Electrocrystallization of nanostructured iron-selenide films for potential application in dye sensitized solar cells

Abstract

Growing need for thin films of materials applied in a variety of electronic devices focused interest of researchers on electrochemical deposition technique as a valuable and inexpensive tool for preparation of layers of various compounds including, among others, transition metal selenides. Iron-selenide system offers a possibility of application of the as grown and annealed nanostructured films in dye-sensitized solar cells (DSSCs). Moreover, by varying the electrodeposition conditions (applied potential or cathodic current density), composition of the starting solution, pH and temperature, it is possible to obtain materials of different structure and composition. Here, we report the synthesis of films of tetragonal FeSe and their transformation into orthorhombic FeSe2 through post-synthetic annealing. Nanocrystalline iron monoselenide was grown on platinum or gold electrodes from acidic aqueous solution containing SeO32− and Fe2+ ions, using either potentiostatic or galvanostatic method. Detailed studies of the as prepared films performed with X-ray diffraction, Raman spectroscopy and scanning electron microscopy combined with energy dispersive spectroscopy microanalysis revealed that the products are selenium rich, indicating that tetragonal FeSe co-deposits together with amorphous selenium. This by-product can be removed from the layers by vacuum evaporation at elevated temperatures, enabling preparation of films of tetragonal FeSe, or alternatively, can be utilized as a Se source in the post-synthetic annealing of as-deposited layers at 400 °C to obtain iron dichalcogenide, FeSe2, of good crystallinity and well developed morphology dedicated to direct use in DSSCs.