Crack detection in photovoltaic cells using electronic speckle pattern interferometry

Abstract

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.