Cationic point defects in CuGaSe2 from a structural perspective

The chalcopyrite semiconductors show large tolerances to deviations from stoichiometry by keeping the crystal structure. Such deviations always cause structural inhomogeneities and charge mismatches which influence the material properties. We studied the type and concentration of cationic point defects on Cu-poor CuGaSe2 powders by the complementary use of neutrons and photons. It is demonstrated that the main existing defects in this Cu-poor wide gap semiconductor are copper-vacancies (VCu) and gallium on interstitial sites (Gai). The latter may explain why tailoring a highly efficient CuGaSe2 solar cell is an even more challenging task than previously expected.