U.S. patent application number 13/319900 was filed with the patent office on 2012-03-15 for processes for preparing copper tin sulfide and copper zinc tin sulfide films.
This patent application is currently assigned to E.I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to John W. Catron, JR., Lynda Kaye Johnson, Meijun Lu, Daniela Rodica Radu.
Application Number | 20120060928 13/319900 |
Document ID | / |
Family ID | 42797237 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120060928 |
Kind Code |
A1 |
Johnson; Lynda Kaye ; et
al. |
March 15, 2012 |
PROCESSES FOR PREPARING COPPER TIN SULFIDE AND COPPER ZINC TIN
SULFIDE FILMS
Abstract
This invention relates to processes for preparing films of CTS
and CZTS and their selenium analogues on a substrate. Such films
are useful in the preparation of photovoltaic devices. This
invention also relates to processes for preparing coated substrates
and for making photovoltaic devices.
Inventors: |
Johnson; Lynda Kaye;
(Wilmington, DE) ; Lu; Meijun; (Hockessin, DE)
; Catron, JR.; John W.; (Smyrna, DE) ; Radu;
Daniela Rodica; (West Grove, PA) |
Assignee: |
E.I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
42797237 |
Appl. No.: |
13/319900 |
Filed: |
May 21, 2010 |
PCT Filed: |
May 21, 2010 |
PCT NO: |
PCT/US10/35810 |
371 Date: |
November 10, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61180179 |
May 21, 2009 |
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61180181 |
May 21, 2009 |
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61180186 |
May 21, 2009 |
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61180184 |
May 21, 2009 |
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Current U.S.
Class: |
136/264 ;
257/E21.464; 438/502 |
Current CPC
Class: |
C09D 11/037 20130101;
H01L 21/02614 20130101; H01L 21/02557 20130101; C01P 2004/64
20130101; B01J 2/006 20130101; H01L 31/0324 20130101; H01L 21/02628
20130101; B82Y 30/00 20130101; C01G 19/006 20130101; H01L 21/0256
20130101; C01P 2004/04 20130101; C23C 18/1204 20130101; H01L 31/18
20130101; C23C 18/1279 20130101; C01P 2004/62 20130101; H01L
21/02568 20130101; C01P 2002/72 20130101 |
Class at
Publication: |
136/264 ;
438/502; 257/E21.464 |
International
Class: |
H01L 31/0272 20060101
H01L031/0272; H01L 21/368 20060101 H01L021/368 |
Claims
1. A process comprising: a) preparing an ink comprising: i) a
copper source selected from the group consisting of copper
complexes of nitrogen-, oxygen-, carbon-, sulfur-, and
selenium-based organic ligands, copper sulfides, copper selenides,
and mixtures thereof; ii) a tin source selected from the group
consisting of tin complexes of nitrogen-, oxygen-, carbon-,
sulfur-, and selenium-based organic ligands, tin hydrides, tin
sulfides, tin selenides, and mixtures thereof; iii) optionally, a
zinc source selected from the group consisting of zinc complexes of
nitrogen-, oxygen-, carbon-, sulfur-, and selenium-based organic
ligands, zinc sulfides, zinc selenides, and mixtures thereof; iv)
optionally, a chalcogen compound selected from the group consisting
of: elemental S, elemental Se, CS.sub.2, CSe.sub.2, CSSe,
R.sup.1S--Z, R.sup.1Se--Z, R.sup.1S--SR.sup.1,
R.sup.1Se--SeR.sup.1, R.sup.2C(S)S--Z, R.sup.2C(Se)Se--Z,
R.sup.2C(Se)S--Z, R.sup.1C(O)S--Z, R.sup.1C(O)Se--Z, and mixtures
thereof, with each Z independently selected from the group
consisting of: H, NR.sup.4.sub.4, and SiR.sup.5.sub.3; wherein each
R.sup.1 and R.sup.5 is independently selected from the group
consisting of: hydrocarbyl and O-, N-, S-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyl; each R.sup.2 is
independently selected from the group consisting of hydrocarbyl,
O-, N-, S-, Se-, halogen- and tri(hydrocarbyl)silyl-substituted
hydrocarbyl, and O-, N-, S-, and Se-based functional groups; and
each R.sup.4 is independently selected from the group consisting of
hydrogen, O-, N-, S-, Se-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyl, and O-, N-, S-, and
Se-based functional groups; v) optionally, a solvent; and b)
disposing the ink onto a substrate to form a coated substrate;
provided that: if there is no solvent, then at least one of the
chalcogen compound and the tin source is a liquid at room
temperature; and if the copper source is selected from copper
sulfide and copper selenide, and the tin source is selected from
tin sulfide and tin selenide, then the solvent is not
hydrazine.
2. The process of claim 1, wherein the ratio of the total number of
moles of the chalcogen compound, the sulfur- and selenium-based
organic ligands, and the copper-, tin- and zinc-sulfides and
selenides to the total number of moles of the copper, tin and zinc
complexes is at least about 1.
3. The process of claim 1, wherein the ink comprises a chalcogen
compound or a zinc source.
4. The process of claim 1, wherein the ink comprises elemental
sulfur, elemental selenium, or a mixture of elemental sulfur and
selenium, and the molar ratio of (S+Se) is about 0.2 to about 5
relative to the tin source.
5. The process of claim 1, wherein the coated substrate comprises:
a) one or more copper compounds selected from the group consisting
of binary copper chalcogenides, binary copper oxides, and CTS-Se;
and b) one or more tin compounds selected from the group consisting
of binary tin chalcogenides, binary tin oxides, and CTS-Se, wherein
the chalcogenides comprise sulfides, selenides or mixtures
thereof.
6. The process of claim 5, wherein the ink comprises a zinc source
and the coated substrate further comprises one or more zinc
compounds selected from the group consisting of binary zinc
chalcogenides, ZnO, and CZTS-Se, wherein the chalcogenides comprise
sulfides, selenides or mixtures thereof.
7. The process of claim 1, wherein the nitrogen-, oxygen-, carbon-,
sulfur- and selenium-based organic ligands are selected from the
group consisting of: amidos; alkoxides; acetylacetonates;
carboxylates; hydrocarbyls; O-, N-, S-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyls; thio- and
selenolates; thio-, seleno-, and dithiocarboxylates; dithio-,
diseleno-, and thioselenocarbamates; and dithioxanthogenates.
8. The process of claim 1, wherein a solvent is present and is
selected from the group consisting of aromatics, heteroaromatics,
nitriles, amides, alcohols, pyrrolidinones, amines, and mixtures
thereof.
9. The process of claim 1, further comprising a drying step at
about 80.degree. C. to about 350.degree. C.
10. The process of claim 9, wherein the coated substrate comprises
CZTS-Se.
11. The process of claim 1, wherein the substrate comprises
material selected from the group consisting of metal foils,
plastics, polymers, metalized plastics, glass, solar glass,
low-iron glass, green glass, soda-lime glass, steel, stainless
steel, aluminum, ceramics, metal plates, metalized ceramic plates,
and metalized polymer plates.
12. The process of claim 1, further comprising a step of heating
the ink to a temperature of greater than about 100.degree. C. prior
to disposing it onto the substrate.
13. The process of claim 12, wherein the coated substrate comprises
CZTS-Se.
14. The process of claim 12, wherein the process is carried out at
atmospheric pressure, a solvent is present, and the boiling point
of the solvent is greater than about 100.degree. C. at atmospheric
pressure.
15. The process of claim 1, further comprising an annealing step at
about 350.degree. C. to about 800.degree. C., and wherein the
annealing comprises thermal processing, rapid thermal processing,
rapid thermal annealing, pulsed thermal processing, laser beam
exposure, heating via IR lamps, electron beam exposure, pulsed
electron beam processing, heating via microwave irradiation, and
combinations thereof.
16. The process of claim 15, wherein the annealing is carried out
under an atmosphere comprising an inert gas and a reactive
component selected from the group consisting of: selenium vapor,
sulfur vapor, hydrogen, hydrogen sulfide, hydrogen selenide, and
mixtures thereof.
17. The process of claim 15, wherein the annealing is carried out
under an atmosphere comprising an inert gas and the ratio of the
total number of moles of the chalcogen compound, the sulfur- and
selenium-based organic ligands, and the copper-, tin- and
zinc-sulfides and selenides to the total number of moles of the
copper, tin and zinc complexes is at least about 1.
18. The process of claim 15, further comprising disposing one or
more layers selected from the group consisting of buffer layers,
top contact layers, electrode pads, and antireflective layers onto
the annealed CZTS-Se film.
19. A photovoltaic device produced by the process of claim 18.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) from, and claims the benefit of, the following U.S.
Provisional Applications: No. 61/180,179, No. 61/180,181, No.
61/180,184, and No. 61/180,186; each of which was filed on May 21,
2009, and each of which is by this reference incorporated in its
entirety as a part hereof for all purposes.
FIELD OF THE INVENTION
[0002] This invention relates to processes for preparing films of
CZTS and its selenium analogues on a substrate. Such films are
useful in the preparation of photovoltaic devices. This invention
also relates to processes for preparing coated substrates and for
making photovoltaic devices.
BACKGROUND
[0003] Crystalline multinary-metal chalcogenide compositions
containing only non-toxic and abundant elements are of particular
interest in developing environmentally sustainable processes and
devices. Copper tin sulfide (Cu.sub.2SnS.sub.3 or "CTS") and copper
zinc tin sulfide (Cu.sub.2ZnSnS.sub.4 or "CZTS") are particularly
useful examples of this class of materials, and are of interest due
to their potential applications as small band-gap semiconductors,
as nonlinear materials, and as suitable candidates for photovoltaic
cell materials.
[0004] Thin-film photovoltaic cells typically use semiconductors
such as CdTe or copper indium gallium sulfide/selenide (CIGS) as an
energy absorber material. Due to toxicity of cadmium and the
limited availability of indium, alternatives are sought. CZTS
possesses a band gap energy of about 1.5 eV and a large absorption
coefficient (approx. 10.sup.4 cm.sup.-1), making it a promising
CIGS replacement.
[0005] Challenges in making CZTS thin-films are illustrative of the
general challenges that must be surmounted in making films of
crystalline multinary-metal chalcogenide compositions. Current
techniques to make CZTS thin films (e.g., thermal evaporation,
sputtering, hybrid sputtering, pulsed laser deposition and electron
beam evaporation) require complicated equipment and therefore tend
to be expensive. Electrochemical deposition is an inexpensive
process, but compositional non-uniformity and/or the presence of
secondary phases prevents this method from generating high-quality
CZTS thin-films. CZTS thin-films can also be made by the spray
pyrolysis of a solution containing metal salts, typically CuCl,
ZnCl.sub.2, and SnCl.sub.4, using thiourea as the sulfur source.
This method tends to yield films of poor morphology, density and
grain size. Photochemical deposition has also been shown to
generate p-type CZTS thin films. However, the composition of the
product is not well-controlled, and it is difficult to avoid the
formation of impurities such as hydroxides. The synthesis of CZTS
nanoparticles, which incorporate high-boiling amines as capping
agents, has also been disclosed. The presence of capping agents in
the nanoparticle layer may contaminate and lower the density of the
annealed CZTS film.
[0006] A hybrid solution-particle approach to CZTS involving the
preparation of a hydrazine-based slurry comprising dissolved Cu--Sn
chalcogenides (S or S--Se), Zn-chalcogenide particles, and excess
chalcogen has been reported. However, hydrazine is a highly
reactive and potentially explosive solvent that is described in the
Merck Index as a "violent poison."
[0007] Hence, there still exists a need for simple, low-cost,
scalable materials and processes with a low number of operations
that provide high-quality, crystalline CTS and CZTS films with
tunable composition and morphology. There also exists a need for
low-temperature routes to these materials using solvents and
reagents with relatively low toxicity.
