Solvent-free conductive paste composition and solar cell element employing the same
A solvent-free conductive paste composition including (a) a binder, (b) an initiator, (c) a glass powder and (d) a conductive powder; and a solar cell element having an electrode or wire made by coating and sintering the conductive paste composition coated on a silicon semiconductor substrate. The conductive paste composition is solvent-free so that it will not cause environmental problems with respect to the evaporation of solvents and will not be easy to spread out. The conductive paste composition facilitates the development of fine wire and high aspect ratio designs and can efficiently enhance the photoelectric conversion efficiency.
1. A solvent-free conductive paste composition comprising: (a) a binder, (b) an initiator, (c) a glass powder and (d) a conductive powder, wherein the conductive paste composition comprises, based on the total weight of the conductive paste composition, 13-20% of the binder, 73-80% of the conductive powder, 3-5% of the glass powder, and 0.05-10% of the initiator; and exhibits a thixotropic index of 3.5-5.5, and wherein the conductive paste composition does not comprise a solvent, wherein the binder comprises:
(i) a monomer comprising an acrylic monomer, an acrylate monomer or a mixture thereof; and
(ii) an acrylate oligomer; and
wherein the acrylate oligomer has a molecular weight in a range from about 1,000 to about 100,000 and is selected from the group consisting of a urethane acrylate, an epoxy acrylate, a polyester acrylate, a polyester polyol based acrylate, an acrylate homopolymer and a mixture thereof.
2. The conductive paste composition of claim 1 , wherein the binder further comprises (iii) an acrylate polymer.
3. The conductive paste composition of claim 2 , wherein the acrylate polymer a molecular weight of more than 100,000 and is pressure sensitive and selected from the group consisting of a urethane acrylate, an epoxy acrylate, a polyester acrylate, a polyester polyol based acrylate, an acrylate homopolymer and a mixture thereof.
4. The conductive paste composition of claim 1 , wherein the monomer is used in an amount of 20-70%, based on the total weight of the binder.
5. The conductive paste composition of claim 4 , wherein the amount of the monomer is 30-65%.
6. The conductive paste composition of claim 1 , wherein the monomer is an acrylate monomer having a molecular weight of less than 1,000 and is selected from the group consisting of 2-phenoxy ethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, isoborny acrylate, 1,4-butanediol diacrylate, triethylene glycol dimethacrylate, trimethylol propane triacrylate and a mixture thereof.
7. The conductive paste composition of claim 6 , wherein the monomer has a molecular weight in a range from 180 to 700.
8. The conductive paste composition of claim 1 , wherein the initiator is a thermal initiator or a photoinitiator.
9. The conductive paste composition of claim 8 , wherein the thermal initiator is selected from the group consisting of phenyl peroxide, dicumyl peroxide, butyl hydroperoxide, cumene hydroperoxide, tert-butyl maleic acid peroxide, acetyl peroxide, lauroyl peroxide, a mixture of one or more of the above peroxides with an amino acid or a sulfonic acid, a mixture of one or more of the above peroxides with a cobalt-containing compound, azodiisobutyronitrile and a mixture thereof.
10. The conductive paste composition of claim 1 , wherein the photoinitiator is selected from the group consisting of benzophenone, benzoin, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxy cyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl diphenyl phosphine oxide and a mixture thereof.
11. The conductive paste composition of claim 1 , wherein the conductive powder is a conductive metal, an alloy of a conductive metal, or a mixture thereof.
12. A solar cell element comprising an electrode or wires, wherein the electrode or wires comprises a cured conductive paste composition of claim 1 .
13. A process for making an electrode or wires for use in a solar cell element, which comprises printing the conductive paste composition of claim 1 on a substrate to form a desired pattern, and curing the pattern by irradiation with energy rays and/or heat.
14. The conductive paste composition of claim 1 , which further comprises an additive selected from the group consisting of a synergist, a sensitizer, a coupling agent, a thickening agent, an antifoaming agent, and a thixotroping agent.
15. The conductive paste composition of claim 1 , wherein the composition has a viscosity of 30000-60000 cps.