Innovation in analog flow controller design

No Abstract.Nigerian Journal of Physics Vol. 20 (1) 2008: pp.69-7

Reliability and Physics Failure of Stretchable Organic Solar Cells

Organic solar (OPV) cells are cheap electronics that can replace the widely used high cost silicon-based electronics for electricity generation. They are cheap because of the easy techniques involved in their fabrication processes and they can be produced to cover a large surface area. However, the current low performance of organic electronics has been traced to failure due to interfacial adhesion problems, material processes, and service conditions. Therefore, transportation of charge carriers across the bulk heterojunction system of OPV cells becomes very difficult in the presence of these flaws. In this paper a combined experimental and computational technique is used to study the reliability and physics failure of stretchable OPV cells. Interfacial adhesion energies in the layered structures of OPV cells are measured and compared with theoretical estimated energies. The limit stresses/strains applied on layered OPV cells during service condition are estimated using critical values of the measured interfacial adhesion. The results obtained are, therefore, explained to improve the design of reliable OPV cells

Adhesion and degradation of organic and hybrid organic-inorganic light-emitting devices

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Momodu, D. Y., T. Tong, M. G. Zebaze Kana, A. V. Chioh, and W. O. Soboyejo. "Adhesion and degradation of organic and hybrid organic-inorganic light-emitting devices." Journal of Applied Physics 115, no. 8 (2014): 084504. and may be found at http://dx.doi.org/10.1063/1.4867051This 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 an atomic force microscopy technique. The interfacial failure mechanisms associated with blister formation in OLEDs and those due to the addition of TiO2 nanoparticles into the 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, interfacial fracture mechanics models, and prior reports of diffusion-assisted phenomena. The implications of the work are then discussed for the design of OLED structures with improved lifetimes and robustness

Pressure-assisted fabrication of organic light emitting diodes with MoO3 hole-injection layer materials

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Du, Jing, V. C. Anye, E. O. Vodah, T. Tong, M. G. Zebaze Kana, and W. O. Soboyejo. "Pressure-assisted fabrication of organic light emitting diodes with MoO3 hole-injection layer materials." Journal of Applied Physics 115, no. 23 (2014): 233703. and may be found at http://dx.doi.org/10.1063/1.4881780In this study, pressures of ∼5 to ∼8 MPa were applied to organic light emitting diodes containing either evaporated molybdenum trioxide (MoO3) or spin-coated poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulphonate) (PEDOT:PSS) hole-injection layers (HILs). The threshold voltages for both devices were reduced by about half, after the application of pressure. Furthermore, in an effort to understand the effects of pressure treatment, finite element simulations were used to study the evolution of surface contact between the HIL and emissive layer (EML) under pressure. The blister area due to interfacial impurities was also calculated. This was shown to reduce by about half, when the applied pressures were between ∼5 and 8 MPa. The finite element simulations used Young's modulus measurements of MoO3 that were measured using the nanoindentation technique. They also incorporated measurements of the adhesion energy between the HIL and EML (measured by force microscopy during atomic force microscopy). Within a fracture mechanics framework, the implications of the results are then discussed for the pressure-assisted fabrication of robust organic electronic devices

Surface texture and optical properties of crystalline silicon substrates

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Fashina, A. A., K. K. Adama, O. K. Oyewole, V. C. Anye, J. Asare, M. G. Zebaze Kana, and W. O. Soboyejo. "Surface texture and optical properties of crystalline silicon substrates." Journal of Renewable and Sustainable Energy 7, no. 6 (2015): 063119. and may be found at http://dx.doi.org/10.1063/1.4937117This paper presents the results of an experimental study of the effects of surface texture on the optical and light trapping properties of silicon wafers. Surface texture is controlled by anisotropic etching with potassium hydroxide (KOH) and isopropyl alcohol (IPA) solutions. The anisotropic etching of (001) crystalline silicon wafers is shown to result in the formation of {111} pyramidal facets on the surfaces of the wafers. A combination of profilometry, optical microscopy, scanning electron microscopy, and atomic force microscopy is used to study the effects of KOH/IPA etching on the morphology and roughness of the textured surfaces. The results show that IPA concentration has the strongest effect on the surface roughness of (001)-single crystal crystals at temperatures up to 80 °C. Above this value, evidence of temperature-induced cracking was revealed on the silicon substrate. The best volume concentration ratio of KOH:IPA is also found to be 2:4. The implications of the study are discussed for the design of light trapping in silicon solar cells

Lamination of organic solar cells and organic light emitting devices: Models and experiments

In this paper, a combined experimental, computational, and analytical approach is used to provide new insights into the lamination of organic solar cells and light emitting devices at macro- and micro-scales. First, the effects of applied lamination force (on contact between the laminated layers) are studied. The crack driving forces associated with the interfacial cracks (at the bi-material interfaces) are estimated along with the critical interfacial crack driving forces associated with the separation of thin films, after layer transfer. The conditions for successful lamination are predicted using a combination of experiments and computational models. Guidelines are developed for the lamination of low-cost organic electronic structures

Micro-wrinkling and delamination-induced buckling of stretchable electronic structures

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Oyewole, O. K., D. Yu, Jing Du, J. Asare, D. O. Oyewole, V. C. Anye, A. Fashina, M. G. Zebaze Kana, and W. O. Soboyejo. "Micro-wrinkling and delamination-induced buckling of stretchable electronic structures." Journal of Applied Physics 117, no. 23 (2015): 235501. and may be found at http://dx.doi.org/10.1063/1.4922665This paper presents the results of experimental and theoretical/computational micro-wrinkles and buckling on the surfaces of stretchable poly-dimethylsiloxane (PDMS) coated with nano-scale Gold (Au) layers. The wrinkles and buckles are formed by the unloading of pre-stretched PDMS/Au structure after the evaporation of nano-scale Au layers. They are then characterized using atomic force microscopy and scanning electron microscopy. The critical stresses required for wrinkling and buckling are analyzed using analytical models. The possible interfacial cracking that can occur along with film buckling is also studied using finite element simulations of the interfacial crack growth. The implications of the results are discussed for potential applications of micro-wrinkles and micro-buckles in stretchable electronic structures and biomedical devices

Extended pulsated drug release from PLGA-based minirods

The kinetics of degradation and sustained cancer drugs (paclitaxel (PT) and prodigiosin (PG)) release are presented for minirods (each with diameter of ~5 and ~6 mm thick). Drug release and degradation mechanisms were studied from solvent-casted cancer drug-based minirods under in vitro conditions in phosphate buffer solution (PBS) at a pH of 7.4. The immersed minirods were mechanically agitated at 60 revolutions per minute (rpm) under incubation at 37 °C throughout the period of the study. The kinetics of drug release was studied using ultraviolet visible spectrometry (UV-Vis). This was used to determine the amount of drug released at 535 nm for poly(lactic-co-glycolic acid) loaded with prodigiosin (PLGA-PG) samples, and at 210 nm, for paclitaxel-loaded samples (PLGA-PT). The degradation characteristics of PLGA-PG and PLGA-PT are elucidated using optical microscope as well as scanning electron microscope (SEM). Statistical analysis of drug release and degradation mechanisms of PLGA-based minirods were performed. The implications of the results are discussed for potential applications in implantable/degradable structures for multi-pulse cancer drug delivery