Structural, microstructural and optical properties of Cu2ZnSnS4 thin films prepared by thermal evaporation: Effect of substrate temperature and annealing

Thin films of Cu2ZnSnS4 (CZTS), a promising solar cell absorber, were grown by thermal evaporation of ZnS, Sn and Cu precursors and subsequent annealing in sulphur atmosphere. Two aspects are chosen for investigation: (i) the effect of substrate temperature (TS) used for the deposition of precursors and (ii) (N₂+S₂) pressure during annealing, to study their impact on the growth of CZTS films. X-ray diffraction analysis of these films revealed the structure to be kesterite with (112) preferred orientation. Crystallite size is found to slightly increase with increase in TS as well as pressure during annealing. From optical absorption studies, the direct optical band gap of CZTS films is found to be ∼1.45 eV. Room temperature electrical resistivity of the films obtained on annealing the stacks at 10 and 100 mbar pressures is found to be in the ranges 25-55 and 5-25ω cm, respectively, depending on TS. Films prepared by annealing the stack deposited at 300°C under 100 mbar pressure for 90 min are slightly Cu-poor and Zn-rich with compact grain morphology.