Holger Kühnlein received his master degree and PhD in chemistry from University of Dresden in Germany in 2007. In parallel he worked as PhD student for Atotech GmbH in Berlin and Dresden. Since 2007 Holger is with RENA Technologies GmbH in different functions as specialist in wet chemical technologies and management. Since August 2014 he is head of Technology & Innovation at RENA.
Title and Abstract of the Speech:
Metal-free texturing for diamond-wire-sawn multi-crystalline silicon (DWS-mc)
Christian Schmitt*, Boxuan Zhou, Benedikt Straub, Benedikt Burgenmeister, Alexis Pediaditakis, Bernd-Uwe Sander, Holger Kühnlein
RENA Technologies GmbH, Hans-Bunte-Str. 19, D-79108 Freiburg
Since diamond-wire-sawing had its break through on Cz-silicon, the price for Cz-silicon and mc-silicon converges. On the one hand because of capacity increase for Cz-silicon, on the other hand it is possible to give the benefit in sawing one-to-one to the end of the value chain. Only minor changes have to be implemented, i.e. the texturing process has to be adapted slightly – the rest of the process chain stays the same.
Figure 1: a) SEM-picture of a Slurry-mc wafer as cut. b) SEM-picture of a Slurry-mc wafer, HF/HNO3 textured. c) SEM-picture of a DWS-mc wafer as cut. d) SEM-picture of a DWS-mc wafer, HF/HNO3 textured. e+f) SEM pictures of DWS-mc wafer, textured by HF/HNO3 and dw-TEX2 (RENA additive)
Typical solutions for the DWS-mc texturing issue are e. g. the Reactive-Ion-Etching (RIE) texturing and the Metal-Assisted-Etching (MAE)-texturing. Both solutions are suffering from extremely high investment costs and extensive subsequent-cleaning steps after texturing process, which increase the machine footprint and the chemistry consumption.
The RENA solution is based on an organic additive optimized for mc-SI Wafers. The additive dw-TEX (diamond-wire texture) yields an effective texture on DWS wafer surfaces. The reflection is similar to slurry sawn wafers with default HF/HNO3 texture and is typically between 25-27% (weighted average from 400 to 1100 nm). The additive dw-TEX promise slightly higher efficiency of up to +0,1/0,2% compared to slurry wafers. Cell results from industrial production will be shown at EUPVSEC in September 2018. The dosage unit can be integrated in existing InTex tools.
The additive dw-TEX promise slightly lower reflectance and higher efficiency from up to +0,1/0,2%. Industrial cell results from production will be shown at EUPVSEC in September 2018.
Figure 2: Reflectance for DWS and slurry wafer with different texture solutions (HF/HNO3 with and without additive)
Current results from at customer with RENA dw-TEX additive on Al-BSF cells: