Effects of hydrazine on the solvothermal synthesis of Cu2ZnSnSe4 and Cu2CdSnSe4 nanocrystals for particle-based deposition of films

• Hydrazine enhances the growth of pure Cu2ZnSnSe4 and Cu2CdSnSe4 nanocrystals.
• The nanocrystals can be fabricated to films by spin coating without annealing.
• This solvothermal processing is promising for the fabrication of thin film devices.

The effects of hydrazine on the synthesis of Cu2ZnSnSe4 (CZTSe) and Cu2CdSnSe4 (CCTSe) nanocrystals in an autoclave as a function of temperature and time were explored. On heating at 190 °C for 24-72 h, pure CZTSe and CCTSe nanocrystals could readily grow in the hydrazine-added solution, while in the hydrazine-free solution the intermediate phases such as ZnSe, Cu2Se, and Cu2SnSe3, and Cu2SnSe3 and CdSe associated with the CZTSe and CCTSe nanocrystals grew, respectively. This result reveals that hydrazine can speed up the synthesis of pure CZTSe and CCTSe nanocrystals via a solvothermal process. The mechanisms for the hydrazine-enhanced growth of CZTSe and CCTSe nanocrystals were discussed. The pure CZTSe and CCTSe nanocrystals were subsequently fabricated to the smooth films by spin coating without further annealing in selenium atmosphere. This processing may be beneficial to the fabrication of the absorber layer for solar cells and thermoelectric devices.