| PV-5000 Integrated System for Thin Film Solar |
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The increasing cost of silicon which is half the cost of a finished module, has resulted in a number of new ventures exploiting thin film approaches for manufacturing Photo-Voltaic (PV) panels.
The three most common semiconductor materials employed in thin film PV are amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS). Whereas crystalline silicon solar cells are a few hundred microns thick, thin film thicknesses are on the order of a few microns greatly reducing the cost of raw materials. Furthermore, these films are scalable for processing panels in excess of 1 meter square and hence low cost high volume manufacturing.
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The thin film layers are deposited onto glass sheets consisting of three main layers P1, P2, and P3. A transparent conducting oxide layer (such as Indium Tin Oxide - ITO) forms the front electrical contact (P1), the semiconductor layer (P2) and then a metal layer (Molybdenum – Mo) forms the rear contact (P3). In order to generate useful voltage from thin film panels, they must be isolated into 100 or more cells which are interconnected in series. A laser is used to scribe parallel lines across the full width of the panel. By alternating laser scribes with deposition steps, the cells are connected in series. In production, three laser scribing systems are required, one for each of the three layers.
JPSA, as a result of its extensive experience in semiconductor wafer scribing, has incorporated proprietary scribing methods in the PV-5000 system.
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JPSA has spent years developing scribing techniques on a variety of customer supplied substrates. For those not skilled in the art, simply focusing a laser beam on target produces unacceptable results as shown in the image to the left.
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The energy distribution within the DPSS laser beam creates considerable heating at the edges of the scribe due to the Gaussian spatial distribution of the energy. This ridge of melted material is non-uniformly adhered to the surface resulting in failures due to poor adhesion of subsequent film depositions and may result in short circuits. Additionally, the round beam requires considerable overlap, >50% to ensure proper removal of material within the scribe.
JPSA’s patent pending beam delivery technology ensures uniform exposure with very high beam utilization and efficiency. Furthermore, results show optimum accuracy, repeatability, negligible heat affected zone and requires minimal pulse overlap to permit the highest throughput
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