Conductive ink composition containing gold complex

Abstract

Conductive ink compositions are provided that include gold complexes. Methods of preparing the conductive ink compositions, methods of forming conductive structures from the conductive ink compositions, and structures formed from the conductive ink compositions are also provided. The conductive ink compositions preferably include gold metal, an alkylamine ligand, and a solvent. The conductive ink compositions can be used to form conductive structures including gold at temperatures at or below 300° C., for example, by inkjet or other printing methods. Such conductive structures can be formed on a variety of substrates.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 339,313, filed May 6, 2022, the disclosure of which is incorporated by reference herein in its entirety.

[0002] FIELD OF THEINVENTION The present disclosure relates generally to novel ink compositions containing gold, and methods of their preparation and use. More particularly, the present disclosure relates to particle-free conductive ink compositions containing gold complexes, including inks prepared using novel gold organometallic complexes. The inks are particularly useful in inkjet printing, including aerosol jet mechanical printing applications. [Background technology]

[0003] 2. Background of the Invention The electronics, display, and energy industries rely on the production and use of coatings and patterns of conductive materials to form circuits on organic and inorganic substrates. Printed electronics offers an attractive alternative to conventional technologies by enabling the fabrication of large-area flexible devices at low cost. There is a great need for highly conductive materials with fine-scale features in modern electronics such as solar cell electrodes, flexible displays, radio frequency identification tags, antennas, and many others. To make these high technology devices more affordable, the substrates used typically have relatively low temperature resilience and must be processed at low temperatures to maintain their integrity.

[0004] Most commercially manufactured conductive inks are specifically designed for inkjet, screen printing, or roll-to-roll processing methods to process large areas with fine-scale features in a short time. These inks have completely different viscosity and composition parameters. Particle-based inks are based on conductive metal particles, which are typically synthesized separately and then incorporated into the ink formulation. The resulting ink is then tailored for the specific particle processing.

[0005] Typically, precursor-based inks are based on thermally unstable precursor complexes that undergo reduction to conductive metals upon heating. Conventional particle- and precursor-based methods generally rely on high temperatures to form conductive coatings and therefore may not be compatible with substrates that require low-temperature processing to maintain their integrity. For example, particle- and precursor-based conductive ink compositions are available that decompose at temperatures around 150° C., resulting in conductivities approaching those of bulk metals. Unfortunately, even at these temperatures, the inks are incompatible with many plastic and paper substrates commonly used in flexible electronics and biomedical devices.

[0006] Metal-organic precursor materials are beginning to attract attention for the preparation of particle-free conductive ink formulations. Compounds having a metal atom and one or more organic ligands bonded to the metal atom by a heteroatom such as oxygen or nitrogen are typically known as metal-organic compounds. For comparison, compounds having a direct connection between a metal atom and a carbon atom are typically called organometallic compounds. As a result of the strong metal-carbon bond in organometallic compounds, organometallic compounds are generally considered less suitable for low-temperature printing applications. In contrast, metal-organic compounds are typically considered more susceptible to decomposition because the metal-heteroatom bond is often weaker. Summary of the Invention [Problem to be solved by the invention]

[0007] Printable ink compositions containing gold have been previously described for printing conductive features. However, most of the known gold-based inks rely on nanoparticle-based formulations. Thus, there remains a need for conductive ink compositions containing gold that exhibit improved properties. It is therefore an object of the present invention to provide particle-free conductive gold ink compositions and methods for their preparation and use, particularly compositions that are capable of forming conductive structures at low temperatures. [Means for solving the problem]

[0008] Summary of the Invention The present disclosure addresses these and other considerations, in one aspect, by providing a particle-free conductive ink composition comprising gold metal, an alkylamine ligand, and a solvent, which forms a conductive metal film structure upon curing at elevated temperatures.

[0009] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the gold metal is gold(I) metal ions.

[0010] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the alkylamine ligand is volatile at temperatures of about 200° C. or less.

[0011] In some embodiments, the techniques described herein provide a method for preparing a cyclic amine ligand comprising the steps of: 3 ~C 12 The present invention relates to a particle-free conductive ink composition, which is an alkylamine ligand.

[0012] In some aspects, the technology described herein relates to particle-free conductive ink compositions, where the alkylamine ligand is a branched alkylamine ligand.

[0013] In some aspects, the technology described herein relates to particle-free conductive ink compositions, where the alkylamine ligand is a primary alkylamine ligand.

[0014] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the alkylamine ligand is an alkyl-substituted hexylamine. More specifically, the alkyl-substituted hexylamine is a methyl- or ethyl-substituted hexylamine, or even 2-ethyl-1-hexylamine or 2-amino-5-methylhexane.

[0015] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the alkylamine ligand is a di-chelated primary, secondary, or tertiary alkyldiamine compound.

[0016] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the alkylamine ligand has a particular structure.

[0017] In some embodiments, the techniques described herein involve the step of preparing a C alkylamine ligand substituted with at least one heteroatom. 2 ~C 12 The present invention relates to a particle-free conductive ink composition, which is an alkylamine ligand.

[0018] In some aspects, the technology described herein relates to particle-free conductive ink compositions, where the at least one heteroatom is at least one oxygen or sulfur.

[0019] In some embodiments, the techniques described herein provide a method for preparing a cyclic amine ligand comprising the steps of: 4 ~C 10 The present invention relates to a particle-free conductive ink composition, which is a 2-amino-alkyl compound.

[0020] In some aspects, the technology described herein relates to particle-free conductive ink compositions, where the solvent comprises an aromatic solvent.

[0021] In some aspects, the technology described herein relates to particle-free conductive ink compositions, where the solvent comprises an alkyl or aromatic ether solvent.

[0022] In some aspects, the technology described herein relates to particle-free conductive ink compositions, where the solvent comprises tetrahydrofuran or 2-methyltetrahydrofuran.

[0023] In some aspects, the technology described herein relates to particle-free conductive ink compositions, where the solvent comprises an amide-based solvent.

[0024] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the solvent comprises an aromatic heterocyclic solvent. More specifically, the aromatic heterocyclic solvent may comprise pyridine or pyrazine, or may even comprise pyridine or 2,5-dimethylpyrazine.

[0025] In some aspects, the technology described herein relates to particle-free conductive ink compositions that further comprise a counterion.

