Influence of Sulfurization Time on the Properties of Cu2ZnSnS4 Thin Films Deposited on Mo-coated Soda Lime Glass Substrates by Co-sputtering Technique

Abstract

In this work, Cu2ZnSnS4 (CZTS) absorber films were prepared by sulfurization of co-sputtered precursor films at different time periods. The influence of sulfurization time on physical characteristics of the grown films was investigated in detail. The sulfurized CZTS films exhibited the characteristic diffraction peak of the kesterite phase corresponding to the (112) crystal plane, the main Raman mode of kesterite phase at around 337 cm−1 and Cu-deficient and Zn-rich composition. From the atomic force microscopy surface and cross-sectional scanning electron microscopy images, it was revealed out that the films were uniform, compact without any cracks and consisted of micron-sized and closely packed grains. In addition, the films showed tail-to-tail, band-to-tail and band-to-band transitions at around 1.41 eV (E1), 1.45 eV (E2) and 1.51 eV (E3), respectively. Secondary ion mass spectroscopy analysis showed that the sodium ions deeply diffused through the molybdenum layer into the CZTS film from the soda lime glass substrate for all samples. All of the films exhibited an optical band gap of around 1.4 eV, an absorption coefficient over 104 cm−1, p-type conductivity with a high concentration of free holes in the order of 1017-1018 cm−3 and low mobility in the range from 0.63 cm²/V.s to 8.11 cm²/V.s.