Photon-induced defects and dynamics of photogenerated carriers in Cu(In,Ga)Se2 thin film solar cells

A detailed understanding of charge-carrier behavior could provide new avenues to improve the performance of the solar cell by enhancing the active materials and electronic properties. In the present work, the transport mechanism of photogenerated carriers in Cu(In,Ga)Se-2 or CIGS)-based solar cells is investigated by analysis of the temperature-dependent current density-voltage (J-V) curves obtained under various illumination (i.e., dark, AM 1.5G, 650 nm, and 405 nm). The results demonstrate that J-V curve distortion, termed the "roll-over" effect, is significantly correlated with the illumination wavelength and, more importantly, is strongly associated with the persistent characteristics of the CIGS solar cell. In addition, the nature of the photo-induced defects and their influence on the transport mechanism of the photogenerated carriers were investigated via deep level capacitance profiling (DLCP) and admittance spectroscopy (AS) under various illumination conditions. The photo capacitance results indicate distinct spatial distributions and persistent behaviors depending upon the illumination wavelength. Based on the findings in this work, the origin of the non-ideal J-V behavior in the CIGS solar cell is explained, and the spatial defect distribution and illumination wavelength sensitivity are discussed.