[0026] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the counterion is a carboxylate.

[0027] In some aspects, the technology described herein relates to particle-free conductive ink compositions that release carbon dioxide when heated.

[0028] In some aspects, the technology described herein relates to particle-free conductive ink compositions that release carbon dioxide when heated below about 300°C.

[0029] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the counterion is a haloacetate.

[0030] In some aspects, the technology described herein relates to a particle-free conductive ink composition, where the haloacetate is a trifluoroacetate.

[0031] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the counterion is nitrate, nitrite, tetrafluoroborate, or hexafluorophosphate.

[0032] In some aspects, the technology described herein relates to particle-free conductive ink compositions that form conductive metal films upon curing at or below 300°C.

[0033] In some aspects, the technology described herein relates to particle-free conductive ink compositions in which the conductive metal film exhibits a conductivity of at least 1% of the bulk metal conductivity.

[0034] In some aspects, the techniques described herein relate to methods for applying a particle-free conductive ink composition to a substrate and curing the composition at elevated temperatures to form a conductive film.

[0035] In some aspects, the techniques described herein relate to a method, wherein the applying step includes a printing step.

[0036] In some aspects, the techniques described herein relate to a method, wherein the printing step is a jet printing step.

[0037] In some aspects, the techniques described herein relate to a method, wherein the jet printing step is an aerosol jet printing step.

[0038] In some aspects, the techniques described herein relate to methods where the composition cures at or below 300°C.

[0039] In some aspects, the techniques described herein relate to conductive films formed by applying a particle-free conductive ink composition to a substrate and curing the composition at elevated temperatures to form a conductive film.

[0040] In some embodiments, the techniques described herein relate to conductive films that are cured at 300° C. or less.

[0041] In some aspects, techniques described herein relate to a method of preparing a particle-free conductive ink composition comprising providing an alkylamine-gold complex and dissolving the alkylamine-gold complex in a solvent to form a particle-free conductive ink composition, wherein the alkylamine-gold complex comprises gold metal and an alkylamine ligand, and wherein the particle-free conductive ink composition is cured at an elevated temperature to form a conductive metal film.

[0042] In some aspects, the techniques described herein relate to methods, wherein the gold metal is a gold(I) metal ion.

[0043] In some aspects, the techniques described herein relate to methods where the alkylamine ligand is volatile at temperatures below about 200° C.

[0044] In some embodiments, the techniques described herein provide a method for preparing a cyclic amine ligand comprising the steps of: 3 ~C 12 The present invention relates to a method of preparing a compound comprising the steps of:

[0045] In some aspects, the technology described herein relates to methods, wherein the alkylamine ligand is a branched alkylamine.

[0046] In some aspects, the techniques described herein relate to methods, wherein the alkylamine ligand is a primary alkylamine.

[0047] In some aspects, the technology described herein relates to methods in which the alkylamine ligand is an alkyl-substituted hexylamine. More specifically, the alkyl-substituted hexylamine is a methyl- or ethyl-substituted hexylamine, or even 2-ethyl-1-hexylamine or 2-amino-5-methylhexane.

[0048] In some aspects, the technology described herein relates to methods where the alkylamine ligand is a dichelated primary, secondary, or tertiary alkyldiamine compound.

[0049] In some aspects, the techniques described herein relate to methods, wherein the alkylamine ligand has a particular structure.

[0050] In some embodiments, the techniques described herein include C amines in which the alkylamine ligand is substituted with at least one heteroatom. 2 ~C 12 The present invention relates to a method of treating a cancer cell comprising administering to a patient a therapeutically effective amount of a cancer cell, the method ... being an alkylamine ligand.

[0051] In some aspects, the techniques described herein relate to methods, wherein the at least one heteroatom is at least one oxygen or sulfur.

[0052] In some embodiments, the techniques described herein provide a method for preparing a cyclic amine ligand comprising the steps of: 4 ~C 10 The compound is a 2-amino-alkyl compound.

[0053] In some aspects, the techniques described herein relate to methods, wherein the solvent comprises an aromatic solvent.

[0054] In some aspects, the techniques described herein relate to methods where the solvent comprises an alkyl or aromatic ether solvent.

[0055] In some embodiments, the techniques described herein relate to methods, wherein the solvent comprises tetrahydrofuran or 2-methyltetrahydrofuran.

[0056] In some aspects, the techniques described herein relate to methods, wherein the solvent comprises an amide-based solvent.

[0057] In some aspects, the techniques described herein relate to methods in which the solvent comprises an aromatic heterocyclic solvent. More specifically, the aromatic heterocyclic solvent may comprise pyridine or pyrazine, or may further comprise pyridine or 2,5-dimethylpyrazine.

[0058] In some aspects, the techniques described herein relate to methods, wherein the particle-free conductive ink composition further comprises a counterion.

[0059] In some aspects, the techniques described herein relate to methods where the counterion is a carboxylate.

[0060] In some aspects, the techniques described herein relate to methods whereby a particle-free conductive ink composition releases carbon dioxide when heated.

[0061] In some embodiments, the techniques described herein relate to methods whereby the particle-free conductive ink composition releases carbon dioxide when heated below about 300°C.

[0062] In some aspects, the techniques described herein relate to methods where the counterion is a haloacetate.

[0063] In some aspects, the techniques described herein relate to methods where the haloacetate is a trifluoroacetate.

[0064] In some aspects, the techniques described herein relate to methods in which the counterion is nitrite, nitrate, tetrafluoroborate, or hexafluorophosphate. [Brief description of the drawings]

[0065] [Figure 1]FIG. 1 shows an image of an ink formulation prepared according to the present disclosure.

[0066] [Diagram 2] FIG. 2 shows the results of printing the ink formulation of the present disclosure on a glass substrate.

[0067] [Diagram 3] FIG. 3 shows the results of printing the ink formulation of the present disclosure onto a circuit board substrate.

[0068] [Figure 4] FIG. 4 shows the circuit board used to measure the resistance of gold films printed using the ink formulations of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Detailed Description of the Invention Conductive Gold Ink Composition Particle-free inks containing metal-organic compounds have several advantages over nanoparticle-based inks. Most importantly, particle-free inks containing metal-organic compounds decompose more easily and often at lower temperatures than inks containing nanoparticles. For example, prints of several hours with fine features can be achieved using particle-free inks containing metal-organic compounds. Metal-organic inks also have a longer shelf life when compared to nanoparticle-based inks. Disclosed herein are gold(I) amine-based ink formulations that have been used to produce dry prints of highly conductive fine lines by aerosol jet printing technology, as well as methods for their synthesis and use.

