Characterization of metastabilities in Cu(In,Ga)Se2 thin-film solar cells by capacitance and current-voltage spectroscopy

Metastabilities in Cu(In,Ga)Se2 (CIGS)-based solar cells induced by red light illumination, blue light illumination, and voltage bias treatment are investigated by admittance spectroscopy, capacitance-voltage profiling, thermally stimulated capacitance, and temperature dependent current-voltage (IVT) measurements. It is found that the characteristic N1-admittance response exhibits changes in the activation energy after light soaking and forward bias treatment, whereas no significant change of the activation energy is observed after reverse bias treatment. A roll-over effect is observed in the IVT characteristics for conditions of the sample for which the N1-activation energy is larger than 100 meV. We show that these results are in good agreement with a recently proposed interpretation of admittance spectra, which relates the N1 signature to a back-contact barrier in CIGS solar cells. We also show that, within this model, the changes in the IV characteristics upon light soaking with blue light can be cons...