SUMMARY
[0008] One aspect of this invention is a process comprising:
a) preparing an ink comprising:
[0009] i) a copper source selected from the group consisting of
copper complexes of nitrogen-, oxygen-, carbon-, sulfur-, and
selenium-based organic ligands, copper sulfides, copper selenides,
and mixtures thereof;
[0010] ii) a tin source selected from the group consisting of tin
complexes of nitrogen-, oxygen-, carbon-, sulfur-, and
selenium-based organic ligands, tin hydrides, tin sulfides, tin
selenides, and mixtures thereof;
[0011] iii) optionally, a zinc source selected from the group
consisting of zinc complexes of nitrogen-, oxygen-, carbon-,
sulfur-, and selenium-based organic ligands, zinc sulfides, zinc
selenides, and mixtures thereof;
[0012] iv) optionally, a chalcogen compound selected from the group
consisting of: elemental S, elemental Se, CS.sub.2, CSe.sub.2,
CSSe, R.sup.1S--Z, R.sup.1Se--Z, R.sup.1S--SR.sup.1,
R.sup.1Se--SeR.sup.1, R.sup.2C(S)S--Z, R.sup.2C(Se)Se--Z,
R.sup.2C(S)S--SC(S)R.sup.2, R.sup.2C(Se)Se--SeC(Se)R.sup.2,
R.sup.1C(O)S--Z, and mixtures thereof, with each Z independently
selected from the group consisting of: H, NR.sup.4.sub.4, and
SiR.sup.5.sub.3; wherein each R.sup.1 and R.sup.5 is independently
selected from the group consisting of: hydrocarbyl and O-, N-, S-,
halogen- and tri(hydrocarbyl)silyl-substituted hydrocarbyl; each
R.sup.2 is independently selected from the group consisting of
hydrocarbyl, O-, N-, S-, Se-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyl, and O-, N-, S-, and
Se-based functional groups; and each R.sup.4 is independently
selected from the group consisting of hydrogen, O-, N-, S-, Se-,
halogen- and tri(hydrocarbyl)silyl-substituted hydrocarbyl, and O-,
N-, S-, and Se-based functional groups;
[0013] v) optionally, a solvent; and
b) disposing the ink onto a substrate to form a coated
substrate;
[0014] provided that:
if there is no solvent, then at least one of the chalcogen compound
and the tin source is a liquid at room temperature; and if the
copper source is selected from copper sulfide and copper selenide,
and the tin source is selected from tin sulfide and tin selenide,
then the solvent is not hydrazine.
[0015] Another aspect of this invention is a photovoltaic
device.
DETAILED DESCRIPTION
[0016] Herein, the terms "solar cell" and "photovoltaic cell" are
synonymous unless specifically defined otherwise. These terms refer
to devices that use semiconductors to convert visible and
near-visible light energy into usable electrical energy. The terms
"band gap energy", "optical band gap", and "band gap" are
synonymous unless specifically defined otherwise. These terms refer
to the energy required to generate electron-hole pairs in a
semiconductor material, which in general is the minimum energy
needed to excite an electron from the valence band to the
conduction band.
[0017] Herein, element groups are represented utilizing CAS
notation. As used herein, the term "chalcogen" refers to Group VIA
elements, and the terms "metal chalcogenides" or "chalcogenides"
refer to materials that comprise metals and Group VIA elements.
Suitable Group VIA elements include sulfur, selenium and tellurium.
Metal chalcogenides are important candidate materials for
photovoltaic applications, since many of these compounds have
optical band gap values well within the terrestrial solar
spectra.
[0018] Herein, the term "binary-metal chalcogenide" refers to a
chalcogenide composition comprising one metal. The term
"ternary-metal chalcogenide" refers to a chalcogenide composition
comprising two metals. The term "quaternary-metal chalcogenide"
refers to a chalcogenide composition comprising three metals. The
term "multinary-metal chalcogenide" refers to a chalcogenide
composition comprising two or more metals and encompasses ternary
and quaternary metal chalcogenide compositions.
[0019] Herein, the terms "copper tin sulfide" and "CTS" refer to
Cu.sub.2SnS.sub.3; "copper tin selenide" and "CTSe" refer to
Cu.sub.2SnSe.sub.3; and "copper tin sulfide/selenide" and "CTS-Se"
encompass all possible combinations of Cu.sub.2Sn(S,Se).sub.3,
including Cu.sub.2SnS.sub.3, Cu.sub.2SnSe.sub.3, and
Cu.sub.2SnS.sub.xSe.sub.3-x, where 0.ltoreq.x.ltoreq.3. The terms
"copper tin sulfide", "copper tin selenide", "copper tin
sulfide/selenide", "CTS", "CTSe" and "CTS-Se" further encompass
fractional stoichiometries, e.g., Cu.sub.1.80Sn.sub.1.05S.sub.3.
That is, the stoichiometry of the elements can vary from a strictly
2:1:3 molar ratio.
[0020] Herein, the terms copper zinc tin sulfide and "CZTS" refer
to Cu.sub.2ZnSnS.sub.4; copper zinc tin selenide and "CZTSe" refer
to Cu.sub.2ZnSnSe.sub.4; and copper zinc tin sulfide/selenide and
"CZTS-Se" encompass all possible combinations of
Cu.sub.2ZnSn(S,Se).sub.4, including Cu.sub.2ZnSnS.sub.4,
Cu.sub.2ZnSnSe.sub.4, and Cu.sub.2ZnSnS.sub.xSe.sub.4-x, where
0.ltoreq.x.ltoreq.4. The terms "CZTS," "CZTSe," and "CZTS-Se"
further encompass copper zinc tin sulfide/selenide semiconductors
with fractional stoichiometries, e.g.,
Cu.sub.1.94Zn.sub.0.63Sn.sub.1.3S.sub.4. That is, the stoichiometry
of the elements can vary from a strictly 2:1:1:4 molar ratio.
Materials designated as CTS-Se and CZTS-Se may also contain small
amounts of other elements such as sodium. To date, the highest
efficiencies have been measured for copper-poor CZTS-Se solar
cells, where by "copper-poor" it is understood that the ratio
Cu/(Zn+Sn) is less than 1.0. For high efficiency devices, a molar
ratio of zinc to tin is greater than one is also desirable.
[0021] The term "kesterite" is commonly used to refer to materials
belonging to the kesterite family of minerals and is also the
common name of the mineral CZTS. As used herein, the term
"kesterite" refers to crystalline compounds in either the I4- or
I4-2m space groups having the nominal formula
Cu.sub.2ZnSn(S--Se).sub.4, and also "atypical kesterites" wherein
zinc has replaced a fraction of the copper or copper has replaced a
fraction of the zinc to give Cu.sub.cZn.sub.zSn(S--Se).sub.4
wherein c is greater than two and z is less than one; or c is less
than two and z is greater than one. The term "kesterite structure"
refers to the structure of these compounds. X-ray absorption
spectroscopy (XAS) reveals spectral features unique to the
kesterite form and allows for determination of the ratio of Cu to
Zn in the kesterite phase. This allows for the identification of
atypical kesterite compositions, which are clearly distinguished
from a mixture of separate sulfide phases producing the same
elemental ratios in aggregate. Control of stoichiometry in this
phase allows for control of electronic properties for improved
performance in a photovoltaic device.
[0022] As used herein, "coherent domain size" refers to the size of
crystalline domains over which a defect-free, coherent structure
may exist. The coherency comes from the fact that the
three-dimensional ordering is not broken inside of these
domains.
[0023] Herein, the term "metal salts" refers to compositions
wherein metal cations and inorganic anions are joined by ionic
bonding. Relevant classes of inorganic anions comprise oxides,
sulfides, carbonates, sulfates and halides. Herein, the term "metal
complexes" refers to compositions wherein a metal is bonded to a
surrounding array of molecules or anions, typically called
"ligands" or "complexing agents". The atom within a ligand that is
directly bonded to the metal atom or ion is called the "donor atom"
and, herein, often comprises nitrogen, oxygen, selenium, or
sulfur.
[0024] Herein, ligands are classified according to the "Covalent
Bond Classification (CBC) Method" (Green, M. L. H. J. Organomet.
Chem. 1995, 500, 127-148). An "X-function ligand" is one which
interacts with a metal center via a normal 2-electron covalent
bond, composed of 1 electron from the metal and 1 electron from the
X ligand. Simple examples of X-type ligands include alkyls and
thiolates. Herein, the term "nitrogen-, oxygen-, carbon-, sulfur-,
and selenium-based organic ligands" refers specifically to
carbon-containing X-function ligands, wherein the donor atom
comprises nitrogen, oxygen, carbon, sulfur, or selenium. Herein,
the term "complexes of nitrogen-, oxygen-, carbon-, sulfur-, and
selenium-based organic ligands" refers to the metal complexes
comprising these ligands. Examples include metal complexes of
amidos, alkoxides, acetylacetonates, acetates, carboxylates,
hydrocarbyls, O-, N-, S-, Se- and halogen-substituted hydrocarbyls,
thiolates, selenolates, thiocarboxylates, selenocarboxylates,
dithiocarbamates, and diselenocarbamates.
[0025] As defined herein, a "hydrocarbyl group" is a univalent
group containing only carbon and hydrogen. Examples of hydrocarbyl
groups include unsubstituted alkyls, cycloalkyls, and aryl groups,
including alkyl-substituted aryl groups. Suitable hydrocarbyl
groups and alkyl groups contain 1 to about 30 carbons, or 1 to 25,
1 to 20, 1 to 15, 1 to 10, 1 to 5, 1 to 4, or 1 to 2 carbons. By
"heteroatom-substituted hydrocarbyl" is meant a hydrocarbyl group
that contains one or more heteroatoms wherein the free valence is
located on carbon, not on the heteroatom. Examples include
hydroxyethyl and carbomethoxyethyl. Suitable heteroatom
substituents include O-, N-, S-, halogen, and
tri(hydrocarbyl)silyl. In a substituted hydrocarbyl, all of the
hydrogens may be substituted, as in trifluoromethyl. Herein, the
term "tri(hydrocarbyl)silyl" encompasses silyl substituents,
wherein the substituents on silicon are hydrocarbyls. Herein, by
"O-, N-, S-, and Se-based functional groups" is meant univalent
groups other than hydrocarbyl and substituted hydrocarbyl that
comprise O-, N-, S-, or Se-heteroatoms, wherein the free valence is
located on this heteroatom. Examples of O-, N-, S-, and Se-based
functional groups include alkoxides, amidos, thiolates, and
selenolates.
Preparation of Inks
[0026] One aspect of this invention is a process comprising:
a) preparing an ink comprising:
[0027] i) a copper source selected from the group consisting of
copper complexes of nitrogen-, oxygen-, carbon-, sulfur-, and
selenium-based organic ligands, copper sulfides, copper selenides,
and mixtures thereof;
[0028] ii) a tin source selected from the group consisting of tin
complexes of nitrogen-, oxygen-, carbon-, sulfur-, and
selenium-based organic ligands, tin hydrides, tin sulfides, tin
selenides, and mixtures thereof;
[0029] iii) optionally, a zinc source selected from the group
consisting of zinc complexes of nitrogen-, oxygen-, carbon-,
sulfur-, and selenium-based organic ligands, zinc sulfides, zinc
selenides, and mixtures thereof;
[0030] iv) optionally, a chalcogen compound selected from the group
consisting of: elemental S, elemental Se, CS.sub.2, CSe.sub.2,
CSSe, R.sup.1S--Z, R.sup.1Se--Z, R.sup.1S--SR.sup.1,
R.sup.1Se--SeR.sup.1, R.sup.2C(S)S--Z, R.sup.2C(Se)Se--Z,
R.sup.2C(Se)S--Z, R.sup.1C(O)S--Z, R.sup.1C(O)Se--Z, and mixtures
thereof, with each Z independently selected from the group
consisting of: H, NR.sup.4.sub.4, and SiR.sup.5.sub.3; wherein each
R.sup.1 and R.sup.5 is independently selected from the group
consisting of: hydrocarbyl and O-, N-, S-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyl; each R.sup.2 is
independently selected from the group consisting of hydrocarbyl,
O-, N-, S-, Se-, halogen- and tri(hydrocarbyl)silyl-substituted
hydrocarbyl, and O-, N-, S-, and Se-based functional groups; and
each R.sup.4 is independently selected from the group consisting of
hydrogen, O-, N-, S-, Se-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyl, and O-, N-, S-, and
Se-based functional groups;
[0031] v) optionally, a solvent; and
b) disposing the ink onto a substrate to form a coated
substrate;
[0032] provided that:
if there is no solvent, then at least one of the chalcogen compound
and the tin source is a liquid at room temperature; and if the
copper source is selected from copper sulfide and copper selenide,
and the tin source is selected from tin sulfide and tin selenide,
then the solvent is not hydrazine.
