Reaction routes for the synthesis of CuInSe ₂ using bilayer compound precursors

The reaction pathways and phase evolution during synthesis of CuInSe ₂ (CIS) by a novel bilayer approach were investigated using in situ high-temperature X-ray diffraction. Two bilayer precursor structures, glass/Mo/γ-In ₂Se ₃/β-CuSe + β-Cu ₂Se/Se and glass/Mo/γ-In ₂Se ₃/β- Cu ₂Se/Se, were examined in this study. Temperature ramp experiments revealed that the phase transformation sequence for each bilayer precursor qualitatively follows that predicted by the phase diagram and that the onset temperatures for decomposition of the sub-binary compounds depend on the Se partial pressure. Measurement of the isothermal rate of formation of CuInSe ₂ at six temperatures in the range 260 to 310 °C for the γ-In ₂Se ₃/β-CuSe + β-Cu ₂Se/Se bilayer suggests relatively slow nucleation followed by diffusion-limited reaction with estimated activation energy of 162(±7) and 225 (±16) kJ/mol from Avrami and parabolic models, respectively. Interestingly, the measured activation energy for the same precursor in a 4 mol % H ₂/He ambient (108 (±8) kJ/mol) was lower than that observed in pure N ₂ (158 (±16) kJ/mol). The results of isothermal measurements in the temperature range 250 to 300 °C for the γ-In ₂Se ₃/β-Cu ₂Se/Se precursor film in an inert ambient are consistent with one-dimensional diffusion-limited growth with estimated activation energy from the Avrami and parabolic models of 194 (±10) and 203 (±12) kJ/mol, respectively.