Flexible membrane for applying a pattern to a substrate
A method is disclosed for applying an electrical conductor to a solar cell, which comprises providing a flexible membrane with a pattern of groove formed on a first surface thereof, and loading the grooves with a composition comprising conductive particles. The composition is, or may be made, electrically conductive. Once the membrane is loaded, the grooved first surface of the membrane is brought into contact with a front or/and back of a solar cell. A pressure is then applied between the solar cell and the membrane(s) so that the composition loaded to the grooves adheres to the solar cell. The membrane(s) and the solar cell are separated and the composition in the groove is left on the solar cell surface. The electrically conductive particles in the composition are then sintered or otherwise fused to form a pattern of electrical conductor on the solar cell, the pattern corresponding to the pattern formed in the membrane(s).
1. A flexible membrane suitable for applying a pattern of electrical conductors to a substrate, the membrane comprising:
a) at least a first layer comprising a formable thermoplastic polymer capable of being cast or embossed, the first layer having at least a first surface;
b) the first surface having a pattern comprising a plurality of grooves cast or embossed therein, the first surface further comprising ungrooved parts; and
c) a dry transferable composition loaded into the grooves of the pattern, the composition comprising as components thereof particles made of an electrically conductive material and an adhesive, the composition being substantially level with the first surface of the membrane and being adapted to become electrically conductive upon sintering by application of energy thereto, the composition being substantially absent from the ungrooved parts;
at least the first layer of the membrane being conformable to the substrate and being such that upon pressing the first surface of the membrane and the substrate against one another, the transferable composition in the grooves adheres more strongly to the substrate than to the membrane, and such that a subsequent separation of the membrane from the substrate results in the composition remaining on the substrate in a pattern mirroring that of the loaded grooves, the conformability of the first surface and the transferability of the composition being independent of the presence or absence of an adhesive layer between the membrane and the substrate.
2. The flexible membrane of claim 1 , wherein the composition in the grooves is constituted of two or more layers.
3. The flexible membrane of claim 2 , wherein at least two layers of the two or more layers have different components and/or different relative proportions of the components of the composition.
4. The flexible membrane of claim 1 , further comprising a release coating disposed at least on walls of the grooves and between the composition loaded into the grooves and the walls of the grooves.
5. The flexible membrane of claim 1 , further comprising a light modifying coating disposed between the composition loaded into the grooves and walls of the grooves.
6. The flexible membrane of claim 1 , further comprising a release coating disposed at least on walls of the grooves and a light modifying coating disposed between the release coating and the composition loaded into the respective groove.
7. The flexible membrane of claim 1 , wherein at least two grooves in the pattern, or two different segments of the same groove, have different cross-sectional dimensions.
8. The flexible membrane of claim 1 , wherein the composition loaded into the grooves, or a layer thereof, further comprises a glass frit, as an additional composition component.
9. The flexible membrane of claim 1 , further comprising at least a second layer coupled to the first layer.
10. The flexible membrane of claim 1 , wherein the formable thermoplastic polymer is selected from the group consisting of cyclic olefin copolymer (COC), polyethylene (PE), cast polypropylene (CPP), any other type of polypropylene (PP), thermoplastic polyurethane (TPU), and combinations thereof.
11. The flexible membrane of claim 1 , wherein the first surface of the flexible membrane has a mean roughness Rz of 1 μm or less, 500 nm or less, 250 nm or less, or 100 nm or less.
12. The flexible membrane of claim 1 , wherein the particles of electrically conductive material are made of compounds selected from the group consisting of metals, alloys, organo-metals, conductive polymers, conductive polymers precursors, salts thereof and combinations thereof.
13. The flexible membrane of claim 1 , wherein the adhesive includes at least one of (i) an organic binder, (ii) an organic adhesive that is a pressure and/or heat sensitive adhesive, and (iii) a glass frit.
14. The flexible membrane of claim 1 , wherein at least a portion of the electrical conductors applicable thereby have a tapering cross-section profile having a base width W B and a height h, such that a dimensionless aspect ratio ASP between the height and the base width (ASP=h/W B ) of the profile is within a range of 5:1 to 1:5, 5:1 to 0.7:1, 3:1 to 1:1, 2:1 to 1:2, 1.75:1 to 1:1.75, and 1.5:1 to 1:1.5.
15. The flexible membrane of claim 1 , wherein at least a portion of the electrical conductors applicable thereby have a tapering cross-section profile selected from a group comprising a triangular, trapezoidal, polygonal, semi-circular, and semi-elliptic profile.
16. The flexible membrane of claim 1 , wherein at least a portion of the electrical conductors applicable thereby have a tapering cross-section profile and wherein a tapering face of the cross-section profile (a) forms an angle with the first surface of the membrane of at least 30°, at least 40°, at least 45°, at least 50° or at least 60° and/or (b) has an averaged slope of at least 0.75, at least 1, at least 1.3, or at least 1.4.
17. The flexible membrane of claim 1 , wherein at least a portion of the electrical conductors applicable thereby have a tapering cross-section profile and wherein a tapering face of the cross-section profile (a) forms an angle with the first surface of the membrane of at most 90°, at most 85° or at most 80°; and/or (b) has an averaged slope of at most 10, at most 8, at most 4 or at most 2.
18. The flexible membrane of claim 1 , wherein the plurality of grooves includes more than five grooves and at least five of the plurality of grooves are adapted to form a plurality of substantially identical grid lines upon transfer of the composition loaded therein to the substrate, the grid lines having at least one of the following features in substantially identical respective segments of the grid lines:
a) a width variability of 5% or less;
b) a depth variability of 5% or less; and
c) a cross-section area variability of 5% or less.
19. The flexible membrane of claim 1 , wherein at least the first layer of the membrane is sufficiently conformable to the surface of the substrate to permit transfer of the composition to the substrate upon pressing the first surface of the membrane and the substrate against one another, in the absence of any adhesive layer between the flexible membrane and the substrate.
20. The flexible membrane of claim 1 , wherein the membrane is disposable.
21. The flexible membrane of claim 1 , wherein at least the first layer of the membrane is sufficiently conformable to the surface of the substrate to permit transfer of the composition to the substrate upon pressing the first surface of the membrane and the substrate against one another, in the presence of an adhesive layer on the first surface of the flexible membrane, the adhesive layer having a dried thickness of 2 μm or less.