Interface models of CZTSe: Ge bilayers solar cells with Impedance Spectroscopy

We introduce a spectral response of impedance of CZTSe nanoscale Ge bi-layers solar cells with an improved equivalent circuit model. Improved AC circuit models are applied, considering a realistic device structure with lumped bulk resistance, resistance, and capacitance of one heterojunction interface, and two effective back-contact interfaces. The impedance model is characterized by series/parallel resistance, and constant phase element to accurately analyze the device structure, which shows a good agreement of the fitting to data $(\chi^{2}=4.19\ \times\ 10^{-4})$ . Two indicative parameters of back-contact interfaces are close to 1, implying the improved back-contact interface by adding nanolayer Ge (2.5 nm) between CZTSe and MoSe 2 . Resistances of both back-contact interfaces are less than 0.3% of the CdS/CZTSe heterojunction interfaces.