Controllable Synthesis of Monodispersed Fe_{1- x}S₂ Nanocrystals for High-Performance Optoelectronic Devices

The optical properties of stoichiometric iron pyrite (FeS₂) nanocrystals (NCs) are characterized by strong UV-Visible (UV-Vis) absorption within the cutoff while negligible absorption beyond the cutoff in near-infrared and longer wavelengths. Herein, we show this bandgap limitation can be broken through controllable synthesis of nonstoichiometric Fe_{1- x}S₂ NCs ( x = 0.01-0.107) to induce localized surface plasmonic resonance (LSPR) absorption beyond the cutoff to short-wave infrared spectrum (SWIR, 1-3 μm) with remarkably enhanced broadband absorption across UV-Vis-SWIR spectra. To illustrate the benefit of the broadband absorption, colloidal LSPR Fe_{1- x}S₂ NCs were printed on graphene to form LSPR Fe_{1- x}S₂ NCs/graphene heterostructure photodetectors. Extraordinary photoresponsivity in exceeding 4.32 × 10⁶ A/W and figure-of-merit detectivity D* > 7.50 × 10¹² Jones have been demonstrated in the broadband of UV-Vis-SWIR at room temperature. These Fe_{1- x}S₂ NCs/graphene heterostructures are printable and flexible and therefore promising for practical optical and optoelectronic applications.