The profitability of silicon solar cells is a critical point for the PV market and it requires improved electrical performance, lower wafer production costs and enhancing reliability and durability of the cells. Innovative processes are emerging that provide thinner wafers with less raw material loss. But the induced crystallinity and distribution of defects compared to the classical wafers are unclear. It is therefore necessary to develop methods of microstructural and mechanical characterization to assess the rigidity and mechanical strength of these materials. In this work, 4-point bending tests were performed under quasi-static loading. This allowed to conduct both the stiffness estimation and the rupture study. A high speed camera was set up in order to track the fracture process thanks to a 45° tilted mirror. Fractographic analysis were performed using confocal optical microscope, scanning electron microscope and atomic force microscope. Electron Back-Scatter Diffraction and Laue X-Ray diffraction were used to explore the relationship between the microstructural grains orientations/textures of our material and the observed mechanical behavior. Jointly, finite element modeling and simulations were carried out to provide auxiliary characterization tools and help to understand the involved fracture mechanism. Thanks to the experiment-simulation coupled method, we have assessed accurately the rigidity of silicon wafers stemming from different manufacturing processes. A fracture origin identification strategy has been proposed combining high speed imaging and post-mortem fractography. Fracture investigations on silicon single crystals have highlighted the deflection free (110) cleavage path, the high initial crack velocity, the velocity dependent crack front shape and the onset of front waves in high velocity crack propagation. The investigations on the fracture of multi-crystalline wafers demonstrate a systematic transgranular cracking. Furthermore, thanks to twin multi-crystalline silicon plates, we have addressed the crack path reproducibility. A special attention has been paid to the nature of the cleavage planes and the grain boundaries barrier effect. Finally, based on these observations, an extended finite element model (XFEM) has been carried out which fairly reproduces the experimental crack path.

ABSTRACT: The solar energy, or photovoltaic (PV) industry, driven by economic competition with traditional fossil energy sources, strives to produce solar panels of the highest conversion efficiency and best reliability at the lowest production cost. Solar cells based on crystalline silicon are currently the dominant commercial PV technology by a large margin, and they are likely to remain dominant for at least one decade. The problem of improvement mechanical stability of silicon wafers and finished solar cell is one of the most critical for entire PV industry. Mechanical defects in wafer and cells in the form of periphery or internal cracks can be initiated at various steps of the manufacturing process and becomes the trigger for the fracture. There are a limited number of characterization methods for crack detection but only a few of those are able to satisfy PV industry needs in sensitivity of the crack detection incorporated with the analysis time. The most promising are a Resonance Ultrasonic Vibrations (RUV) technique and Photoluminescence (PL) imaging. The RUV method was further developed in this thesis project for fast non-destructive crack detection in full-size silicon wafers and solar cells. The RUV methodology relies on deviations of the resonance frequency response curve measured on a wafer with peripheral or bulk millimeter-length crack when it is compared with identical non-cracked wafers. It was observed that statistical variations of the RUV parameters on a similarly processed silicon wafers/cells with the same geometry lead to false positive events reducing accuracy of the RUV method. A new statistical approach using three independent RUV crack detection criteria was developed and applied to resolve this issue. This approach was validated experimentally. Crack detection using RUV technique was applied to a set of production-grade Cz-Si wafers and finished solar cells from the Isofoton's S.A. (Spain) production line. Cracked solar cells rejected by the RUV method using the statistical approach were imaged with room temperature PL mapping and independently controlled with Scanning Acoustic Microscopy (SAM). A comparison of three independent techniques for crack detection, RUV, PL and SAM, was performed on selected samples. A high accuracy and selectivity of the RUV method to identify mm-size cracks in wafers and cells was confirmed.

The utilization of sun light is one of the hottest topics in sustainable energy research. To efficiently convert sun power into a reliable energy – electricity – for consumption and storage, silicon and its derivatives have been widely studied and applied in solar cell systems. This handbook covers the photovoltaics of silicon materials and devices, providing a comprehensive summary of the state of the art of photovoltaic silicon sciences and technologies. This work is divided into various areas including but not limited to fundamental principles, design methodologies, wafering techniques/fabrications, characterizations, applications, current research trends and challenges. It offers the most updated and self-explanatory reference to all levels of students and acts as a quick reference to the experts from the fields of chemistry, material science, physics, chemical engineering, electrical engineering, solar energy, etc..

Polycrystalline Silicon for Integrated Circuits and Displays, Second Edition presents much of the available knowledge about polysilicon. It represents an effort to interrelate the deposition, properties, and applications of polysilicon. By properly understanding the properties of polycrystalline silicon and their relation to the deposition conditions, polysilicon can be designed to ensure optimum device and integrated-circuit performance. Polycrystalline silicon has played an important role in integrated-circuit technology for two decades. It was first used in self-aligned, silicon-gate, MOS ICs to reduce capacitance and improve circuit speed. In addition to this dominant use, polysilicon is now also included in virtually all modern bipolar ICs, where it improves the basic physics of device operation. The compatibility of polycrystalline silicon with subsequent high-temperature processing allows its efficient integration into advanced IC processes. This compatibility also permits polysilicon to be used early in the fabrication process for trench isolation and dynamic random-access-memory (DRAM) storage capacitors. In addition to its integrated-circuit applications, polysilicon is becoming vital as the active layer in the channel of thin-film transistors in place of amorphous silicon. When polysilicon thin-film transistors are used in advanced active-matrix displays, the peripheral circuitry can be integrated into the same substrate as the pixel transistors. Recently, polysilicon has been used in the emerging field of microelectromechanical systems (MEMS), especially for microsensors and microactuators. In these devices, the mechanical properties, especially the stress in the polysilicon film, are critical to successful device fabrication. Polycrystalline Silicon for Integrated Circuits and Displays, Second Edition is an invaluable reference for professionals and technicians working with polycrystalline silicon in the integrated circuit and display industries.

Designed for science and engineering students, this text focuses on emerging trends in processes for fabricating MEMS and NEMS devices. The book reviews different forms of lithography, subtractive material removal processes, and additive technologies. Both top-down and bottom-up fabrication processes are exhaustively covered and the merits of the different approaches are compared. Students can use this color volume as a guide to help establish the appropriate fabrication technique for any type of micro- or nano-machine.

Now in its third edition, Fundamentals of Microfabrication and Nanotechnology continues to provide the most complete MEMS coverage available. Thoroughly revised and updated the new edition of this perennial bestseller has been expanded to three volumes, reflecting the substantial growth of this field. It includes a wealth of theoretical and practical information on nanotechnology and NEMS and offers background and comprehensive information on materials, processes, and manufacturing options. The first volume offers a rigorous theoretical treatment of micro- and nanosciences, and includes sections on solid-state physics, quantum mechanics, crystallography, and fluidics. The second volume presents a very large set of manufacturing techniques for micro- and nanofabrication and covers different forms of lithography, material removal processes, and additive technologies. The third volume focuses on manufacturing techniques and applications of Bio-MEMS and Bio-NEMS. Illustrated in color throughout, this seminal work is a cogent instructional text, providing classroom and self-learners with worked-out examples and end-of-chapter problems. The author characterizes and defines major research areas and illustrates them with examples pulled from the most recent literature and from his own work.