Impedance spectroscopy (IS) is a powerful tool to characterize devices since it allows to easily decouple the contribution of different interfaces existing in the device by only accessing the external terminals. The collected data are interpreted by means of equivalent electrical circuit. In this thesis, an automated procedure is developed to automatically extract lumped circuit parameters from impedance measured data, adding physical constraints deriving from experimental capacitance. In this work, Graphene-Silicon solar cells are characterized using impedance spectra, allowing to assess a new front contact technology that ameliorates these cells performance compared to the conventional. Impedance spectroscopy is also employed to characterize perovskite solar cells. The equivalent circuit coming from these devices allows to gain knowledge on perovskite layer and recombination mechanisms. An important focus of this thesis concerns capacitance versus voltage curves in forward bias region. This analysis is made using both experimental data and numerical results obtained from TCAD environment. This study is made on Metal-Semiconductor structure, finding the analytical expression of the forward bias capacitance peak and considering the effects of interface defects on capacitance behavior. The observation of multiple peaks arising in the high forward bias region suggests that interface properties are not uniform in the entire structure. Capacitance is also investigated in SiC MOSFETs devices permitting the TCAD model calibration and SiC/SiO2 interface characterization
