Intermetallic compounds dynamic formation during annealing of stacked elemental layers and its influences on the crystallization of Cu2ZnSnSe4 films

A combined in-situ investigation using X-ray diffraction and differential scanning calorimetry during annealing was carried out to investigate the formation of intermetallic compounds in the stacked elemental layers and to reveal its influences on the crystallization of kesterite Cu₂ZnSnSe₄. The Mo/Cu/Zn, Mo/Cu/Sn/Zn, Mo/Cu/Zn/Se and Mo/Cu/Sn/Zn/Se stacked films were prepared with a composition resembling a typical kesterite Cu-poor and Zn-rich metallic composition. In-situ experiments during annealing of pure metallic stacked films reveal a dynamic intermetallic compounds formation of Cu₅Zn₈ → CuZn → Cu₂Zn → Cu₃Zn and Cu₆Sn₅ → Cu₄₁Sn₁₁. The CuZn and Cu₅Zn₈ layer formed at the interface of metals/Se may prevent the stacked metallic layers from selenization below 320 °C. On the other side, the dynamic formation of Cu–Zn phases in the stacked films is found to be an origin of a ZnSe gradual formation starting from 320 °C. Phase analysis suggests that the ternary Cu₂SnSe₃ phase forms almost immediately after the formation of Cu₂Se and SnSe. The formation of Cu₂SnSe₃ is indicated by the consumption of SnSe by the Cu₂Se which occurs at 530–540 °C. Crystallization of kesterite takes place above 540 °C. On a phenomenological basis of present results, consequences for the thin film kesterite fabrication for solar cell application are discussed.