Passivation of polycrystalline silicon solar cells by low-energy hydrogen ion implantation

Abstract

It has been demonstrated that hydrogen can be used to saturate dangling bonds in amorphous silicon, so this element has been chosen to passivate the defects present in polycrystalline materials. In recent years, it has been recognized that hydrogen ion implantation at low energy also results in a great improvement in the electrical properties of polycrystalline silicon solar cells. Technically, the best approach is to use a Kaufman-type ion source or similar equipment in order to reduce the processing time. We have used a multiple-beam ion source based on the same principle as the Kaufman-type source, but equipped with a post-acceleration electrode providing H + ions with 0.5–10 keV energies. For this equipment, we have determined the following: (1) the effective distribution and concentration profiles of the introduced hydrogen and the modification of the optical properties; (2) the conditions under which two cast multicrystalline materials (Polyx and Silso) will give the greatest improvement in cell performance; (3) the long-term electrical stability of solar cells processed by the methods described. This work provides the first consistent picture of the relationship between hydrogen-ion-beam parameters and optimal and electrical properties.