Telescoping synthesis and goldilocks of CZTS nanocrystals

Facile, low-temperature synthesis of kesterite CZTS nanocrystals (NCs) using single solvent by heating up approach is presented for the first time. Temperature and time dependence on the structural, morphological and compositional properties are investigated in detail. The size of the NCs was found to increase from 15 to 45 nm with increases in the reaction temperature. From the structural analysis, secondary and ternary phases were detected at less reaction time, and pure phase of CZTS was obtained at 3 h. On the basis of the detailed time-dependent phase evolution, a plausible formation mechanism of CZTS NCs was proposed. The sequence of CZTS phase evolved from Cu2S phase to Cu2SnS3 intermediate compound and finally to pure kesterite CZTS. The optimal composition of Cu/(Zn + Sn) and Zn/Sn ratio was obtained at 3 h. The calculated band gap was found to be 1.5 eV which is an optimum value for solar cell applications. Thus, the results revealed that the reaction temperature and time played a determining role to obtain pure phase CZTS with controlled composition and optimum band gap.