Preparation of Cu2ZnSnS4 single crystals from Sn solutions

We investigated the phase diagrams of the Cu2ZnSnS4 (CZTS)–Sn pseudobinary system in order to obtain knowledge useful for the growth of high-quality CZTS single crystals using a solution-based method. For Sn solutions saturated with less than ∼60 mol% CZTS, the solutes are separated into two phases (CZTS phase+SnSx phase+liquid phase). On the other hand, for solutions with more than 60 mol% CZTS, the solutes are single phase (CZTS phase+liquid phase). The CZTS single crystals were obtained from a 70 mol% CZTS solution (liquid temperature 850 °C) at 900 °C. The powder X-ray diffraction (XRD) pattern of the CZTS single crystal shows preferred orientations of (112), (220) and (312) planes, confirming the Kesterite structure of CZTS. The Raman spectrum shows three peaks at 287, 338, 371 cm−1, which corresponded to CZTS peaks. The composition of the CZTS single crystal along the growth direction is found to be slightly Cu-poor, Zn-rich and S-rich. Therefore, it is assumed that the Cu vacancy is the dominant p-type conduction mechanism.

► We investigated the phase diagrams of the CZTS–Sn pseudobinary system.
► The Sn solution X < 30 mol% is separated into CZTS phase and Sn phase.
► The Sn solution 30 mol%► The Sn solution X>60 mol% is single phase (CZTS phase+liquid phase).
► A CZTS single crystal was grown from a X=70 mol% Sn solution at 900 °C.