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Controlling the surface tension of alkaline etching solutions

: Birmann, K.; Zimmer, M.; Rentsch, J.


Sinke, W. ; WIP - Renewable Energies, München; European Commission; UNESCO; World Council for Renewable Energy; International Photovoltaic Equipment Association:
24th European Photovoltaic Solar Energy Conference 2009. CD-ROM : The compiled State-of-the-Art of PV Solar Technology and Deployment. Proceedings of the International Conference held in Hamburg, 21-25 September 2009
München, 2009
ISBN: 3-936338-25-6
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <24, 2009, Hamburg>
Conference Paper
Fraunhofer ISE ()

Alkaline anisotropic etching with potassium hydroxide (KOH) and the additive 2-propanol (IPA) is a widely used process to texture monocrystalline silicon wafers industrially in order to reduce their reflection. Using IPA as additive in hot KOH (aq) the alcohol evaporates easily during the texturisation and the bath composition changes. Therefore IPA has to be redosed either during the texturisation or afterwards. The IPA concentration strongly influences the air to liquid surface tension of the etching solution. Adding IPA to an alkaline etching solution reduces its surface tension because IPA is surface active, resulting in a reciprocal proportionality. Online measurement of the surface tension allows dosing IPA to the bath solution using the surface tension as a control parameter. A proportional-integral-derivative controller can keep the surface tension and IPA concentration constant. This means that a texturisation can be processed at well defined conditions.