[0033] In some embodiments, the ratio of the total number of moles
of the chalcogen compound, the sulfur- and selenium-based organic
ligands, and the copper-, tin-, and zinc-sulfides and selenides to
the total number of moles of the copper, tin and zinc complexes is
at least about 1.
[0034] In some embodiments, a chalcogen compound is present.
[0035] In some embodiments, a zinc source is present.
[0036] In some embodiments, elemental sulfur, elemental selenium,
or a mixture of elemental sulfur and selenium is present, and the
molar ratio of (S+Se) is about 0.2 to about 5, or about 0.5 to
about 2.5, relative to the tin source.
[0037] In some embodiments, the nitrogen-, oxygen-, carbon-,
sulfur-, and selenium-based organic ligands are selected from the
group consisting of: amidos; alkoxides; acetylacetonates;
carboxylates; hydrocarbyls; O-, N-, S-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyls; thio- and
selenolates; thio-, seleno-, and dithiocarboxylates; dithio-,
diseleno-, and thioselenocarbamates; and dithioxanthogenates.
[0038] Suitable amidos include: bis(trimethylsilyl)amino,
dimethylamino, diethylamino, diisopropylamino,
N-methyl-t-butylamino, 2-(dimethylamino)-N-methylethylamino,
N-methylcyclohexylamino, dicyclohexylamino,
N-ethyl-2-methylallylamino, bis(2-methoxyethyl)amino,
2-methylaminomethyl-1,3-dioxolane, pyrrolidino,
t-butyl-1-piperazinocarboxylate, N-methylanilino,
N-phenylbenzylamino, N-ethyl-o-toluidino,
bis(2,2,2-trifluoromethyl)amino, N-t-butyltrimethylsilylamino, and
mixtures thereof. Some ligands may chelate the metal center, and,
in some cases, comprise more than one type of donor atom, e.g., the
dianion of N-benzyl-2-aminoethanol is a suitable ligand comprising
both amino and alkoxide groups.
[0039] Suitable alkoxides include: methoxide, ethoxide,
n-propoxide, i-propoxide, n-butoxide, t-butoxide, neopentoxide,
ethylene glycol dialkoxide, 1-methylcyclopentoxide,
2-fluoroethoxide, 2,2,2,-trifluoroethoxide, 2-ethoxyethoxide,
2-methoxyethoxide, 3-methoxy-1-butoxide, methoxyethoxyethoxide,
3,3-diethoxy-1-propoxide, 2-dimethylaminoethoxide,
2-diethylaminoethoxide, 3-dimethylamino-1-propoxide,
3-diethylamino-1-propoxide, 1-dimethylamino-2-propoxide,
1-diethylamino-2-propoxide, 2-(1-pyrrolidinyl)ethoxide,
1-ethyl-3-pyrrolidinoxide, 3-acetyl-1-propoxide,
4-methoxyphenoxide, 4-chlorophenoxide, 4-t-butylphenoxide,
4-cyclopentylphenoxide, 4-ethylphenoxide,
3,5-bis(trifluoromethyl)phenoxide, 3-chloro-5-methoxyphenoxide,
3,5-dimethoxyphenoxide, 2,4,6-trimethylphenoxide,
3,4,5-trimethylphenoxide, 3,4,5-trimethoxyphenoxide,
4-t-butyl-catecholate(2-), 4-propanoylphenoxide,
4-(ethoxycarbonyl)phenoxide, 3-(methylthio)-1-propoxide,
2-(ethylthio)-1-ethoxide, 2-(methylthio)ethoxide,
4-(methylthio)-1-butoxide, 3-(methylthio)-1-hexoxide,
2-methoxybenzylalkoxide, 2-(trimethylsilyl)ethoxide,
(trimethylsilyl)methoxide, 1-(trimethylsilyl)ethoxide,
3-(trimethylsilyl)propoxide, 3-methylthio-1-propoxide, and mixtures
thereof.
[0040] Herein, the term acetylacetonate refers to the anion of
1,3-dicarbonyl compounds, A.sup.1C(O)CH(A.sup.2)C(O)A.sup.1,
wherein each A.sup.1 is independently selected from hydrocarbyl,
substituted hydrocarbyl, and O-, S-, and N-based functional groups
and each A.sup.2 is independently selected from hydrocarbyl,
substituted hydrocarbyl, halogen, and O-, S-, and N-based
functional groups. Suitable acetylacetonates include:
2,4-pentanedionate, 3-methyl-2-4-pentanedionate,
3-ethyl-2,4-pentanedionate, 3-chloro-2,4-pentanedionate,
1,1,1-trifluoro-2,4-pentanedionate,
1,1,1,5,5,5-hexafluoro-2,4-pentanedionate,
1,1,1,5,5,6,6,6,-octafluoro-2,4-hexanedionate, ethyl
4,4,4-trifluoroacetoacetate, 2-methoxyethylacetoacetate,
methylacetoacetate, ethylacetoacetate, t-butylacetoacetate,
1-phenyl-1,3-butanedionate, 2,2,6,6-tetramethyl-3,5-heptanedionate,
allyloxyethoxytrifluoroacetoacetate,
4,4,4-trifluoro-1-phenyl-1,3-butanedionate,
1,3-diphenyl-1,3-propanedionate,
6,6,7,7,8,8,8,-heptafluoro-2-2-dimethyl-3,5-octanedionate, and
mixtures thereof.
[0041] Suitable carboxylates include: acetate, trifluoroacetate,
propionate, butyrates, hexanoate, octanoate, decanoate, stearate,
isobutyrate, t-butylacetate, heptafluorobutyrate, methoxyacetate,
ethoxyacetate, methoxypropionate, 2-ethyl hexanoate,
2-(2-methoxyethoxy)acetate, 2-[2-(2-methoxyethoxy)ethoxy]acetate,
(methylthio)acetate, tetrahydro-2-furoate, 4-acetyl butyrate,
phenylacetate, 3-methoxyphenylacetate, (trimethylsilyl)acetate,
3-(trimethylsilyl)propionate, maleate, benzoate,
acetylenedicarboxylate, and mixtures thereof.
[0042] Suitable hydrocarbyls include: methyl, ethyl, n-propyl,
i-propyl, n-butyl, i-butyl, sec-butyl, t-butyl, n-pentyl, n-hexyl,
n-heptyl, n-octyl, neopentyl, 3-methylbutyl, phenyl, benzyl,
4-t-butylbenzyl, 4-t-butylphenyl, p-tolyl, 2-methyl-2-phenylpropyl,
2-mesityl, 2-phenylethyl, 2-ethylhexyl, 2-methyl-2-phenylpropyl,
3,7-dimethyloctyl, allyl, vinyl, cyclopentyl, cyclohexyl, and
mixtures thereof.
[0043] Suitable O-, N-, S-, halogen- and
tri(hydrocarbyl)silyl-substituted hydrocarbyls include:
2-methoxyethyl, 2-ethoxyethyl, 4-methoxyphenyl, 2-methoxybenzyl,
3-methoxy-1-butyl, 1,3-dioxan-2-ylethyl, 3-trifluoromethoxyphenyl,
3,4-(methylenedioxy)phenyl, 2,4-dimethoxyphenyl,
2,5-dimethoxyphenyl, 3,4-dimethoxyphenyl, 2-methoxybenzyl,
3-methoxybenzyl, 4-methoxybenzyl, 3,5-dimethoxyphenyl,
3,5-dimethyl-4-methoxyphenyl, 3,4,5-trimethoxyphenyl,
4-methoxyphenethyl, 3,5-dimethoxybenzyl,
4-(2-tetrahydro-2H-pyranoxy)phenyl, 4-phenoxyphenyl,
2-benzyloxyphenyl, 3-benzyloxyphenyl, 4-benzyloxyphenyl,
3-fluoro-4-methoxyphenyl, 5-fluoro-2-methoxyphenyl,
2-ethoxyethenyl, 1-ethoxyvinyl, 3-methyl-2-butenyl, 2-furyl,
carbomethoxyethyl, 3-dimethylamino-1-propyl,
3-diethylamino-1-propyl, 3-[bis(trimethylsilyl)amino]phenyl,
4-(N,N-dimethyl)aniline, [2-(1-pyrrolidinylmethyl)phenyl],
[3-(1-pyrrolidinylmethyl)phenyl], [4-(1-pyrrolidinylmethyl)phenyl],
[2-(4-morpholinylmethyl)phenyl], [3-(4-morpholinylmethyl)phenyl],
[4-(4-morpholinylmethyl)phenyl], (4-(1-piperidinylmethyl)phenyl),
(2-(1-piperidinylmethyl)phenyl), (3-(1-piperidinylmethyl)phenyl),
3-(1,4-dioxa-8-azaspiro[4,5]dec-8-ylmethyl)phenyl,
1-methyl-2-pyrrolyl, 2-fluoro-3-pyridyl, 6-methoxy-2-pyrimidyl,
3-pyridyl, 5-bromo-2-pyridyl, 1-methyl-5-imidazolyl,
2-chloro-5-pyrimidyl, 2,6-dichloro-3-pyrazinyl, 2-oxazolyl,
5-pyrimidyl, 2-pyridyl, 2-(ethylthio)ethyl, 2-(methylthio)ethyl,
4-(methylthio)butyl, 3-(methylthio)-1-hexyl, 4-thioanisole,
4-bromo-2-thiazolyl, 2-thiophenyl, chloromethyl, 4-fluorophenyl,
3-fluorophenyl, 4-chlorophenyl, 3-chlorophenyl,
4-fluoro-3-methylphenyl, 4-fluoro-2-methylphenyl,
4-fluoro-3-methylphenyl, 5-fluoro-2-methylphenyl,
3-fluoro-2-methylphenyl, 4-chloro-2-methylphenyl,
3-fluoro-4-methylphenyl, 3,5-bis(trifluoromethyl)-phenyl,
3,4,5-trifluorophenyl, 3-chloro-4-fluorophenyl,
3-chloro-5-fluorophenyl, 4-chloro-3-fluorophenyl,
3,4-dichlorophenyl, 3,5-dichlorophenyl, 3,4-difluorophenyl,
3,5-difluorophenyl, 2-bromobenzyl, 3-bromobenzyl, 4-fluorobenzyl,
perfluoroethyl, 2-(trimethylsilyl)ethyl, (trimethylsilyl)methyl,
3-(trimethylsilyl)propyl, and mixtures thereof.
[0044] Suitable thio- and selenolates include: 1-thioglycerol,
phenylthio, ethylthio, methylthio, n-propylthio, i-propylthio,
n-butylthio, i-butylthio, t-butylthio, n-pentylthio, n-hexylthio,
n-heptylthio, n-octylthio, n-nonylthio, n-decylthio, n-dodecylthio,
2-methoxyethylthio, 2-ethoxyethylthio, 1,2-ethanedithiolate,
2-pyridinethiolate, 3,5-bis(trifluoromethyl)benzenethiolate,
toluene-3,4-dithiolate, 1,2-benzenedithiolate,
2-dimethylaminoethanethiolate, 2-diethylaminoethanethiolate,
2-propene-1-thiolate, 2-hydroxythiolate, 3-hydroxythiolate,
methyl-3-mercaptopropionate anion, cyclopentanethiolate,
2-(2-methoxyethoxy)ethanethiolate,
2-(trimethylsilyl)ethanethiolate, pentafluorophenylthiolate,
3,5-dichlorobenzenethiolate, phenylthiolate, cyclohexanethiolate,
4-chlorobenzenemethanethiolate, 4-fluorobenzenemethanethiolate,
2-methoxybenzenethiolate, 4-methoxybenzenethiolate, benzylthiolate,
3-methylbenzylthiolate, 3-ethoxybenzenethiolate,
2,5-dimethoxybenzenethiolate, 2-phenylethanethiolate,
4-t-butylbenzenethiolate, 4-t-butylbenzylthiolate,
phenylselenolate, methylselenolate, ethylselenolate,
n-propylselenolate, i-propylselenolate, n-butylselenolate,
i-butylselenolate, t-butylselenolate, pentylselenolate,
hexylselenolate, octylselenolate, benzylselenolate, and mixtures
thereof.
