電子光斑干涉術應用於矽晶太陽能電池之裂縫檢測

Abstract

在太陽能電池製造過程中，裂縫缺陷是一非常普遍且嚴重的問題。本研究採用電子光斑干涉術(ESPI)為量測工具，快速的確認及辨識太陽能電池上的裂縫。研究步驟先數值分析有、無裂縫之太陽能電池的熱變形，以確認方法的可行性，之後再以ESPI的面外變形量測系統進行實驗。數值模擬及實驗量測皆顯示一致的結果，由面外位移的等高線或干涉條紋可清楚判斷太陽能電池裂縫的存在，並量化顯現裂縫的長度、位置及種類。光斑干涉條紋在表面刮傷、表面裂縫及貫穿裂縫三種缺陷附近的特徵分別是連續的、V形狀及條紋斷裂。為了增加本研究方法的參考價值，實驗以目前太陽能業界出貨檢驗標準的電激螢光法(EL)作為對照，並討論兩種方法個別的優勢。EL影像雖然可以掌握太陽能電池的所有缺陷，但無法如本研究方法清楚的分辨出裂縫或僅稍微影響電性的表面刮傷。本研究方法之太陽能電池的熱變形是在很小的加熱溫度(<0.5 oC)形成，卻可以使裂縫產生很高的辨識特徵，又不會破壞太陽能電池，很適合應用於生產線上做即時的檢測。

Cracking is a common problem encountered during the fabrication of crystalline silicon photovoltaic (PV) cells. In this study, electronic speckle pattern interferometry (ESPI) is used 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 oC) 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.