Polarized light emission from grain boundaries in photovoltaic silicon

Some crystalline defects in photovoltaic silicon have deleterious effects on the energy conversion efficiency of the material. Distinguishing the harmful defects from the benign defects is a critical problem in the mechanics of materials for solar energy conversion. Interestingly, the visible light absorbed by silicon in the same part of the solar spectrum that is used to generate photocurrent, can also excite photoluminescence, which may be used to generate images of the microstructure. Slightly longer wavelengths in the near infrared (IR) may be used to measure strain in the material via photoelastic (PE) imaging. These two imaging modalities have recently been combined in a single instrument, and we show here the additional capability to identify and categorize defects directly by capturing the narrow band of photoluminescence emitted by regions of high dislocation density. We use this method to show that dislocations arranged in low angle grain boundaries emit polarized light, while dislocation structures in neighboring high angle grain boundaries do not emit polarized light. This capability may form the basis for next-generation, full-field optomechanics-based characterization of materials for solar energy conversion.