[0045] Suitable thio-, seleno-, and dithiocarboxylates include:
thioacetate, thiobenzoate, selenobenzoate, dithiobenzoate, and
mixtures thereof.
[0046] Suitable dithio-, diseleno-, and thioselenocarbamates
include: dimethyldithiocarbamate, diethyldithiocarbamate,
dipropyldithiocarbamate, dibutyldithiocarbamate,
bis(hydroxyethyl)dithiocarbamate, dibenzyldithiocarbamate,
dimethyldiselenocarbamate, diethyldiselenocarbamate,
dipropyldiselenocarbamate, dibutyldiselenocarbamate,
dibenzyldiselenocarbamate, and mixtures thereof.
[0047] Suitable dithioxanthogenates include: methylxanthogenate,
ethylxanthogenate, i-propylxanthogenate, and mixtures thereof.
[0048] For the chalcogen compounds, suitable R.sup.1S-- and
R.sup.1Se-- of R.sup.1S--Z and R.sup.1Se--Z are selected from the
above list of suitable thio- and selenolates.
[0049] For the chalcogen compounds, suitable R.sup.1S--SR.sup.1,
R.sup.1Se--SeR.sup.1 include: dimethyldisulfide,
2,2'-dipyridyldisulfide, di(2-thienyl)disulfide,
bis(2-hydroxyethyl)disulfide, bis(2-methyl-3-furyl)disulfide,
bis(6-hydroxy-2-naphthyl)disulfide, diethyldisulfide,
methylpropyldisulfide, diallyldisulfide, dipropyldisulfide,
isopropyldisulfide, dibutyldisulfide, sec-butyldisulfide,
bis(4-methoxyphenyl)disulfide, dibenzyldisulfide, p-tolyldisulfide,
phenylacetyldisulfide, tetramethylthiuram disulfide,
tetraethylthiuram disulfide, tetrapropylthiuram disulfide,
tetrabutylthiuram disulfide, methylxanthic disulfide, ethylxanthic
disulfide, i-propylxanthic disulfide, dibenzyldiselenide,
dimethyldiselenide, diphenyldiselenide, and mixtures thereof.
[0050] For the chalcogen compounds, suitable R.sup.2C(S)S--Z,
R.sup.2C(Se)Se--Z, R.sup.2C(Se)S--Z, R.sup.1C(O)S--Z, and
R.sup.1C(O)Se--Z are selected from the above lists of suitable
thio-, seleno-, and dithiocarboxylates; suitable dithio-,
diseleno-, and thioselenocarbamates; and suitable
dithioxanthogenates.
[0051] Suitable NR.sup.4.sub.4 include: Et.sub.2NH.sub.2,
Et.sub.4N, Et.sub.3NH, EtNH.sub.3, NH.sub.4, Me.sub.2NH.sub.2,
Me.sub.4N, Me.sub.3NH, MeNH.sub.3, Pr.sub.2NH.sub.2, Pr.sub.4N,
Pr.sub.3NH, PrNH.sub.3, Bu.sub.3NH, Me.sub.2PrNH, (i-Pr).sub.3NH,
and mixtures thereof.
[0052] Suitable SiR.sup.5.sub.3 include: SiMe.sub.3, SiEt.sub.3,
SiPr.sub.3, SiBu.sub.3, Si(i-Pr).sub.3, SiEtMe.sub.2,
SiMe.sub.2(i-Pr), Si(t-Bu)Me.sub.2, Si(cyclohexyl)Me.sub.2, and
mixtures thereof.
[0053] Many of these ligands and chalcogen compounds are
commercially available or readily synthesized by the addition of an
amine, alcohol, or alkyl nucleophile to CS.sub.2 or CSe.sub.2 or
CSSe.
[0054] Components and by-products of the ink may be liquids at room
temperature or at the heating temperature and coating temperature.
In such cases, the ink need not comprise a solvent. In some
embodiments, a chalcogen compound is present and is a liquid at
room temperature. In other embodiments, the tin source is a liquid
at room temperature. In yet other embodiments, a chalcogen compound
is present and is a liquid at room temperature and the tin source
is a liquid at room temperature.
[0055] In some embodiments, a solvent is present and the boiling
point of the solvent is greater than about 100.degree. C. or
110.degree. C. or 120.degree. C. or 130.degree. C. or 140.degree.
C. or 150.degree. C. or 160.degree. C. or 170.degree. C. or
180.degree. C. or 190.degree. C. at atmospheric pressure. In some
embodiments, the process is conducted at atmospheric pressure.
Suitable solvents include: aromatics, heteroaromatics, nitriles,
amides, alcohols, pyrrolidinones, amines, and mixtures thereof.
Suitable heteroaromatics include pyridine and substituted
pyridines. Suitable amines include compounds of the form
R.sup.6NH.sub.2, wherein each R.sup.6 is independently selected
from the group consisting of: O-, N-, S-, and Se-substituted
hydrocarbyl. In some embodiments, the solvent comprises an
amino-substituted pyridine. In some embodiments, the solvent
comprises about 95 to about 5 wt %, or 90 to 10 wt %, or 80 to 20
wt %, or 70 to 30 wt %, or 60 to 40 wt %, based upon the total
weight of the ink.
[0056] Suitable aromatic solvents include: benzene, toluene,
ethylbenzene, chlorobenzene, o-xylene, m-xylene, p-xylene,
mesitylene, i-propylbenzene, 1-chlorobenzene, 2-chlorotoluene,
3-chlorotoluene, 4-chlorotoluene, t-butylbenzene, n-butylbenzene,
i-butylbenzene, s-butylbenzene, 1,2-dichlorobenzene,
1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,3-diisopropylbenzene,
1,4-diisopropylbenzene, 1,2-difluorobenzene,
1,2,4-trichlorobenzene, 3-methylanisole, 3-chloroanisole,
3-phenoxytoluene, diphenylether, and mixtures thereof.
[0057] Suitable heteroaromatic solvents include: pyridine,
2-picoline, 3-picoline, 3,5-lutidine, 4-t-butylpyridine,
2-aminopyridine, 3-aminopyridine, diethylnicotinamide,
3-cyanopyridine, 3-fluoropyridine, 3-chloropyridine,
2,3-dichloropyridine, 2,5-dichloropyridine,
5,6,7,8-tetrahydroisoquinoline, 6-chloro-2-picoline,
2-methoxypyridine, 3-(aminomethyl)pyridine, 2-amino-3-picoline,
2-amino-6-picoline, 2-amino-2-chloropyridine, 2,3-diaminopyridine,
3,4-diaminopyridine, 2-(methylamino)pyridine,
2-dimethylaminopyridine, 2-(aminomethyl)pyridine,
2-(2-aminoethyl)pyridine, 2-methoxypyridine, 2-butoxypyridine, and
mixtures thereof.
[0058] Suitable nitrile solvents include: acetonitrile,
3-ethoxypropionitrile, 2,2-diethoxypropionitrile,
3,3-diethoxypropionitrile, diethoxyacetonitrile,
3,3-dimethoxypropionitrile, 3-cyanopropionaldehyde dimethylacetal,
dimethylcyanamide, diethylcyanamide, diisopropylcyanamide,
1-pyrrolidinecarbonitrile, 1-piperidinecarbonitrile,
4-morpholinecarbonitrile, methylaminoacetonitrile,
butylaminoacetonitrile, dimethylaminoacetonitrile,
diethylaminoacetonitrile, N-methyl-beta-alaninenitrile,
3,3'-iminopropionitrile, 3-(dimethylamino)propionitrile,
1-piperidinepropionitrile, 1-pyrrolidinebutyronitrile,
propionitrile, butyronitrile, valeronitrile, isovaleronitrile,
3-methoxypropionitrile, 3-cyanopyridine,
4-amino-2-chlorobenzonitrile, 4-acetylbenzonitrile, and mixtures
thereof.
[0059] Suitable amide solvents include: N,N-diethylnicotinamide,
N-methylnicotinamide, N,N-dimethylformamide, N,N-diethylformamide,
N,N-diisopropylformamide, N,N-dibutylformamide,
N,N-dimethylacetamide, N,N-diethylacetamide,
N,N-diisopropylacetamide, N,N-dimethylpropionamide,
N,N-diethylpropionamide, N,N,2-trimethylpropionamide, acetamide,
propionamide, isobutyramide, trimethylacetamide, nipecotamide,
N,N-diethylnipecotamide, and mixtures thereof.
[0060] Suitable alcohol solvents include: methoxyethoxyethanol,
methanol, ethanol, isopropanol, 1-butanol, 2-pentanol, 2-hexanol,
2-octanol, 2-nonanol, 2-decanol, 2-dodecanol, ethylene glycol,
1,3-propanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,
1,7-heptanediol, 1,8-octanediol, cyclopentanol, cyclohexanol,
cyclopentanemethanol, 3-cyclopentyl-1-propanol,
1-methylcyclopentanol, 3-methylcyclopentanol, 1,3-cyclopentanediol,
2-cyclohexylethanol, 1-cyclohexylethanol, 2,3-dimethylcyclohexanol,
1,3-cyclohexanediol, 1,4-cyclohexanediol, cycloheptanol,
cyclooctanol, 1,5-decalindiol, 2,2-dichloroethanol,
2,2,2-trifluoroethanol, 2-methoxyethanol, 2-ethoxyethanol,
2-propoxyethanol, 2-butoxyethanol, 3-ethoxy-1-propanol,
propyleneglycol propyl ether, 3-methoxy-1-butanol,
3-methoxy-3-methyl-1-butanol, 3-ethoxy-1,2-propanediol,
di(ethyleneglycol) ethylether, diethylene glycol,
2,4-dimethylphenol, and mixtures thereof.
[0061] Suitable pyrrolidinone solvents include:
N-methyl-2-pyrrolidinone, 5-methyl-2-pyrrolidinone,
3-methyl-2-pyrrolidinone, 2-pyrrolidinone,
1,5-dimethyl-2-pyrrolidinone, 1-ethyl-2-pyrrolidinone,
1-(2-hydroxyethyl)-2-pyrrolidinone, 5-methoxy-2-pyrrolidinone,
1-(3-aminopropyl)-2-pyrrolidinone, and mixtures thereof.
[0062] Suitable amine solvents include: butylamine, hexylamine,
octylamine, 3-methoxypropylamine, 2-methylbutylamine, isoamylamine,
1,2-dimethylpropylamine, hydrazine, ethylenediamine,
1,3-diaminopropane, 1,2-diaminopropane,
1,2-diamino-2-methylpropane, 1,3-diaminopentane,
1,1-dimethylhydrazine, N-ethylmethylamine, diethylamine,
N-methylpropylamine, diisopropylamine, dibutylamine, triethylamine,
N-methylethylenediamine, N-ethylethylenediamine,
N-propylethylenediamine, N-isopropylethylenediamine,
N,N'-dimethylethylenediamine, N,N-dimethylethylenediamine,
N,N'-diethylethylenediamine, N,N-diethylethylenediamine,
N,N-diisopropylethylenediamine, N,N-dibutylethylenediamine,
N,N,N'-trimethylethylenediamine, 3-dimethylaminopropylamine,
3-diethylaminopropylamine, diethylenetriamine, cyclohexylamine,
bis(2-methoxyethyl)amine, aminoacetaldehyde diethyl acetal,
methylaminoacetaldehyde dimethyl acetal, N,N-dimethylacetamide
dimethyl acetal, dimethylaminoacetaldehyde diethyl acetal,
diethylaminoacetaldehyde diethyl acetal, 4-aminobutyraldehyde
diethyl acetal, 2-methylaminomethyl-1,3-dioxolane, ethanolamine,
3-amino-1-propanol, 2-hydroxyethylhydrazine,
N,N-diethylhydroxylamine, 4-amino-1-butanol,
2-(2-aminoethoxy)ethanol, 2-(methylamino)ethanol,
2-(ethylamino)ethanol, 2-(propylamino)ethanol, diethanolamine,
diisopropanolamine, N,N-dimethylethanolamine,
N,N-diethylethanolamine, 2-(dibutylamino)ethanol,
3-dimethylamino-1-propanol, 3-diethylamino-1-propanol,
1-dimethylamino-2-propanol, 1-diethylamino-2-propanol,
N-methyldiethanolamine, N-ethyldiethanolamine,
3-amino-1,2-propanediol, and mixtures thereof.
