Single-component organic photodetectors (SC-OPDs), in which the active layer consists only of one organic material, show higher reproducibility and improved morphological stability. Their simplified architecture also provides a powerful platform for better isolating and understanding interfacial effects. Here, SubNc-based SC-OPDs incorporating an ultrathin (3 nm) PhOSubPc interfacial layer to control and probe the interaction between the SubNc absorber and the BPhen electron-transport layer (ETL) is investigated. The PhOSubPc layer acts as an energetic spacer, effectively decoupling SubNc energetically and morphologically from BPhen while maintaining high device performance. Ambient photoelectron spectroscopy (APS) confirms the energetic isolation of SubNc from BPhen, enabling a clear assessment of interfacial effects in single-component architectures. The optimized device achieves an EQE of 56% at 0 V, an ultra-low dark current density of 7.4 · 10⁻¹² A cm⁻² at −0.1 V, and a specific detectivity D^* of 1.69 · 10¹² Jones at 0 V (based on measured noise). Due to their simplified single-component architecture, these SC-OPDs offer fundamental insight into interface effects, which result in state-of-the-art SC-OPD performance.