Single phase FeS₂ (pyrite) thin films prepared by combined electrodeposition and hydrothermal low temperature techniques

In current work the synthesis of single phase of FeS₂ (pyrite) thin films from a combined electrochemical and hydrothermal techniques and without the need for a post sulfurization process is reported. Electrodeposition has been carried out in a non aqueous based electrolytic bath (diethylene glycol (DEG)). Voltamperometric measurements were conducted to study the electrochemical response of the precursors in this organic DEG solvent. These experiences allowed determining the best experimental conditions in DEG for obtaining the FeS/FeS₂ mixture phases which were obtained applying a constant potential of -1.10V. The hydrothermal technique that was developed in a microwave oven improved stoichiometry and crystallinity of the deposits obtained by electrodeposition and led to obtaining a single pyrite phase. SEM micrographs exhibited complete substrate coverage whereas EDS analysis gave atomic ratio S/Fe very close to 2. XRD analysis of the final thin film shows that the deposit has a cubic structure without the presence of other undesired phases. However, Raman spectra indicate a later formation of amorphous superficial hematite. The optical measurements show an optical direct bandgap of 0.985 eV. Results open the possibility of applying the procedure to the formation of a thin film of FeS₂ of good structural and optical characteristics that can be employed as an absorber material in solar cells.