[0063] In some embodiments, the ink comprises up to about 10 wt %
or 7.5 wt % or 5 wt % or 2.5 wt % or 1 wt % of one or more
additives selected from the group consisting of: dispersants,
surfactants, polymers, binders, ligands, capping agents, defoamers,
thickening agents, corrosion inhibitors, plasticizers, and dopants.
Suitable dopants include sodium and alkali-containing compounds
selected from the group consisting of: alkali compounds comprising
nitrogen-, oxygen-, carbon-, sulfur-, or selenium-based organic
ligands, alkali sulfides, alkali selenides, and mixtures thereof.
In other embodiments, the dopant comprises an alkali-containing
compound selected from the group consisting of: alkali-compounds
comprising amidos; alkoxides; acetylacetonates; carboxylates;
hydrocarbyls; O-, N-, S-, halogen-, and
tri(hydrocarbyl)silyl-substituted hydrocarbyls; thio- and
selenolates; thio-, seleno-, and dithiocarboxylates; dithio-,
diseleno-, and thioselenocarbamates; and dithioxanthogenates.
[0064] In some embodiments, the ink comprises one or more binders
or surfactants selected from the group consisting of: decomposable
binders; decomposable surfactants; cleavable surfactants;
surfactants with a boiling point less than about 250.degree. C.;
and mixtures thereof. Suitable decomposable binders include: homo-
and co-polymers of polyethers; homo- and co-polymers of
polylactides; homo- and co-polymers of polycarbonates; homo- and
co-polymers of poly[3-hydroxybutyric acid]; homo- and co-polymers
of polymethacrylates; and mixtures thereof.
[0065] In some embodiments, the molar ratio of copper to tin is
about 2:1 in the ink. In other embodiments, zinc is present in the
ink and the molar ratio of copper to zinc to tin is about 2:1:1 in
the ink.
[0066] Preparing the ink typically comprises mixing the components
(i)-(v) by any conventional method. If one or more of the copper-,
tin-, zinc-, or chalcogen sources is a liquid at room temperature
or at the processing temperatures, the use of a separate solvent is
optional. Otherwise, a solvent is used. In some embodiments, the
ink is a solution; in other embodiments, the ink is a suspension or
dispersion. Typically, the preparation is conducted under an inert
atmosphere, taking precautions to protect the reaction mixtures
from air and light.
[0067] In some embodiments, the ink is prepared at low
temperatures, e.g., when low boiling point and/or highly reactive
reagents such as CS.sub.2 and ZnEt.sub.2 are utilized. In such
cases, the ink is typically stirred for 48 hours or longer at room
temperature prior to heat processing. In some embodiments, the ink
is prepared at about 20-100.degree. C., e.g., when the reagents are
solids or have high boiling points and/or when one or more of the
solvents is a solid at room temperature, e.g., 2-aminopyridine or
3-aminopyridine. In some embodiments, all of the ink components are
added together at room temperature. In some embodiments, elemental
chalcogen is added last, following the mixing of all the other
components for about half an hour at room temperature. In some
embodiments, the components are added consecutively. For example,
all of the reagents except copper can be mixed and heated at about
100.degree. C. prior to addition of the copper source, or all of
the reagents except tin can be mixed and heated at about
100.degree. C. prior to the addition of the tin source.
[0068] In some embodiments two or more inks are prepared, with each
ink comprising a complete set of reagents, e.g., each ink comprises
at least a zinc source, a copper source, and a tin source for inks
useful for forming CZTS-Se. The two or more inks can then be
combined following mixing or following heat-processing. This method
is especially useful for controlling stoichiometry and obtaining
CTS-Se or CZTS-Se of high purity, as prior to mixing, separate
films from each ink can be coated, annealed, and analyzed by XRD.
The XRD results can guide the selection of the type and amount of
each ink to be combined. For example, an ink yielding an annealed
film of CZTS-Se with traces of copper sulfide and zinc sulfide can
be combined with an ink yielding an annealed film of CZTS-Se with
traces of tin sulfide, to form an ink that yields an annealed film
comprising only CZTS-Se, as determined by XRD.
[0069] In some embodiments, the ink has been heat-processed at a
temperature of greater than about 100.degree. C. or 110.degree. C.
or 120.degree. C. or 130.degree. C. or 140.degree. C. or 150
C..degree. or 160.degree. C. or 170.degree. C. or 180.degree. C. or
190.degree. C. before coating on the substrate. Suitable heating
methods include conventional heating and microwave heating. In some
embodiments, it has been found that this heat-processing step aids
the formation of CZTS-Se, with XAS analysis of films formed from
heat-processed inks indicating the presence of kesterite upon
heating the films at heating temperatures as low as 120.degree. C.
This optional heat-processing step is typically carried out under
an inert atmosphere. The ink produced at this stage can be stored
for extended periods (e.g., a couple of months) without any
noticeable decrease in efficacy.
Coated Substrate
[0070] The substrate can be rigid or flexible. In one embodiment,
the substrate comprises in layered sequence: (i) a base film; and
(ii) optionally, an electrically conductive coating. The base film
is selected from the group consisting of: glass, metals, and
polymeric films. Suitable electrically conductive coatings include:
metal conductors, transparent conducting oxides, and organic
conductors. Of particular interest are substrates of
molybdenum-coated soda-lime glass, molybdenum-coated polyimide
films, or molybdenum-coated polyimide films with a thin layer of a
sodium compound (e.g., NaF, Na.sub.2S, or Na.sub.2Se). In one
embodiment, the substrate comprises material selected from the
group consisting of metal foils, plastics, polymers, metalized
plastics, glass, solar glass, low-iron glass, green glass,
soda-lime glass, steel, stainless steel, aluminum, ceramics, metal
plates, metalized ceramic plates, and metalized polymer plates.
[0071] The ink is disposed on a substrate to provide a coated
substrate by any of a variety of solution-based coating and
printing techniques, including spin-coating, spray-coating,
dip-coating, rod-coating, drop-cast coating, roller coating,
slot-die coating, draw-down coating, ink-jet printing, contact
printing, gravure printing, flexographic printing, and screen
printing. The coating can be dried by evaporation, by applying
vacuum, by heating, or by combinations thereof. In some
embodiments, the substrate and disposed ink are heated at a
temperature from 80-350.degree. C., or 100-300.degree. C., or
120-250.degree. C., or 150-190.degree. C. to remove at least a
portion of the solvent, if present, and by-products derived from
the ligands and chalcogen source. The drying step can be a
separate, distinct step, or can occur as the substrate and
precursor ink are heated in an annealing step. In some embodiments,
it has been found that CZTS-Se is formed during this heating step,
with XAS analysis indicating the presence of kesterite. In some
embodiments, heated layers comprising CTS-Se or CZTS-Se are formed
at heating temperatures as low as 120.degree. C.
[0072] In some embodiments, the heated layers comprise CZTS-Se
wherein the Cu/Zn ratio of kesterite is approximately 2/1, falling
in the range of about 1.6.ltoreq.Cu/Zn.ltoreq.3.1. In some
embodiments, the heated layers comprise CZTS-Se wherein the Cu/Zn
ratio of the kesterite is greater than about 3.1.
[0073] In other embodiments, the heated layers comprise CZTS-Se
wherein the Cu/Zn ratio of the kesterite is less than about 1.6. In
yet other embodiments, the heated layers comprise CZTS-Se wherein
the coherent domain size of the kesterite is 2-30 nm.
[0074] In some embodiments, the coated substrate comprises one or
more copper compounds selected from the group consisting of binary
copper chalcogenides, binary copper oxides, and CTS-Se, and one or
more tin compounds selected from the group consisting of binary tin
chalcogenides, binary tin oxides, and CTS-Se, wherein the
chalcogenides comprise sulfides, selenides or mixtures thereof. In
some embodiments, the molar ratio of copper to tin in the coated
substrate is about 2:1. In another embodiment, the coated substrate
further comprises one or more zinc compounds selected from the
group consisting of binary zinc chalcogenides, ZnO, and CZTS-Se,
wherein the chalcogenides comprise sulfides, selenides or mixtures
thereof. In some embodiments, the molar ratio of copper to zinc to
tin is about 2:1:1. In other embodiments, the molar ratio of copper
to (zinc plus tin) is less than one, and the molar ratio of zinc to
tin is greater than one.
Annealing
[0075] In some embodiments, the process further comprises an
annealing step in which the coated substrate is heated at about
350-800.degree. C., or 400-650.degree. C., or 450-600.degree. C.,
or 450-525.degree. C. Typically, the annealing comprises one or
more of thermal processing, rapid thermal processing (RTP), rapid
thermal annealing (RTA), pulsed thermal processing (PTP), laser
beam exposure, heating via IR lamps, electron beam exposure, pulsed
electron beam processing, and heating via microwave irradiation.
Herein, RTP refers to a technology that can be used in place of
standard furnaces and involves single wafer processing, fast
heating and cooling rates, thermal nonequilibrium and controlled
ambient. RTA is a subset of RTP, which consists of unique heat
treatments for different effects, including activation of dopants,
changing substrate interfaces, densifying and changing states of
films, repairing damage, and moving dopants. Rapid thermal anneals
are performed using either lamp-based heating, a hot chuck, or a
hot plate. PTP involves thermally annealing structures at extremely
high power densities for periods of very short duration, resulting,
for example, in defect reduction. Similarly, pulsed electron beam
processing uses pulsed high energy electron beam with short pulse
duration. Pulsed processing is useful for processing thin films on
temperature-sensitive substrates. The duration of the pulse is so
short that little energy is transferred to the substrate, leaving
the substrate undamaged.
[0076] The annealing step can be carried out under an inert
atmosphere, provided that the ratio of the total number of moles of
the chalcogen compound, the sulfur- and selenium-based organic
ligands, and the copper-, tin- and zinc-sulfides and selenides to
the total number of moles of the copper, tin and zinc complexes is
at least about 1. In some embodiments, the annealing step is
carried out in an atmosphere comprising an inert gas and reactive
component selected from the group consisting of: selenium vapor,
sulfur vapor, hydrogen, hydrogen sulfide, hydrogen selenide, and
mixtures thereof. In some embodiments, at least a portion of the
chalcogen can be exchanged (e.g., S can be replaced by Se) by
conducting the annealing step in the presence of selenium vapor or
hydrogen selenide. In some embodiments, annealings are conducted
under a combination of atmospheres, e.g., a first annealing is
carried out under an inert atmosphere and a second annealing is
carried out in an atmosphere comprising an inert gas and a reactive
component as described above.
[0077] It has been found that CTS-Se and/or CZTS-Se can be formed
in high yield during the annealing step, as determined by XRD or
XAS. In some embodiments, annealed films consist essentially of
CTS-Se or CZTS-Se, according to XRD analysis. In some embodiments,
the coherent domain size of the CTS-Se or CZTS-Se is greater than
about 30 nm, or greater than 40, 50, 60, 70, 80, 90 or 100 nm, as
determined by XRD. In some embodiments, the molar ratio of copper
to tin is about 2:1 in the annealed film. In some embodiments, the
molar ratio of copper to zinc to tin is about 2:1:1 in the annealed
film. In other embodiments, the molar ratio of copper to (zinc plus
tin) is less than one, and a molar ratio of zinc to tin is greater
than one in the annealed film comprising CZTS-Se.
