Study on the role of Mn in Ag and Mn co-doped Cu 2 ZnSnS 4 thin films

The reported Ag and Mn co-doped Cu 2 ZnSnS 4 thin film has better properties than single-doped Cu 2 ZnSnS 4. However, the role of Mn in co-doped Cu 2 ZnSnS 4 thin film is still unclear. In this paper, Ag and Mn co-doped Cu 2 ZnSnS 4 thin films with different Mn amounts were prepared by sol-gel method. The crystal phases, morphologies, element compositions, and optical properties of co-doped Cu 2 ZnSnS 4 thin films were characterized to investigate the role of Mn doping. Compared with Ag single-doped Cu 2 ZnSnS 4 thin film, after the incorporation of Mn into Ag-doped Cu 2 ZnSnS 4, the crystallinity of Cu 2 ZnSnS 4 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 MoS 2 interface layer between Cu 2 ZnSnS 4 and Mo becomes thinner and the Urbach energy of Cu 2 ZnSnS 4 decreases after Mn doping. Therefore, Mn in the co-doped Cu 2 ZnSnS 4 thin films shows beneficial effects of enhanced structural, morphological, and optical properties of the films.