Application of thermoreflectance imaging to identify defects in photovoltaic solar cells

Thermoreflectance imaging is used to identify various defects in solar cells with sub-micrometer spatial resolution. Lock-in transient and four-bucket imaging techniques in a megapixel silicon-based CCD are used to obtain the thermoreflectance and electroluminescence signals simultaneously. Linear and non-linear shunts are discovered in thin-film a-Si, poly-Si, and CdTe solar cells. Electroluminescent defects are found in poly-Si solar cells at reverse biases of 5V. Thermal images of micrometer-size defects are taken through 3mm of glass encapsulation.