Browsing by Author "Wen, Tzu-Kuei"

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Crack detection in photovoltaic cells by interferometric analysis of electronic speckle patterns
(2012-03-01)
Wen, Tzu-Kuei
;
Yin, Ching-Chung
;
機械工程學系
;
Department of Mechanical Engineering
Cracking is a common problem encountered during the fabrication of crystalline silicon photovoltaic (PV) cells. In this study, electronic speckle pattern interferometry (ESPI) is developed as a tool for rapid identification of cracks in PV cells. Thermally induced cell deformation of defect-free and defect-bearing PV cells was first modeled with numerical simulations and then experimentally studied by optical configuration for ESPI measurement of out-of-plane deformations. Both numerical and experimental results indicate that the speckle patterns imparted during thermal deformation of a cell allow for simultaneous quantification of crack size, location and type in both single- and poly-crystalline PV cells. Speckle patterns near defects were manifested as continuous, chevron-shaped, and broken fringes for scratch, surface cracks, and through cracks, respectively. For comparison to other existing techniques, full field electroluminescent images were also provided for every defective PV cell. Electroluminescent imaging is capable of detecting cracks, but unlike ESPI, is unable to distinguish between the different types of cracks. Because the amount of heating needed to induce out-of-plane deformation resolvable by ESPI is small (<0.5 degrees C) and because ESPI is sensitive to crack type, the ESPI-based imaging study presented here can potentially be developed into a rapid, non-destructive inspection tool for the structural integrity of solar cells at any point within the manufacturing process. (C) 2011 Elsevier B.V. All rights reserved.
Crack detection in photovoltaic cells using electronic speckle pattern interferometry
(2010)
Wen, Tzu-Kuei
;
Yin, Ching-Chung
;
機械工程學系
;
Department of Mechanical Engineering
This paper presents a full field nondestructive testing method to inspect the micro-defects embedded in photovoltaic (PV) cells by using electronic speckle pattern interferometry. The edge-clamped solar cells were heated to induce thermal deflection. Interference fringe enhanced by speckle patterns correlated to thermal deformation were determined by subtraction of two pictures recorded at different temperatures and image processing technique based on Fourier optics. The interference fringes produced at the defect free specimen exhibit a number of polygons with regular patterns of bright and dark fringes which are concentric with the center of the specimen. The thermal deformation will be redistributed due to appearance of the defects. The heating-induced interference fringes become quite different from those of the undamaged one. Tangential discontinuities of interference fringes or locally concentric polygon patterns occur in the contiguous area around the micro-defects or damages. The application of large temperature gradient to silicon substrates will induce crack propagation and should be prevented in ESPI inspection.
ESPI Solution for Defect Detection in Crystalline Photovoltaic Cells
(2011)
Yin, Ching-Chung
;
Wen, Tzu-Kuei
;
機械工程學系
;
Department of Mechanical Engineering
The yield of photovoltaic (PV) cells is often reduced by micro-defects in crystalline silicon substrates during fabrication. Common optical inspection for a thin crack in such a large silicon photovoltaic cell is extremely time-consuming and fails in efficiency. This study developed a method of using electronic speckle pattern interferometry (ESPI) for rapidly testing for cracks in an entire field of PV cells. Thermally induced flexural cell deformation was measured by optical configuration for ESPI measurement of out-of-plane deformations. Experimental results indicate that the speckle patterns correlating with thermal deformation of cell enable simultaneous estimation of crack size and location in both single- and poly-crystalline PV cells. This nondestructive detection method has potential applications in PV cell sorting.