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EnglishApplications of Laser Micro Machining in Photovoltaics - Thin-Film Solar Cells
The reduction of fabrication costs in comparison with conventional, wafer-based solar cells inheres top priority. Therefore, manufacturers of solar cells readily invest in fully automated state-of-the-art production lines for thin-film solar cells. In such fabs, the utilization of lasers guarantees high efficiency and throughput at best attainable precision and minor damage to the cells.
Particular advantages of laser machining of the very fragile thin-film solar cells consists in contactless energy insertion, the capability of flexible beam guidance, and the exact control over supply of energy. Damage to the material is avoided that way as well as failure rates are minimised.
For application in the photovoltaics industry, the follwoing thin-film technologies proved suitable:
1. Thin-film technology on glass substrates
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Silicon thin-film modules consisting of amor- phous or microcrystalline silicon
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Cadmiumtelluride (CdTe) cells
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Copper Indium Gallium Selenide (CIS/CIGS) cells
2. Thin-film technology on flexible substrates
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Silicon-based systems
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CIS/CIGS-based systems
3D-Micromac AG provides powerful and highly precise stand-alone systems as well as integrated solutions for existing, fully automated production lines for laser machining of thin-film solar cells. Numerous process monitoring methods including tracking and tracing of process parameters and online energy monitoring ensure additional process reliability. As a qualified partner, we are also ready to develop new processes or systems on customer’s demands.
Most important machining procedures include:
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Edge isolation
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Laser surface structuring in process steps P1, P2 und P3
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Laser marking
All of the aforementioned machining technologies do guarantee high efficiency of the completed solar cell at a minimum of materials damage and least material’s loss.
Edge Isolation
For edge isolation, heavy-duty Nd:YAG lasers featuring a flat-top beam profile are utilized. With the latter tool, area-ablation rates of 10 to 50 cm²/s are reached. The maximum machining speed amounts to 4,000 mm/s, with a typical width of isolation trenches between 10 and 100 µm.
Laser Structuring (Selective Ablation)
Upon fabrication of thin-film solar cells, the substrate is coated with conducting and non-conducting layers. The latter layers, consisting of TCO, silicon, or other active media, and metal, reach maximum thicknesses of a few microns and can be machined with lasers of different wavelengths (IR, VIS, UV) in processing steps P1, P2, and P3. The scribe-line widths are between 20 and 50 µm. Machining speeds of up to 2,000 mm/s can be achieved. A necessary prerequisite for highest precision in laser structuring is the utilisation of laser featuring premium beam quality (TEM00) and very high repetition rates of some hundred kilohertz.
Laser Marking
For product tracking and tracing, solar cells are endued with marks generated by solid-state lasers. The marking ought to be machine-readable, should not exert any influence on other fabrication steps and should, even at the end of the manufacturing process, enable doubtless identification. Besides alphanumeric symbols, data matrix codes and bar codes as well as manufacturer’s logos can be generated. The size of the markings ranges from semi visible (with a font size of about 75 µm) to an extension of several centimetres. The minimum font width amounts to 10 µm.