Degradation Mechanisms in Perovskite Solar Cells Probed by Low-Frequency Carrier Kinetics

Hybrid organic-inorganic perovskite solar cells have emerged as leading candidates for third-generation solar cell technology. Despite their superlative power conversion efficiencies (PCEs), hysteresis and degradation limit their applications, thus motivating detailed studies of the underlying physical mechanisms. We introduce correlated low-frequency noise and impedance spectroscopy characterization that reveals carrier kinetics in perovskite solar cells. We employ cells with different hole transport layers that also elucidate tradeoffs between solar cell performance metrics and stability. We focus on the technologically relevant planar cell structure using an emerging SnO₂ electron transport layer and two widely used hole transport layers: poly(triarylamine) (PTAA) and Spiro-OMe TAD. PTAA and Spiro-OMe TAD cells with moderate PCEs of 5–12% show a Lorentzian feature at ~200 Hz corresponding to a single fluctuator. Spiro-OMe TAD cells with high PCE (>15%) show four orders of magnitude larger 1/f noise amplitude with a distinctive peak, which is indicative of a cyclostationary process that is correlated with an inductive loop in impedance spectra. The observed current fluctuations are consistent with trapping and de-trapping of methylammonium ions near the SnO₂ interface.