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

• In-situ investigation revealed intermetallic compounds and Cu2ZnSnSe4 formations.
• Cu–Zn alloy layers tend to act as a passivating layer for selenization below 320 °C.
• ZnSe phase gradually forms through a denzincification-like process in corrosion.
• Cu2Se and SnSe phases form after Cu–Zn alloy passivating layer disappears.
• Kesterite Cu2ZnSnSe4 initial crystallization temperature is most probably above 540 °C.

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.