含裂縫太陽能電池基板面內共振的電子光斑干涉檢測

Abstract

基板面積愈來愈大，厚度愈來愈薄是矽基太陽能電池的發展趨勢。矽的剛性高、韌性低，製程中矽基板容易產生寬度細微的裂縫，造成模組程序或日後應用上發生災難性破損。以目視或機器視覺辨識這些裂縫耗費時間甚巨。本文應用電子光斑干涉術，量測太陽能電池基板的面內共振模態，研發基板裂縫的全域光學非破壞檢測技術。平板結構之面外共振的模態密度高，不易辨識裂縫對於共振模態的影響，故採取模態間隔較疏之面內共振檢測裂縫位置。本研究採用一片壓電纖維複材作為致動器，黏貼於基板邊緣，驅動基板產生面內振動。以振幅擾動電子光斑干涉術量測太陽能電池基板之低階面內共振模態，證實數值分析完整太陽能電池基板面內共振結果的正確性。含裂縫太陽能電池基板的結構剛性減少，面內共振頻率較完整的電池基板低，裂縫兩側面內位移之不連續突顯出裂縫的存在，電子光斑條紋朝向裂縫處偏移，成功地標示出裂縫位置。

The trend of silicon-based photovoltaic cells is toward increasing wafer size and decreasing substrate thickness. However, silicon has high stiffness and low toughness. Micro-defects having tiny crack width are frequently generated in the brittle cell substrates during manufacture and results in catastrophic failure in module process or later application. It is very time consuming to detect those defects by human eyes or machine vision technology. This thesis develops a full-field optical nondestructive technique to detect defects in cell substrates by application of electronic speckle pattern interferometry (ESPI) to measure its in-plane resonant vibration. The modal density of out-of-plane resonant vibration is high for a planar structure. It is of difficulty to identify the influence of cracks in accordance with out-of-plane resonance. The in-plane resonance featuring clear modal separation has potential to detect the crack and its position. An active fiber composite adhered to one edge of the cell substrate is used to actuate in-plane vibration. Lower in-plane resonant modes are measured by the amplitude-fluctuation ESPI method. Numerical analysis of in-plane vibration for the integrated photovoltaic cells has been validated by experimental measurement. The cracked cell substrate has lower resonant frequency for in-plane vibration than the integrated one due to lower stiffness. The discontinuous displacement field across the crack faces characterizes the appearance of defect. Further, the speckle fringes intensively moving toward the crack could be an indication of the crack position.