Papers by Author: M.G. Zebaze Kana

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Authors: D.Y. Momodu, T. Tong, M.G. Zebaze Kana, W.O. Soboyejo
Abstract: This paper presents the results of a combined analytical, computational and experimental study of adhesion and degradation of Organic Light Emitting Devices (OLEDs). The adhesion between layers that are relevant to OLEDs is studied using force microscopy during Atomic Force Microscopy. The interfacial failure mechanisms associated with blister formation in OLEDs and the addition of TiO2 nanoparticles (into active regions) are then elucidated using a combination of fracture mechanics/finite element modeling and experiments. The blisters observed in the models are shown to be consistent with the results from adhesion and interfacial fracture mechanics models. The implications of the work are discussed for the future design of OLED structures with improved lifetimes and robustness.
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Authors: A.A. Fashina, K.K. Adama, M.G. Zebaze Kana, Winston O. Soboyejo
Abstract: We investigate the effect of surface texturing on the light trapping properties of Silicon wafers as a function of reflection reduction and surface morphology. This was achieved by structuring a random square-based pyramids pattern on the surface of Silicon substrate using anisotropy etching. The light trapping effect was optimized for silicon solar cells by investigating the dependence of the silicon surface texturing on the process parameters such as etchant concentration, etching time and temperature. We study the surface morphology by analyzing the surface behaviour of the textured substrate using the atomic force microscope and scanning electron microscope. The results of roughness and optical reflection were obtained using the surface profiler and the UV/VIS the spectrometer respectively. In addition, an analytical modelling method was developed to determine the angles of incidence of light rays with each of the facets of the pyramids and the coordinate of the reflected light rays. The method used here is based on 3-D vector geometry of the pyramidal facets. The optimum parameters are found to be 40min, a temperature of 80oC and with KOH/IPA/DI in the ratio [2:4:46] by volume, yielding a surface roughness over 600 nm and a relative optical reflectance in the visible spectrum less than 10%, using polished Si as reference. The results and analysis of both the modelled and measured reflectance, suggest that the performance of the light trapping technique has a big potential in silicon solar cells application.
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Authors: B. Agyei-Tuffour, E.R. Rwenyagila, J. Asare, O.K. Oyewole, M.G. Zebaze Kana, D.M. O’Carroll, W.O. Soboyejo
Abstract: This paper explored the effects of pressure on contacts between layers of organic photovoltaic cells with poly (3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as the active layer. The contacts between the layers are modeled using analytical concepts and finite element models. The potential effects of surface roughness and dust particles are modeled along with the effects of lamination pressure and adhesion energy. The results show that, increased pressure is associated with decreased void length or increased contact length. The contacts associated with the interfaces between the active layer and the hole/electron injection layer poly (3,4-ethylenedioxythiophene: poly styrenesulphonate (PEDOT.PSS) and Molybdenum trioxide (MoO3) are also compared. The implications of the results are discussed for the design of stamping/lamination processes for the fabrication of organic photovoltaic cells.
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Authors: K. Mustapha, M.G. Zebaze Kana, O.S. Odusanya, W.O. Soboyejo
Abstract: This paper presents the results of a combined experimental and theoretical study of the strength and fracture toughness of earth-based materials. They include mixtures of laterite, clay and straw that is stabilized with controlled levels of Portland cement. The compositional dependence of compressive, flexural strength and the fracture toughness is explored for different proportions of the constituent materials. Composites and fracture mechanics models are used to estimate the strength and fracture toughness of the resulting composites. The applications of the results are discussed for the design of earth-based building materials for affordable housing.
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