  Electronic structure calculations within screened-exchange hybrid density
functional theory show that Cu(In,Ga) antisites in both CuInSe2 and CuGaSe2 are
localized hole traps, which can be attributed to the experimentally observed N2
level. In contrast, GaCu antisites and their defect complexes with copper
vacancies exhibit an electron trap level, which can limit the open-circuit
voltage and efficiency in Ga-rich Cu(In,Ga)Se2 alloys. Low-temperature
photoluminescence measurements in CuGaSe2 thin-film solar cells show a
free-to-bound transition at an energy of 1.48 eV, in very good agreement with
the calculated transition energy for the GaCu antisite. Since the intrinsic DX
center does not exhibit a pinning level within the band gap of CuInSe2,
metastable DX behaviour can only be expected for GaCu antisites.
