Phase diagram of the selenide kesterite photovoltaic materials and NMR investigation of Cu/Zn disorder in CZTSe

Synthesis The compounds were prepared by the solid state reaction of Cu, Zn, Sn, and S powders in the appropriate ratios in evacuated, sealed, fused silica tubes. They were heated at 750 °C (ramp 300 °C/h) for 170 h and then cooled down at 20 °C/h. The obtained powders were then ground and pressed into pellets which were again put into a sealed tube. The second heating sequence was: ramp 300 °C/h; plateau 750 °C; cooling ramp 50 °C/h. For some samples, attention was paid to the cooling mode at the end of the heating process. Samples were heated at 350 °C for 2 days and subsequently ice-quenched (sample A2Q). A part of the obtained samples was reheated at 350 °C for 2 days, slow cooled down to 150°C (2 °C/h), annealed at this temperature for 1 day and finally slow cooled to room temperature. For example, from sample A2 (see Table 1) we got sample A2Q (quenched) and sample A2S (slow cooled).