Figure 3
The results from the first principle calculation. (a) Upper panel: crystal structures upon the occupation of Se in S sites; (b) Lower panel: the density of States (DOS) for Se incorporated Cu4Sn7.5S16. The DOS is more localized in both the valence and conduction bands, and sharply increases in the vicinity of the Fermi level (Fr) for the samples at x = 0.5 and 1.0, exhibiting resonant states. Fr seems to be pinned in the middle of conduction band, with no visible tendency of movement. The formation energy (dH) gradually increases from 0.78 (eV) to 2.73 (eV) as Se content increases from x = 0 to x = 2.0.