[0070] Thus, the present disclosure provides, in one aspect, a particle-free conductive ink composition comprising gold metal, an alkylamine ligand, and a solvent, which is cured at an elevated temperature to form a conductive metal film structure.

[0071] By elevated temperature is meant a temperature above room temperature. In some embodiments, the particle-free conductive ink composition of the present disclosure is cured at about 400° C. or less, about 300° C. or less, about 200° C. or less, or even about 100° C. or less to form a conductive metal film structure.

[0072] In some embodiments, the alkylamine ligand of the conductive ink composition is 3 ~C 12 In a more specific embodiment, the alkylamine ligand is 4 ~C 10 Alkylamine ligands, C 5 ~C 8 Alkylamine ligands, or even C 8 In some embodiments, the alkylamine ligand is a branched alkylamine ligand. In some embodiments, the alkylamine ligand is a primary alkylamine ligand. In some embodiments, the alkylamine ligand is a primary C 3 ~C 12 Alkylamine ligands, C1 5 ~C 10 Alkylamine ligands, or more specifically, primary C 8 Alkylamine Ligands In some embodiments, the particle-free conductive ink composition comprises more than one alkylamine ligand.

[0073] In some embodiments, the alkylamine ligand is an alkyl-substituted hexylamine. In more specific embodiments, the alkyl-substituted hexylamine is a methyl- or ethyl-substituted hexylamine. Even more specifically, the alkyl-substituted hexylamine is 2-ethyl-1-hexylamine or 2-amino-5-methylhexane.

[0074] The alkylamine ligands of the present conductive ink compositions are preferably volatile at temperatures of about 400°C or less, about 300°C or less, about 200°C or less, or even about 100°C or less.

[0075] In some embodiments, the conductive ink composition comprises specially designed gold(I) amine complexes that provide particularly stable precursors to particle-free conductive ink formulations. Gold(I) amine complexes containing the above alkylamine ligands can be synthesized, for example, as shown in the following reaction scheme: [ka]

[0076] In some embodiments, the alkylamine ligand can be 2-amino-5-methylhexane. An ink containing a gold complex with this ligand can be prepared, for example, by using 2-amino-5-methylhexane gold chloride: [ka] In particular, such inks can be prepared by dissolving the precursor in a suitable solvent, for example, an aromatic heterocyclic solvent, such as pyridine or 2,5-dimethylpyrazine. The solids content of such inks can be, for example, about 4%. The inks can be cured at low temperatures for short periods of time, for example, at 160° C. for 15 minutes or at 100° C. for 16 hours.

[0077] In some embodiments, the alkylamine in the particle-free conductive ink composition is a dichelated primary, secondary or tertiary C 3 ~C 14 A stable diamine gold(I) precursor ink composition containing such a compound can be prepared, for example, as shown in the following scheme: [ka] In these complexes, the alkylamine ligand has the formula (I): [ka] wherein each R group is independently H or C 1 ~C 14an alkyl group, and each n is independently 1 to 14. (i.e., the linker comprises 1 to 14 methylene groups). In more specific embodiments, each R group is independently H or C 1 ~C 4 and each n is independently 1 to 10, 1 to 8, or even 1 to 6. In other more specific embodiments, n is 2 to 14, 4 to 14, 6 to 14, or even 8 to 14. In yet other more specific embodiments, n is 2 to 12, 4 to 10, or even 6 to 8.

[0078] In some embodiments, the alkylamine ligand of the particle-free ink composition is 2 ~C 12 In some embodiments, the alkylamine ligand is an alkylamine ligand, the alkyl chain being substituted with at least one heteroatom. More specifically, the alkyl chain may be substituted with at least one oxygen or sulfur. Even more specifically, the alkyl chain may be substituted with at least one oxygen. In some embodiments, the alkylamine ligand is an alkylamine ligand, the alkyl chain being substituted with at least one heteroatom. More specifically, the alkyl chain may be substituted with at least one oxygen. 3 ~C 12 Alkylamine ligands, C 4 ~C 10 Alkylamine ligands, C 5 ~C 8 Alkylamine ligands, or even C 8 They are alkylamines, in which the alkyl chain is substituted with at least one heteroatom, in particular at least one oxygen or sulfur, or at least one oxygen.

[0079] The preparation of exemplary gold(I) amine complexes containing oxygen-substituted alkylamines suitable for use in the particle-free ink compositions of the present disclosure is shown in the following scheme. [ka] In these complexes, the R group is H or C 1 ~C 4is an alkyl group, and n is 1 to 14 (i.e., the ink contains 1 to 14 methylene groups). In more specific embodiments, n is 1 to 10, 1 to 8, or even 1 to 6. In other more specific embodiments, n is 2 to 14, 4 to 14, 6 to 14, or even 8 to 14. In yet other more specific embodiments, n is 2 to 12, 4 to 10, or even 6 to 8.

[0080] In some embodiments, the alkylamine ligand in the particle-free conductive ink composition can be 2-amino-5-methylhexane, 2-amino-6-methylheptane, or another similar 2-amino-alkyl compound containing 4 to 10 carbons. Details of the preparation of exemplary complexes of this type are described below. [ka]

[0081] In some embodiments, the particle-free conductive ink composition may include a counterion that includes a carboxylate. In these compositions, decarboxylation of the counterion may produce conductive gold metal, carbon dioxide, decarboxylated carbon residues, and uncoordinated amines. In some embodiments, the carboxylate may be a haloacetate, e.g., a fluoroacetate. An exemplary gold(I) complex that includes trifluoroacetate (TFA) ions as an anionic ligand is illustrated below. The gold(I) amine complex may be prepared, for example, using a silver-mediated metathesis reaction, as illustrated in the reaction scheme below. [ka]

[0082] In some embodiments, the particle-free conductive ink composition may include counterions other than carboxylate. For example, gold(I) complexes can be prepared with counter anions containing nitrate, nitrite, tetrafluoroborate, or hexafluorophosphate as depicted in the following reaction scheme: [ka] Particle-free conductive ink compositions containing these alternative counterions can be prepared using any of the alkylamine ligands described above.

