In order to maximize the power output of polycrystalline silicon PV-modules, in previous work we have already tested rectangular cells of 39 × 156 mm which are overlapped along the long sides. The low current density at the cell overlap allows interconnections which need neither soldering nor glueing, but use metallic strips inserted between the cells in the overlap region. The contact is established by the pressure applied to the module during lamination and is retained by the slightly bent cells in the solidified encapsulant. Here we report on the long term stability of different contact materials and contact cross sections applied in eight modules of the 240 W class monitored for up to 24 months of outdoor operation and in a variety of small 5-cell modules exposed to rapid ageing tests with up to 1000 thermal cycles. Cells with three different electrode designs were tested and the contact materials were Cu, Ag, SnPbAg and Sn. Focussing especially on series resistance, fill factor and peak power, it is found that Ag-coated contact strips perform equally well and have practically the same stability as soldered cell interconnections. Due to 70-90% savings in copper and simpler manufacturing the cost of PV-modules may thus be reduced further.
The angular dependence of the probability for electron induced surface plasmon excitation has been measured on semi-infinite planar polycrystalline Al and Au surfaces for energies between 500 and 4000 eV. The results agree accurately with the simple model in which the surface excitation probability is proportional to the surface penetration time. However, the penetration time differs from the rectilinear motion model due to deflections during elastic collisions within the surface scattering zone. A simple formula to account for the effect of elastic scattering in the surface scattering zone is given.
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