Fig. 4: Composition-dependent CuInSe2 surface reactivity against O2 at room temperature.
From: Chemical instability at chalcogenide surfaces impacts chalcopyrite devices well beyond the surface
a XPS surface analysis of Cu-poor CIS (P, red), stoichiometric CIS (S, black) and Cu-rich CIS (R, cyan) films after removal of Cu-Se phases by KCN (bold)etching and subsequent exposure to air at room temperature for 24 h. Schematics representation of point defect oxidation reactions in CIS-P (b) and CIS-R (c) drawn to match the XPS results, i.e., larger share of In-O outgrowth in Cu-poor material and of Cu-Se in Cu-rich material. d Diagram of free energy vs. reaction coordinate for the oxidation of CuInSe2 to In2O3, Cu2Se and Se showing the spontaneous (negative) bulk Gibbs free energy of reaction at room temperature (ΔG°), and the proposed occurrence of different Gibbs free activation energies (ΔG≠) for the oxidation pathways under Cu-poor and Cu-rich CIS compositions.
