Integrated Series Connection of a-Si:H Solar Cells
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INTEGRATED SERIES CONNECTION OF a-Si:H SOLAR CELLS W. Juergens, H. Kausche, W. Peters, W. Stetter Siemens Research Laboratories, Otto-Hahn-Ring 6, 8 M~nchen 83, FRG ABSTRACT We tested several methods of patterning amorphous-silicon (a-Si:H) solar cells to form stripe cells and to connect these stripe cells integrated with cell deposition process to a series-connected module. The patterning techniques used included: laser cut, screen print lift-off techniques, adhesive tapes with lift-off, and a special mechanical milling method. The three layers of a cell which must be patterned are 1. Sn0 2 :F on glass, 2. a-Si (p(C)in), 3. metal-electrode. We developed a convenient patterning method for a laboratory size with a loss of area of 13 %: 1. laser cut, 2. milling, 3. adhesive tape lift-off. For a higher level of production we tested the following sequence with a loss of area of 4 %: 1. screenprint and lift-off, 2. milling/slotting, 3. screen print and lift-off. The last method has the advantage that without any laser treatment the costs are only third of those of the other methods with a laser cut; so we will eliminate the laser cut in future for manufacturing modules.
Amorphous-silicon (a-Si:H) solar cells are developed with relatively high efficiency and sufficient stability. With this in mind low cost manufacture of integrated modules is of current interest. With small cells of the type: glass/Sn0 2 /p(C)in/metal, we obtained a conversion efficiency of 10.1 %. Cells of size 10cm x 10cm showed a conversion efficiency up to 7.5 %. For low-current loss, these cells are series-connected into stripes /l/. For the realization of low-cost modules, it is important, first to deposit large area cells of > 30cm x 30cm, second to evaluate patterning processes for large areas consisting of stripe cells; and third to connect these cells in series by the deposition process of the upper electrodes. For this, three selective steps of patterning are needed: First for the TCO (transparent conductive oxide layer), second for amorphous silicon; and third for the metal layer. The line patterns are shift positioned relative to each other, causing a loss of active cell area defined by the width and the edge quality of the lines and the precision of the positioning process. So we have a integrated series connection of the cells and no further internal connections are needed (Fig. 1).
Mat. Res. Soc. Symp. Proc. Vol. 70. 1986 Materials Research Society
502
Our interest was focused on methods to pattern and to connect these stripe cells with low cost. We tested several patterning processes, materials and deposition methods with cells of the type: glass/Sn02 /P(C)in/metal. The a-Si:H layer (pin) was deposited in a two-chamber reactor with separate deposition of the p- and n-layers in chamber 1 and the i-layer in chamber 2. The RF electrodes have a size of 40cm x 40cm, so a-Si:H layers and cells of 30cm x 30cm can be deposited. Our test modules had a size of 10cm x 10cm, which led to an output voltage of 5 V to 6 V. Our aim was to find out
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