The role of Sb in solar cell material Cu2ZnSnS4
In this study, based on first-principles calculations we report a possible mechanism of efficiency improvement of Sb-doped Cu2ZnSnS4 (CZTS) solar cells from the Sb-related defect point of view. Different from Sb in CuInSe2 which substituted the Cu atomic site and acted as group-13 elements under Cu-poor growth conditions, we find out that Sb prefers to substitute Sn atomic sites and acts as group-14 elements under Cu-poor growth conditions in CZTS. At low Sb concentration, SbSn produces a deep defect level which is detrimental for the solar cell application. At high Sb concentration, Sb 5s states form an isolated half-filled intermediate band at 0.5 eV above the valence band maximum which will increase the photocurrent as well as the solar cell efficiency.