Phase controlled solvothermal synthesis of Cu2ZnSnS4, Cu2ZnSn(S,Se)4 and Cu2ZnSnSe4 Nanocrystals: The effect of Se and S sources on phase purity

• Solvothermal synthesis of CZTS, CZTSSe and CZTSe nanocrystals and discussion on possible formation mechanism.
• Use of dodecanethiol/oleylamine mixture to synthesize phase-pure CZTSSe nanocrystals.
• Formation of impurity phases can be controlled with proper S and Se sources.

In this study, we have reported the synthesis of Cu2ZnSnSe4 (CZTSe), Cu2ZnSnS4 (CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) nanocrystals with tunable band gap and composition obtained by solvothermal method. The crystalline structure, composition, morphology and optical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman scattering, energy dispersive X-ray spectroscopy, transmission electron microscopy and diffuse reflectance (DR) spectroscopy. While the XRD patterns of CZTS and CZTSe nanoparticles prepared with elemental S/Se powder revealed the presence of phase pure nanoparticles, the CZTSSe nanoparticles obtained using a mixture of S and Se, were found to contain many secondary phases under the same synthesis protocol. Formation of impurity phases in CZTSSe sample, can be avoided by using a mixture of 1-dodecanethiol (DT; CH3(CH2)11SH)/oleylamine (OLA) instead of S powder and following the same experimental procedure. The incorporation of S in CZTSe nanocrystals prepared in presence of DDT/OLA mixture was confirmed through structural and optical characterizations. The optical properties of the quaternary chalcogenide nanocrystals were found to vary with the chemical composition of the material.