Study on the role of Mn in Ag and Mn co-doped Cu2ZnSnS4 thin films

The reported Ag and Mn co-doped Cu2ZnSnS4 thin film has better properties than single-doped Cu2ZnSnS4. However, the role of Mn in co-doped Cu2ZnSnS4 thin film is still unclear. In this paper, Ag and Mn co-doped Cu2ZnSnS4 thin films with different Mn amounts were prepared by sol-gel method. The crystal phases, morphologies, element compositions, and optical properties of co-doped Cu2ZnSnS4 thin films were characterized to investigate the role of Mn doping. Compared with Ag single-doped Cu2ZnSnS4 thin film, after the incorporation of Mn into Ag-doped Cu2ZnSnS4, the crystallinity of Cu2ZnSnS4 improves and the micro-strain and dislocation density in the crystal reduce. The valence states of Cu, Zn, Sn, S, Ag, and Mn in co-doped thin film are +1, +2, +4, -2, +1, and +2, respectively. Mn doping can make the grains on the thin film surface enlarge. The MoS2 interface layer between Cu2ZnSnS4 and Mo becomes thinner and the Urbach energy of Cu2ZnSnS4 decreases after Mn doping. Therefore, Mn in the co-doped Cu2ZnSnS4 thin films shows beneficial effects of enhanced structural, morphological, and optical properties of the films.