[0083] The solvent of the conductive ink composition can be any solvent capable of completely or nearly completely dissolving the gold metal complex. The solvent is also selected for compatibility with the patterning technique used with the ink. In some embodiments, the solvent comprises an aromatic solvent, such as anisole, toluene, etc.

[0084] In some embodiments, the solvent comprises an alkyl or aromatic ether solvent. In more specific embodiments, the solvent comprises tetrahydrofuran or 2-methyltetrahydrofuran.

[0085] In some embodiments, the solvent comprises an amide solvent, such as N,N-dimethylformamide or N,N-dimethylacetamide.

[0086] In some embodiments, the solvent may include an aromatic heterocyclic solvent. More specifically, the solvent may include a nitrogen-containing aromatic heterocyclic solvent, such as pyridine or pyrazine. Even more specifically, the solvent may include pyridine or 2,5-dimethylpyrazine.

[0087] The conductive ink composition may have a low viscosity, making it compatible with a wide range of patterning techniques, including slot-die coating, spin coating, gravure, flexography, rotary screen printing, screen printing, aerosol jet printing, inkjet printing, airbrush, Mayer rod coating, flood coating, 3D printing, and roll-to-roll printing, including electrohydrodynamic printing. In particular, the ink is compatible with inkjet printing, dip coating, and spray coating. The patterning features are highly conductive at room temperature and may achieve bulk conductivity when decomposed at mild temperatures (e.g., less than about 100° C. in some cases). Finally, the ink composition may remain stable at room temperature for several months without particle precipitation.

[0088] In a preferred embodiment, the conductive ink composition can be applied in an aerosol jet application using, for example, an Optomec Aerosol Jet 300 series system to produce conductive features for 3D printing electronics.

[0089] Thus, conductive ink compositions (also referred to as "conductive inks" or "inks") have been created for printing highly conductive features at low temperatures. Such inks can be stable, particle-free, and suitable for a wide range of patterning techniques. In some embodiments, a "particle-free" ink is an ink that does not contain any particles with a diameter greater than about 10 nm. In some embodiments, a "particle-free" ink is an ink that has less than about 1% particles, preferably less than about 0.1% particles. Gold complexes are used in the inks as precursor materials, which ultimately result in gold in the conductive gold coating, lines, or patterns of the film formed in the printing process.

[0090] In some embodiments, the gold ink composition is first applied to a substrate. In some embodiments, the gold ink composition is converted to a conductive gold film structure at a temperature of about 250° C. or less. In some embodiments, the gold ink composition is converted to a conductive gold film structure at a temperature of about 100° C. or less. In some embodiments, the gold ink composition is converted to a conductive gold film structure at a temperature of about 220° C., about 210° C. or less, about 190° C. or less, about 180° C. or less, about 170° C. or less, about 160° C. or less, about 150° C. or less, about 140° C. or less, about 130° C. or less, about 120° C. or less, about 110° C. or less, about 90° C. or less, about 80° C. or less, about 70° C. or less, about 60° C. or less, or even about 50° C. or less.

[0091] In some embodiments, the gold conductive ink composition has a gold concentration of about 1 to about 50 percent by weight of the conductive ink composition. In some embodiments, the conductive ink composition has a gold concentration of about 1 to about 40 percent by weight of the conductive ink composition. In some embodiments, the conductive ink composition has a gold concentration of about 1 to about 30 percent by weight of the conductive ink composition. In some embodiments, the conductive ink composition has a gold concentration of about 1 to about 20 percent by weight of the conductive ink composition. In some embodiments, the conductive ink composition has a gold concentration of about 1 to about 10 percent by weight of the conductive ink composition. In some embodiments, the conductive ink composition has a gold concentration of about 5 to about 15 percent by weight of the conductive ink composition. In some embodiments, the conductive ink composition comprises about 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent), about 5 weight percent, about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent), about 11 weight percent), about 12 weight percent, about 13 weight percent, about 14 weight percent, about 15 weight percent, about 16 weight percent), about 17 weight percent), about 18 weight percent, about 19 weight percent, about 20 weight percent, about 21 weight percent, about 22 weight percent), about 23 weight percent, about 24 weight percent, about 25 weight percent, about 26 weight percent, about 27 weight percent, about 28 weight percent), about 29 weight percent, about 30 weight percent, about 31 weight percent, about 32 weight percent, about 33 weight percent, about 34 weight percent), about 35 weight percent, about 36 weight percent, about 37 weight percent, about 38 weight percent, about 39 weight percent, about 40 weight percent, about 41 weight percent, about 42 weight percent, about 43 weight percent, about 44 weight percent, about 45 weight percent, about 46 weight percent, about 47 weight percent, about 48 weight percent, about 49 weight percent, about 50 weight percent, or even higher weight percent gold concentrations.

[0092] In some embodiments, the conductivity of a conductive structure formed from the conductive ink composition is measured. In some embodiments, the conductivity of the conductive structure is about 2×10 -6 ohm cm ~ approx. 1×10 -5 In some embodiments, the conductivity of the conductive structure is about 3×10 ohm-cm. -6 ohm cm ~ approx. 6 × 10 -6 In some embodiments, the electrical conductivity of the conductive structure is at least about 2×10 -6 Ohm cm, approximately 3 x 10 -6 Ohm cm, approximately 4 x 10 -6 ohm cm, approximately 5 x 10 -6 Ohm cm, approximately 6 x 10 -6 Ohm cm, approximately 7 x 10 -6 Ohm cm, approximately 8 x 10 -6 ohm cm, or approximately 9 x 10 -6 In some embodiments, the electrical conductivity of the conductive structure is at most about 1×10 -5 Ohm cm, approximately 9 x 10 -6 Ohm cm, approximately 8 x 10 -6 Ohm cm, approximately 7 x 10 -6 Ohm cm, approximately 6 x 10 -6 ohm cm, approximately 5 x 10 -6 Ohm cm, approximately 4 x 10 -6 ohm cm, or approximately 3 x 10 -6 is ohm·cm.

