Charge Transfer at the PEDOT:PSS/Perovskite Interface in RP Sn Perovskite Solar Cells Elucidated by Operando ESR Spectroscopy

Ruddlesden-Popper (RP) Sn-based perovskite solar cells (PSCs) have emerged as an alternative to Pb-based PSCs because of their reduced environmental impact, and superior stability among Sn-based PSCs. However, the charge diffusion mechanisms remain insufficiently understood despite their critical role in device performance. In this study, we employ electron spin resonance (ESR) spectroscopy to elucidate the charge diffusion mechanism in ITO/PEDOT:PSS/(BA0.5PEA0.5)2FA3Sn4I13/PC61BM/PDINO/Ag PSCs. Under illumination, no significant charge accumulation was observed in the PDINO layer. Furthermore, consistent with our previous report, electron injections from (BA0.5PEA0.5)2FA3Sn4I13 into PEDOT:PSS and open-circuit voltage improvement were observed during operando ESR measurements. These results provide strong support for the hypothesis that electron injection from (BA0.5PEA0.5)2FA3Sn4I13 to PEDOT:PSS enhances the electron barrier at the interface, which dominantly contributes to the performance improvement during device operation. These findings provide deeper insight into the interfacial properties of RP Sn-based PSCs and may contribute to further performance optimization.