Formation of Cu2SnSe3 from stacked elemental layers investigated by combined in situ X-ray diffraction and differential scanning calorimetry techniques

Highlights: • In situ investigation revealed intermetallic compounds and Cu2SnSe3 formations. • CuSe phase dominates binary phase formations at a low annealing temperature. • SnSe forms from liquid phase reaction of Sn and Se. • Binary Cu-selenide phase exerts sequential phase decompositions. • Crystalline Cu2SnSe3 forms above 450 °C. -- Abstract: Stacked elemental layers of Mo/Cu/Sn and Mo/Cu/Sn/Se were employed as samples for investigating the formation reaction of Cu–Sn intermetallic compounds as well as Cu2SnSe3 phases by in situ technique of X-ray diffraction and differential scanning calorimetry. The use of a combined in situ technique allows a real-time observation on solid-state reactions as well as any crystalline phase changes during annealing towards the crystallization of Cu2SnSe3. It is found that Cu and Sn form intermetallic compounds of Cu6Sn5, Cu3Sn and Cu41Sn11 as the annealing temperature rises from 30 to 550 °C. The reaction of Se with Cu to form a CuSe phase dominates the binary phase formation at a low annealing temperature. The annealing of a stacked Mo/Cu/Sn/Se layer suggests that only Cu6Sn5 intermetallic compound directly acts as a reactant for the Cu-selenide phase formation. A SnSe phase mostly forms from a liquid-state reaction of Sn and Se above the Sn melting point. The in situ investigation also reveals a complete set of Cu-selenide peritectic decompositions of CuSe2 → CuSe → Cu1.8Se at 360 and 412 °C. The formation of Cu2SnSe3 phase starts at 450 °C as a product from a reaction between Cu1.8Se and SnSe in a presence of liquid Se. Comparisons on the initial formation temperatures of all involved phases and on the formation pathways between Cu2SnSe3 and Cu2SnS3 are discussed as well