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

Abstract

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.