SBIR-STTR Award

The copper/solder/metallization/silicon layers used to bondelectrical leads to solar cells have vastly different thermalexpansion rates. This causes severe stresses when continuoussolder joints are used. This problem has been solved with aspecial lead design that uses a multitude of fingers soldered tothe cells. The purpose of this project is to develop a morecost-effective lead/cell design. Two technical approaches will beinvestigated, to be used singularly or together. The firstapproach is to add a strain relief feature to a continuous lead.The second approach is to add a solder resist pattern so thatcontinuous leads are only bonded to the cell in spots. Finiteelement stress analysis will be used in Phase I to investigatedifferent designs, and proof-ofconcept samples of the mostpromising candidates will be manufactured and subjected toenvironmental testing. Phase II will introduce the mostsuccessful design into the production line.Anticipated Results /Potential Commercial Applications as described by the awarded: This project could have far reachingapplications in the photovoltaic industry. If successful, thetechnique can be applied to other concentrators and to one-sunmodules. Given modest volume, the introduction of a morecost-effective lead/cell design, and other planned improvements,could enable the grid to be sold for under $1.10 per installed ACWatt.

Cost effective, efficient, current extraction from concentrating photovoltaic (PV) cells has been a barrier to low cost PV power. An innovative external bus bar attachment method for concentrating PV cells has been developed which promises to both reduce manufacturing time and improve cell output, thereby lowering overall costs. Phase I resulted in a workable specific design to form wire attachment leads to the top and bottom contacts of the cell which minimized the on-cell bus bar area, reduced grid obscuration, used off-shelf materials, and was suitable for automated production. Prototypes were built and tested which indicated a 12% increase in output and a 30% reduction in cost. In Phase II, the Phase I concepts will be refined, automated volume assembly equipment will be designed, and this equipment will be constructed and tested in order to terminate concentrating PV cells resulting in cell subassemblies according to this improved design.Anticipated Results/Potential Commercial Applications as described by the awardee: The world market for low-cost, non-polluting electric power is enormous. This project will permit production of volume PV power at under 5c/KW-hr whereas the average US cost is approximately 8c/KW-hr, and the average world price is greater that 20›/KW-hr. The work has applicability to other solar cells and should help US industry dominate this new important pollution-reducing trillion-dollar market