Papers by Author: O.K. Oyewole

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Authors: Joseph Asare, B. Agyei-Tuffour, O.K. Oyewole, G.M. Zebaze-Kana, W.O. Soboyejo
Abstract: This research investigates the effects of bending on the electrical, optical, structural and mechanical properties of flexible organic photovoltaic (OPV) cells. Bulk heterojunction organic solar cells were fabricated on Polyethylene terephthalate (PET) substrates using Poly-3-hexylthiophene: [6, 6]-phenyl-C61-butyric acid methyl ester (P3HT: PCBM) as the active layer and Poly (3, 4-ethylenedioxythiophene) Polystyrenesulfonate (PEDOT: PSS) as the hole injection layer. All the organic layers were deposited by spin coating while the Al cathode was vacuum thermally evaporated. The Indium Tin Oxide (ITO) anode has an average optical transmittance of 85% in the visible spectrum, a sheet resistivity of 60 ohms per square and an average surface roughness of 3nm. The relationship between the optoelectronic performance of the various device layers and the applied mechanical strains has been analyzed. The effects of stress and strain on the current-voltage characteristics of the device and its failure were modeled using the Abaqus software.
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Authors: O.K. Oyewole, J. Asare, D.O. Oyewole, B. Agyei-Tuffour, V.C. Anye, M.G. Zebaze Kana, W.O. Soboyejo
Abstract: This paper presents the results of a study of the adhesion and optical properties of layered structures that are relevant to stretchable organic solar cells. A combination of modeling and experiments is used to investigate the effects of adhesion and stretching on failure mechanisms and optical properties. The adhesion between the possible bi-layers is determined by incorporating force microscopy measurements of pull-off forces into adhesion models. The failure mechanisms associated with the tensile stretching of the structures are then investigated using a combination of in-situ/ex-situ microscopy observations and analytical/computational models. The resulting changes in optical properties are elucidated before discussing their implications for the design of stretchable organic solar cells
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Authors: J. Asare, B. Agyei-Tuffour, O.K. Oyewole, V.C. Anye, D.Y. Momodu, G.M. Zebaze-Kana, W.O. Soboyejo
Abstract: This paper examines the effects of cyclic bending on the deformation and failure of layers that are relevant to flexible organic solar cells (with Polyethylene Terephthalate (PET) substrates and Poly-3-hexylthiophene: [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) active layers). The deformation and cracking mechanisms are elucidated along with the stresses and crack driving forces associated with the bending of flexible organic solar cells. The changes in the optical properties (transmittance) of the individual layers and multilayers are then explored for layers/multilayers deformed to flexural strains and stresses that are computed using finite element models. The implications of the results are then discussed for the design of flexible organic solar cells.
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Authors: O.K. Oyewole, D.O. Oyewole, J. Asare, B. Agyei-Tuffor, M.G. Zebaze Kana, W.O. Soboyejo
Abstract: In this paper, we present the results of a combined theoretical, computational and experimental study of failure mechanisms in model multilayers that are relevant to stretchable organic solar cells. The deformation of these structures is elucidated under monotonic loading that simulates possible stretching phenomena. The stress distributions within the layers and the possible interfacial crack driving forces are computed for model layered structures with well controlled thicknesses and elastic properties. The implications of the results are discussed for the improved design of stretchable organic solar cells with reliable optical properties.
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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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