Techniques for fabricating thin film solar cells, such as CuZnSn(S,Se) (CZTSSe) solar cells are provided. In one aspect, a method of fabricating a solar cell is provided that includes the following steps. A substrate is provided. The substrate is coated with a molybdenum (Mo) layer. A stress-relief layer is deposited on the Mo layer. The stress-relief layer is coated with a diffusion barrier. Absorber layer constituent components are deposited on the diffusion barrier, wherein the constituent components comprise one or more of sulfur (S) and selenium (Se). The constituent components are annealed to form an absorber layer, wherein the stress-relief layer relieves thermal stress imposed on the absorber layer, and wherein the diffusion barrier blocks diffusion of the one or more of S and Se into the Mo layer. A buffer layer is formed on the absorber layer. A transparent conductive electrode is formed on the buffer layer.