Effects of growth temperatures on the physical properties of Cu₂ZnSnS₄ thin films deposited through spray pyrolysis for solar cell applications

Abstract

This paper reports the effects of substrate temperature on the structural, optical, and electrical properties of Cu₂ZnSnS₄ (CZTS) thin films deposited on soda lime glass through spray pyrolysis without sulfurization. Substrate temperatures ranged from 250 to 500 °C at a step of 50 °C, and a precursor solution was prepared by dissolving copper chloride, zinc acetate, zinc chloride, and thiourea in ethanol and di-ionized water. The films were characterized through X-ray diffraction (XRD), field emission scanning electron microscopy, ultraviolet–visible spectroscopy, and electrical resistance and Hall effect measurements, respectively, obtained by two-point probe and van der Pauw techniques. XRD revealed the formation of polycrystalline CZTS thin films and the appearance of relatively intense and sharp diffraction peaks at (112), (200), (220), and (312) of a kesterite phase with (112) preferential orientation, in which the crystalline degree increased as substrate temperature increased. Surface morphological analysis demonstrated the formation of a smooth, compact, and uniform CZTS surface. When substrate temperature increased from 250 to 500 °C, single-crystal grains increased from 6.38 to 28 nm, carrier concentration increased from 3.4 × 10¹⁷ to 2.36 × 10¹⁹ cm⁻³, Hall mobility increased from 30.96 to 68.52 cm²/V.S, optical band gap decreased from 1.74 to 1.14 eV, and resistivity decreased from 0.59 to 3.87 × 10⁻³ Ωcm. Hall effect analysis indicated that the films exhibited p-type conductivity.