Film Thickness and Fine-Tuning the Film Composition
[0078] By varying the ink concentration and/or coating technique
and temperature, films of varying thickness can be coated in a
single-coating step. The coating thickness can also be increased by
repeating the coating and drying steps. The annealed film typically
has an increased density and/or reduced thickness versus that of
the wet precursor layer. In some embodiments, the film thicknesses
of the dried and annealed coatings are 0.1-200 microns, or 0.1-100
microns, or 0.1-50 microns, or 0.1-25 microns, or 0.1-10 microns,
or 0.5-5 microns.
[0079] In some embodiments, the coating thickness can be increased
by repeating the coating and drying steps. These multiple coatings
can be conducted with the same ink formulation or with different
ink formulations. As described above, wherein two or more inks were
mixed, the coating of multiple layers with different inks can be
used to fine-tune stoichiometry and purity of the CTS-Se and
CZTS-Se films by fine tuning Cu to Sn and Cu to Zn to Sn
ratios.
[0080] Application of multiple coatings and/or washing the film can
also serve to reduce carbon-based impurities in the films. For
example, after an initial coating, the coated substrate can be
dried and then a second coating can be applied and coated by
spin-coating. The spin-coating step can wash organics out of the
first coating. Alternatively, the coated film can be soaked in a
solvent and then the solvent removed by spin-coating. Suitable
solvents for washing include hydrocarbyls. Alternatively, binary
sulfides and other impurities can be removed by etching using
techniques known in the art, such as those used for CIGS films.
Preparation of Devices, Including Thin-Film Photovoltaic Cells
[0081] Various electrical elements can be formed, at least in part,
by the use of the inks and processes described herein. One aspect
of this invention provides a process for manufacturing thin-film
photovoltaic cells comprising CZTS-Se.
[0082] A typical photovoltaic cell includes a substrate, a back
contact layer (e.g., molybdenum), an absorber layer (also referred
to as the first semiconductor layer), a buffer layer (also referred
to as the second semiconductor layer), and a top contact layer. The
photovoltaic cell can also include an electrical contact of
electrode pad on the top contact layer, and an anti-reflective (AR)
coating on the front (light-facing) surface of the substrate to
enhance the transmission of light into the semiconductor layer.
[0083] In one embodiment, the process provides a electronic device
and comprises depositing one or more layers in layered sequence
onto the annealed coating of the substrate. The layers can be
selected from the group consisting of: conductors, semiconductors,
and dielectrics. In another embodiment, the process provides a
photovoltaic device and comprises depositing the following layers
in layered sequence onto the annealed coating of the substrate
having an electrically conductive layer present: (i) a buffer
layer; (ii) a transparent top contact layer, and (iii) optionally,
an antireflective layer. In yet another embodiment, the process
provides a photovoltaic device and comprises disposing one or more
layers selected from the group consisting of buffer layers, top
contact layers, electrode pads, and antireflective layers onto the
annealed CZTS-Se film. In some embodiments, construction and
materials for these layers are analogous to those of a CIGS
photovoltaic cell.
[0084] Suitable substrate materials for the photovoltaic cell
substrate are as described above and below. The photovoltaic cell
substrate can also comprise an interfacial layer to promote
adhesion between the substrate material and metal layer. Suitable
interfacial layers can comprise metals (e.g., V, W, Cr), glass, or
compounds of nitrides, oxides, and/or carbides. In one embodiment,
interfacial layers are derived from adhesion promoters. Suitable
adhesion promoters comprise siloxy-substituted sulfur compounds,
including thiols, sulfides, disulfides, tetrasulfides, and
polysulfides. In some embodiments, adhesion promoters are selected
from the group consisting of:
bis[m-(2-triethoxysilylethyl)tolyl]polysulfide,
bis[3-triethoxysilyl]propyl]disulfide,
bis[3-triethoxysilyl]propyl]tetrasulfide, and
2,2-dimethoxy-1-thia-2-silacyclopentane.
[0085] Typical photovoltaic cell substrates are glass or plastic,
coated on one side with a conductive material, e.g., a metal. In
one embodiment, the substrate is molybdenum-coated glass.
Depositing and annealing the CZTS-Se layer on the photovoltaic cell
substrate to form an absorber layer can be carried out as described
above.
[0086] Useful analytical techniques for characterizing the
composition of the CTS-Se and CZTS-Se layers of the present
invention include XRD (X-Ray Diffraction) and XAS.
EXAMPLES
General
[0087] Materials. All reagents were purchased from Aldrich
(Milwaukee, Wis.), Alfa Aesar (Ward Hill, Mass.), TCI (Portland,
Oreg.), or Gelest (Morrisville, Pa.). Solid reagents were used
without further purification. Liquid reagents that were not
packaged under an inert atmosphere were degassed by bubbling argon
through the liquid for 1 hr. Anhydrous solvents were used for the
preparation of all formulations and for all cleaning procedures
carried out within the drybox. Solvents were either purchased as
anhydrous from Aldrich or Alfa Aesar, or purified by standard
methods (e.g., Pangborn, A. G., et. al. Organometallics, 1996, 15,
1518-1520) and then stored in the drybox over activated molecular
sieves.
[0088] Formulation and Coating Preparations. Substrates (SLG
slides) were cleaned sequentially with aqua regia, Millipore.RTM.
water and isopropanol, dried at 110.degree. C., and coated on the
non-float surface of the SLG substrate. All formulations and
coatings were prepared in a nitrogen-purged drybox. Vials
containing formulations were heated and stirred on a magnetic
hotplate/stirrer. Coatings were dried in the drybox.
[0089] Slide Preparation: In some instances, SLG slides were
treated with 3-(mercaptopropyl)-trimethoxysilane. .about.100 mL of
3-(mercaptopropyl)-trimethoxysilane and .about.1 mL of
2-(2-methoxyethoxy)acetic acid were mixed in a glass bottle in the
drybox. SLG slides and Mo-patterned SLG slides were soaked in this
solution for more than 24 hr. Next, the slides were soaked in
methylene chloride for .about.0.5 hr, rinsed with MeOH, and then
dried with a wipe.
[0090] Annealing of Coated Substrates in a Tube Furnace. Annealings
were carried out either under a nitrogen, nitrogen/sulfur, or
nitrogen/selenium atmosphere. Annealings under a nitrogen
atmosphere were carried out in either a single-zone Lindberg/Blue
(Ashville, N.C.) tube furnace equipped with an external temperature
controller and a one-inch quartz tube, or in a Lindberg/Blue
three-zone tube furnace (Model STF55346C) equipped with a
three-inch quartz tube. A gas inlet and outlet were located at
opposite ends of the tube, and the tube was purged with nitrogen
while heating and cooling. The coated substrates were placed on
quartz plates inside of the tube.
[0091] Annealings under a nitrogen/sulfur atmosphere were carried
out in the single-zone furnace in the one-inch tube. A 3-inch long
ceramic boat was loaded with 2.5 g of elemental sulfur and placed
near the nitrogen inlet, outside of the direct heating zone. The
coated substrates were placed on quartz plates inside the tube. In
the following Examples, annealings were carried out under a
nitrogen/sulfur atmosphere, unless noted otherwise.
[0092] Prior to selenization, samples were first annealed under a
nitrogen-purge in the three-inch tube in the three-zone furnace.
Then, the samples were placed in a 5''.times.1.4''.times.1''
graphite box with 1/8'' walls that was equipped with a lid with a
lip and a 1 mm hole in the center. Each graphite box was equipped
with two ceramic boats (0.984''.times.0.591''.times.0.197'') at
each end, containing 0.1 g of selenium. The graphite box was then
place in a two-inch tube, with up to two graphite boxes per tube.
House vacuum was applied to the tube for 10-15 min, followed by a
nitrogen purge for 10-15 min. This process was carried out three
times. The tube containing the graphite boxes was then heated in
the single-zone furnace with both heating and cooling carried out
under a nitrogen purge.
[0093] Rapid Thermal Annealing (RTA). A MILA-5000 Infrared Lamp
Heating System by ULVAC-RICO Inc. (Methuen, Mass.) was used for
heating and the system was cooled using a Polyscience (Niles, Ill.)
recirculating bath held at 15.degree. C. Samples were heated under
nitrogen purge as follows: 20.degree. C. for 10 min; ramp to
400.degree. C. in 1 min; hold at 400.degree. C. for 2 min; cool to
20.degree. C. during .about.30 min.
Details of the Procedures Used for Device Manufacture
[0094] Mo-Sputtered Substrates. Substrates for photovoltaic devices
were prepared by coating a SLG substrate with a 500 nm layer of
patterned molybdenum using a Denton Sputtering System. Deposition
conditions were: 150 watts of DC Power, 20 sccm Ar, and 5 mT
pressure. Cadmium Sulfide Deposition. 12.5 mg CdSO.sub.4
(anhydrous) was dissolved in a mixture of nanopure water (34.95 mL)
and 28% NH.sub.4OH (4.05 mL). Then a 1 mL aqueous solution of 22.8
mg thiourea was added rapidly to form the bath solution.
Immediately upon mixing, the bath solution was poured into a
double-walled beaker (with 70.degree. C. water circulating between
the walls), which contained the samples to be coated. The solution
was continuously stirred with a magnetic stir bar. After 23
minutes, the samples were taken out, rinsed with and then soaked in
nanopure water for an hour. The samples were dried under a nitrogen
stream and then annealed under a nitrogen atmosphere at 200.degree.
C. for 2 minutes. Insulating ZnO and AZO Deposition. A transparent
conductor was sputtered on top of the CdS with the following
structure: 50 nm of insulating ZnO (150 W RF, 5 mTorr, 20 sccm)
followed by 500 nm of Al-doped ZnO using a 2% Al.sub.2O.sub.3, 98%
ZnO target (75 or 150 W RF, 10 mTorr, 20 sccm). ITO Transparent
Conductor Deposition. A transparent conductor was sputtered on top
of the CdS with the following structure: 50 nm of insulating ZnO
[100 W RF, 20 mTorr (19.9 mTorr Ar+0.1 mTorr O.sub.2)] followed by
250 nm of ITO [100 W RF, 12 mTorr (12 mTorr Ar+5.times.10.sup.-6
Torr O.sub.2)]. The sheet resistivity of the resulting ITO layer is
around 30 ohms per square. Deposition of Silver Lines. Silver was
deposited at 150 WDC, SmTorr, 20 sccm Ar, with a target thickness
of 750 nm.
Details of X-ray, IV, EQE, and OBIC Analysis.
[0095] XAS Analysis. XANES spectroscopy at the Cu, Zn and Sn
K-edges were carried out at the Advanced Photon Source at the
Argonne National Laboratory. Data were collected in fluorescence
geometry at beamline 5BMD, DND-CAT. Thin film samples were
presented to the incident x-ray beam as made. An Oxford
spectroscopy-grade ion chamber was used to determine the X-ray
incident intensity (I.sub.0). The I.sub.0 detector was filled with
570 Torr of N.sub.2 and 20 Torr of Ar. The fluorescence detector
was a Lytle Cell filled with Xe installed perpendicular to the beam
propagation direction. Data were collected from 8879 eV to 9954 eV
for the Cu edge. The high final energy was used in order to capture
a portion of the Zn edge in the same data set, to allow edge step
ratio determination as an estimate of Cu:Zn ratio in the film. The
Zn edge data were collected over the range 9557 eV to 10,404 eV. Sn
edge data covered the range of 29,000 eV to 29,750 eV. The data
energy scales were calibrated based on data from metal reference
foils collected prior to sample data collection. A second order
background was subtracted and the spectra were normalized. Data
from several Cu, Zn and Sn sulfide and oxide standards
(Cu.sub.2ZnSnS.sub.4, Cu.sub.2SnS.sub.3, CuS, Cu.sub.2S, CuO,
Cu.sub.2O, ZnS, ZnO, SnS, SnO and SnO.sub.2) were obtained under
the same conditions. Non-linear least squares fitting of a linear
combination of the appropriate standards to the spectra obtained
from the samples yielded the phase distribution for each element.
