PVD systems for thin film solar cells on glass
Thin film solar cells generally consist of a light absorbing layer sandwiched by two thin film electrodes which are necessary to extract the electrical currents to a connected inverter system. While the quality of the light absorber determines the maximum efficiency of every solar cell, inferior quality of the electrodes can give it all away. At least one of the electrodes needs to consist of optically transparent material. These materials are generally classified as TCO (transparent conductive oxide) and usually comprise either aluminum or boron doped zinc oxide or fluorine doped tin oxide.
Very good solar cell results can be obtained with aluminum doped zinc oxide which is produced by magnetron sputtering from ceramic targets. LEYBOLD OPTICS offers highly productive magnetron cathode technology integrated in vertical, carrier-based and horizontal In-Line coating systems. Both types of In-Line coating systems are equipped with single or double load-lock stages for substrate transfer into and out of the vacuum environment, depending on the desired machine tact time. A carrier-based vertical In-Line coating system should be the preferred choice in the case of anticipated particle contamination. Horizontal In-Line systems for large flat substrates are usually shipped with a maintenance-friendly carrier-free roller transport system but can be fitted with a carrier-based transport if required (e.g. for substrate edge masking).
Both types of In-Line systems can be equipped with a selection of magnetron sputtering cathodes of planar or cylindrical shape, or the newly designed moving-target cathode. Supplied with electric or electromagnetic power in DC, pulsed DC, mid-frequency or radiofrequency mode, substrates will be coated by target material in a direct or reactive regime while passing the individual sputtering cathodes in a continuous substrate flow. System height or width is individually adjusted to accommodate the designated target lengths of the respective magnetron sputter cathodes. The standard systems are designed to accomodate magnetron sputtering cathodes in the range from 550 mm to 1500 mm for vertical systems and from 750 mm to 1700 mm for horizontal systems. Vertical In-Line systems are usually tilted by -7° towards the sputtering tools to avoid the (expensive) use of substrate clamping to the carrier. All In-Line systems can be fitted with infrared heaters for elevated substrate temperatures during the deposition process.
