PVD systems for thin film solar cells on flexible substrates
Thin film solar cells on flexible substrates bear a great potential for future cost reduction. WEB 750sp is a first step to support this trend in the industry. Designed as a full-scale production system, WEB 750sp is a highly-integrated modular coater for the deposition of TCO (transparent conductive oxide) and metal films as electrode and absorber materials for thin film solar cells on steel strips of a maximum width of 600 mm, currently.
WEB 750sp consists of three modules made of stainless steel. Four coils on an extractable carriage inside the substrate handling module are necessary to unwind and wind the steel strips together with a protective interleaf foil. The substrate handling module is sandwiched between the two coating modules, each containing a 1500 mm diameter coating roll at the center, which is temperature-controlled from -40°C to 180°C. The coating modules can accommodate up to 10 magnetron sputter cathodes, arranged in a semicircle close to the surface of each coating roll.
The unusual design von WEB 750sp is caused by the necessity to prevent the transport rolls from touching the sensitive coated front surface of the steel foil. The machine can be fitted with DC or pulsed DC power propelled cylindrical magnetron sputter cathodes for the high rate deposition of ZnO:Al at 150 nm*m/min from a ceramic target and metals such as Al and Ag. Insulating layers such as i-ZnO, which are needed for CIGS solar cells, can be sputtered from a ceramic target by using radio-frequency power. The quality of the deposited thin films can be monitored by contact-free optical scanners. Exchange of substrate coils is possible without venting the two coating modules, which is beneficial for high productivity.
