Effect of sulfur quantity in post-treatment on physicals and electrical properties of electrodeposited Kesterite Cu2ZnSnS4 thin films

Abstract

In this work, thin films of Cu2ZnSnS4 (CZTS) have been successfully electrodeposited onto FTO substrate. The films are post-sulfurized with different amount of sulfur varied from 0 to 0.5 g at 550 °C under N2 atmosphere. Effect of sulfur quantity during the annealing treatment on structural, morphological, optical and electrical properties of CZTS films have been investigated using various techniques. XRD analysis shows that CZTS thin film annealed at 550 °C in the presence of 0.3 g of sulfur element exhibited the best crystalline quality of kesterite phase with (112) preferential orientation. This result was confirmed by Raman spectroscopy. Surface morphology studied by scanning electron microscopy revealed that the post-sulfurization and especially the quantity of sulfur have a significant effect on the surface and roughness of thin films. According to the UV–Vis measurements, all films show high absorption in the visible region (~ 104 cm− 1) with a direct energy band gap ranging from 2.18 to 1.65 eV, which depends on the sulfur amount during the post-sulfurization. Finally, the electrical characterization by means of electrochemical impedance spectroscopy was carried out to analyze the capacitive nature of CZTS/Na2SO4 interface. This interface was modeled by an equivalent circuit approach. From the Mott–Schottky plot, the flat band potential and the acceptor density for CZTS thin films are determined. All the films demonstrated a p-type semiconductor character with a carrier density varying between 1016 and 1020 cm− 3.