Properties of thermally evaporated CZTS thin films and numerical simulation of earth abundant and non toxic CZTS/Zn(S,O) based solar cells

Abstract

Earth abundant Cu2ZnSnS4 (CZTS) films were grown by thermal evaporation technique onto non heated substrates. As deposited CZTS films were annealed under two different atmospheres: (1) vaccum annealing atmosphere and (2) sulfur annealing atmosphere followed by vacuum annealing. The samples were analyzed for their microstructural, electrical and optical properties before and after annealing. X-Ray Diffraction (XRD) analysis revealed that the as deposited film was amorphous whereas the annealed ones were polycrystalline with a highly (1 1 2) orientation. Raman spectroscopy confirmed the phase purity of annealed CZTS films. Both annealing atmospheres were found to decrease the band gap energy and the resistivity of the samples. All films exhibited p-type electrical conductivity. Numerical simulation of earth abundant CZTS thin film solar cells with non toxic Zn(S,O) buffer layer was performed by Solar Cell Capacitance Simulator (SCAPS-1D) using the experimental results obtained for CZTS and Zn(S,O) films. Zn(S,O) was used to substitute toxic CdS in earth-abundant Cd-free CZTS solar cells. A maximum conversion efficiency of 12.60% was obtained for Mo/p-Cu2ZnSnS4/n-Zn(S,O)/i-ZnO/n-ZnO:Al structure with CZTS film annealed under sulfur annealing atmosphere followed by vacuum annealing.