XRD Analysis. Powder X-ray diffraction was used for the
identification of crystalline phases. Data were obtained with a
Philips X'PERT automated powder diffractometer, Model 3040. The
diffractometer was equipped with automatic variable anti-scatter
and divergence slits, X'Celerator RTMS detector, and Ni filter. The
radiation was CuK(alpha) (45 kV, 40 mA). Data were collected at
room temperature from 4 to 120.degree.. 2-theta; using a continuous
scan with an equivalent step size of 0.02.degree.; and a count time
of from 80 sec to 240 sec per step in theta-theta geometry. Thin
film samples were presented to the X-ray beam as made. MDI/Jade
software version 9.1 was used with the International Committee for
Diffraction Data database PDF4+ 2008 for phase identification and
data analysis. IV Analysis. Current (I) versus voltage (V)
measurements were performed on the samples using two Agilent 5281B
precision medium power SMUs in a E5270B mainframe in a four point
probe configuration. Samples were illuminated with an Oriel 81150
solar simulator under 1 sun AM 1.5G. EQE Analysis. External Quantum
Efficiency (EQE) determinations were carried out as described in
ASTM Standard E1021-06 ("Standard Test Method for Spectral
Responsivity Measurements of Photovoltaic Devices"). The reference
detector in the apparatus was a pyroelectric radiometer (Laser
Probe (Utica, N.Y.), LaserProbe Model RkP-575 controlled by a
LaserProbe Model Rm-6600 Universal Radiometer). The excitation
light source was a xenon arc lamp with wavelength selection
provided by a monochrometer in conjunction with order sorting
filters. Optical bias was provided by a broad band tungsten light
source focused to a spot slightly larger than the monochromatic
probe beam. Measurement spot sizes were approximately 1 mm.times.2
mm. OBIC Analysis. Optical beam induced current measurements were
determined with a purpose-constructed apparatus employing a focused
monochromatic laser as the excitation source. The excitation beam
was focused to a spot .about.100 microns in diameter. The
excitation spot was rastered over the surface of the test sample
while simultaneously measuring photocurrent so as to build a map of
photocurrent vs position for the sample. The resulting photocurrent
map characterizes the photoresponse of the device vs. position. The
apparatus can operate at various wavelengths via selection of the
excitation laser. Typically, 440, 532 or 633 nm excitation sources
were employed.
Example 1
##STR00001##
[0097] Zinc diethyldithiocarbamate (0.5919 g, 1.635 mmol),
copper(II) dimethyldithiocarbamate (0.9930 g, 3.267 mmol), and
di-n-butyltinsulfide (0.4506 g, 1.701 mmol) were placed in a 40 mL
amber vial equipped with a stir bar. 4-t-Butylpyridine (4.4144 g)
was added, and the resulting mixture was stirred well. Next, 0.0520
g (1.621 mmol) of elemental sulfur was added. The reaction mixture
was stirred for .about.12 hr at room temperature and then .about.40
hr at a first heating temperature of 105.degree. C. Next, the
reaction mixture was stirred for .about.8 hr at a second heating
temperature of 190.degree. C. A SLG slide was coated via
drop-coating according to the following procedure: While being
maintained at 105.degree. C. with stirring, a small portion of the
formulation was drawn into a pipette and then spread uniformly onto
the substrate, which was also heated to 105.degree. C. The coating
on the SLG slide was then dried in the drybox by raising the
temperature of the hotplate from 105.degree. C. to 170.degree. C.
for 0.5 h. The dried sample was annealed under a nitrogen/sulfur
atmosphere at 550.degree. C. for 1 hr. Analysis of the annealed
sample by XRD and XAS confirmed the presence of CZTS.
Example 1A
[0098] Example 1 was repeated using pyridine or toluene or
3-aminopyridine in place of 4-t-butylpyridine, with the second
heating temperature of .about.105.degree. C., 105.degree. C., and
170.degree. C., respectively. For samples prepared in pyridine, the
annealing temperature/time was 400.degree./0.5 h for the sample
prepared in pyridine; 500.degree./0.5 h for the toluene sample; and
550.degree. C./1 h for the 3-aminopyridine sample. Analysis of the
annealed samples by XRD and XAS also confirmed the presence of
CZTS.
Example 1B
[0099] Example 1 was repeated with annealing carried out under a
nitrogen atmosphere by RTA. Analysis of the annealed sample by XRD
also confirmed the presence of CZTS.
Example 1C
[0100] Example 1 was repeated, but the formulation was deposited on
a Mo-patterned SLG slide. Also, the temperature of the hotplate was
raised from 105 to 180.degree. C. over the course of 2 hr, and the
coating was annealed at 550.degree. C. for 0.5 hr. Cadmium sulfide,
insulating ZnO and AZO, and silver lines were deposited. Analysis
by OBIC at 440 nm and 633 nm showed photoresponses greater than 5
and 0.75 micro-Amp, respectively, adjacent to the silver line.
Example 2
##STR00002##
[0102] In the drybox, zinc diethyldithiocarbamate (0.2956 g, 0.817
mmol), copper(II) acetate (0.2974 g, 1.64 mmol), and tin(II)
acetylacetonate (0.2634 g, 0.831 mmol) were placed in a 20 mL vial
equipped with a stir bar. Pyridine (0.8 mL) was added, and the
resulting mixture was stirred well. Next, a solution of 0.6789 g
(5.05 mmol) of (ethylthio)trimethylsilane in 0.2 mL of pyridine was
added. The reaction mixture was stirred for .about.12 hr at room
temperature and then .about.40 hr at a first heating temperature of
105.degree. C. Next, the reaction mixture was stirred for .about.8
hr at a second heating temperature of 110.degree. C. An untreated
glass slide was coated via drop-coating in a manner similar to
described above in Example 1. The coated substrate was then placed
on a hot plate and heated to 120.degree. C. for .about.0.5 hr. The
coated substrate was allowed to remain on the hotplate as it cooled
to room temperature. The coated substrate was annealed in the tube
furnace at 500.degree. C. under a nitrogen/sulfur atmosphere for
0.5 hr. Analysis of the annealed sample by XRD confirmed the
presence of CZTS. Spectrophotometric measurements showed a bandgap
at 110 nm (.about.1.13 eV) for a 4 micron-thick film.
Example 2A
[0103] Example 2 was repeated using 2-aminopyridine in place of
pyridine, with the second heating temperature about 190.degree. C.,
a drying temperature of 170.degree. C., and an annealing
temperature of 550.degree. C. for 1 hr. Analysis of the annealed
sample by XRD and XAS also confirmed the presence of CZTS.
Example 2B
[0104] Example 2 was repeated using no additional solvent and the
solution was stirred at room temperature for several days without
heating prior to coating. The coating was produced via
blade-coating, with both the formulation and substrate initially at
room temperature. The thickness of the coating was controlled by
placing 0.003 feeler stock on either side of the area to be coated,
and a thicker piece of feeler stock was used as the blade. The
drying temperature was 110.degree. C. for .about.0.5 hr, and the
annealing temperature was 550.degree. C. for 0.5 hr. Analysis of
the annealed sample by XRD and XAS also confirmed the presence of
CZTS. Spectrophotometric measurements showed a bandgap at 850 nm
(-1.45 eV) for an .about.5 micron-thick film.
Example 2C
[0105] Example 2 was repeated, but the formulation was deposited on
a Mo-patterned SLG slide. Cadmium sulfide and insulating ZnO and
AZO were deposited. Analysis by OBIC at 440 nm showed a
photoresponse greater than 0.2 micro-Amp. Also, IV analysis showed
diode-like behavior, with V.sub.oc of 78 mV, J.sub.SC of 0.119
mA/cm.sup.2, FF of 23.6%, and efficiency of 0.002%.
Example 3
##STR00003##
[0107] A formulation was prepared according to the procedure of
Example 1, using zinc methoxyethoxide (0.8184 mmol), copper(I)
acetate (1.636 mmol), di-n-butyltinsulfide (0.8276 mmol),
2-mercaptoethanol (3.426 mmol), and sulfur (0.7795 mmol) in
diethylnicotinamide (1.0871 g). The reaction mixture was stirred
for .about.12 hr at room temperature and then .about.40 hr at
105.degree. C. Next, the reaction mixture was stirred .about.8 hr
at 190.degree. C. An untreated glass slide was coated via
drop-coating according to the procedure of Example 1, and then
dried at 170-190.degree. C. on the hotplate in the drybox.
Annealing was carried out at 550.degree. C. for 30 min in a
nitrogen/sulfur atmosphere. Analysis of the annealed sample by XRD
confirmed the presence of CZTS.
Example 3A
[0108] Example 3 was repeated using 4-t-butylpyridine,
1,2,4-trichlorobenzene, or 3-methoxypropionitrile as the solvent.
The temperature of the second heating step was 160-190.degree. C.,
190.degree. C., and 150.degree. C., respectively for these
solvents. Analysis of the annealed samples by XRD confirmed the
presence of CZTS.
Example 3B
[0109] Example 3 was also repeated using zinc methoxyethoxide
(0.8829 mmol), copper(I) acetate (1.518 mmol), di-n-butyltinsulfide
(0.8884 mmol), 2-mercaptoethanol (3.673 mmol), and sulfur (0.8045
mmol) in 2- or 3-aminopyridine (1.0314 g), and a second heating
temperature of 170.degree. C. CZTS was detected in both the dried
and the annealed samples by XAS.
Example 4
##STR00004##
[0111] In the drybox, zinc diethyldithiocarbamate (0.2952 g, 0.816
mmol), copper(II) dimethyldithiocarbamate (0.4959 g, 1.631 mmol),
and di-n-butylbis(1-thioglycerol)tin (0.3648 g, 0.834 mmol) were
placed together in a 20 mL vial equipped with a stir bar. Pyridine
(2.5 mL) was added, and the resulting mixture was stirred well. One
equiv of sulfur was added and the resulting mixture was stirred
overnight at room temperature. Next, the formulation was heated
.about.40 hr at 110.degree. C.
[0112] While maintaining the formulation at 105.degree. C. with
stirring, a small portion was drawn into a pipette and then spread
uniformly onto two untreated glass substrates, which were heated to
105.degree. C. The coatings were further dried by raising the
temperature of the hotplate to 120.degree. C. for .about.1 h. One
of the coatings was then annealed under a nitrogen/sulfur
atmosphere at 500.degree. C. for 30 min.
[0113] XAS analysis confirmed the presence of CZTS in both the
dried coating and the annealed coating.
Example 5
##STR00005##
[0115] A formulation was prepared according to the procedure of
Example 4 using zinc methoxyethoxide (0.2385 g, 0.271 mmol); 1.4965
g of a 10-12 wt % solution (0.545 mmol assuming 11 wt %) of
copper(II) methoxyethoxyethoxide in methoxyethoxyethanol; 0.1218 g
(0.272 mmol) of di-n-butylbis(1-thioglycerol)tin; 0.1326 g (1.697
mmol) of 2-mercaptoethanol; and 0.0089 g (0.278 mmol) of elemental
sulfur. A coating on treated glass was dried at 120.degree. C. for
0.5 hr and then annealed under a nitrogen/sulfur atmosphere at
650.degree. C. for 30 min. Analysis of the annealed sample by XRD
and XAS confirmed the presence of CZTS.
Example 6
##STR00006##
[0117] In the drybox, 0.5917 g (1.635 mmol) of zinc
diethyldithiocarbamate, 0.4092 g (3.257 mmol) of copper(II)
methoxide, 0.7097 of di-n-butyltin bis(acetylacetonate), 0.7625 g
(10.01 mmol) of carbon disulfide, and 1.6 mL of pyridine were
placed in separate vials and cooled in the -25.degree. C. freezer.
Next, one-fourth of the cold pyridine (.about.0.4 mL) was added to
each of the reagent vials and the vials were returned to the
freezer. Approximately two-thirds of the carbon disulfide solution
in pyridine was added to the copper suspension, and the remaining
one-third of the carbon disulfide solution was added to the tin
solution. The contents were mixed well and the vials were returned
to the freezer. The cold zinc mixture and the cold tin solution
were added to the copper suspension. The resulting mixture was
stirred overnight and allowed to warm to room temperature. The next
day, 0.0522 g (1.628 mmol) of elemental sulfur was added to the
reaction mixture and it was stirred at room temperature for more
than 48 hr before heating.
