Department of Physics

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Browsing Department of Physics by Author "Botha, Nandipha L."

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    Co-sensitization effect of chlorophyll and anthocyanin on optical absorption properties and power conversion efficiency of dye-sensitized solar cells
    (Springer, 2024-04) Mukhokosi, Emma Panzi; Mohammed, Tibenkana; Loyce, Namanya; Botha, Nandipha L.; Maaza, Maliki; Velauthapillai, Dhayalan
    In this article, the chemical structure, optical absorption and photoluminescence properties of un/adsorbed dyes of hibiscus flower (H), pumpkin leaf (P), sweet potato leaf (S) and their composites (H: P & H: S) have been studied. The chemical structural properties revealed the O–H, C–C and C = O as the main anchoring functional groups. The optical absorption properties revealed two definite bands in between 450–500 nm and 600–680 nm wavelength for chlorophyll-based dyes and a peak at 526 nm for anthocyanin based dye extract. The composite dye extracts revealed optical absorption bands corresponding to chlorophyll and anthocyanin pigments with enhanced absorption of light. Five different solar cells based on H, P, S, H:P-3:1 and H:S-3:1 were developed and revealed an efficiency of ~ 0.08, 0.3, 0.5, 0.7 and ~ 1% respectively. The efficiency was reduced by half after 30 days. The composites had the highest power conversion efficiency due to more O–H, C–C and C = O binding sites on TiO2 nanoparticles, reduced rate of electron–hole pair recombination and a wide range of optical absorption. These studies suggest that co-pigmentation can be an alternative strategy to increasing the power conversion efficiency in DSSCs.
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    Green synthesis of hematite nano flakes and their application as a counter electrode in dye-sensitized solar cells
    (Scientific Reports, 2025-06-05) Mukhokosi, Emma Panzi; Mushebo, Emmanuel; Nassejje, Stella; Botha, Nandipha L.; Velauthapillai, Dhayalan; Maaza, Malik
    This study pioneers using hematite nanoflakes as a viable alternative to traditional platinum counter-electrodes in dye-sensitized solar cells (DSSCs), demonstrating its effectiveness for the first time. Besides such a novelty, the used hematite nanoflakes were bio-engineered using ginger extract as an effective chelating reducing agent. From the X-ray diffraction studies, it was observed that the sample annealed at 700 °C formed a highly crystalline α-Fe2O3, with a crystallite nano-scaled size of the order of 46.3 nm. The scanning electron microscopy investigations indicated a preferred layered nanoflakes morphology while the optical properties revealed a direct band gap of 2.30 eV. Using N-719 dye as a sensitizer on TiO2 photoanode and I−/I3− as electrolyte, the DSSC was fabricated. Such a cell exhibited significant DSSC responses, namely; a short circuit current density (JSC) of 7.0 mAcm−2, an open circuit voltage (VOC) of 389 mV, and a fill factor (FF) of 75.3% in addition to an efficiency (η) of 2.05%. Based on such a significant photo-conversion response using bio-engineered active counter electrodes, this study provides a cost-effective approach for synthesizing hematite NFs that have potential applications not only in DSSC but also in sensors, water splitting, and electrochemical devices.