A Fast 3D System for AR Film Thickness Measurement of Single Crystalline Silicon Solar Cells

摘要

For increasing marketing competence, silicon solar cell manufacturers have adopted optical inspection techniques in production lines to perform product classification and statistical process analysis. The product classification is based on overall photoelectric conversion efficiency of the solar cell itself. Two factors directly influence the overall photoelectric conversion efficiency of the solar cell, i.e., composed materials and anti-reflection (AR) film coating on substrate. Since film thickness variation of the AR layer will induce color change on the surface of solar cell, a cost-effective three dimensional (3D) system is proposed to perform fast AR film thickness measurement of single silicon crystalline solar cells. The proposed system first uses a color CCD to capture the red-green-blue color image of inspected single silicon crystalline solar cell, and transforms it to hue-saturation-lightness image format. And then the area and boundary of different hue-value images are calculated and sorted with the image thresholding and label operation. Besides, with the corresponding measurement procedure on specified hue-value regions of using a precise height measurement instrument, such as the wavelength scanning profiler, the regression equation between the hue value and AR film thickness is obtained, and then implemented into the proposed 3D system to perform large area scanning AR film thickness measurement of single silicon crystalline solar cells. Compared to the optical ellipsometry, the measurement speed of the proposed system is fast. It take only 0.1 seconds to finish the AR film thickness measurement of a 12.5 cm × 12.5 cm solar-cell image, and the measurement accuracy can reach 3 nm.