Hydrogenation in crystalline silicon materials for photovoltaic application

Abstract

In this contribution an overview of hydrogenation issues for (multi-)crystalline silicon material is given. Crystalline silicon material for photovoltaic application contains more defects than material used for other semiconductor device fabrication. Therefore passivation of bulk defects has to be performed to reach higher efficiencies and exploit the cost reduction potential of these materials. Especially minority charge carrier lifetimes of ribbon silicon can be drastically improved by hydrogenation in combination with a gettering step. Apart from bulk passivation atomic hydrogen plays an important role in surface passivation via dielectric layers. Performance of single dielectric layers or stack systems can be increased after a hydrogenation step. It is believed that hydrogen can passivate defects at the silicon/dielectric interface allowing for lower surface recombination velocities. In industrial application hydrogenation is performed via deposition of a hydrogen-rich PECVD SiNx layer followed by a belt furnace annealing step. Surface passivation for characterization of charge carrier bulk lifetime is often performed with the same technique, omitting the annealing step to avoid in-diffusion of hydrogen. It is shown that for some crystalline silicon materials even the PECVD SiNx deposition alone (without annealing step) can cause significant bulk defect passivation, which in this case causes an unwanted change of bulk lifetime.