Changes in the electronic structure of CuInS2 thin films by Na incorporation

For Na-free and Cu-deficient ${\mathrm{CuInS}}_{\mathrm{2}}$ thin films with chalcopyrite structure, electron spectra of core levels and valence band were similar to each other in spite of a difference in Cu deficiency. Incorporation of Na with the ${\mathrm{CuInS}}_{\mathrm{2}}$ films caused peak shifts by −0.5 eV for the core levels without changes in both linewidth and shape. The electron density of states, deeper by 1–5 eV than that from $\mathrm{Cu}\mathrm{\hspace{0.5em}d–}\mathrm{S}\mathrm{\hspace{0.17em}p}$ hybridization centered at around 2.5 eV, increased by the Na incorporation, and increments in the electron density of states were larger for the films with larger the Cu deficiency. The Na incorporation yielded a surface layer expressed as $({\mathrm{Na,Cu)InS}}_{\mathrm{2}}$ on the Cu deficient ${\mathrm{CuInS}}_{\mathrm{2}}$ films.