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

Abstract

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 °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 °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. © 2019 The Korean Society of Industrial and Engineering Chemistry