Photoluminescence of sulfur-incorporated CIGS solar cells through post-annealing

The photoluminescence (PL) of Cu(In,Ga)Se2 solar cell with sputtered Zn(O,S) buffer layers annealed at various temperatures were measured. As the annealing temperature increased, the peak positions of PL spectra shifted to higher energies. The broad PL spectra were separated two or three emissions, which are suggested to be mostly to donor-acceptor pair transitions with an acceptor due to copper vacancy and donors due to selenium vacancy or IIICu antisite. The changes of PL spectra were discussed from the view of the diffusion of elements, especially sulfur from buffer to absorber during the post-annealing process.