Fig. 2
From: Origin of apparent light-enhanced and negative capacitance in perovskite solar cells
EIS data as a function of applied voltage in the dark. Left: negative-capacitance device (0.02% Bi). Right: device without negative capacitance (0% Bi). a, b Nyquist plots showing approximately two semi-circles and the appearance of negative capacitance for voltages larger than 0.7 V. c, d Real part of impedance, visualizing the electrode series resistance for frequencies >105 Hz, a plateau at 1 kHz, and a higher (lower for negative C) low-f resistance. The symbols indicate the differential resistance obtained from JV scans with 10 mV s−1 (circles) and 10 V s−1 (stars). e, f Apparent capacitance \(\frac{{{\mathrm{Im}}(1/Z)}}{\omega }\), where in e C values for frequencies lower than the one where the dip occurs are negative. g, h Resistance and capacitance (negative values shaded) obtained by describing the EIS data measured in the dark and under 1 sun by two RC elements in series. Rlow f ∝ 1/Clow f is striking, in particular in h
