Photoluminescence and Raman study of Cu 2ZnSn(Se xS 1 − x ) 4 monograins for photovoltaic applications

Abstract

The quaternary semiconductors Cu 2ZnSnSe 4 and Cu 2ZnSnS 4 have attracted a lot of attention as possible absorber materials for solar cells due to their direct bandgap and high absorption coefficient (> 10 4 cm −1). In this study we investigate the optical properties of Cu 2ZnSn(Se xS 1 − x ) 4 monograin powders that were synthesized from binary compounds in the liquid phase of potassium iodide (KI) flux materials in evacuated quartz ampoules. Radiative recombination processes in Cu 2ZnSn(Se xS 1 − x ) 4 monograins were studied by using low-temperature photoluminescence (PL) spectroscopy. A continuous shift from 1.3 eV to 0.95 eV of the PL emission peak position with increasing Se concentration was observed indicating the narrowing of the bandgap of the solid solutions. Recombination mechanisms responsible for the PL emission are discussed. Vibrational properties of Cu 2ZnSn(Se xS 1 − x ) 4 monograins were studied by using micro-Raman spectroscopy. The frequencies of the optical modes in the given materials were detected and the bimodal behaviour of the A 1 Raman modes of Cu 2ZnSnSe 4 and Cu 2ZnSnS 4 is established.