From cells to laminate: probing and modeling residual stress evolution in thin silicon photovoltaic modules using synchrotron X‐ray micro‐diffraction experiments and finite element simulations

• Published in: Progress in photovoltaics Vol. 25; no. 9; pp. 791 - 809
• Main Authors: Tippabhotla, Sasi Kumar, Radchenko, Ihor, Song, W.J.R., Illya, Gregoria, Handara, Vincent, Kunz, Martin, Tamura, Nobumichi, Tay, Andrew A.O., Budiman, Arief S.
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.09.2017; Wiley
• Subjects: Computer simulation; Cracking (fracturing); Crystal structure; crystalline silicon cell; CTE mismatch; Encapsulation; encapsulation stress; Evolution; Failure; finite element analysis; Finite element method; Fracture mechanics; Mathematical analysis; Modelling; Modules; Photovoltaic cells; Residual stress; Silicon; Silicon wafers; Solar cells; SOLAR ENERGY; solar PV; Soldering; soldering stress; synchrotron X-ray microdiffraction; thermo-mechanical residual stress; X-ray diffraction
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2891

Fracture of silicon crystalline solar cells has recently been observed in increasing percentages especially in solar photovoltaic (PV) modules involving thinner silicon solar cells (<200 μm). Many failures due to fracture have been reported from the field because of environmental loading (snow, wind, etc.) as well as mishandling of the solar PV modules (during installation, maintenance, etc.). However, a significantly higher number of failures have also been reported during module encapsulation (lamination) indicating high residual stress in the modules and thus more prone to cell cracking. We report here, through the use of synchrotron X‐ray submicron diffraction coupled with physics‐based finite element modeling, the complete residual stress evolution in mono‐crystalline silicon solar cells during PV module integration process. For the first time, we unravel the reason for the high stress and cracking of silicon cells near soldered inter‐connects. Our experiments revealed a significant increase of residual stress in the silicon cell near the solder joint after lamination. Moreover, our finite element simulations show that this increase of stress during lamination is a result of highly localized bending of the cell near the soldered inter‐connects. Further, the synchrotron X‐ray submicron diffraction has proven to be a very effective way to quantitatively probe mechanical stress in encapsulated silicon solar cells. Thus, this technique has ultimately enabled these findings leading to the enlightening of the role of soldering and encapsulation processes on the cell residual stress. This model can be further used to suggest methodologies that could lead to lower stress in encapsulated silicon solar cells, which are the subjects of our continued investigations. Copyright © 2017 John Wiley & Sons, Ltd. Residual stress in crystalline silicon cells in photovoltaic modules was investigated using Synchrotron X‐ray Micro‐diffraction before and after encapsulation. The mechanism of residual stress evolution was explained by virtue of 2D and 3D finite element simulations, which are in good agreement with the experimental results. Highly localized bending of the cell near the solder joint after encapsulation was found to be the reason for high stress in the encapsulated cells.