It is demonstrated that crystallization of alpha-Si:H in cells grown on metallized polymer substrates occurs at temperatures below similar to 160 degrees C. X-ray diffraction and Raman studies indicate that the extent of crystallization is larger for silver than for aluminum coated polymers, and increases with deposition temperature. Results are presented for the strong impediment of the crystallization of alpha-Si:H with the insertion of a thin ZnO buffer-layer between the metal and alpha-Si:H. It is further demonstrated that aluminum crystallizes when alpha-Si:H is deposited onto it.