Light-Capturing Interconnect Wire for 2% Module Power Gain

In order to interconnect industrial solar cells with a front grid pattern, flat solder-coated copper wires are usually soldered to 2 or 3 busbars on the front surface. In order to minimize the resistive power loss in the wires and minimize stress in the cells, these wires are thin and wide, and the shading of the cells by these wires represents a significant power loss in the encapsulated modules. In order to eliminate this power loss component, researchers are exploring more complicated and expensive cell designs whereby all contacts are either placed on or are led to the rear side of the cells. We have developed a much simpler and more cost effective solution whereby the effective shading of the wires is greatly reduced. This is accomplished by forming triangular grooves on the top surface of the wire and coating the surface with a reflective layer such as silver. The grooves are designed so that incident light is reflected up toward the glass coversheet of the module at an angle shallow enough that it undergoes total internal reflection at the glass-air interface and is reflected back down onto the solar cell. As much as 80% of the light hitting the busbars can potentially be recaptured. Experiments with industrial solar cells have shown a 2% relative gain in encapsulated cell current and power with use of this light-capturing interconnect wire as compared to the controls with standard wire. Further gains are expected with reoptimization of the wire width. Only minor modifications are needed to a tabber-stringer to enable the use of this wire. A method to manufacture and store the wire has been developed by Schlenk Metallfolien, and sampling has begun to interested module manufacturers. Module reliability tests are ongoing, but initial data on thermal cycling and damp heat testing shows no degradation in the short circuit current benefit vs. the controls. The concept applies to interconnection of discrete thin-film cells as well as to Si-wafer cells.