# US 2019/0172967 A1 · Application of Electrical Conductors of a Solar Cell > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0172967 A1 - Document ID: US20190172967A1 - Status: Published application - Kind: A1 - Application number: 16/258,808 - Filed: 2019-01-28 - Published: 2019-06-06 - Earliest claimed: 2016-08-28 - Assignees: Landa Labs (2012) Ltd. - Applicants: Landa Labs (2012) Ltd - Inventors: Benzion LANDA; Naomi ELFASSY; Stanislav THYGELBAUM - Web page: https://patentgrep.com/patent/US20190172967A1 ## CPC - H05K 3/207: {using a prefabricated paste pattern, ink pattern or powder pattern} - B41M 1/12: Stencil printing; Silk-screen printing - H05K 1/0393: {Flexible materials (H05K1/038 takes precedence; specific organic compositions are classified in H05K1/0313 and subgroups)} - H05K 1/092: {Dispersed materials, e.g. conductive pastes or inks} - H05K 3/3485: Application of solder paste, slurry or powder (using printing techniques to form the desired conductive pattern of the printed circuit by applying conductive material H05K3/12) - H05K 3/386: {by the use of an organic polymeric bonding layer, e.g. adhesive} - H10F 71/107: {Continuous treatment of the devices, e.g. roll-to roll processes or multi-chamber deposition} - H10F 77/1698: {the metallic or insulating substrates being flexible} - H10F 77/211: {for photovoltaic cells} - H10F 77/215: {Geometries of grid contacts} - H10F 77/311: {for photovoltaic cells} - H05K 1/0284: {Details of three-dimensional rigid printed circuit boards (H05K1/119 takes precedence; shaping of the substrate H05K3/0014)} - H05K 1/165: {incorporating printed inductors} - H05K 2201/0195: Dielectric or adhesive layers comprising a plurality of layers, e.g. in a multilayer structure - H05K 2201/0338: Layered conductor, e.g. layered metal substrate, layered finish layer or layered thin film adhesion layer - H05K 2201/035: Paste overlayer, i.e. conductive paste or solder paste over conductive layer - H05K 2201/0391: Using different types of conductors - H05K 2201/10098: Components for radio transmission, e.g. radio frequency identification [RFID] tag, printed or non-printed antennas - H05K 2203/0139: Blade or squeegee, e.g. for screen printing or filling of holes - H05K 2203/1105: Heating or thermal processing not related to soldering, firing, curing or laminating, e.g. for shaping the substrate or during finish plating - H05K 2203/1131: Sintering, i.e. fusing of metal particles to achieve or improve electrical conductivity - H05K 2203/1476: Same or similar kind of process performed in phases, e.g. coarse patterning followed by fine patterning - H05K 2203/1545: Continuous processing, i.e. involving rolls moving a band-like or solid carrier along a continuous production path - Y02E 10/50: Photovoltaic [PV] energy - Y02E 10/52: PV systems with concentrators - H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS - B41M: PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING, (correction of typographical errors B41J; processes for applying transfer pictures or the like B44C1/16; fluid media for correction of typographical errors by coating C09D10/00; printing textiles D06P) - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract 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). ## Claims ### Claim 1 A method of applying a pattern of electrical conductors to a substrate formed by a surface of a solar cell, which method comprises: a) providing a flexible membrane, wherein a first surface of the membrane has a pattern of grooves formed therein, the pattern corresponding at least partially to a desired pattern of electrical conductors to be applied to the substrate; b) loading into the grooves of the first surface of the membrane a composition that includes, as composition components, electrically conductive particles and an adhesive, said loading being performed in one or more filling cycle(s) such that on completion of loading the composition substantially fills the grooves, level with the first surface of the membrane, and parts of the first surface between the grooves are substantially devoid of the composition; c) contacting the membrane with the substrate, with the first surface of the membrane facing the substrate; d) applying pressure to the membrane to cause the composition loaded into the grooves in the first surface of the membrane to adhere to the substrate; e) separating the membrane from the substrate to transfer the composition from the grooves in the first surface of the membrane to the substrate; and f) applying sufficient energy to sinter the electrically conductive particles and to render electrically conductive the pattern of composition transferred to the substrate from the grooves. ### Claim 2 (depends on 1) The method of claim 1, wherein the composition loaded into the grooves comprises, as an additional composition component, a liquid carrier to form a wet composition, and wherein each filling cycle includes the steps of: (i) applying an excess of the wet composition to the whole of the first surface of the membrane; (ii) removing excess wet composition from the first surface to leave the wet composition substantially only within the grooves in the first surface of the membrane; and (iii) substantially drying the wet composition within the grooves by removing the liquid carrier to leave dried composition. ### Claim 3 (depends on 2) The method of claim 2, wherein the relative proportions of the components of the composition applied during different filling cycles differ from one another. ### Claim 4 (depends on 1) The method of claim 1, wherein a release coating is applied to the grooves of the membrane and dried thereon, prior to loading of the composition into the grooves. ### Claim 5 (depends on 1) The method of claim 1, further