Negative capacitance and hysteresis in encapsulated MAPbI 3 and lead–tin (Pb–Sn) perovskite solar cells

Impedance measurements on encapsulated Pb–Sn and MAPbI 3 perovskite solar cells reveal unique capacitance and hysteresis behavior. Power conversion efficiency (PCE) of Pb–Sn and MAPbI 3 solar cells remains around 9% and 10% after 71 and 51 days, respectively. Trap density and trap energy of around 10 16 cm −3 and 0.45 eV were observed in Pb–Sn perovskite solar cells and around 10 16 cm −3 and 0.13 eV for the MAPbI 3 solar cell. The origin of negative capacitance was analyzed by impedance spectroscopy and an equivalent circuit based on the surface polarization model was used to extract transport parameters. The electric field within the depletion region, diffusion coefficient, diffusion length, mobility of ions, diffusion, and drift of mobile ions were calculated. We found that the negative capacitance behavior is directly related to the aging of perovskite samples. The results of impedance spectroscopy on PSC can be explained by a simple model of diffusion-controlled hysteresis. Graphical abstract