Influence of Na and Ga on the electrical properties of perfect 60° dislocations in Cu(In, Ga)Se2 thin-film photovoltaic absorbers

Abstract

The segregation of GaIn and NaCu to perfect 60° dislocations in CuIn1–xGaxSe2 is investigated by means of density functional theory calculations. We find that the segregation process is mainly driven by the elastic interaction of both defect types with the strain field of the dislocation. GaIn moves into the negatively strained region, while NaCu is found in the positively strained region. We show that both defects affect the electronic defect levels induced by the dislocation core and GaIn is able to passivate the β-core in CuInSe2. This result indicates that β-cores are inactive in CuIn1–xGaxSe2. NaCu; however, they do not have a significant effect on the electrical properties of the studied dislocation cores. Therefore, the experimentally observed sodium segregation to dislocation cores in CuIn1–xGaxSe2 cannot be considered as the passivation mechanism of the electrically active cores in that material.