Composition dependence of the structure and optical properties of Cu₂Mn_xZn_1-xSnS₄ thin films

Cu₂Zn_1-xMn_xSnS₄ (CMZTS) thin films with composition controllability and tunable band gap have been firstly prepared by sol-gel technique followed by a post-annealing treatment at 580 °C for 10 min in nitrogen gas atmosphere. Effects of Mn variation in CMZTS thin films with x = 0.0-1.0 on the morphological, structural, and optical properties have been investigated. XRD and Raman studies reveal the incorporation of Mn into Cu₂ZnSnS₄ (CZTS) thin films, and demonstrate the structural transition from kesterite to stannite with increasing Mn content. SEM images show that compact, homogeneous and densely packed grains could be formed. Furthermore, UV-vis spectroscopy indicate that the band gaps of the CMZTS films can be tuned almost linearly between 1.23 and 1.51 eV with a small bowing constant of the band gap (∼0.10 eV), which confirms the good miscibility of the alloyed constituents in the crystal lattice.