Deep recombination centers in Cu2ZnSnSe4 revealed by screened-exchange hybrid density functional theory

We present a comprehensive study of the thermodynamic and electronic properties of intrinsic point defects in the solar energy conversion materials Cu2ZnSnSe4 and CuInSe2 based on the screened-exchange hybrid density functional theory. A comparison between the defect transition levels for Cu2ZnSnSe4 and CuInSe2 reveals that in Cu2ZnSnSe4, the SnCu and SnZn antisite defects can be recombination centers with defect states close to midgap, while the InCu antisite defect has a shallow defect level in CuInSe2. The resultant higher Shockley-Read-Hall recombination rate in Cu2ZnSnSe4 reduces the steady-state concentration of minority carriers and quasi-Fermi level separation under illumination. This may explain the origin of the low open-circuit voltage values for Cu2ZnSnSe4 solar cells compared to CuInSe2 solar cells.