In this paper, CIGS heterojunction solar cells have been proposed and analyzed by SCAPS “Solar Cell Capacitance Simulator” the effect of temperature and thickness on cell characteristics such as (η, FF, J _sc and V _oc). The effects of various layer parameters like thickness, carrier concentration, defect density, mobility, and conduction band offset. The photovoltaic cell has been studied further through capacitance-voltage simulations to obtain the net built-in potential and the apparent doping profile. The impedance plot (IS) analytical theory to the characterization of Cu (In, Ga) Se ₂ (CIGS)-based solar cells was investigated. The equivalent circuit of the CIGS solar cell consisting of series and parallel resistances and a “capacitance-like element” labeled as constant phase element (CPE) around the CdS/CIGS interface was developed. The CPE reflects the depletion layer thickness and the p-n interface uniformity and quality. In particular, the CPE-p-value, which is an index of the impedance of CPE, affects the quality around the CdS/CIGS and CIGS-Si interface in terms of defect existence and inhomogeneity of the heterojunction. These results show a possible candidate for the practical application of IS as a simple method for characterizing the heterogeneity of a p-n interface.