Zurich,Switzerland -- (SBWire) -- 04/15/2011 -- Ultrapure water in solar cell production
Large quantities of ultra-high quality ultrapure water are required in solar cell production. It is used to clean raw wafers after they are cut from the silicon ingots, after surface texturing, before phosphor diffusion and coating, and during construction of the cells themselves.
The quality of the ultrapure water in the distribution system and after production is monitored in-line using high-precision conductivity measurements and TOC determination. In addition, the decision is made based on these measurements, whether low-contamination rinse water is recycled to the UPW treatment system or used otherwise (reclaimed), which can substantially reduce the not insignificant costs of water treatment.
High-precision conductivity measurement
Since 1964, Mettler-Toledo Thornton has operated very successfully in the field of ultrapure water analytics and is recognized as having the most precise measurement systems for determining specific resistance/electrolytic conductivity in pure and ultrapure waters. At the Thornton manufacturing plant the cell constants of the conductivity sensors are determined with a maximum unreliability of only 1% on the special Autoloop test rig. Here ultrapure water is used as the calibration medium which corresponds also to the later operating range of the measurement cells in UPW applications. The cell constants are, moreover, traceable to generally accepted standards such as those established by ASTM and NIST.
Fastest TOC determination
The Thornton 5000TOC sensor is currently the fastest analyzer on the market. Instead of batch oxidation that requires analysis times of typically 7 to 15 minutes, the 5000TOC uses the dynamic UV oxidation process. This method is not only especially fast but also particularly maintenance-friendly, since moving parts such as pumps, and chemicals and membranes have been eliminated. Only the UV lamp must be replaced periodically. With a detection limit of 0.025 ppb C and a response time of < 1 minute the stringent requirements of the photovoltaic and semiconductor industry on the measurement system are completely satisfied.
High flexibility
The Thornton 770MAX transmitter is a multi-channel measurement instrument that features two analog pulse inputs and four Smart channels. The analog pulse inputs are utilized for flow measurement
Product update
The 5000TOC has now been superseded by the 5000TOCe. Physical and software improvements mean that the new model is even more reliable and robust than the previous version.
Summary
The quality of ultrapure water is decisive for product quality of solar wafers, cells and modules. Modern ultrapure water analysis systems ensure the required water quality with regard to conductivity and TOC, and in virtue of their modular design are very versatile for utilization in system control and quality assurance.
Ultrapure Water for Maximum Efficiency of Solar Cells
In the creation of solar wafers and solar cells, the highest purity requirements are imposed on the water used for cleaning and rinsing. High-precision modern conductivity and TOC instruments monitor in real time the quality of ultrapure water (UPW) with regard to trace ionic and organic contamination.