[0093] In some embodiments, the conductivity of the conductive structure may be expressed in terms of sheet resistance (i.e., bulk resistivity divided by thickness) in ohms per square (also called ohms / square or OPS). In some embodiments, for example, the resistance of the conductive structure is 5 ohms per square or less, 2 ohms per square or less, 1 ohm per square or less, 0.5 ohms per square or less, or even lower. Preferably, the resistance of the conductive structure is 1 ohm per square or less.

[0094] The conductive ink compositions of the present disclosure can be used to form conductive structures having high levels of bulk gold. Specifically, in some embodiments, the conductive structures have a bulk gold content of at least 1%. In more specific embodiments, the conductive structures have a bulk gold content of at least 2%, at least 5%, at least 10%, at least 15%, at least 20%, or even higher.

[0095] Method for producing a conductive ink composition According to another aspect, the present disclosure provides methods for producing conductive ink compositions, in particular conductive ink compositions as described above, comprising the steps of providing a gold precursor complex, for example a reactive gold complex as described above, and dissolving the gold precursor complex in an organic solvent to form a particle-free conductive ink composition.

[0096] Method for forming a conductive structure - Patent application In another aspect, a method of manufacturing a conductive structure is disclosed. In some embodiments, the method includes applying the conductive ink composition described above to a substrate. In some embodiments, the method includes heating the conductive ink composition on the substrate at a decomposition temperature of about 300° C. or less to form a conductive structure. In some embodiments, the method includes heating the conductive ink composition on the substrate at a decomposition temperature of about 100° C. or less to form a conductive structure. In some embodiments, the method includes heating the conductive ink composition on the substrate at a decomposition temperature of about 250° C. or less, about 200° C. or less, about 150° C., about 100° C. or less, or even lower to form a conductive structure. In some embodiments, the conductive ink composition is heated using a heat source. Examples of heat sources include IR lamps, an oven, or a heated substrate.

[0097] In some embodiments, the conductive ink composition of the method has a desired viscosity. In some embodiments, the desired viscosity is obtained using a Micro VISC viscometer. In some embodiments, the conductive ink composition has a viscosity of about 50 centipoise to about 1000 centipoise. In some embodiments, the conductive ink composition has a viscosity of about 5 centipoise to about 50 centipoise. In some embodiments, the conductive ink composition has a viscosity of about 10 centipoise to about 40 centipoise. In some embodiments, the conductive ink composition has a viscosity of about 20 centipoise to about 30 centipoise. In some embodiments, the conductive ink composition has a viscosity of about 18 centipoise to about 20 centipoise. In some embodiments, the conductive ink composition has a viscosity of about 18, about 19, or about 20 centipoise. In some embodiments, the conductive ink composition has a viscosity of at least about 5 centipoise, about 10 centipoise, about 20 centipoise, about 30 centipoise, about 40 centipoise, about 50 centipoise, about 60 centipoise, about 70 centipoise, about 80 centipoise, about 90 centipoise, about 100 centipoise, about 200 centipoise, about 300 centipoise, about 400 centipoise, about 500 centipoise, about 600 centipoise, about 700 centipoise, about 800 centipoise, or about 900 centipoise. In some embodiments, the conductive ink composition has a viscosity of at most about 1000 centipoise, about 900 centipoise, about 800 centipoise, about 700 centipoise, about 600 centipoise, about 500 centipoise, about 400 centipoise, about 300 centipoise, about 200 centipoise, about 100 centipoise, about 90 centipoise, about 80 centipoise, about 70 centipoise, about 60 centipoise, about 50 centipoise, about 40 centipoise, about 30 centipoise, about 20 centipoise, or about 10 centipoise. Viscosity is typically measured at room temperature.

[0098] In some embodiments, the gold conductive ink composition of the present method has a gold complex concentration of about 0.1 to 50 percent by weight of the ink composition. In some embodiments, the ink composition of the present method has a gold complex concentration of about 0.1 to 40 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 1 to 30 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 1 to 20 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 1 to 10 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 5 to 15 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 0.1 weight percent, about 0.2 weight percent, about 0.3 weight percent, about 0.4 weight percent, about 0.5 weight percent, about 0.6 weight percent, about 0.7 weight percent, about 0.8 weight percent, about 0.9 weight percent, about 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent, about 5 weight percent, about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent, about 11 weight percent, about 12 weight percent, about 13 weight percent, about 14 weight percent, about 15 weight percent, about 16 weight percent, about 17 weight percent, about 18 weight percent, about 19 weight percent, or about 20 weight percent of the ink composition.

[0099] In some embodiments, the ink composition of the present method has a gold complex concentration of about 0.1 to 50 percent by weight of the ink composition. In some embodiments, the ink composition of the present method has a gold complex concentration of about 0.1 to 40 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 1 to 30 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 1 to 20 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 1 to 10 percent by weight of the ink composition. In some embodiments, the ink composition has a gold complex concentration of about 5 to 15 percent by weight of the ink composition.

