Unveiling Charge Carrier Dynamics at Organic-Inorganic S-Scheme Heterojunction Interfaces: Insights From Advanced EPR

Understanding charge carrier transfer at heterojunction interfaces is critical for advancing solar energy conversion technologies. This study utilizes continuous wave (CW), pulse, and time-resolved (TR) electron paramagnetic resonance (EPR) spectroscopy to explore the radical species formed at the TAPA (tris(4-aminophenyl)amine)-PDA (Terephthaldicarboxaldehyde)/ZnIn₂S₄ (TP/ZIS) heterojunction interface. CW and pulse EPR identify stable radical defects localized near the interface, accessible to water molecules. Time-resolved EPR reveals a photoinduced electron transfer from TP to ZIS, leading to the generation of spin-correlated radical pairs under light irradiation, signifying efficient charge carrier separation and spatial transfer within the S-scheme heterojunction. This electron transfer mechanism, confirmed through in situ X-ray photoelectron spectroscopy and femtosecond transient absorption spectroscopy, suppresses undesirable carrier recombination, extending charge carrier lifetimes. These findings provide novel insights into the transport direction of charge carriers at the S-scheme heterojunction interface, offering valuable guidance for designing highly efficient and stable organic-inorganic heterojunction photocatalysts for solar energy applications.