Solder paste for module fabrication of solar cells
A method of fabricating a solar module by interconnection of a plurality of photovoltaic (PV) cells in which at least a first PV cell is interconnected to a second PV cell using an electrically-conductive adherent comprising or consisting of a solder paste. The solder paste comprises particles of solder alloy dispersed in a solder flux. The solder alloy comprises a Sn-containing solder alloy having a liquidus temperature of less than 225° C.
1 . A method of fabricating a solar module by interconnection of a plurality of photovoltaic (PV) cells in which at least a first PV cell is interconnected to a second PV cell using an electrically-conductive adherent comprising or consisting of a solder paste;
the solder paste comprising particles of solder alloy dispersed in a solder flux;
wherein the solder alloy comprises from 48 to 51 wt. % Bi, from 0.7 to 1.1 wt. % Cu, from 0.02 to 0.09 wt. % Co, from 0.8 to 1.1 wt. % Ag, and the balance being tin together with any unavoidable impurities, and wherein the solder alloy has a liquidus temperature of less than 225° C.;
wherein the solder flux comprises:
from 25 to 40 wt. % of a rosin and/or a resin,
from 12 to 20 wt. % of an activator,
from 10 to 20 wt. % of a surfactant, and
from 20 to 40 wt. % of a solvent;
wherein the solar module comprises a back-contact assembly in which a rear face of the first PV cell is directly interconnected with a rear face of the second PV cell by one or more ribbons, wherein the one or more ribbons are connected to the rear face of the first PV cell and the rear face of the second PV cell using the electrically-conductive adherent comprising or consisting of the solder paste; and
wherein the solder paste is stencil printed or jet printed.
2 . The method of claim 1 , further comprising laminating the plurality of PV cells.
3 . The method of claim 2 , wherein the interconnection between the first PV cell and the second PV cell is established and then subsequently the plurality of PV cells are laminated;
and optionally wherein lamination is performed at a lamination temperature below the liquidus temperature of the solder alloy; or optionally wherein lamination is performed at a lamination temperature above the liquidus temperature of the solder alloy.
4 . The method of claim 2 , wherein the interconnection between the first PV cell and the second PV cell is established in-situ during lamination of the plurality of PV cells;
wherein lamination is performed at a lamination temperature at or above the liquidus temperature of the solder alloy.
5 . The method of claim 1 , wherein the solder paste is reflowed by heating after being stencil printed, or jet printed and the reflow temperature is 20 to 60° C. higher than the liquidus temperature.
6 . The method of claim 5 , wherein the solder paste is reflowed using infra-red, a convection oven or a zoned reflow oven for a period of less than 1 minute, optionally less than 10 seconds.
7 . The method of claim 1 , wherein the solder alloy comprises from 0.8 to 1 wt. % Cu.
8 . The method of claim 1 , wherein the solder alloy comprises from 0.03 to 0.08 wt. % Co.
9 . The method of claim 1 , wherein the solder alloy comprises from 0.9 to 1 wt. % Ag.
10 . The method of claim 1 , wherein the solder alloy consists of:
from 48 to 51 wt. % Bi,
from 0.7 to 1.1 wt. % Cu,
from 0.02 to 0.09 wt. % Co,
from 0.8 to 1.1 wt. % Ag,
the balance being tin together with any unavoidable impurities.
11 . The method of claim 1 , wherein the one or more ribbons are copper foil ribbon(s).