Today, triple-junction solar cells are typically delivered on 4 inch wafers. For the assembly process, the wafers are diced on a foil. The cells are picked automatically by a die bonding machine and are mounted onto a substrate. In a FLATCON module, the substrate consists basically of copper, which acts as heat sink and simultaneously as the electrical rear-side contact for the cell. This is achieved by using an electrically conducting adhesive to mount the cell on the copper plate. The front-side contact of the triple-junction solar cell is gold wire bonded to a layer that is electrically isolated to the copper substrate. Figure 14.9 shows the mounted solar cell on the cooper heat spreader. This unit is called solar cell assembly. In a pick-and-place process, the solar cell assembly is mounted with high precision onto the bottom glass plate of a FLATCON module [43]. The top plate of a module carries the quadratic Fresnel lenses, which are arranged in a matrix. The bottom
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Figure 14.9. The most important assembly steps necessary for a FLATCON concentrator assembly are shown. Upper left: the photo of a 4-in. wafer with about 1000 triple-junction concentrator solar cells is shown. Upper right: the cells are mounted onto a copper heat sink. The front side of the cell is contacted with gold wire bond technology. Lower right: many of the solar cell assemblies are mounted in the focus of their corresponding Fresnel lens— the position of one solar cell assembly in the module is marked. Lower left: many FLATCON modules are mounted on a two-axis tracking system—the position of one FLATCON module is marked. |
glass plate with the solar cell assembly and the Fresnel lens plate are adjusted to each other. In the next step, the frames between the two plates are sealed together. A photo of the complete module is shown in Figure 14.9 . In order to complete a fUll FLATCON system, many modules are mounted on a two-axis tracking system. Figure 14.9 shows photos of how a FLATCON system is assembled.
