Defect spectroscopy of Cu(In,Ga)Se2-based thin film solar cells on polyimide substrate

Cells made on a polyimide substrate, with sodium supplied at different stages of the absorber deposition, have been studied by defect spectroscopy methods. In all of the cells, admittance spectroscopy measurements revealed the presence of two defect levels. Discussion on the origin of the observed levels, based on the correlation with free carrier concentration profiles and photocurrent results, is presented. We attribute one of the levels as belonging to interface defects, and the second one to a bulk deep defect. A distinctive feature of defects' sensitivity to a hole concentration, which leads to unusual behaviour of defect parameters is discussed.

► Two defect signatures have been identified by admittance spectroscopy.
► One of the levels is attributed to interface defects.
► The second level is attributed to a bulk defect.
► Activation energies and thermal emission rates depend on hole concentration.