On the interpretation of space charge profiles in CIGSe-based solar cells in presence of deep metastable defects

Experimental evidence is provided for the presence of large density of metastable defects in the Cu(In, Ga)Se₂ (CIGSe) absorber layer which within the range of milliseconds to seconds are able to adjust their charge state to the actual electron and hole concentrations. It is shown that the concentration of these defects may exceed the net shallow acceptor concentration even by orders of magnitude. The consequences of this fact for the interpretation of space charge profiles are discussed. It is shown that the difference between capacitance - voltage (CV) and drive level (DL) profiles as well as their U-shape can be explained by the bi-stable behavior of these defect states.