The role and the characteristics of hydrogen in different polycrystalline silicon material are studied in this paper. The hydrogen diffusion through the grains and the grain boundaries, and its diffusion coefficient, are investigated, Moreover, the influence of the oxygen and the carbon contents on the diffusion mechanism of hydrogen in silicon is addressed. Also, it is found that the minority carrier diffusion length of polycrystalline silicon wafers considerably improves when annealed in hydrogen at high temperatures (>1000 degrees C). Consequently, a significant amount of oxygen is out-diffused from the bulk of the wafers,