Probing the stoichiometry dependent catalytic activity of nickel selenide counter electrodes in the redox reaction of iodide/triiodide electrolyte in dye sensitized solar cells |
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Authors: | Mildred A. Airo Francis Otieno Lineo Mxakaza Adewale Ipadeola Rudo S. Kadzutu-Sithole Lerato F. E. Machogo-Phao Caren Billing Makwena Moloto Nosipho Moloto |
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Affiliation: | Molecular Science Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, Wits, 2050 Republic of South Africa, +27 73 761 0875, +27 11 717 6774 ; Department of Chemistry, Vaal University of Technology, Private Bag X021, Vanderbijlpark 1900 Republic of South Africa ; Department of Physics, University of the Witwatersrand, Private Bag 3, Wits, 2050 Republic of South Africa ; Analytical Services Division, Mintek, 200 Malibongwe Drive, Randburg, South Africa |
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Abstract: | Nickel selenide (NixSey) systems have received much attention in recent years as potential low cost counter electrodes (CEs) in dye sensitized solar cells (DSSCs). Their electrocatalytic activities are comparable to that of the conventional platinum CE. Despite their achievements, the effect of stoichiometry on their catalytic performance as CEs in DSSCs still remains unclear, hence the motivation for this work. Different stoichiometries of NixSey were synthesized via a colloidal method in oleylamine or oleylamine/oleic acid mixture at the appropriate synthetic temperature and Ni to Se precursor ratio. X-ray diffraction revealed that different stoichiometries of nickel selenide were formed namely, NiSe2, Ni3Se4, Ni0.85Se, NiSe and Ni3Se2. Scanning electron microscopy showed that all the stoichiometries had predominantly spherical-like morphologies. Cyclic voltammetry, electrochemical impedance spectroscopy analysis and the photovoltaic performances of the DSSCs fabricated using the different NixSey CEs revealed that selenium rich stoichiometries performed better than the nickel rich ones. Consequently, the catalytic activity towards the redox reaction of the triiodide/iodide electrolyte and hence the power conversion efficiency (PCE) followed the order of NiSe2 > Ni3Se4 > Ni0.85Se > NiSe > Ni3Se2 with PCE values of 3.31%, 3.25%, 3.17%, 2.35% and 1.52% respectively under ambient conditions.Nickel selenide (NixSey) systems have received much attention in recent years as potential low cost counter electrodes (CEs) in dye sensitized solar cells (DSSCs). |
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