π-π Electronic Coupling and Gap-Plasmonic Enhancement via Fe@Cx Nanoparticles: Synergistic Hole-Transport Engineering for High-Responsivity Perovskite Photodetectors.

We report a multifunctional interface-engineering strategy in which carbon-encapsulated iron nanoparticles (Fe@Cx NPs) are blended into poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) to co-optimize energetics, charge transport, and optical field confinement. Organic-inorganic hybrid optoelectronic interfaces suffer from energetic misalignment and charge transport limitations. This study addresses these challenges through carbon-encapsulated iron nanoparticles (Fe@Cx NPs) derived from carbon nanotube synthesis byproducts, which modulate the work function of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) from 5.03 to 5.24 eV via π-π electronic coupling, representing a 0.21 eV improvement, with optimized energy level alignment of the highest occupied molecular orbital. When the concentration of incorporated iron nanoparticles is optimal at 2.5 v%, the dark current of the devices reduces by 87% from 2.12 × 10- 8 to 2.71 × 10- 9 A/cm2, and a 53% decrease in defect-state energy from 2.31 to 1.08 meV. Under self-powered conditions (0 V), the responsivity increases by 13% from 0.38 to 0.43 A/W, whereas shot-noise-limited detectivity improves 3.2-fold from 4.65 × 101 2 to 1.49 × 101 3 Jones. Frequency response analysis demonstrates a 6.6-dB signal-to-noise ratio enhancement from 59.3 to 65.9 dB with stable operation beyond 300 kHz. This synergistic electronic-plus-plasmonic approach provides a scalable route to the development of high-performance optoelectronic devices.