[0118] A coating on glass was annealed under a nitrogen/sulfur
atmosphere at 550.degree. C. for 30 min. Analysis by XRD and XAS
confirmed the presence of CZTS.
Example 6A
[0119] Example 6 was repeated, but the formulation was deposited on
a Mo-patterned SLG substrate. Cadmium sulfide and insulating ZnO
and AZO were deposited. Analysis by OBIC at 440 nm showed a
photoresponse greater than 0.1 micro-Amp adjacent. Analysis of the
sample via EQE demonstrated that the PV device exhibited a
photoresponse consistent with the semiconductor absorber having a
band gap energy of 1.53+/-0.04 eV, consistent with the absorber
being assigned as CZTS.
Examples 7-9
##STR00007##
[0121] Formulations were prepared according to the procedure of
Example 1 using 0.2952 g (0.816 mmol) of zinc
diethyldithiocarbamate, 0.4960 g (1.632 mmol) of copper(II)
dimethyldithiocarbamate, 0.2696 g (0.851 mmol) of tin(II)
acetylacetonate, and 0.2469 g (1.838 mmol) of
(ethylthio)trimethylsilane. After being thoroughly mixed, the
reaction mixture was divided into thirds and placed in three 4 mL
vials equipped with stir bars. One of these vials was used for
Example 7 and received no additional reagents. The second heating
temperature was 110.degree. C., two SLG slides were drop-coated
according to the procedure of Example 1, both coatings were dried
at 120.degree. C. and one of these coatings was annealed at
400.degree. C. Another vial was used for Example 8, and 0.0082 g of
elemental sulfur (1 equiv) was added to the vial. The second
heating temperature was 110.degree. C., a coating was prepared on a
SLG slide with drying temperature at 120.degree. C., and the
annealing temperature was 400.degree. C. The formulation of Example
9 was analogous to that of Example 8, except that 2-aminopyridine
was used as the solvent. The second heating temperature was
190.degree. C., the drying temperature was 170-190.degree. C., and
the annealing temperature was 550.degree. C.
[0122] CZTS was detected in all of the annealed samples and the
dried sample of Example 7 by XRD and/or XAS.
Example 10
##STR00008##
[0124] A formulation was prepared according to the procedure of
Example 1 using 0.1768 g (0.820 mmol) of zinc methoxyethoxide,
0.2047 g (1.630 mmol) of copper(II) methoxide, 0.4004 g (0.911
mmol) of bis[bis(trimethysilyl)amino]tin(II), 0.8990 g (6.692 mmol)
of ethylthiotrimethylsilane, 0.0259 g (0.808 mmol) of elemental
sulfur, and 0.4700 g of 3,5-lutidine. The second heating
temperature was 165.degree. C.
[0125] The formulation was coated on an untreated glass slide and
dried at 170.degree. C. The coating was annealed at 550.degree. C.
for 30 min, and was then analyzed by XRD, which indicated kesterite
as the predominant component and a trace amount of covelite
(CuS).
Example 11
##STR00009##
[0127] A formulation was prepared according to the procedure of
Example 1 using 0.1754 g (0.814 mmol) of zinc methoxyethoxide,
0.2055 g (1.636 mmol) of copper(II) methoxide, 0.3983 g (0.906
mmol) of bis[bis(trimethysilyl)amino]tin(II), 0.5226 g (6.69 mmol)
of 2-mercaptoethanol, 0.0258 g (0.804 mmol) of elemental sulfur and
0.9520 g of 3,5-lutidine. The second heating temperature was
165.degree. C.
[0128] The formulation was drop-cast onto two untreated slides and
two treated slides. The two coatings on the untreated slides were
dried at 210.degree. C., and the two coatings on the treated slides
were dried at 250.degree. C. One of the coatings on an untreated
slide was annealed at 550.degree. C. for 1 hr, and one of the
coatings on a treated slide was annealed at 550.degree. C. for 0.5
hr. The coatings were analyzed by XAS, and the presence of CZTS was
confirmed in the annealed coatings.
Examples 12-13
##STR00010##
[0130] According to the procedure of Example 1, the formulation of
Example 12 was prepared using 0.1829 g (0.849 mmol) of zinc
methoxyethoxide, 0.2110 g (1.680 mmol) of copper(II) methoxide,
0.2299 g (0.868 mmol) of di-n-butyltin sulfide, 0.4085 g (5.23
mmol) of 2-mercaptoethanol, and 0.916 g of 4-t-butylpyridine. The
second heating temperature was 190.degree. C.
[0131] According to the procedure of Example 1, the formulation of
Example 13 was prepared using 0.1830 g (0.849 mmol) of zinc
methoxyethoxide, 0.1947 g (1.550 mmol) of copper(II) methoxide,
0.2440 g (0.921 mmol) of di-n-butyltin sulfide, 0.4049 g (5.18
mmol) of 2-mercaptoethanol, 0.792 mmol of sulfur, and 0.926 g of
4-t-butylpyridine. The second heating temperature was 190.degree.
C.
[0132] Each formulation was drop-cast onto two untreated glass
slides and the coatings were dried at 170.degree. C. One coating of
each formulation was then annealed at 550.degree. C. for 0.5 hr.
The coatings were analyzed by XAS, and the presence of CZTS was
confirmed in the annealed coatings.
Example 14
##STR00011##
[0134] 1-Butanethiol (0.6024 g, 6.68 mmol) was weighed into a vial
and combined with 0.2 mL of pyridine. Copper(II) acetate (0.2971 g,
1.636 mmol) and tin(II) acetate (0.1931 g, 0.815 mmol) were placed
together in 20 mL vial equipped with a stir bar. Next, 0.8 mL of
pyridine was added to the vial followed by the addition of the
1-butanethiol solution. The contents of the vial were mixed well
for 30 min. Diethylzinc (816 micro-L of a 1.0 M solution in
hexanes) was then added to the reaction mixture, which was again
mixed well for .about.10 min. Next, approximately one-fifth of the
reaction mixture was added to a 4 mL vial that was equipped with a
stir bar and contained 0.0054 g of sulfur (.about.1 equiv). The
reaction mixture was stirred at room temperature for several
days.
[0135] Following heating at 110.degree. C., the formulation was
drop-coated onto untreated glass, dried at 120.degree. C., and then
annealed at 500.degree. C. for 0.5 hr. Analysis by XRD indicates
the presence of CZTS.
Example 15
##STR00012##
[0137] According to the procedure of Example 1, the formulation of
Example 15 was prepared using 0.0.2312 g (0.821 mmol) of zinc
2,4-pentanedionate monohydrate, 0.1999 g (1.631 mmol) of copper(I)
acetate, 0.3885 g (0.901 mmol) of di-n-butyltin
bis(acetylacetonate), 1.0881 g (4.89 mmol) of diethyldithiocarbamic
acid diethylammonium salt, 0.0264 g (0.823 mmol) of elemental
sulfur, and 1.433 g of 4-t-butylpyridine. The second heating
temperature was 190.degree. C.
[0138] The formulation was drop-coated onto untreated glass, dried
at 180.degree. C., and annealed at 550.degree. C. for 0.5 hr.
Analysis by XAS confirmed the presence of CZTS in the annealed
sample.
Example 16
##STR00013##
[0140] According to the procedure of Example 1, the formulation of
Example 16 was prepared using 0.851 mmol of zinc
diethyldithiocarbamate, 1.595 mmol of copper(II)
dimethyldithiocarbamate, 0.949 mmol of tin(II) sulfide, 0.823 mmol
of elemental sulfur, and 2.895 g of N-methyl-2-pyrrolidinone. The
second heating temperature was at 170-190.degree. C.
[0141] The formulation was drop-coated onto two untreated glass
slides, the coatings were dried at 180.degree. C. and then one of
the coatings was annealed at 550.degree. C. for 1 hr. Analysis by
XRD and XAS confirmed the presence of CZTS in the annealed sample;
XAS analysis confirmed the presence of CZTS in the dried
(un-annealed) sample.
[0142] This procedure was repeated using 4-t-butylpyridine
(1.237-1.5 g), 2-aminopyridine (1.067-1.103 g) or 3-aminopyridine
(1.016-1.048 g) as solvent, with or without the addition of
elemental sulfur. Prior to coating, .about.1 mL of
4-t-butylpyridine was added to the aminopyridine-based
formulations. Analysis by XRD confirmed the presence of CZTS in all
six of the annealed samples.
Example 17
[0143] A formulation analogous to that of Example 1 and a treated
SLG substrate were both heated to 105.degree. C. After drop-coating
the formulation, the coated substrate was maintained at 105.degree.
C. for 20 min and then at 220.degree. C. for a total of 83 min. The
substrate was cooled to 105.degree. C. and a second layer of the
same formulation was drop-coated onto it. The temperature was
maintained at 105.degree. C. for .about.2.5 hr and then at
220.degree. C. for .about.1 hr. The substrate was then allowed to
cool to room temperature. Next, the formulation of Example 16 using
3-amino-pyridine as the solvent without the addition of elemental
sulfur was spun-coated to give a third layer. The substrate was
heated at 105.degree. C. for several hr and then for 20-30 min at
220.degree. C., then cooled to room temperature. The substrate was
annealed for 90 min under a nitrogen/sulfur atmosphere at
550.degree. C. Analysis by XRD confirmed the presence of CZTS.
Example 18
[0144] A coated substrate was prepared analogously to that of
Example 17 except that the third layer was not applied. The
substrate was annealed for 90 min under a nitrogen/selenium
atmosphere. XRD analysis indicated the presence of CZTS-Se, with
sulfur partially (67.8%) replaced with selenium.
Example 19
[0145] The formulation of Example 16 using 2-aminopyridine as the
solvent and without the addition of elemental sulfur was
spun-coated onto a treated SLG substrate. The substrate was then
heated at 105.degree. C. for at least 2 hr, cooled to room
temperature, heated to 170.degree. C. for 70 min, and cooled to
room temperature. Next, a formulation analogous to that used for
Example 1, except with only 2.2 g of 4-t-butylpyridine, was spun on
top of the first coating. The substrate was heated at 105.degree.
C. for several hr, then at 170.degree. C. for 20 min, and cooled to
room temperature. After annealing by RTA under nitrogen, XRD
indicated the presence of CZTS. The substrate was then annealed in
a furnace under a selenium/nitrogen atmosphere for 90 min at
550.degree. C. XRD indicated the presence of CZTS-Se, with sulfur
partially (67.1%) replaced with selenium.
Example 20
[0146] Zinc sulfide (0.915 mmol), copper(II) sulfide (1.539 mmol),
and tin(II) sulfide (0.884 mmol) were placed in a 40 mL amber vial
equipped with a stir bar. 3-Methoxypropylamine (0.893 g) was added,
and the resulting mixture was stirred well. Next, 0.798 mmol of
elemental sulfur was added. The reaction mixture was stirred for
.about.12 hr at room temperature and then .about.48 hr at
105.degree. C. The formulation was then drop-coated onto a treated
SLG slide according to procedure of Example 1. The coating was then
dried in the drybox by raising the temperature of the hotplate from
105.degree. C. to 170.degree. C. for 0.5 hr. The coating was
annealed at 550.degree. C. for 0.5 hr. Analysis of the annealed
sample by XAS confirmed the presence of CZTS.
Example 21
[0147] Formulation and coating was analogous to that of Example 1,
except that no zinc compound was used in the formulation. The
coated substrate was annealed under selenium/nitrogen vapor for 90
min at 550.degree. C. The XRD analysis indicated the presence of
CTS-Se, with sulfur partially (71.4%) replaced with selenium and
with an average grain size of greater than 100 nm.
Example 22
[0148] Example 16 was repeated using 4-t-butylpyridine as the
solvent and tin(II) selenide in place of tin(II) sulfide. The XRD
analysis indicated the presence of CTS-Se, with sulfur partially
(76.8%) replaced with selenium and with an average grain size of
35.2 nm
* * * * *