perovskite solar cell at a different aging time*

Negative capacitance behavior in the low-frequency region is a familiar feature in perovskite solar cells. In this study, we have investigated the negative capacitance behavior of encapsulated MAPbI₃ perovskite solar cell at different aging times (15 days, 30 days, and 51 days) with impedance measurement technique.  For the study, we have used impedance spectroscopy to analyze the response of MAPbI₃ perovskite solar cell at different bias voltages. The origin of this kind of behavior is still under debate. Here, we have used the surface polarization model (SPM) to explain this behavior. An equivalent circuit based on the SPM was implemented to model the impedance spectra and a kinetic relaxation time of 0.96 s was observed. The performance of solar cell slowly decreases with time. However, the power conversion efficiency remains around 10% even after 51 days of encapsulation. We found that negative capacitance behavior is directly related to the aging of the solar cell. This aging of cell leads to the formation of traps states and/or the accumulation of charges or ions at the interface. To understand the nature of ionic movement along with finding activation energy and capture cross-section, we performed the deep level transient spectroscopy (DLTS) measurement. Overall, our study may provide valuable information about the mechanism inside the MAPbI3 perovskite solar cell that has a direct effect on its performance.