Hydrogen passivation of multicrystalline silicon

Hydrogen passivation using SiN_x remains one of the most technologically significant developments of the solar cell industry. However, the nature of hydrogen diffusion through the bulk of the solar cell during high temperature processing and the details of how hydrogen passivates defects is a topic of ongoing investigation and debate. The model for diffusion of hydrogen in single-crystal silicon includes hydrogen trapping at impurities and vacancies and the existence of several charge states. In multicrystalline silicon the presence of dislocations and grain boundaries presents an even more complex situation for modeling the interaction between hydrogen and defects and impurities. In this review, hydrogen passivation of impurities and passivation of extended defects, such as dislocations and grain boundaries, are summarized, as well as diffusion of hydrogen through the solar cell bulk. Finally, implications for current understanding of hydrogen passivation of solar cells using industrial processing is discussed.