ZnS is an excellent candidate for the substitution of the CdS buffer layer inCZTS based solar cells, is nontoxic and is relatively less costly.It has been shown that a surface composition adaptation is favorable for the replacement of the buffer layer CdS by ZnS so as to obtain an interface quality with the CZTS layer that makes it possible to control the diffusion phenomenon of faults to this interface. SCAPS-1Dsoftware is used to simulate CZTS/ZnS/ZnO:F thin-film solar cell where the key parts are p-CZTS absorber layer and n-ZnS buffer layer.