comprising, prior to step b), the steps of: A. applying a light modifying coating to the first surface of the membrane, B. wiping the first surface to leave the coating substantially only within the grooves, and C. subsequently drying the light modifying coating to leave the dried light modifying coating only on the walls of the grooves. ### Claim 6 (depends on 1) The method of claim 1, wherein prior to contacting said membrane with said substrate according to step c), an adhesive coating is applied to at least one of the first surface of the membrane and the substrate so as to coat any composition present in the grooves, a dried thickness of said adhesive coating not exceeding 2 μm. ### Claim 7 (depends on 1) The method of claim 1, wherein at least two grooves in the pattern, or two different segments of the same groove, have different cross-sectional dimensions. ### Claim 8 (depends on 1) The method of claim 1, wherein the substrate comprises a semiconductor wafer, and wherein at least one of the compositions loaded into the grooves includes a glass frit, as an additional composition component, and wherein the substrate and the composition are heated, following step e), to cause the composition to fuse with the substrate. ### Claim 9 (depends on 1) The method of claim 1, wherein the flexible membrane is selected from a preformed membrane of plastics polymer and a cast plastics polymer. ### Claim 10 (depends on 9) The method of claim 9, wherein the plastics polymer is a thermoplastic polymer, 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. ### Claim 11 (depends on 1) The method of claim 1 wherein the first surface of the flexible membrane has a mean roughness Rz of 1 μm or less. ### Claim 12 (depends on 1) The method 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. ### Claim 13 (depends on 1) The method 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. ### Claim 14 (depends on 1) The method of claim 1, wherein the step of providing a flexible membrane having a pattern of grooves formed in a first surface thereof comprises advancing a continuous membrane between a die roller and a counter die, the die roller having protruding rules complementary to the pattern of grooves to be formed on the membrane. ### Claim 15 (depends on 1) The method of claim 1, wherein the step of applying sufficient energy to sinter the electrically conductive particles comprises raising heating the composition at at least one temperature within a range of 150° C. to 800° C. for a duration not exceeding two minutes. ### Claim 16 (depends on 1) The method of claim 1, wherein the pattern of grooves includes longitudinal grooves forming contiguous or distinct straight or curved lines, at least a portion of each line having a tapering cross section profile selected from a triangular, trapezoidal, polygonal, semi-circular, or semi-elliptic profile, any of the profiles having at least a base width WB and a height h, the dimensionless aspect ratio ASP between the height and the base width being within a range of 5:1 to 0.7:1. ### Claim 17 (depends on 16) The method of claim 16, wherein the electrically conductive pattern of electrical conductors includes grid lines for collecting current generated by the solar cell, and wherein a sum of the lengths of any segments of a grid line cross-section width that are inclined to the plane of the substrate at an angle of less than 45° does not exceed 15 μm. ### Claim 18 (depends on 1) The method of claim 1, wherein the electrically conductive pattern of electrical conductors includes grid lines for collecting current generated by the solar cell, wherein when, for at least five grid lines, at least ten width measurements are made at spaced points along each grid line and a mean width value and a standard deviation is calculated for each grid line, the average of the standard deviations calculated for the at least five grid lines is no more than 5% of the average of the mean width values calculated for the at least five grid lines. ### Claim 19 (depends on 1) The method of claim 1, wherein the electrically conductive pattern of electrical conductors includes grid lines for collecting current generated by the solar cell, said grid lines having a normalized contact resistance of at most 0.3 Ω.cm when the substrate has a sheet resistance of at least 50 Ω/□ (i.e. 50 Ω/sq) and at most 110 Ω/□ and when the grid lines have a width of at least 15 μm and a height of at least 8 μm; or the grid lines have a normalized contact resistance of at most 0.6 Ω.cm when the substrate has a sheet resistance of at least 111 Ω/□ and at most 140 Ω/□, and when the grid lines have a width of at least 15 μm and a height of at least 8 μm. ### Claim 20 (depends on 1) The method of claim 1, further comprising following step (d), cooling the membrane and substrate down to a predetermined temperature, wherein in step (d) the pressure applied to the membrane also causes the membrane to retain contact with the substrate until after the membrane and substrate have cooled down to the predetermined temperature, regardless of any amount of adhesive between the first surface of the membrane and the substrate. ### Claim 21 A flexible membrane suitable for applying a pattern of electrical conductors to a substrate formed by a surface of a solar cell, the membrane having a first surface that includes a pattern of grooves, the grooves being loaded so as to be substantially level with the surface of the membrane with a composition that includes electrically conductive particles and an adhesive, the composition being adapted to become electrically conductive upon sintering by application of energy thereto, and ungrooved parts of the first surface being substantially devoid of the composition; the membrane