Ensuring high efficiency of thin film photovoltaic modules with inline measurement

In the manufacture of thin film solar panels or foils (e.g. CIS/CIGS, CdTe) it is crucial to maintain the specified limits of thickness and composition exactly, as this directly affects the efficiency of the panel. Only with a precise, fast and reliable inline measuring system can the production parameters be continuously monitored and, thus, the quality of the coating processes ensured.

A typical thin film photovoltaic (PV) system is comprised of a fairly complex stack of layers coated onto substrates like glass or foils. As manufacturers strive to develop lower-cost, dependable CdTe/CIS/CIGS products, some of their most critical issues are:

· ever-higher module efficiencies

· ever-thinner absorber layers of less than 1µm

· consistent absorber film stoichiometry and uniformity over large areas

This is where mature, non-destructive measurement technology, such as X-ray fluorescence (XRF), helps to improve uniformity and stoichiometry – and thus, the cell efficiency and production yield. The FISCHERSCOPE® X-RAY 5400 enables accurate and precise measure­ment of the layer thicknesses and composition in complex CIS/CIGS/CdTe systems, for continuous inline quality control at various stages during production.

Fig.1: X-ray head of a FISCHERSCOPE® X-RAY 5400 (left) and detailed view of the easy-to-change protective foil

Because the X-ray heads are mounted via cooled standard interfaces to the vacuum chamber system, they can even be used in production machinery under condi­tions in which substrate temperatures approach 500°C.

Movement and bulging of the product can occur during the production process, which causes the distance between sample and measurement head to fluctuate. To prevent falsifying effects, FISCHER’s WinFTM® Software uses information already contained in the measured XRF spectra, achieving reliable distance compensation without any moving parts and thus obviating the need for secondary distance sensors.

Fig.2: CIGS thickness readings and change in measurement distance – blue points are with distance compensation, red are without.

With the distance compensation feature activated, the measurement distance can be altered by up to +/- 5 mm without significantly affecting the measurement readings.

Production quality of thin film solar cells can be accurately and precisely monitored using XRF technology. FISCHER’s specially designed inline X-ray measurement head, FISCHERSCOPE® X-RAY 5400, also fulfils all the robustness requirements of live production environments. For more information please contact your local FISCHER representative.

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Fischer Technology Inc.
Windsor/United States

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