Morphology evolution and stability of Cu2ZnSnS4 nanocrystals in sodium halides salt solution

• CZTS nanocrystals were found to transform to large grains with NaI treatment.
• Composition analysis revealed that NaI treatment resulted in significant Zn loss.
• The mechanism for the decomposition and growth of CZTS nanocrystals was revealed.

Stability and morphology evolution of Cu2ZnSnS4 (CZTS) films consisting of nanoparticles treated with NaX (X = I, Cl, F) based aqueous solution was investigated. It has been found that the size of the nanoparticles increased with the increase of NaI solution treatment duration. Dipping the CZTS film in NaI solution for 10 min led to the complete transformation of CZTS nanocrystals to large grains with sizes around 1–3 μm after thermal annealing. The investigation of the material composition has revealed that NaI solution treatment resulted in significant loss of Zn. Further investigation has showed that the dissolution of Zn from CZTS is even more serious when the film of CZTS nanoparticles was soaked in NaCl and NaF solution for a short time. This is attributed to the strong complexation reaction between Zn2 + and the halides. X-ray diffraction measurement has confirmed that the complexation reaction led to the formation of Na2S and Raman spectroscopy has revealed that the loss of Zn resulted in the formation of Cu3SnS4 in the film. This work provides insights into stability and grain growth of CZTS material.