Photoluminescence and Raman study of Cu2ZnSn(SexS1 − x)4 monograins for photovoltaic applications

The quaternary semiconductors Cu2ZnSnSe4 and Cu2ZnSnS4 have attracted a lot of attention as possible absorber materials for solar cells due to their direct bandgap and high absorption coefficient (> 104 cm−1). In this study we investigate the optical properties of Cu2ZnSn(SexS1 − 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 Cu2ZnSn(SexS1 − 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 Cu2ZnSn(SexS1 − 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 A1 Raman modes of Cu2ZnSnSe4 and Cu2ZnSnS4 is established.