[0100] In some embodiments, the conductivity of the conductive structure is measured. In some embodiments, the conductivity of the conductive structure is about 1×10 -6 In some embodiments, the electrical conductivity of the conductive structure is about 1×10 ohm·cm or higher. -6 ohm cm ~ approx. 8 × 10 -4 In some embodiments, the conductivity of the conductive structure is about 3×10 ohm-cm. -6 ohm cm ~ approx. 6 × 10 -6 In some embodiments, the electrical conductivity of the conductive structure is at least about 1×10 -6 Ohm cm, approximately 2 x 10 -6 Ohm cm, approximately 3 x 10 -6 Ohm cm, approximately 4 x 10 -6 ohm cm, approximately 5 x 10 -6 Ohm cm, approximately 6 x 10 -6 Ohm cm, approximately 7 x 10 -6 Ohm cm, approximately 8 x 10 -6 Ohm cm, approximately 9 x 10 -6 Ohm cm, approximately 1×10 -5 Ohm cm, approximately 2 x 10 -5 Ohm cm, approximately 3 x 10 -5 Ohm cm, approximately 4 x 10 -5 ohm cm, approximately 5 x 10 -5 Ohm cm, approximately 6 x 10 -5 Ohm cm, approximately 7 x 10 -5 Ohm cm, approximately 8 x 10 -5 Ohm cm, approximately 9 x 10 -5 Ohm cm, approximately 1 x 10 -4 Ohm cm, approximately 2 x 10 -4 Ohm cm, approximately 3 x 10 -4 Ohm cm, approximately 4 x 10 -4 ohm cm, approximately 5 x 10 -4 Ohm cm, approximately 6 x 10 -4 ohm cm, or approximately 7 x 10 -4 In some embodiments, the electrical conductivity of the conductive structure is at most about 8×10 -4 Ohm cm, 7×10 -4Ohm cm, approximately 6 x 10 -4 ohm cm, approximately 5 x 10 -4 Ohm cm, approximately 4 x 10 -4 Ohm cm, approximately 3 x 10 -4 Ohm cm, approximately 2 x 10 -4 ohm cm, or approximately 1 x 10 -4 Ohm cm, approximately 9 x 10 -5 Ohm cm, approximately 8 x 10 -5 Ohm cm, approximately 7 x 10 -5 Ohm cm, approximately 6 x 10 -5 ohm cm, approximately 5 x 10 -5 Ohm cm, approximately 4 x 10 -5 Ohm cm, approximately 3 x 10 -5 Ohm cm, approximately 2 x 10 -5 Ohm cm, approximately 1 x 10 -5 Ohm cm, approximately 9 x 10 -6 Ohm cm, approximately 8 x 10 -6 Ohm cm, approximately 7 x 10 -6 Ohm cm, approximately 6 x 10 -6 ohm cm, approximately 5 x 10 -6 Ohm cm, approximately 4 x 10 -6 Ohm-cm, approximately 3×10 -6 ohm cm, or approximately 2 x 10 -6 is ohm·cm.

[0101] Application of the ink composition The ink compositions of the present disclosure can be used in a variety of printing applications including slot die coating, spin coating, gravure, flexography, rotary screen printing, screen printing, aerosol jet printing, inkjet printing, airbrushing, Mayer rod coating, flood coating, 3D printing, and roll-to-roll printing including electrohydrodynamic painting. In particular, the inks can be used for inkjet printing, dip coating, and spray coating. Additionally, patterns can be created using photolithography to create masks to etch gold from specific areas, thereby creating high fidelity features.

[0102] In a preferred embodiment, the ink composition is used in an aerosol jet printing application to print conductive structures including gold metal. This method, also known as maskless mesoscale materials deposition or M3D (see, for example, U.S. Pat. No. 7,485,345), involves spraying of particle-free ink compositions via ultrasonic or pneumatic techniques to generate micrometer-scale droplets. The aerosolized ink is combined with a carrier gas and directed through a flow head onto a substrate where the ink eventually hardens into conductive structures.

[0103] In some embodiments, the ink composition is compatible with many non-polar polymeric, glass and ceramic substrates where polar complexes are particularly poorly wetted. In some embodiments, the ink composition is applied to a polymeric substrate. In some embodiments, the ink composition is applied to a non-polar polymeric substrate. In some embodiments, the ink composition is applied to a glass substrate. In some embodiments, the ink composition is applied to a ceramic substrate.

[0104] Additionally, elastomers and particularly 3D substrates having non-planar topography can be used in conjunction with the conductive structures. In some embodiments, the ink composition is applied to the elastomer. In some embodiments, the ink composition is applied to the 3D substrate.

[0105] It will be readily apparent to those skilled in the relevant art that other suitable modifications and adaptations to the compositions and methods described herein may be made without departing from the scope of the invention or any embodiment thereof. Having now described the invention in detail, the same will be more clearly understood by reference to the following examples, which are included herein for illustrative purposes only and are not intended to be limiting of the invention. EXAMPLES

[0106] Working Example Synthesis of (chloro)(2-ethyl-1-hexylamine)gold(I): To a 250 mL reaction flask was added chloro(tetrahydrothiophene)gold(I) (10 g) under nitrogen atmosphere. To this was added 120 mL of dry dichloromethane followed by 18 mL of dry acetonitrile. The reaction mixture was stirred for 5 minutes followed by the addition of 2-ethyl-1-hexylamine (5.11 mL). The reaction mixture was left stirring at room temperature for about 12 hours, protected from light. After this time, the volatiles were removed by rotary evaporation to obtain a white fluffy solid crude product. To this was added 10 mL of dry pentane to form a slurry of the product. The product was finally filtered using a glass fritted funnel and washed with 10 mL of pentane (2x). The resulting white product was collected and dried under high vacuum for 16 hours. Yield: 90%. 1 H NMR (CDCl 3 , 400 MHz, ppm) δ 4.67 (s), 4.41 (s), 2.95-2.98 (m), 2.60-2.61(m), 1.61-1.65 (m), 1.27-1.43 (m), 0.87-0.92 (m).

[0107] Synthesis of (trifluoroacetato)(2-ethyl-1-hexylamine)gold(I): An oven dried 500 mL reaction flask was charged with a stir bar and (chloro)(2-ethyl-1-hexylamine)gold(I) (5 g). The atmosphere of the flask was replaced with nitrogen using three vacuum and nitrogen refill cycles using a Schlenk line. To the reaction flask, 140 mL of anhydrous tetrahydrofuran was added via syringe. In a separate reaction flask, silver trifluoroacetate (2.244 g, 0.9 equiv.) was dissolved in 114 mL of anhydrous acetonitrile. The solution was then injected in one portion into the previous reaction mixture. Immediate formation of a white precipitate was observed. The reaction was stirred for 1 hour and filtered using a 0.22 um PTFE filter. The clear filtrate was collected. The volatiles were removed using a rotary evaporator. A thick liquid was obtained, which was further dried using a Schlenk line for 2-3 hours, protected from light, to give a thick gel-like consistency. Yield: 72%. 1 H NMR (CDCl 3 , 400 MHz, ppm) δ 4.95 (s), 2.86-2.88 (m), 2.63-2.64 (m), 1.72(s), 1.72 (m), 1.27-1.44 (m), 0.86-0.92 (m). 19 F NMR (CDCl 3 ,400 MHz, ppm) δ -75.10 (s).

[0108] Exemplary ink formulations using (chloro)(2-ethyl-1-hexylamine)gold(I) precursors and their cure profiles: Formulation 1: 0.200 g (20 wt%) (chloro)(2-ethyl-1-hexylamine)gold(I) was dissolved in 0.800 g (80 wt%) toluene. The solution was stirred for 10 minutes. After filtering through a 0.22 um filter, a clear, transparent solution with a viscosity of 1.2 centipoise and solids content of 4.5 wt% was obtained.

