IR Reflectance Imaging for Crystalline Si Solar Cell Crack Detection

A novel, contactless, noninvasive, and nondestructive method of crack detection in crystalline Si solar cells has been developed. A thermal imaging camera detecting in the 7.5-13-μm wavelength range was used to image the specular reflection of an IR source on the surface of a crystalline Si cell. The surface distortion caused by the presence of a crack was found to affect a change in the local surface normal, a phenomenon exploited to observe the change in specular reflection and the resultant distortion captured in an IR thermal image. The system has been found to reliably and reproducibly reveal cracks in Si cells that are not observable at visible wavelengths. The detection rate and temperature operating range were found to be readily tailored to the requirements of different manufacturing and inspection environments.