Effect of deposition temperature on the structural and electrical properties of spray deposited kesterite (Cu2ZnSnS4) films

Abstract

Spray technique is used for the deposition of Cu2ZnSnS4 (CZTS) films, taking the chlorides of Cu(I), Zn and Sn(II) along with thiourea as precursors for the spray solution, with the substrate temperature varying from 200°C to 450°C. Use of these precursors results in CZTS phase formation starting at 200°C and only beyond 350°C the secondary phases are formed. CZTS films deposited at 200°C and 250°C show high resistivity’s of 502.39Ω-cm and 51.84Ω-cm, respectively and carrier concentrations of 2.85×1014cm−3 and 5.55×1015cm−3, respectively. The formation of secondary phases at 400°C and 450°C strongly affects the film properties. CZTS films deposited at 350°C show the best resistivity of 0.19Ω-cm. SEM analysis shows growth of nano-flakes on the surface of the film deposited at 350°C, and C-AFM reveals that the film has the highest current range due to high internal conductivity which can be the cause of reduced film resistivity and enhanced optical absorption. CZTS film at 350°C had the lowest activation energy calculated from the Arrhenius plot of ln σ vs 1000/T. Energy dispersive spectroscopy (EDS) analysis shows that the atomic percentages of the constituents in the CZTS films change with the temperature and accordingly affect the band gap. The film deposited at 350°C is nearly stoichiometric with the band gap of 1.45eV making it best suited for solar cell fabrication.