Development of dip-coated Cu₂ZnSnS₄ absorber material without sulphurisation

Quaternary semiconductor Cu₂ZnSnS₄ absorber material was synthesized by the sol-gel method deposited by the dip-coating technique on ordinary glass substrates. In this study, we have investigated the effects of dip-coating cycle at different cycles: 2, 4 and 6, and annealing temperature at various temperatures: 300, 325 and 375 °C on the structural, morphological compositional, optical and electrical properties. The films have been characterized by different characterization techniques such as X-ray diffractometer (XRD), Raman scattering experiments, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), UV–visible spectrophotometer and four-point probe method. XRD patterns indicated kesterite CZTS with preferential orientation along (112) plane, Cu_2-xS, SnS₂ and SnS secondary phases were observed with CZTS phase in some samples. The pure CZTS phase was formed for the sample annealed at 375 °C and sample deposited at 2 cycles. Raman spectroscopy confirmed the presence of CZTS thin films in all samples using Raman characteristic peak at 332 cm⁻¹. EDS analysis showed near-stoichiometric CZTS thin films. (SEM) images showed the uniform and dense surfaces morphologies. The gap energy is estimated from absorbance data by using absorption spectra fitting (ASF). The optical band gap decreases with the increasing of dip-coating cycle in the range of 1.33–1.44 ∓ 0.01 eV and also increases with the increasing of annealing temperature in the range of 1.38–1.47 ∓ 0.01 eV. The electrical sheet resistance increased from 2.60 ∓ 0.01 to 4.67 ∓ 0.01 × 10³ (Ω/square) when the annealing temperature increased and decreased when the dip-coating cycle increased in range of 0.99 ∓ 0.01 and 1.19 ∓ 0.01 × 10³ (Ω/square). These characteristics are suitable for solar cells applications.