Effects of the annealing temperature on the properties of sulfur-graded Cu2ZnSn(S,Se)4 thin films grown by a modified two-step process

In this study, we investigated the electrical and structural properties of sulfur-graded Cu2ZnSn(S,Se)(4) (CZTSSe) thin films grown using a modified two-step process according to the annealing temperature. The sulfur content of the CZTSSe thin film was increased with annealing temperature and a Zn(S, Se) secondary phase was observed at temperatures higher than 500 degrees C. The Raman spectrum of the CZTSSe thin film shifted continuously toward the high frequency direction with increasing S content and the Cu2SnSe3 (CTSe) secondary phase was present below 440 degrees C. From the results of dimpling Raman spectroscopy and scanning transmission electron microscopy (STEM) line scanning, we confirmed that the S content increased gradually from the Mo back contact to the surface of the CZTSSe thin film. Finally, a sulfur-graded CZTSSe thin film with a photovoltaic efficiency of 7.03% was fabricated by optimizing the annealing temperature. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.