Hydrogen passivation of defects in multicrystalline silicon solar cells

Abstract

The knowledge of how hydrogen interacts with defects and impurities in silicon is crucial for the understanding of device performance, especially for solar cells made from disordered silicon wafers. Hydrogen can be introduced in silicon by several techniques, but this paper will be focused on hydrogenation by means of plasma enhanced chemical vapor deposition of hydrogen-rich silicon nitride layer on the surface of the wafer. Passivation effects are observed after annealing and evaluated using minority carrier diffusion length measurements and light-beam-induced current scan maps. It was found that individual intragrain defects are well passivated, while deep levels are transformed into poorly recombining shallow levels at grain boundaries and dislocation clusters. In solar cells, the stability of the hydrogen passivation is much higher with this technique than with other hydrogenation techniques. This is probably due to an encapsulation of hydrogen by the frontwall silicon nitride coating layers and by the backside aluminum film.