being such that upon pressing the membrane and the substrate against one another, the composition in the grooves adheres more strongly to the substrate than to the membrane, and such that subsequent separation of the membrane from the substrate results in the composition remaining on the substrate in a pattern mirroring that of the grooves. ### Claim 22 A solar cell consisting of a substrate and an electrically conductive pattern comprising a pattern of electrical conductors including grid lines for collecting current generated by the solar cell, wherein the pattern of electrical conductors is applied to the substrate by a method comprising: a) providing a flexible membrane, wherein a first surface of the membrane has a pattern of grooves formed therein, the pattern corresponding at least partially to a desired pattern of electrical conductors to be applied to the substrate; b) loading into the grooves of the first surface of the membrane a composition that includes, as composition components, electrically conductive particles and an adhesive, said loading being performed in one or more filling cycle(s) such that on completion of loading the composition substantially fills the grooves, level with the first surface of the membrane, and parts of the first surface between the grooves are substantially devoid of the composition; c) contacting the membrane with the substrate, with the first surface of the membrane facing the substrate; d) applying pressure to the membrane to cause the composition loaded into the grooves in the first surface of the membrane to adhere to the substrate; e) separating the membrane from the substrate to transfer the composition from the grooves in the first surface of the membrane to the substrate; and f) applying sufficient energy to sinter the electrically conductive particles and to render electrically conductive the pattern of composition transferred to the substrate from the grooves. ### Claim 23 A solar cell having an electrically conductive pattern comprising a pattern of electrical conductors applied on a light harvesting side of the solar cell, the electrical conductors including grid lines for collecting current generated by the solar cell, wherein at least part of the electrical conductors fulfils the following structural features: a) the electrical conductors have a cross-section profile with a base of a width WB contacting the light harvesting side of the solar cell, an orthogonal distance h between the base and a top point of the profile (also termed the height of the profile), and an aspect ratio ASP between the height of the profile and the base width (ASP=h/WB), wherein: i. WB is at most 50 μm, ii. h is at most 50 μm; and iii. ASP is at least 0.7:1 and at most 5:1; b) wherein when, for at least five grid lines, at least ten width measurements are made at spaced points along each grid line and a mean width value and a standard deviation is calculated for each grid line, the average of the standard deviations calculated for the at least five grid lines is no more than 5% of the average of the mean width values calculated for the at least five grid lines; c) wherein when, for at least five grid lines, at least ten height measurements are made at spaced points along each grid line and a mean height value and a standard deviation is calculated for each grid line, the average of the standard deviations calculated for the at least five grid lines is no more than 5% of the average of the mean height values calculated for the at least five grid lines; and d) the grid lines have a normalized contact resistance of at most 0.3 Ω.cm when a sheet resistance of the light harvesting side is at least 50 Ω/□ and at most 110 Ω/□ and when the grid lines have a width of at least 15 μm and a height of at least 8 μm, or the grid lines have a normalized contact resistance of at most 0.6 Ω.cm when a sheet resistance of the light harvesting side is at least 111 Ω/□ and at most 140 Ω/□, and when the grid lines have a width of at least 15 μm and a height of at least 8 μm. ### Claim 24 (depends on 23) The solar cell of claim 23, wherein the grid lines fulfil features a) to d). ### Claim 25 (depends on 23) The solar cell of claim 23, wherein at least part of the electrical conductors additionally fulfils one or more of the following features: a. the electrical conductors consist of one or more sintered electrically conductive materials; b. a cross-section slice of the electrical conductors perpendicular to the light harvesting side of the solar cell comprises two or more layers of different sintered materials, the layers optionally following the profile of the cross-section of the conductors, and symmetric on opposite sides of an axis traversing the layers; c. the grid lines have an external surface with light reflective and low light diffusivity properties; d. a cross-section profile of the electrical conductors has at least two sides rising from a base of the profile, wherein an average of a slope along half of the width of the basis, as assessed by the tangent value of the angles formed between at least one of the two sides and the base of the profile, is at least 1.4 and at most 10; e. a sum of the lengths of any segments of a grid line cross-section that are inclined to the plane of the substrate at an angle of less than 45° does not exceed 15 μm; and f. wherein when, for at least five grid lines, at least ten cross-section area measurements are made at spaced points along each grid line and a mean cross-section area value and a standard deviation is calculated for each grid line, the average of the standard deviations calculated for the at least five grid lines is no more than 5% of the average of the mean cross-section area values calculated for the at least five grid lines.