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

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

Probing stress and fracture mechanism in encapsulated thin silicon solar cells by synchrotron X-ray microdiffraction

Thin (<150 µm) silicon solar cell technology is attractive due to the significant cost reduction associated with it. Consequently, fracture mechanisms in the thin silicon solar cells during soldering and lamination need to be fully understood quantitatively in order to enable photovoltaics (PV) systems implementation in both manufacturing and field operations. Synchrotron X-ray Microdiffraction (µSXRD) has proven to be a very effective means to quantitatively probe the mechanical stress which is the driving force of the fracture mechanisms (initiation, propagation, and propensity) in the thin silicon solar cells, especially when they are already encapsulated. In this article, we present the first ever stress examination in encapsulated thin silicon solar cells and show how nominally the same silicon solar cells encapsulated by different polymer encapsulants could have very different residual stresses after the lamination process. It is then not difficult to see how the earlier observation, as reported by Sander et al. (2013) [1], of very different fracture rates within the same silicon solar cells encapsulated by different Ethylene Vinyl Acetate (EVA) materials could come about. The complete second degree tensor components of the residual stress of the silicon solar cells after lamination process are also reported in this paper signifying the full and unique capabilities of the Synchrotron X-Ray Microdiffraction technique not only for measuring residual stress but also for measuring other potential mechanical damage within thin silicon solar cells

Crack initiation and growth in PV module interconnection

As the cost of PV (photovoltaic) solar panels drops, it is widely expected that solar energy will become the cheapest source of electricity in many parts of the world over the next two decades. To ensure that PV solar modules have a long service life and can meet the PV manufacturer's warranty, the PV modules need to have high reliability. Solar PV module manufacturers typically provide two warranties: a performance warranty which guarantees 90% of original power output after 10 years and 80% of original output of at 25 years; and an equipment warranty which guarantees their PV module will have a minimum of 10–12 years operation before failure. A critical part of the solar PV module assembly is the ribbon interconnection between the solar cells (i.e. the solder joint interconnections), and failure of the ribbon interconnection can adversely affect the performance and reliability of whole PV module. Ribbon interconnection failures have been linked to the thermal cracks which are initiated in the solder joint material during the high temperature ribbon interconnection manufacturing process; and then the crack propagation and growth associated with the thermal cycling of the ribbon interconnections under higher than ambient temperature PV module operating conditions. This paper reports on the study of high temperature crack initiation and propagation in different PV Module interconnection configurations by using XFEM in ABAQUS software. It concerns a necessary, urgent and fundamental revision of the manufacturing process that lies at the heart of PV module ribbon interconnection manufacture

Interaction Patterns and Web-Structures of Resonant Solitons of the Kadomtsev-Petviashvili Equation

In this thesis, the interaction pattern for a class of soliton solutions of the Kadomtsev- Petviashvili (KP) equation (−4ut + uxxx + 6uux )x + 3uyy = 0 is analyzed. The complete asymptotic properties of the soliton solutions for y → ±∞ are determined. The resonance characteristic of two sub-classes of the soliton solutions, in which N- incoming line solitons for y → −∞ interact to form N+ outgoing line solitons for y → ∞, is described. These two specific sub-classes of (N-,N+)-soliton solutions are the following: 1) [(2, 3), (2, 4), (2, 5)], 2) [(3, 2), (3, 3), (3, 4)]. The intermediate solitons and the interaction regions of the above soliton solutions are determined, and their various interaction patterns are explored. Maple and Mathematica are used to get the 3 dimensional plots and contour plots of the soliton solutions to show their interaction patterns. Finally, the spider-web-structures of the discussed solitons of the KP equation are displayed

Developing Printable Fly Ash–Slag Geopolymer Binders with Rheology Modification

The rheology of mixtures of fly ash-slag geopolymers, optimized for strength is not favorable for printing. Rheology modification is required using additives, which provide specific improvements in yield stress and thixotropy. These binders typically exhibit a pseudo-yield type behavior with a continuously deformable response under applied stress. A printable (both extrudable and buildable) material requires a yield-type behavior and adequate thixotropy, which can be brought out by addition of clay and Carboxymethyl Cellulose (CMC). The modification in rheology is attempted using commonly available Kaolinite clay. Specific changes in rheology caused due to the rheology modifiers are evaluated and are related with the performance in printing. Addition of clay contributes to an increase in the stiffness of the paste and improves buildability of the mix. A synergy between clay and CMC is established for proper printability. Clay in combination with CMC increases the storage modulus and produces a yield type behavior. CMC improves flocculation of clay but delays buildup due to its negative influence on reaction kinetics. Excess CMC increases the resistance to flow and produces a continuously deformable Maxwell response, which is not suitable for buildability. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG

In situ embedded PZT sensor for monitoring 3D concrete printing: application in alkali-activated fly ash-slag geopolymers

An embedded PZT sensor is developed for in situ monitoring of 3D-printed materials formed by extrusion-based layer deposition. The PZT sensor with a two-layer protection coating is embedded in the material during the layer deposition, and continuous measurements are obtained through the post-printing period. The PZT sensor is used to detect the physio-chemical changes in the alkali-activated fly ash-slag geopolymer with time. The effect of the added weight of each layer of print is sensitively reflected in the electrical impedance (EI) measurement obtained from the PZT sensor. The changes in EI measurements obtained from the embedded PZT sensor are compared with the measurements on the material related to the changes in the rheological behavior, reaction kinetics assessed using calorimetry, and setting behavior in the material. The build-up of the internal structure within the material, which allows buildability, is assessed from the conductance signature of the embedded PZT sensor. The changes produced by the chemical reactions within the binder, which bring about irreversible changes leading to the setting of the printed structure, are also sensitively detected in the EI measurements from the embedded PZT sensor. The amplitude of conductance is sensitive to the setting of the material. The frequency changes from the recorded EI signature reflect the continuous increase in the material stiffness with time. © 2021 IOP Publishing Ltd

Probing Phase Transformations and Microstructural Evolutions at the Small Scales: Synchrotron X-ray Microdiffraction for Advanced Applications in 3D IC (Integrated Circuits) and Solar PV (Photovoltaic) Devices

Synchrotron x-ray microdiffraction (μ XRD ) allows characterization of a crystalline material in small, localized volumes. Phase composition, crystal orientation and strain can all be probed in few-second time scales. Crystalline changes over a large areas can be also probed in a reasonable amount of time with submicron spatial resolution. However, despite all the listed capabilities, μ XRD is mostly used to study pure materials but its application in actual device characterization is rather limited. This article will explore the recent developments of the μ XRD technique illustrated with its advanced applications in microelectronic devices and solar photovoltaic systems. Application of μ XRD in microelectronics will be illustrated by studying stress and microstructure evolution in Cu TSV (through silicon via) during and after annealing. The approach allowing study of the microstructural evolution in the solder joint of crystalline Si solar cells due to thermal cycling will be also demonstrated