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

Abstract 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.