Microanalysis of post-deposition annealing of Cu(In,Ga)Se2 solar cells

The influence of selenium background pressure during post-deposition annealing of Cu(In,Ga)Se2 (CIGS) is investigated. Solar cells made from samples post-annealed with selenium showed the same solar cell parameters as references without any annealing treatment. Dark JV measurements of microscopic devices with sizes of 10 μ m × 10 μ m from the sample annealed with selenium showed good agreement with the corresponding macroscopic solar cells. Samples annealed without selenium showed degradation in terms of open circuit voltage and fill factor. Electron beam induced current (EBIC) imaging for these degraded solar cells revealed patches of reduced current. Microscopic JV measurements showed that the deterioration is not limited to these patches. Cross-sectional transmission electron microscopy analysis showed phase decomposition of the CIGS absorber in areas of the patches toward the back contact. We conclude that in addition to the local phase decomposition of the CIGS leading to patches in the EBIC image the anneal in vacuum without selenium background pressure also leads to other modifications of the CIGS layer influencing the interface region on a macroscopic scale.