Abstract
We have unlocked the mechanistic behavior of negative capacitance in perovskite solar cells (PSCs) by analyzing impedance spectra at variable photovoltage and applied bias, temperature-dependent capacitance versus frequency (C-f) spectra, and current-voltage (J-V) characteristics. We noted that p-i-n type PSCs having PEDOT:PSS or PTAA as hole transport layer display negative capacitance feature at low and intermediate frequencies. The activation energies (Ea) for the observance of negative capacitance were found to be in a similar order of magnitude required for the ionic migration. Moreover, the kinetic relaxation time (τkin) estimated to be in the same order of magnitude required to activate the halide ion migration. Our investigation suggests that the primary reason for the appearance of negative capacitance in PSCs with a p-i-n configuration is associated with the migration of halide ions and vacancies in the perovskite layers.
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•Negative capacitance in p-i-n device was unraveled from immittance spectroscopy•Under external bias, halide ions/vacancies migrate toward HTL/perovskites interface•Charge carriers discharge in trap states leading to the negative capacitance•In p-i-n devices PTAA-based HTL display improved charge transport compared with PEDOT:PSS
Energy Resources; Energy Systems; Energy Materials; Devices