Browsing by Author "Iwuoha, Emmanuel I"

Now showing 1 - 7 of 7
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    Crystal engineering and thin-film deposition strategies towards improving the performance of kesterite photovoltaic cell
    (Elsevier, 2021) Nwambaekwe, Kelechi; John-Denk, Vivian Suru; Douman, Samantha F.; Iwuoha, Emmanuel I
    With high absorption coefficient (104 cm 1), optimal bandgap (~1.5 eV), low toxicity and the abundance of its constituent elements, kesterite (Cu2ZnSnS4 or CZTS) displays the properties of an ideal photovoltaic material. Kesterite is structurally analogous to chalcopyrite (Cu2InGaS2 or CIGS) and can thus be produced through the already established techniques for the synthesis of commercial CIGS. Though CIGS- and CdTe-based thin-film solar cells have attained levels of power efficiency values (up to ~22%) that compare with that of crystalline silicon-based wafer solar cell, they contain rare earth elements (indium, tellurium and Cd) that are toxic. This article reviews the crystal structure formation and properties of CZTS. Material synthesis, thin-film deposition methodologies and different layers that have been developed for kesterite-based photovoltaic (PV) cell are reported. Factors that hinder high-power conversion efficiency, including large open-circuit voltage deficit (Voc,def), are discussed. Strategies, such as alloy formation, which have been employed to overcome the limitations of using kesterite in PV cell applications are presented, together with the future direction in the quest for improving the performance of kesterite PV cell devices.
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    Development of Highly Sensitive Electrochemiluminescence Platforms and Application in Disease Biomarker Immunosensing
    (University of the Western Cape, 2018) Douman, Samantha Fiona; Iwuoha, Emmanuel I
    Electrochemiluminescence (ECL) is a light-emitting process generated by electrochemical redox reactions and has been widely used as an analytical tool, especially in the field of biosensing, that is, immunoassays and DNA-probe assays. Thus, the scope of this work was to develop a simple, sensitive ECL immunosensor for cardiac injury and to study and present insights into newly fabricated platforms for bioanalytical applications by using ECL as detection mechanism.
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    Next generation bulk Heterojunction organic Photovoltaic and light emitting diode sytems of Novel Polycyclic Aromatic Hydrocarbon, Polyfluorenes and Polythiophenes
    (University of the Western Cape, 2017) John, Suru Vivian; Iwuoha, Emmanuel I
    In these times of diminishing reserve of fossil fuel, the development of novel - green or renewable? technologies to meet the increasing worldwide demand for energy is of great importance. The sun is the largest carbon free source of energy and an infinite source of renewable energy. However, except for the expensive inorganic crystalline silicon photovoltaic cells, this source of energy has not been utilized. The field of organic photovoltaic cell has made impressive progress in the last few years with the tremendous efforts of researchers working tirelessly to develop organic materials for solar energy conversion. Organic conjugated materials have the advantage of low cost, light weight, process-ability and good flexibility over inorganic materials. They have attracted wide academic and industrial interest due to their promise as semiconductors for photovoltaic applications. Design of advanced organic conjugated materials with the ability to absorb light from the sun and convert it into useful and storable form has and still is one of the most important goals of researchers in the field of renewable energy. This work describes a number of novel exciting and promising materials based on polycyclic aromatic compounds (PACs) for organic photovoltaic cells and organic light emitting diodes.
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    Optical and electronic properties of methylammonium lead halide perovskite solar cells
    (University of the Western Cape, 2017) Tombe, Sekai Lana; Iwuoha, Emmanuel I
    Organic-inorganic hybrid perovskite solar cells have emerged as promising materials for next-generation photovoltaics with certified efficiency of 22.1%. Despite rapid developments, achieving precise control over the morphologies of the perovskite films, enhanced stability and reproducibility of the devices remains challenging. In this work, we employed a low-temperature solution processing technique to attain high efficiency inverted planar heterojunction devices with device architecture ITO/PEDOT:PSS/Perovskite/PCBM/Al (indium doped tin oxide; poly(3,4-ethylenedioxythiophene) polystyrene sulfonate; [6,6]-phenyl-C61-butyric acid methyl ester; aluminium). A perovskite solar cell fabrication technique is developed and opto-electronic characterization of solution-processed planar heterojunction perovskite solar cells based on methylammonium (MA) lead halide derivatives, MAPbI3-xYx (Y = Cl, Br, I) is presented in this thesis work. By employing lead iodide (PbI2) with various amounts of additional methylammonium halides, perovskite precursor solutions were obtained, which were used in the fabrication of four perovskite systems, MAPbI3, MAPbI3-xClx and MAPbI3-xBrx and MAPbBr3. The absorption and photoluminescence (steady state and temperature-dependent) behavior were explored in this compositional space.
