Applications of imaging techniques for solar cell characterization

Minority-carrier lifetime, diffusion length, resistance, and shunting are all useful parameters for monitoring material quality, processing, and cell performance. These data may be quickly obtained, and even potentially used during manufacturing, when collected from recently developed imaging techniques. Point-by-point measurements provide quantitative data that is valuable as a research tool, even though data acquisition time may be lengthy. Imaging data can often be collected in seconds with better resolution, and while it may initially appear only qualitative, correlations and calibrations are possible and can transform the image to a set of values. We present several examples of photoluminescence imaging on multi-crystalline Si wafers compared to microwave reflection lifetime mapping. We also present electroluminescence imaging and dark lock-in thermography on several cells of different efficiency and compare to diffusion length, lifetime, and sheet resistance.