Universal synthesis of air stable, phase pure, controllable FeSe₂ nanocrystals

Iron diselenium (FeSe2) is a promising semiconductor for thin-film solar cells because it has a suitable band gap (E(g) = 1.0 eV) and high absorption coefficient. Despite these prospects, the controllable synthesis of FeSe2 nanostructures and the diversity of their geometries has hardly been studied previously. Here, we described a successful synthesis of phase-pure, high-quality, and stable orthorhombic FeSe2 nanocrystals (NCs) in aqueous solvents. A variety of morphologies of the FeSe2 NCs were achieved by adjusting synthetic methods. FeSe2 nanoparticles with diameters of 30-100 nm were synthesized in the presence of ethylenediamine (en). Moreover, the synthetic approach developed for nanoparticles proved to be quite universal and could be modified to produce nanowires and octahedrons, with which structure the material could display high crystallinity. The diameter of the FeSe2 nanowires was 300-500 nm with a length exceeding 2 μm. The octahedrons displayed lateral dimensions of 1 μm. Meanwhile, the probable growth mechanism and fabrication process of the NCs were proposed. Polycrystalline FeSe2 thin films were fabricated by modifying the sedimentation method. The obvious photoconductivity of FeSe2 has already been observed, and it was considered to be one candidate of solar cell for the very first time.