Research Paper: Visualising ionic screening in perovskite solar cells: a bumpy ride along the J–V curve

Summary

This study aims to elucidate the intricate mechanisms behind scan rate-dependent current density–voltage (J–V) curve hysteresis and the characteristic current overshoot, or 'bump', in carbon-based perovskite solar cells (CPSCs). Combining experimental data with drift-diffusion simulations, the research reveals that mobile ionic charges screen the electric field, lowering the total driving force for charge extraction. Key findings include identifying the 'bump' in the backward scan as a direct consequence of the polarity inversion of ionic space charge layers, which is highly influenced by the interplay of mobile ions, recombination rates, and contact properties. Crucially, the study demonstrates that external quantum efficiency (EQE) measurements can effectively visualise these dynamic ionic screening effects, showing how spectral shifts correlate with internal electric field changes. This provides a clear understanding of current collection losses driven by ion redistribution.

Why it matters

These findings are crucial for optimising perovskite solar cell design, particularly CPSCs, which offer enhanced stability but often suffer from performance-limiting ionic effects. By providing a comprehensive physical understanding of ion redistribution and its impact on charge collection, this research offers significant insights for tackling hysteresis and current losses. The versatile characterisation approach introduced, using EQE mapping, is applicable across all PSC architectures, providing a powerful tool for diagnosing and improving device performance and stability for future photovoltaic technologies.

How Fluxim tools used

The PAIOS platform from Fluxim AG was utilised for experimental characterisation, specifically to record J-V curves under varying LED illumination wavelengths and light intensities. This allowed for precise measurement of scan rate dependencies and transient effects. Additionally, Setfos (Fluxim AG), a drift-diffusion simulator, was instrumental for device simulations. Setfos enabled the researchers to model the mixed ionic-electronic conductivity of perovskite, providing intuitive visual representations of electric field changes and ionic charge profiles during voltage scans. This combined experimental and simulation approach was key to understanding and visualising the complex ionic screening phenomena.

Publication Details

Torre Cachafeiro, M.A., Narbey, S., Ruhstaller, B., Nüesch, F. and Tress, W. (2025), Visualising ionic screening in perovskite solar cells: a bumpy ride along the J–V curve. EES Solar. https://doi.org/10.1039/d5el00133a