Study of Light Induced Ion Migration in Perovskite Solar Cells Using Non-Linear Impedance Spectroscopy

Organic-inorganic hybrid perovskite solar cells (PSCs) offer significant advantages over conventional photovoltaic technologies, positioning them as strong contenders for commercialization. Perovskites serve as the active, light-absorbing layer in solar cells and exhibit tunable bandgaps due to their ionic composition, which sets them apart among next-generation photovoltaic technologies.However, the same factors that enable tunable functional properties also introduce variability in operational and degradation mechanisms. Exposure to heat and light activates mobile ionic defects that migrate, deform the structure, and contribute to overall device degradation, significantly affecting long-term stability. Mobile ions generated by light exposure also lead to hysteresis in the dark J-V curves, a complex nonlinear process. Understanding these phenomena is crucial for ensuring the stability of the perovskite layer and requires an in-depth investigation.
Traditional techniques like impedance spectroscopy (IS) rely on equivalent circuit models that often include passive circuit elements lacking physical relevance. Additionally, IS assumes linearity and time independence, which is particularly problematic for PSCs due to their inherently nonlinear electronic behavior. This presentation highlights results obtained from nonlinear impedance spectroscopy (NLIS), which measures the nonlinear response in the frequency domain, providing a more comprehensive understanding of nonlinear mechanisms.
NLIS data reveal the processes leading to hysteresis and confirm the electronic and ionic coupled mechanisms occurring in the perovskite layer due to light exposure. Relaxation peaks across the frequency domain are characterized, allowing differentiation between relaxation processes caused by ionic migration and electronic phenomena. This study represents the first application of NLIS to PSCs, providing critical insights into nonlinear effects, such as hysteresis, and paving the way for improved device stability and performance.