Impact of Hydrogen in Ga-Doped Silicon on Maximum LeTID Defect Density

Many studies suggest that hydrogen is an important factor for light and elevated temperature-induced degradation (LeTID) in p-type c-Si solar cells. The exact mechanism of this defect is still unknown. Here, Ga-doped Si wafers fired with an SiNx:H layer present were used to establish a correlation between the initial concentration of GaH pairs and H-2 dimers on one and the maximum defect density evolving during degradation on the other hand. Degradation of all samples is performed at constant excess charge carrier injection. The correlation to LeTID defect density is found to be linear in the case of [H-2], hence, a direct involvement of H-2 in the defect formation is expected. In contrast, the correlation between GaH pairs and defects is found to scale with the fraction of GaH on total hydrogen concentration. This fraction is not constant but rather decreases with an increase in total hydrogen concentration. In addition, changes in [GaH] and lifetime are examined under different degradation conditions with either fixed injection up to 10(16) cm(-3) and temperatures up to 180 degrees C. Under these conditions, LeTID evolves but no dissociation of [GaH] takes place. The effective activation energy of LeTID defect formation is determined to be 0.76(17) eV. The cause of light- and elevated temperature-induced degradation is still unknown, but it is clear that hydrogen plays a crucial role in the formation of defects. In this article, the authors show quantitatively how the initial concentrations, i.e., H2 and GaH pairs, affect defect formation. The dependence of defect formation on degradation conditions is also investigated.image (c) 2023 WILEY-VCH GmbH