We examined the electronic properties of CIGS-based polycrystalline thin-film solar cells by Deep Level Transient Spectroscopy (DLTS) and Capacitance-Voltage (C-V) measurements. We prepared four CIGS thin films (by Physical Vapor Deposition) in the region where the film transitions from Cu-rich to In(Ga)-rich. Cu-rich sample exhibits a shallow majority carrier trap with an activation energy of 0.12 eV and another deeper trap with an activation energy of 0.27 eV. The shallow trap with a concentration of about 2.1x10^14 cm^-3 yields the dominant emission in Cu-rich CIGS in the observed temperature and frequency range. The In-rich sample has a shallow minority carrier trap with an activation energy of 0.12 eV. This trap with a concentration of 6x10^14 cm^-3 yields the dominant emission in In(Ga)-rich CIGS in the observed temperature and frequency range. The two samples show evidence of a deeper trap at higher temperature. C-V measurements showed that the carrier concentration around the junction of the cell changed as the film transitions from Cu-rich to In-rich. We see that the acceptor (donor)-like traps are dominant in the Cu(In)-rich samples. The transition from the Cu-rich to the In(Ga)-rich compositions causes an extensive transformation of intrinsic defects from acceptor-like traps (e.g. Cu on In(Ga) sites) to donor-like traps (e.g. In(Ga) on Cu sites).