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    Photophysics of Thiophenosalicylaldimine-functionalized G1-Polyprolyleniminato-Copper Telluride/Antimonide core-shell Nanomaterials
    (University of the Western Cape, 2018) Ramoroka, Morongwa Emmanuel; Iwuoha, Emmanuel I
    This work involves the synthesis of copper telluride-polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (CuTe@PPI) and copper antimonide-polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (CuSb@PPI) core-shell nanoparticles (NPs), using two-pots and one-pot synthesis methods, respectively. Their morphology was studied by X-ray diffraction spectroscopy (XRD), high resolution transmission electron microscopy (HRTEM) and high resolution scanning electron microscopy (HRSEM); while their structures were characterized by Fourier transform infrared spectroscopy (FTIR) and elemental analysis. Photophysical properties of the core-shell NPs were determined from ultraviolet-visible absorption spectroscopy (UV-Vis) and photoluminescence spectroscopy (PL). For core-shell NPs produced via two-pots method only CuTe@PPI exhibited ? ? ?* and n ? ?* which indicate that CuSb@PPI produced via two-pots method was unsuccessfully synthesized. The ? ? ?* and n ? ?* transitions indicate the presence of polypropylenimine tetra(5-(2-thienyl) salicylaldimine) (PPI) on the surface of CuTe NPs and CuSb NPs. FTIR confirmed coordination of PPI on the surface of CuTe NPs and CuSb NPs by showing a shift in wavenumber of C=N group bands from PPI. HR-TEM showed that the CuTe@PPI synthesized via one-pot method have a wide particles sizes distribution with an average particles size of 13.60 nm while for CuTe@PPI synthesized via two-pots it was impossible to determine the particles size due to aggregation. CuSb@PPI synthesized via twopots method and one-pot method has a wide particles sizes distribution with an average size of 7.98 nm and 11.61 nm respectively. The average particles sizes determined by HR-SEM were found to be 35.24 nm (CuTe@PPI two-pots method), 33.90 nm (CuTe@PPI one-pot method), 18.30 nm (CuSb@PPI two-pots method), and 16.18 nm (CuSb@PPI one pot method).
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    Synthesis and analysis of Novel Platinum group Metal Chalcogenide Metal Quantum Dot and Electrochemical Markers
    (University of the Western Cape, 2018) Nxusani, Ezo; Iwuoha, Emmanuel I
    Although cadmium and lead chalcogenide quantum dot have excellent optical and photoluminescent properties that are highly favorable for biological applications, there still exists increasing concerns due to the toxicity of these metals. We, therefore, report the synthesis of new aqueous soluble IrSe quantum dot at room temperature utilizing a bottom-up wet chemistry approach. NaHSe and H2IrCl6 were utilized as the Se and Ir source, respectively. High-resolution transmission electron microscopy reveals that the synthesized 3MPA-IrSe Qd are 3 nm in diameter. The characteristics and properties of the IrSe Qd are investigated utilizing, Selected Area electron diffraction, ATR- Fourier Transform Infra-Red Spectroscopy, Energy Dispersive X-ray spectroscopy, Photoluminescence, Cyclic Voltammetry and chronocoulometry. A 3 fold increase in the optical band gap of IrSe quantum dot in comparison to reported bulk IrSe is observed consistent with the effective mass approximation theory for semiconductor materials of particles sizes < 10 nm. The PL emission of the IrSe quantum dot is at 519 nm. Their electro-activity is studied on gold electrodes and exhibit reduction and oxidation at - 107 mV and +641 mV, with lowered reductive potentials. The synthesized quantum dot are suitable for low energy requiring electrochemical applications such as biological sensors and candidates for further investigation as photoluminescent biological labels.
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    Wood-derived, monolithic chainmail electrocatalyst for biomass-assisted hydrogen production
    (Wiley, 2023) Iwuoha, Emmanuel I; Li, Di; Li, Zengyong
    The chainmail catalyst by encapsulating an active species within the carbon support is a well-established concept to endorse extraordinary stability for catalytic reactions under harsh conditions. Conventional chainmail catalysts inevitably suffer from poor accessibility to active sites, leading to extra voltage to compensate the sluggish diffusion kinetics in electrocatalysis. Herein, the naturally abundant wood material is converted into a monolithic chainmail electrocatalyst by encapsulating cobalt nanoparticles within N-doped carbonized wood. Such a monolithic chainmail catalyst is employed directly as electrode for hydrogen evolution (HER), oxygen evolution (OER), and monosaccharide oxidation reactions (MOR) with benchmark performance. By coupling the HER with MOR, the electrolyzer equipped with the monolithic chainmail catalyst allows hydrogen production at a current density of 100 mA cm−2 with a full cell voltage of only 1.36 V. Such design of wood-derived chainmail catalyst provides a promising way to fabricate robust electrocatalysts for future production of hydrogen and value-added chemicals.