Effect of complexing agents on the electrodeposition of Cu–Zn–Sn metal precursors and corresponding Cu2ZnSnS4-based solar cells

Abstract

Copper zinc tin sulfide (Cu2ZnSnS4; CZTS) precursors were electrochemically deposited on Mo-coated glass substrates from aqueous solutions following by annealing. The effect of three complexing agents, trisodium citrate, ethylenediamine tetraacetic acid and tartaric acid, on the structural, morphological and compositional properties of CZTS thin films was investigated. The annealed thin films were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS), UV–vis absorption and Raman scattering spectroscopies. XRD patterns of the synthesized films revealed the preferred orientation of the (112), (220), (200) and (312) planes, confirming the kesterite structure of CZTS. The film prepared without a complexing agent was uneven with some pores and cracks, whereas those prepared using complexing agents exhibited good coverage with some overgrown particles on the surface of the films. EDS analysis revealed that the films deposited using trisodium citrate were nearly stoichiometric for CZTS. Voltammetric studies suggested that trisodium citrate is a suitable complexing agent because it helps to align the deposition potentials of Cu, Zn, and Sn. UV–vis absorption spectra confirmed the films possessed a direct bandgap between 1.33 and 1.47eV, which is quite close to the optimum value for a semiconductor material as an absorber in solar cells. We fabricated solar cells with the structure soda-lime glass/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Al with a maximum conversion efficiency of ∼2.9%.