Cuprous selenide defect equilibria and homogeneity range determined by coulometric titration

The phase diagram and thermochemistry of the Cu-Se system is of interest to better understand thin film deposition of CIS and CIGS-based solar cells. In this study, the equilibrium solid-state defect chemistry of Cu_2-xSe is explored. The homogeneity range of β-Cu_2-xSe is measured and the thermodynamic functions for defect species are estimated. The homogeneity range of β-Cu_2-xSe was measured by coulometric titration in a solid-state galvanic cell. The composition difference between the selenium-rich and the copper-rich boundaries was measured as Δx=0.012 at 900 K. A defect model was developed based on vacancy formation on the Cu sublattice.