energy, 5, 031608-1 - 031608-7.
2. Synthesis of CZTS in aqueous media by microwave irradiation, Alekhya
Venkata Madiraju, Kshitij Taneja, Manoj Kumar, Anup Kumar Keshri,
Sarang Balkrushna Mahajan and Raghunandan Seelaboyina, Conference
Papers in Energy. Volume 2013 (2013), Article ID 962730.

WE CLAIM :
1. A method of producing Copper indium gallium sulphide/selenide CIGS)
quaternary sputter target of (CulnxGa1-x SE2, wherein x is greater than or
equal to about 0.5) and Copper zinc tin sulphide/selenide CZTS and
(Cu2-aZnbSnc(S/Se)4+d wherein 0<=a< = 1, 0<=c< = 1 and -1<=d< = 1) by
hot iso-static pressing (HIP) uni-axial cold pressing or cold iso-static
pressing (CIP) or cold iso-static pressing of microwave synthesized
powders in mould of appropriate shape, size and thickness followed by
pre-sintering and final sintering, wherein the CIGS powder for the
preparation of target can be synthesized by microwave from any
commercially available salts of Cu, In, Ga, and soluble in oleylamine or
any appropriate solvent and wherein the CZTS powder for the preparation
of target can be synthesized by microwave from any commercially
available salts of Cu, Zn, Sn and S soluble in hydrous media in presence of
ammonium Hydroxide.
2. The method as claimed in claim 1, wherein the size of CIGS and CZTS
powders range from 10-100 mm or 0.1-0.5 μm.
3. The method as claimed in claim 1, wherein the pre-sintering temperature
is from 100-150°C.

4. The method as claimed in claim 4, wherein the final sintering temperature
is from 200-700°C.
5. The method as claimed in claim 1, wherein the average grain size of the
CIGS and CZTS sputtering target achieved after final sintering is about
10-100 μm.
6. The method as claimed in claim 7, wherein the density of CIGS and CZTS
achieved after final sintering is about 97-98%.

ABSTRACT

The invention relates to a method of producing Copper indium gallium
sulphide/selenide CIGS) quaternary sputter target of (CulnxGa1-x Se2, wherein x is
greater than or equal to about 0.5) and Copper zinc tin sulphide/selenide CZTS
and (Cu2-aZnbSnc(S/Se)4+d wherein 0<=a<=1, 0<=c<=1 and -1<=d<=1) by
hot iso-static pressing (HIP) uni-axial cold pressing or cold iso-static pressing
(CIP) or cold iso-static pressing of microwave synthesized powders in mould of
appropriate shape, size and thickness followed by pre-sintering and final
sintering, wherein the CIGS powder for the preparation of target can be
synthesized by microwave from any commercially available salts of Cu, In, Ga,
and soluble in oleylamine or any appropriate solvent and wherein the CZTS
powder for the preparation of target can be synthesized by microwave from any
commercially available salts of Cu, Zn, Sn and S soluble in hydrous media in
presence of ammonium Hydroxide.