Solvothermal synthesis of Cu 2 Zn 1− x Fe x SnS 4 nanoparticles and the influence of annealing conditions on drop-casted thin films

Cu 2 Zn 1− x Fe x SnS 4 (CZFTS) semiconductor alloy sphere-like nanoparticles were synthesized by a solvothermal method and their thin films were fabricated using a facile drop casting route then annealed in Ar and/or sulfur atmosphere. The sphere-like CZFTS nanoparticles demonstrate promising morphological, structural, and optical properties for an absorber layer in thin film solar cells. X-ray diffraction patterns, Raman spectra and EDS measurements of the samples indicate that a phase transition from kesterite to stannite occurred by increasing the Fe content to Fe/Fe + Zn = 0.61 ratio. Moreover, the increase in Fe content (0 ≤ x ≤ 1) resulted in a variation of the band gap energies of CZFTS from ∼1.515 to 1.206 eV on the basis of a parabolic decreasing trend. From a band gap bowing model we derived a small bowing constant of b ∼ 0.2009 ± 0.02 eV, indicating suitable miscibility of alloyed constituents in the host crystal lattice. The films annealed in sulfur showed a dense, uniform, low-crack surface, high thickness and low transmission compared to the films annealed in Ar flow. The four-point probe analysis showed an increasing resistivity of samples annealed in Ar with increasing Fe content.