Low viscosity precursor compositions and methods for the deposition of conductive electronic features
A precursor composition for the deposition and formation of an electrical feature such as a conductive feature. The precursor composition advantageously has a low viscosity enabling deposition using direct-write tools. The precursor composition also has a low conversion temperature, enabling the deposition and conversion to an electrical feature on low temperature substrates. A particularly preferred precursor composition includes silver metal for the formation of highly conductive silver features.
1 . A process for forming a solar cell conductive feature, comprising:
(a) atomizing a precursor composition to form an aerosol comprising droplets of the precursor composition, the precursor composition comprising at least one of metallic particles comprising a metal or a metal precursor compound to the metal;
(b) transporting the droplets to a substrate through a flow channel; and
(c) heating the precursor composition to form the solar cell conductive feature on the substrate, wherein the solar cell conductive feature has a feature width of not greater than 200 μm, a thickness of at least 1 μm, and a conductivity that is no less than 10 percent the conductivity of the equivalent pure metal.
2 . The process of claim 1 , wherein the precursor composition has a viscosity not greater than 20 centipoise.
3 . The process of claim 1 , wherein the atomizing is achieved by ultrasonic atomization, a two-fluid spray head, or a pressure atomizing nozzle.
4 . The process of claim 1 , wherein the droplets have an average droplet size that is not greater than about 10 μm
5 . The process of claim 1 , wherein the droplets have an average droplet size that is not greater than about 5 μm.
6 . The process of claim 1 , wherein the process further comprises removing large droplets from the aerosol with an impactor.
7 . The process of claim 1 , wherein the concentration of the aerosol is increased with a virtual impactor.
8 . The process of claim 1 , wherein the concentration of the aerosol is greater than about 10 6 droplets/cm 3 .
9 . The process of claim 1 , wherein the concentration of the aerosol is greater than about 10 7 droplets/cm 3 .
10 . The process of claim 1 , wherein the process further comprises monitoring the concentration of the aerosol, and maintaining the concentration within 10% of a desired concentration over a period of time.
11 . The process of claim 1 , wherein the droplets are deposited onto a surface of the substrate by inertial impaction.
12 . The process of claim 1 , wherein the droplets are deposited onto a surface of the substrate by inertial impaction of larger droplets, electrostatic deposition of charged droplets, diffusional deposition of sub-micron droplets, interception onto non-planar surfaces or settling of droplets.
13 . The process of claim 1 , wherein the droplets are transported to the substrate in a flow gas through the flow channel.
14 . The process of claim 1 , wherein the thickness is at least 5 μm.
15 . The process of claim 1 , wherein the conductive feature has a resistivity that is not greater than 4 times the resistivity of the equivalent pure metal.
16 . The process of claim 1 , wherein the conductive feature has a resistivity that is not greater than 2 times the resistivity of the equivalent pure metal.
17 . The process of claim 1 , wherein the heating comprises heating the precursor composition to a temperature not greater than 225° C. to form the solar cell conductive feature on the substrate.
18 . The process of claim 1 , wherein the heating comprises heating the precursor composition to a temperature not greater than 185° C. to form the solar cell conductive feature on the substrate.
19 . The process of claim 1 , wherein the substrate has a softening point of not greater than about 225° C.
20 . The process of claim 1 , wherein the substrate comprises a polymer.
21 . The process of claim 1 , wherein the substrate comprises a ceramic.
22 . The process of claim 1 , wherein the precursor composition comprises the metallic particles comprising the metal, and wherein the heating sinters adjacent particles to one another.
23 . The process of claim 1 , wherein the precursor composition comprises the metal precursor compound.
24 . The process of claim 23 , wherein the metal is selected from the group consisting of silver, palladium, copper, gold, platinum and nickel.
25 . The process of claim 1 , wherein the precursor composition comprises the metallic particles.
26 . The process of claim 25 , wherein the metal is selected from the group consisting of silver, palladium, copper, gold, platinum and nickel.
27 . The process of claim 1 , wherein the precursor composition further comprises metal oxide particles.
28 . The process of claim 1 , wherein the precursor composition further comprises glass particles.
29 . The process of claim 1 , wherein the conductive feature comprises a set of finger lines and collector lines deposited essentially at a right angle to the finger lines.
30 . The process of claim 29 , wherein either or both the parallel finger lines or the collector lines have width less than 200 μm.
31 . The process of claim 29 , wherein either or both the parallel finger lines or the collector lines have width less than 100 μm.
32 . The process of claim 1 , wherein the conductive feature comprises a transparent conductive feature.
33 . The process of claim 1 , wherein the conductive feature comprises indium-tin oxide or antimony-tin oxide.
34 . The process of claim 1 , wherein the precursor composition comprises the metallic particles, the metallic particles having a volume median particle size of not greater than 100 nanometers.
35 . The process of claim 1 , wherein the precursor composition comprises the metallic particles, the metallic particles having a volume median particle size of not greater than 0.3 μm.
36 . The process of claim 35 , wherein the metallic particles comprise a cap or coating thereon.
37 . The process of claim 36 , wherein the cap or coating comprises an inorganic cap or coating.
38 . The process of claim 36 , wherein the cap or coating comprises silica.
39 . The process of claim 36 , wherein the cap or coating comprises glass.
40 . The process of claim 36 , wherein the cap or coating comprises an organic cap or coating.
41 . The process of claim 36 , wherein the cap or coating comprises a polymer.
42 . The process of claim 36 , wherein the cap or coating comprises an intrinsically conductive polymer, a sulfonated perfluorohydrocarbon polymer, polystyrene, polystyrene/methacrylate, sodium bis(2-ethylhexyl) sulfosuccinate, tetra-n-octyl-ammonium bromide or an alkane thiolate.
43 . The process of claim 36 , wherein the cap or coating comprises PVP.
44 . The process of claim 1 , wherein the conductive feature comprises a metal-glass composition.
45 . The process of claim 1 , wherein the conductive feature is resistant to solder leaching.
46 . The process of claim 1 , wherein the process further comprises high shear mixing the precursor composition.
47 . The process of claim 1 , wherein the process further comprises surface modifying the substrate with a laser.