Polarization-Resolved Imaging for Both Photoelastic and Photoluminescence Characterization of Photovoltaic Silicon Wafers

The solar industry uses low-cost solidification processing methods to produce silicon wafer-based solar cells. The solidification processing can introduce crystalline defects and residual stresses in the wafers, which may impact the electrical performance and mechanical reliability of a finished solar cell. This paper presents a polarized infrared imaging system that achieves both infrared photoelastic analysis and polarized photoluminescence imaging. A polarization video-processing algorithm is used to resolve the polarization state of the detected photoelastic and photoluminescence signals and simultaneously reduce the noise. Defects in multi-crystalline silicon photovoltaic wafers are investigated using the polarized photoluminescence imaging setup, which can capture both the band-to-band and defect-band photoluminescence emission and spatially resolve the defect structures. The photoluminescence imaging results are qualitatively compared to the infrared photoelastic images to investigate the coupled electrical and mechanical properties of the defect structures. The technology described here creates a pathway to rapid full-field wafer quality inspection in a manufacturing setting and will help to improve wafer material processing.