Hydrogenation Effect on Electrical Behavior of Polysilicon Thin Films

Abstract

Despite their wide availability and relatively low prices, the conventional energy sources have harmful consequences on the environment and are exhaustible. In order to circumvent these negative effects, the renewable energies in general and the photovoltaic energy in particular are becoming more and more attractive. In this type of conversion, the low cost polycrystalline silicon solar cells are promising. However, the photovoltaic parameters of these cells are affected by the existence of the grain boundaries (GBs) and the segregation of impurities at these GBs. In this work, we are interested in studying the effect of hydrogenation on the electrical behavior in polysilicon thin films. The results have shown that the introduction of hydrogen in a polysilicon films reduces the density of trap states at the GBs, and hence their electronic activity. This is translated in the reduction of the resistivity, the improvement the mobility of carriers and an increase in the concentration of free carriers. In addition, it has been shown that the effect of hydrogen on the electrical characteristics is more pronounced, on the one hand, for low doping concentrations, and on the other hands, in boron doped films than in arsenic doped films. This is mainly due to the strong segregation of arsenic atoms at the GBs, which reduces the effect of hydrogen on the density of trap states by reducing its penetration in the GBs.