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

Abstract

High stress and fracture of silicon crystalline solar cells has recently been observed in increasing percentages especially in solar photovoltaics (PV) modules involving thinner silicon solar cells (<200 um). Many failures due to fracture of cells have been reported from the field and handling. However, a significantly higher number of failures have also been reported during module integration (soldering/ stringing and lamination) indicating a PV laminate/module with significantly high residual stresses and hence more prone to cell fractures. We characterize the residual stress evolution in crystalline silicon solar cells during module integration process, which is the current knowledge gap. The residual stress characterization was achieved through a systematic research using synchrotron X-ray submicron diffraction experiments coupled with physics-based Finite Element modeling of the PV module integration process. Thought this work we also demonstrate the unique capability of Synchrotron X-ray submicron diffraction to quantitatively probe residual stress in encapsulated silicon solar cells that has ultimately enabled these findings leading to the enlightening of the role of soldering and encapsulation processes. While our experiments quantify the stress at different process states including encapsulated cells, our FEA simulations, for the first time unravel the physical reasoning for the stress evolution and expected to bridge the knowledge gap. 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.

Probing Stress States in Silicon Nanowires During Electrochemical Lithiation Using In Situ Synchrotron X-Ray Microdiffraction

“…Details regarding the MACE process are described elsewhere (Peng et al, 2007;Choi et al, 2008;Chang et al, 2009), and the SiNWs thus obtained were roughly 6-8 µm high, standing on a 490-µm silicon substrate as shown in the schematic diagram in Figure 1A. A 200-nm thick copper layer was later deposited on the backside of the silicon wafer for electric contact (Tippabhotla et al, 2017a). Further details about the fresh samples are available in Figure S1 in Supplementary Material.…”

“…Synchrotron X-ray microdiffraction (μSXRD) has proven to be effective for revealing insights of mechanical stress and other mechanics considerations in small-scale crystalline structures in many important technological applications, such as microelectronics (Budiman et al, 2006(Budiman et al, , 2009(Budiman et al, , 2010Kim et al, 2012a), nanotechnology (Budiman et al, 2012b,c;Kim et al, 2012b), and photovoltaics (Rengarajan et al, 2016;Handara et al, 2017;Tippabhotla et al, 2017a). This is especially true where the knowledge of how the stress evolves during the operation of the device could reveal the effective methodology to design higherperformance, more robust, and reliable nanostructure-based systems.…”

Probing Plasticity and Strain-Rate Effects of Indium Submicron Pillars Using Synchrotron Laue X-Ray Microdiffraction

“…Synchrotron Laue X-ray Microdiffraction (µSLXRD) is a type of X-ray Laue diffraction technique that has been used for a variety of applications for its non-destructive nature and suitability in examining the defect structure of sub-micron and nanometer scale specimens [4,7,[23][24][25][26][27][28][29][30]. The X-ray beam comes from a powerful synchrotron source, which can be focused into a submicron spot size, close to the grain size of most single crystalline materials.…”

Thermal Residual Stress Analysis of Soldering and Lamination Processes for Fabrication of Crystalline Silicon Photovoltaic Modules

“…In addition, wafer thickness can be further decreased to 120 µm through future innovative technological advances in solar cells and PV modules. However, it is acknowledged that thin wafers may increase mechanical failures during the manufacturing process [2][3][4][5][6][7][8][9]. Mechanical failures arise from the difference in the coefficients of thermal expansion (CTE) of materials.…”