Title:	Ultrasonic Mapping of Voids Generated during the LBSF Formation of PERC Solar Cells
Author(s):	M. Dhamrin, S. Suzuki, M. Matsubara, Y. Nishio, H. Tada
Topic:	WAFER-BASED SILICON SOLAR CELLS AND MATERIALS TECHNOLOGY
Subtopic:	Silicon Solar Cell Characterisation and Modelling
Event:	29th European Photovoltaic Solar Energy Conference and Exhibition
Session:	2BV.8.28
Pages:	1198 - 1201
ISBN:	3-936338-34-5
Paper DOI:	10.4229/EUPVSEC20142014-2BV.8.28
Price:	0,00 EUR
Document(s):	paper, poster

Abstract/Summary:

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Voids generation is one of the problems associated with PERC formation using screen-printed aluminum paste to realize high quality stable devices. The void formation mechanism can be explained by the wellknown Kirkendall effect due to the difference between the diffusity of aluminum in silicon and diffusity of silicon in Aluminium. During the local BSF formation, more silicon is diffused out from the silicon wafer into the aluminum generating voids at the local opening regions between the aluminum contacts and the silicon surface. The stability problems arise from the partially connected voids at the edges which make it subject to disconnection during module fabrication and at harsh weather regions that generate more stress on the module surface. The scanning acoustic microscope that uses ultrasonic waves to investigate the void existence in a complete mapping way is used to evaluate the voids and its generation mechanisms. By using the fact that sound travels with different speeds in materials such as in air, silicon and aluminum, we could clearly see the voids and mapping them on the total wafer area. We used this technique to help us realizing almost Zero void ratio which will insure a very stable PERC solar cell performance.