3-D point defect density distributions in thin film Cu(In,Ga)Se₂ measured by atom probe tomography

This paper will discuss the findings of an ordered vacancy compound (OVC) phase that exists deep into the bulk of a high-efficiency Cu(In,Ga)Se₂ (CIGS) absorber that is shown to be a result of many ordered defect pairs of 2V_Cu + (In,Ga)_Cu as determined by atom probe tomography (APT). To date, literature has shown that absorbers grown with the three-step process exhibit the OVC Cu(In,Ga)₃Se₅ (135 phase) only within the first few nanometers from the CdS/CIGSe interface and at grain boundaries. In this contribution, we have found a small volume (100 nm × 100 nm × 300 nm) of an OVC phase to exist about 400 nm into the absorber. We show through concentration and density profiles that the concentration change from the stoichiometric Cu(In,Ga)Se₂ to the OVC is indeed a result of many ordered defect pairs. We use this volume to perform point defect density distributions to give unique insight to the band structure at the nanoscale.