A method for producing a compound semiconductor composed of pentanary kesterite/stannite of the type Cu2ZnSn(S,Se)4 is described. The method has the following steps: producing at least one precursor layer stack consisting of a first precursor layer and a second precursor layer; thermally treating the at least one precursor layer stack in a process chamber; and feeding at least one process gas into the process chamber during the thermal treatment of the at least one precursor layer stack. Furthermore, a thin-film solar cell with an absorber consisting of the pentanary compound semiconductor Cu2ZnSn(S,Se)4 on a body is described.