Methods of fabricating solar cells using a metal-containing thermal and diffusion barrier layer in foil-based metallization approaches, and the resulting solar cells, are described. For example, a method of fabricating a solar cell includes forming a plurality of semiconductor regions in or above a substrate. The method also includes forming a metal-containing thermal and diffusion barrier layer above the plurality of semiconductor regions. The method also includes forming a metal seed layer on the metal-containing thermal and diffusion barrier layer. The method also includes forming a metal conductor layer on the metal seed layer. The method also includes laser welding the metal conductor layer to the metal seed layer. The metal-containing thermal and diffusion barrier layer protects the plurality of semiconductor regions during the laser welding.