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Product Briefing Outline: LayTec GmbH has introduced what it claims to be the first in-line monitoring systems commercially available for thin film photovoltaic (PV) processes. SolR is capable of monitoring the film thickness of all layers throughout the thin-film PV process: transparent conducting oxide (TCO), absorber and buffer layers. SolR will be available in various editions for copper indium gallium selenide (CIGS) as well as for CdTe based thin-film solar cell processes.

Problem: In all fields of thin-film technology, the trend persists to develop ever more complex and sophisticated thin-film structures. Conventional post-growth evaluation methods of the thin-film production process are becoming obsolete as the need increases for real-time evaluation already during thin-film growth. Specifically related to PV based thin film processing, the main challenge has been to obtain an accurate film thickness measurement despite the reduced reflectance due to intentionally rough absorber layers. Absorber layers (e.g. CdTe or CIGS) are intentionally designed to be very rough in order to maximize internal reflections of the sun-light in the cells, thereby enhancing the efficiency of the solar cell. Reflectance measurements, however, usually work ideally for smooth layers.

Solution: LayTec has found a very robust way to establish film-thickness measurements even under these challenging conditions. SolR helps thin-film PV producers to control their production on-line and thereby enhance their yield. It also helps accelerate development cycles and help to transfer established processes to new lines, aiding the ramp to high yields and reducing ramp-up production costs. If the refractive index and the absorption coefficient of the oxide layer are well known, the layer thickness can be calculated directly from the measured reflectance. Reflectance measurements at longer wavelengths can determine the substrate temperature based on a double wavelength band-edge approach. During thin film growth substrates can experience a temperature offset between the process temperature and the substrate surface temperature that can be measured to improve control of the deposition process.

Applications: Transparent conducting oxide (TCO), absorber and buffer layers. CIGS and CdTe.

Platform: The monitoring system is based on spectroscopic reflectance measurements.

Availability: Currently available.