[0109] The ink was printed at 25°C using an Optomec aerosol jet printer equipped with an ultrasonic spray attachment on the platen, with one to three layers of increasing passes. Regular wires and pads were printed on glass substrates for several hours without clogging or any change in the ink appearance. Printing conditions were optimized to print solid lines without ink bleeding or overflow. From 150°C the film began to cure and a shiny gold color was visible. However, higher conductivity is obtained if the film is further cured at higher temperatures. The printed wire-pad structure was annealed at 240°C for 30 minutes and at 300°C for an additional 30 minutes. After curing at 300°C the resulting conductivity is 21% bulk gold.

[0110] Exemplary ink formulations using (trifluoroacetato)(2-ethyl-1-hexylamine)gold(I) and their cure profiles: Formulation 2: 1.000 g (20 wt%) of (trifluoroacetato)(2-ethyl-1-hexylamine)gold(I) was dissolved in 4.000 g (80 wt%) of toluene. The solution was stirred for 10 minutes. After the precursor was completely dissolved, a clear, transparent solution was obtained with a viscosity of 0.8 centipoise and a solids content of 3.9%.

[0111] The ink was printed using an Optomec aerosol jet printer equipped with an ultrasonic spray attachment on the platen, starting at 25°C, in one to three layers of increasing passes. Regular wires and pads were printed on glass substrates for several hours without clogging or any change in the ink appearance. Printing conditions were optimized to print solid lines without ink bleeding or overflow. From 150°C the film started to cure and a shiny gold color was visible. Higher conductivity can be obtained if the printed samples are further cured at higher temperatures. The printed wire-pad structure was annealed on a hotplate by ramping from 25°C to 300°C in 5 minutes and at 300°C for an additional 30 minutes. The resulting conductivity after curing at 300°C was 43% bulk gold.

[0112] Complex 3: 0.600 g (40 wt%) of (trifluoroacetato)(2-ethyl-1-hexylamine)gold(I) was dissolved in 0.900 g (60 wt%) of anisole. The solution was stirred for 10 minutes. After the precursor was completely dissolved, a clear and transparent solution with a viscosity of 1.9 centipoise and a solid content of 9.3% was obtained.

[0113] Using an Optomec aerosol jet printer equipped with an ultrasonic spray attachment on platinum, the ink was printed from 25 °C, increasing the passes from 1 to 3 layers. Normal wires and pads were printed on a glass substrate over several hours without any clogging or little change in the appearance of the ink. The printing conditions were optimized to print solid lines without ink bleeding or ink pooling. The film began to cure at 150 °C and a shiny gold color was visible. When the printed sample was further cured at a high temperature, a higher conductivity was obtained. The printed wire-pad structure was annealed by heating from 25 °C to 300 °C in 5 minutes on a hot plate and then further heating at 300 °C for 30 minutes. The conductivity obtained after curing at 300 °C was 21% of bulk gold.

[0114] Exemplary ink formulations using 2-amino-5-methylhexane gold chloride and their curing profiles: Complex 4: 2-Amino-5-methylhexane gold chloride (10%) was dissolved in pyridine (90%) to form a clear liquid with a solid content of 4% as shown in Figure 1.

[0115] The various layers of the ink formulation were printed on either a glass substrate (Figure 2) or a circuit board substrate (Figure 3). After curing, the gold structures formed from the ink had the physical, electrical, and structural properties shown in Figures 2 and 3. The two-point resistance between "P1" and "P2" of the printed structure shown in Figure 4 was 9 ohms.

[0116] All patents, patent publications, and other published references mentioned in this specification are incorporated by reference in their entirety herein, as if each was individually and specifically incorporated by reference herein.

[0117] Although specific examples are provided, the above description is illustrative and not limiting. Any one or more of the features of the above-described embodiments can be combined with one or more features of any other embodiment in any manner in the present invention. Furthermore, many variations of the present invention will become apparent to those skilled in the art upon review of this specification. Therefore, the scope of the present invention should be determined by reference to the appended claims, along with their full scope of equivalents.

Claims

1. Gold metal, an alkylamine ligand; Solvent and 1. A particle-free conductive ink composition comprising:

2. 2. The particle-free conductive ink composition of claim 1, wherein said gold metal is gold(I) metal ion.

3. 10. The particle-free conductive ink composition of claim 1, wherein the alkylamine ligand is volatile at a temperature of about 200°C or less.

4. The alkylamine ligand is C ３ ~C １２ 10. The particle-free conductive ink composition of claim 1, wherein the ligand is an alkylamine.

5. The particle-free conductive ink composition of claim 1 , wherein the alkylamine ligand is a branched alkylamine ligand.

6. 2. The particle-free conductive ink composition of claim 1, wherein the alkylamine ligand is a primary alkylamine ligand.

7. 2. The particle-free conductive ink composition of claim 1, wherein said alkylamine ligand is an alkyl-substituted hexylamine.

8. 8. The particle-free conductive ink composition of claim 7, wherein the alkyl-substituted hexylamine is a methyl- or ethyl-substituted hexylamine.

9. 9. The particle-free conductive ink composition of claim 8, wherein the alkyl-substituted hexylamine is 2-ethyl-1-hexylamine or 2-amino-5-methylhexane.

10. 2. The particle-free conductive ink composition of claim 1, wherein the alkylamine ligand is a dichelated primary, secondary or tertiary alkyldiamine compound.

11. The alkylamine ligand has the formula (I): 【Chemistry 9】 wherein each R is independently hydrogen or C １ ~C １４ an alkyl group, and n is 1 to 14.

11. The particle-free conductive ink composition of claim 10 having the structure:

12. Each R group is independently hydrogen or C １ ~C ４ The particle-free conductive ink composition of claim 11, wherein n is an alkyl group and each n is independently 1-10.

13. The alkylamine ligand is a C substituted with at least one heteroatom. ２ ~C １２ 10. The particle-free conductive ink composition of claim 1, wherein the ligand is an alkylamine.

14. 14. The particle-free conductive ink composition of claim 13, wherein said at least one heteroatom is at least one oxygen or sulfur.

15. The alkylamine ligand is C ４ ~C １０ 2. The particle-free conductive ink composition of claim 1, which is a 2-amino-alkyl compound.

