加熱分佈對於多晶矽太陽能電池裂縫的電子光斑干涉檢測之影響

Abstract

6吋多晶矽太陽能電池的厚度很薄，兼具撓性及脆性，製程中難以肉眼發現的缺陷與裂縫在電池模組化後，將造成發電效率降低或電池失效，在產線上將含缺陷太陽能電池淘汰是一項重要課題。矽晶太陽能電池是矽、孔隙鋁材組成的積層複材結構，因熱膨脹係數相異，受熱會產生撓曲變形。本研究數值模擬8種熱通量分佈的暫態分析，歸納出適合裂縫檢測的加熱分佈，以電子光斑干涉術量測電池熱變形的面外位移。除了側緣1/4處之裂縫，由內而外遞減的熱通量分佈使裂縫附近的面外位移等高線及光斑干涉條紋發生明顯變化，V形光斑條紋發生於表面裂縫附近，貫穿裂縫附近呈現斷裂條紋。採用不對稱及長條狀加熱分佈，能辨識側緣1/4處的裂縫特徵。本研究成果適合線上即時全域檢出太陽能電池的表面及貫穿裂縫。 關鍵字：裂縫檢測、電子光斑干涉術、多晶矽太陽能電池、熱變形

The 6-inch polysilicon wafers for use of photovoltaic (PV) cells are thin enough, and possess both flexibility and brittleness. The latent defects which could not be found in PV cells by the unaided eye in the production line usually result in efficiency reduction and damage of solar panel. It remains an important issue to eliminate defective products before module process or end applications. Solar cell is a laminate structure mainly composed of silicon and porous aluminum. Thermal mismatch usually causes a bow of the cell exerted by temperature variation. This study numerically explores eight types of heat flux patterns and their influences on transient thermal deformation of the PV cell by the finite element method (FEM). The out-of-plane thermal deformation measurements were carried out by electronic speckle pattern interferometry (ESPI) with the suitable heat flux patterns that can induce clear fringes for identification of crack. Both the contour of out-of-plane displacement calculated by FEM and speckle fringe patterns detected by ESPI reveal the obvious changes near cracks due to heating profile gradually decreasing from periphery inwards. However, the crack initiated at one-quarter periphery off the center of edge can be only detected by use of unsymmetrical and long stripe-like heating profiles. Speckle patterns for surface cracks at the edge of cells appear with chevron-shaped fringes. Broken fringes are found for the through-cracks. The outcome of this study can be implemented as a real-time, whole field, nondestructive testing system for detection of surface cracks and through cracks in PV cells in the production line.

Keywords: Crack detection, electronic speckle pattern interferometry, polysilicon photovoltaic cells, thermal deformation