Unified model for describing the evolution of negative capacitance in perovskite solar cells

The negative capacitance (NC) effect observed in perovskite-based devices is a unique phenomenon that remains subject to debate regarding its origin. In this study, we present a unified model aimed at describing these NC features, providing valuable insights into the coupling of ionic and electronic properties that give rise to NC behavior. Through meticulous analysis of impedance spectra, capacitance-frequency relationships, and current-voltage profiles under varying conditions of light intensity and bias voltage, we aim to uncover the underlying sources of NC in perovskite solar cells (PSCs). Our findings suggest that the emergence of NC in PSCs directly correlates with the migration of both positive and negative ions toward the uppermost and lowermost surfaces of the perovskite layer. Moreover, the polarity of capacitance at low frequencies is determined by the predominant recombination pathway within the device. We present a unified model that comprehensively describes the evolution of NC in PSCs. This model not only elucidates experimental observations but also confirms the connection between NC and recombination mechanisms.