It is obvious that the hydrothermal process provides an environment-friendly and low-cost route for producing pure kesterite CZTS, as compared with the solvothermal method with DMF as the solvent. Figure 1 XRD patterns of the samples obtained under different

amounts of EDTA. Mole ratio of three metal ions The stoichiometric control of quaternary compounds is complicated by the tendency of forming a plurality of compositional phases, due to the difference in reactivity of the cationic precursors. Consequently, the mole ratio of the three cationic precursors Cilengitide chemical structure in the reaction KPT-8602 system should have an important effect on the phase composition of the obtained samples. Figure 2 shows the PXRD patterns of the samples synthesized buy INK1197 at 180°C for 16 h from the reaction system containing 2 mmol of EDTA at different mole ratios of the three metal ions. At Cu/Zn/Sn = 2:1:1, corresponding to the stoichiometric ratio of CZTS, the obtained sample shows a similar XRD pattern to the one prepared from the reaction system containing no EDTA (Figure 1),

implying that it has a mixed phase of kesterite and wurtzite. Besides, a weak impurity peak located at 31.7° appears. As the amount of ZnCl2 in the reaction system is doubled, and thus Cu/Zn/Sn is accordingly changed from 2:1:1 to 2:2:1, the obtained sample can be identified as kesterite CZTS in high purity and good crystallinity. Note that at Cu/Zn/Sn = 2:3:1, the obtained sample exhibits several diffraction peaks of kesterite CZTS, together with one weak impurity peak located at 31.8°. These results indicate that the mole ratio of the three cationic precursors influences the phase composition of the obtained product. An excessive dose of ZnCl2 (double the stoichiometric ratio of Zn in CZTS) in the reaction Tryptophan synthase system favors the production of pure kesterite CZTS. Figure 2 XRD patterns of the samples obtained at different Cu/Zn/Sn/S mole ratios. Effect of hydrothermal temperature With the amount

of EDTA fixed at 2 mmol and Cu/Zn/Sn set at 2:2:1, the hydrothermal synthesis was conducted at different temperatures for 16 h. Figure 3 displays the PXRD patterns of the samples prepared at 170°C, 180°C, and 190°C. All the obtained samples show the seven diffraction peaks located 28.7°, 33.0°, 47.6°, 56.4°, 59.2°, 69.5°, and 76.7°, which are ascribed to (112), (200), (220), (312), (224), (008), and (332) planes of kesterite CZTS, respectively. However, the two samples prepared at 170°C and 190°C exhibit one weak impurity peak located at 31.8°. It is suggested that kesterite CZTS can be synthesized at the hydrothermal temperatures ranging between 170°C and 190°C from the reaction system containing 2 mmol of EDTA at 2:2:1 of Cu/Zn/Sn. The suitable temperature for producing pure kesterite CZTS should be around 180°C. Figure 3 XRD patterns of the samples obtained at different hydrothermal temperatures.