16. The particle-free conductive ink composition of claim 1 , wherein the solvent comprises an aromatic solvent.

17. The particle-free conductive ink composition of claim 1 , wherein the solvent comprises an alkyl or aromatic ether solvent.

18. The particle-free conductive ink composition of claim 1, wherein the solvent comprises tetrahydrofuran or 2-methyltetrahydrofuran.

19. The particle-free conductive ink composition of claim 1 , wherein the solvent comprises an amide-based solvent.

20. The particle-free conductive ink composition of claim 1 , wherein the solvent comprises an aromatic heterocyclic solvent.

21. 21. The particle-free conductive ink composition of claim 20, wherein the aromatic heterocyclic solvent comprises pyridine or pyrazine.

22. 22. The particle-free conductive ink composition of claim 21, wherein the aromatic heterocyclic solvent comprises pyridine or 2,5-dimethylpyrazine.

23. The particle-free conductive ink composition of claim 1 further comprising a counter ion.

24. 24. The particle-free conductive ink composition of claim 23, wherein the counter ion is a carboxylate.

25. 25. The particle-free conductive ink composition of claim 24, which releases carbon dioxide when heated.

26. 26. The particle-free conductive ink composition of claim 25, which releases carbon dioxide when heated below about 300°C.

27. 24. The particle-free conductive ink composition of claim 23, wherein said counterion is a haloacetate.

28. 28. The particle-free conductive ink composition of claim 27, wherein said haloacetate is a trifluoroacetate.

29. 24. The particle-free conductive ink composition of claim 23, wherein the counterion is nitrate, nitrite, tetrafluoroborate or hexafluorophosphate.

30. 10. The particle-free conductive ink composition of claim 1 which forms a conductive metal film upon curing at or below 300°C.

31. 10. The particle-free conductive ink composition of claim 1, wherein the conductive metal film exhibits a conductivity of at least 1% of the bulk metal conductivity.

32. 1. A method of forming a conductive film, comprising: Providing a particle-free conductive ink composition according to any one of claims 1 to 31; applying the composition to a substrate; curing the composition at an elevated temperature to form the conductive film. A method comprising:

33. 33. The method of claim 32, wherein the applying step comprises printing.

34. 34. The method of claim 33, wherein the printing step is a jet printing step.

35. 35. The method of claim 34, wherein the jet printing step is an aerosol jet printing step.

36. 33. The method of claim 32, wherein the composition cures at or below 300°C.

37. 32. A conductive film formed by applying the particle-free conductive ink composition of any one of claims 1 to 31 to a substrate and curing the composition at elevated temperature to form a conductive film.

38. 38. The conductive film of claim 37, wherein the curing is at or below 300°C.

39. 1. A method for preparing a particle-free conductive ink composition comprising the steps of: Providing an alkylamine-gold complex; dissolving the alkylamine-gold complex in a solvent to form the particle-free conductive ink composition; the alkylamine-gold complex comprises gold metal and an alkylamine ligand; The method of claim 1, wherein the particle-free conductive ink composition forms a conductive metal film by curing at an elevated temperature.

40. 40. The method of claim 39, wherein the gold metal is gold(I) metal ion.

41. 40. The method of claim 39, wherein the alkylamine ligand is volatile at a temperature of about 200° C. or less.

42. The alkylamine ligand is C ３ ~C １２ 40. The method of claim 39, which is an alkylamine.

43. 40. The method of claim 39, wherein the alkylamine ligand is a branched alkylamine.

44. 40. The method of claim 39, wherein the alkylamine ligand is a primary alkylamine.

45. 40. The method of claim 39, wherein the alkylamine ligand is an alkyl substituted hexylamine.

46. 46. ​​The method of claim 45, wherein the alkyl substituted hexylamine is a methyl or ethyl substituted hexylamine.

47. 47. The method of claim 46, wherein the alkyl substituted hexylamine is 2-ethyl-1-hexylamine or 2-amino-5-methylhexane.

48. 40. The method of claim 39, wherein the alkylamine ligand is a dichelated primary, secondary or tertiary alkyldiamine compound.

49. The alkylamine ligand has the formula (I): 【Chemistry 10】 wherein each R is independently hydrogen or C １ ~C １４ an alkyl group, and n is 1 to 14.

49. The method of claim 48 having the structure:

50. Each R group is independently hydrogen or C １ ~C ４ 50. The method of claim 49, wherein each n is independently an alkyl group and each n is 1 to 10.

51. The alkylamine ligand is a C substituted with at least one heteroatom. ２ ~C １２ 40. The method of claim 39, wherein the ligand is an alkylamine.

52. 52. The method of claim 51 , wherein the at least one heteroatom is at least one oxygen or sulfur.

53. The alkylamine ligand is C ４ ~C １０ The method of claim 39, which is a 2-amino-alkyl compound.

54. 40. The method of claim 39, wherein the solvent comprises an aromatic solvent.

55. 40. The method of claim 39, wherein the solvent comprises an alkyl or aromatic ether solvent.

56. 40. The method of claim 39, wherein the solvent comprises tetrahydrofuran or 2-methyltetrahydrofuran.

57. 40. The method of claim 39, wherein the solvent comprises an amide solvent.

58. 40. The method of claim 39, wherein the solvent comprises an aromatic heterocyclic solvent.

59. 59. The method of claim 58, wherein the aromatic heterocyclic solvent comprises pyridine or pyrazine.

60. 60. The method of claim 59, wherein the aromatic heterocyclic solvent comprises pyridine or 2,5-dimethylpyrazine.

61. 40. The method of claim 39, wherein the particle-free conductive ink composition further comprises a counter ion.

62. 62. The method of claim 61 , wherein the counterion is a carboxylate.

63. 63. The method of claim 62, wherein the particle-free conductive ink composition releases carbon dioxide when heated.

64. 64. The method of claim 63, wherein the particle-free conductive ink composition releases carbon dioxide when heated below about 300°C.

65. 62. The method of claim 61 , wherein the counterion is a haloacetate.

66. 66. The method of claim 65, wherein the haloacetate is a trifluoroacetate.

67. 62. The method of claim 61, wherein the counterion is nitrate, nitrite, tetrafluoroborate or hexafluorophosphate.

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