Research Paper: Insights from Impedance Spectroscopy in Perovskite Solar Cells with Self-Assembled Monolayers: Decoding SAM’s Tricks
Scientific Summary
This study investigates the precise mechanism by which self-assembled monolayers (SAMs) enhance the performance and stability of p-i-n perovskite solar cells (PSCs). The main goal was to decode the role of SAMs in increasing photocurrent, reducing hysteresis, and boosting photovoltage and stability. Utilising impedance spectroscopy (IS) and X-ray photoelectron spectroscopy (XPS), key findings demonstrate that SAMs enhance open-circuit voltage (Voc) and stability by suppressing surface recombination. This suppression is achieved through the chemical binding of SAMs with hydroxyl groups (OH⁻) on the indium tin oxide (ITO) substrate, reducing OH⁻ concentration and preventing the accumulation of positive ions/vacancies at the interface. This leads to significantly reduced ionic dynamics (time constants of ~10⁻³ s for SAM vs. ~10⁻² to 10⁻¹ s for PTAA-based devices). The reduced ion accumulation diminishes surface recombination, favours charge separation, and results in higher Voc and superior stability, even under ambient aging conditions.
Publication Details
Aranda, C. A., Li, W., Martínez-Ferrero, E., Pistor, P., Oskam, G., Palomares, E., & Anta, J. A. (2025), Insights from Impedance Spectroscopy in Perovskite Solar Cells with Self-Assembled Monolayers: Decoding SAM’s Tricks. J. Phys. Chem. Lett., 16: 2301−2308. https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.4c03194.
Fluxim Tools Used
SETFOS was utilized for drift-diffusion (DD) numerical simulations. SETFOS simulated the PTAA/perovskite/C60 structure, allowing researchers to vary ionic densities to replicate the effects of replacing PTAA with SAMs and reducing ion accumulation at the interface. These simulations corroborated that a decrease in ionic density (representing the SAM device) results in reduced high-frequency resistance and a weaker inductive effect at low frequencies, consistent with improved charge transport and reduced ion-induced recombination. SETFOS also helped confirm larger concentrations of holes, contributing to inverted hysteresis as described by the modified surface polarization model.
Why it Matters
This research provides a fundamental and robust explanation for the enhanced Voc and stability observed in p-i-n PSCs employing SAMs, overcoming a critical barrier to their industrialization. By identifying the chemical deactivation of surface hydroxyl groups and the consequent suppression of ion accumulation as the core mechanism, this work offers crucial insights for the rational design of more efficient and stable PSCs. Fluxim's SETFOS played a vital role by providing numerical validation for the proposed physical and chemical mechanisms, strengthening the understanding of complex ion-interface interactions and thereby accelerating the development of commercially viable perovskite technology.