Electronic Properties of the Boron–Oxygen Defect Precursor of the Light-Induced Degradation in Silicon

In this work, we study the electronic properties of the boron–oxygen precursor defect responsible for light-induced degradation in crystalline silicon via deep-level transient spectroscopy. Even though this degradation has been known for many decades, and has resulted in severe silicon solar cell degradation, its root cause is poorly understood. The detection of a deep defect correlated to BO degradation has only been reported recently using deep-level transient spectroscopy. The resulting trap has been labeled as H390. In this work, we confirm the existence of this trap and report on the observation of a second defect (H400), which appears to be similarly associated with the BO light-induced degradation. To the best of our knowledge, this level has not been previously reported and could result from a second latent form of the BO light-induced degradation defect, a topic that has been largely debated in the literature. The concentration of both levels increases following dark annealing and decreases following minority carrier injection. The two levels disappear during BO activation and appear during BO deactivation, confirming a link between the observed levels and the latent state of the BO defect. Furthermore, consistent with previous studies, the two traps are metastable and change configurations after hole capture. Finally, we determine the minority carrier capture cross-section of the active BO defect by comparing the latent defect concentration with the minority carrier lifetime.