Influence of magnetic stirrer speed on the properties of chemical bath deposited FeSxOy thin films

Abstract

Iron sulfide has a high potential to replace existing solar cell materials due to its cost-effectiveness and non-toxic. Nonetheless, the reported efficiency is still low, attributed to quality issues of interface/bulk single film. Thus, it is essential to overcome those quality issues by focusing on material synthesis. To date, no reported works on the effects of magnetic stirrer speed in the chemical bath deposition (CBD) of iron sulfide film. Hence, this work elucidates the influence of magnetic stirrer speed (100–700 revolutions per minute-RPM) in the CBD on the properties of iron sulfide (iron-sulfide-oxide: FeSxOy) films. The magnetic stirrer speed was limited to below 1000 RPM because the high stirring speed contributed to weak molecule interaction between the FeSxOy cluster and the grown FeSxOy film. As a result, the solution's fast motion could easily break the molecule interaction between them (poor film adherence). The Scanning Electron Microscopy (SEM)-Energy Dispersive X-Ray Spectroscopy (EDX) showed the number/size of agglomerations relatively increased (reduction in uniformity) and the oxygen increased/sulfur decreased with an increase in the speed. The X-ray diffraction (XRD) patterns revealed that the pyrite transformed to goethite/hematite at a magnetic stirrer speed > 300 RPM. The film with 100 RPM produced a larger crystallite size. The Raman spectra exhibited no FeSxOy and pyrite phases for the film deposited at 700 RPM. The Hall Effect displayed that film at 100 RPM yields the highest carrier density of electrons (n-type). Films with 100 and 300 RPM showed absorption edges at a wavelength of around 400 nm, and their estimated bandgaps via the Tauc plot are 3.35–3.44 eV. Furthermore, a film with 100 RPM showed better quality and was suitable to be applied as a window layer (n-type) in thin film solar cells.