Silicon Dendritic-Web Material Process Development. Final Report

摘要

The purpose of this program was to develop a low-cost contact system for solar cells and to integrate techniques for fabricating, interconnecting, and encapsulating solar cells in order to produce several demonstration modules. Two experimental contact systems were examined and compared to a baseline contact system consisting of evaporated layers of titanium, palladium, and silver and an electroplated layer of copper. The first experimental contact system consisted of evaporated layers of titanium, nickel, and copper and an electroplated layer of copper. This system performed at least as well as the baseline system in all respects, including its response to temperature stress tests, to a humidity test, and to an accelerated aging test. In addition, the cost of this system is estimated to be only 43% of the cost of the baseline system at a production level of 25 MW/year. The second experimental contact system consisted of evaporated layers of nickel and copper and an electroplated layer of copper. Auger electron spectroscopy was used to show that the evaporated-nickel layer is not an adequate barrier to copper diffusion at temperatures at least as low as 250 exp 0 C. This fact brings into question the long-term reliability of this contact system. This system was further afflicted with problems of adherence between the silicon and the evaporated nickel, and for these reasons is not viewed as a promising contact system. Three modules were fabricated using cells made from dendritic web silicon. Ultrasonic seam bonding was used to interconnect the cells into strings, and ethylene vinyl acetate was used to encapsulate these cell strings. The first two modules were of nominal (30 x 60) cm size and the third module was of nominal (36 x 118) cm size. The efficiency of the third module was measured in natural sunlight to be 10.6%. (ERA citation 07:042794)