Structural Transition and Band Gap Tuning of Cu2(Zn,Fe)SnS4 Chalcogenide for Photovoltaic Application

Polycrystalline Cu 2 Zn z Fe 1– z SnS 4 (CZFTS) thin films have been fabricated using chemical spray pyrolysis accompanied by postsulfurization. The postsulfurized CZFTS films demonstrate promising morphological, structural, and optical properties for photoabsorber in thin film photovoltaics. The structural transition from stannite to kesterite is found with the increase of zinc content in CZFTS alloy by using X-ray diffraction and Raman spectroscopy. The band gap energies of postsulfurized CZFTS films are observed to be tuned from ∼1.36 ± 0.02 to 1.51 ± 0.02 eV in parabolic-increase trend with increasing Zn content (0 ≤ z ≤ 1). A small bowing constant b ∼ 0.1 ± 0.05 eV deduced from band gap bowing model implicates good miscibility of alloyed constituents in the host crystal lattice.