Controllable synthesis of monodispersed Fe1-xS2 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 shown this bandgap limitation can be broken through controllable synthesis of nonstoichiometric Fe1-xS2 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 Fe1-xS2 NCs were printed on graphene to form LSPR Fe1-xS2 NCs/graphene heterostructure photodetectors. Extraordinary photoresponsivity in exceeding 4.32×10^6 A/W and figure-of-merit detectivity D* > 7.50×10^12 Jones have been demonstrated in the broadband of UV-Vis-SWIR at room temperature. These Fe1-xS2 NCs/graphene heterostructures are printable and flexible, and therefore promising for practical optical and optoelectronic applications.