Structural, microstructural and optical properties of $$\hbox {Cu}₂\hbox {ZnSnS}₄$$ Cu 2 ZnSnS 4 thin films prepared by thermal evaporation: effect of substrate temperature and annealing

Thin films of $$\hbox {Cu}₂\hbox {ZnSnS}₄$$ (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 ( $$T_{\mathrm{S}})$$ used for the deposition of precursors and (ii) ( $$\hbox {N}₂{+}\hbox {S}₂)$$ 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 $$T_{\mathrm{S}}$$ as well as pressure during annealing. From optical absorption studies, the direct optical band gap of CZTS films is found to be $${\sim }$$ 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 5–25 $$\Omega $$ cm, respectively, depending on $$T_{\mathrm{S}}$$ . Films prepared by annealing the stack deposited at 300 $${^\circ }$$ C under 100 mbar pressure for 90 min are slightly Cu-poor and Zn-rich with compact grain morphology.