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Thesis (MTech( Electrical Engineering)) -- Cape Peninsula University of Technology, 2012 / Due to the complex design of existing electric mobility vehicles in South Africa and their imported parts, make them unaffordable to the majority of disabled people in South Africa. The traditional electric units are also not practical for use in rural areas due to the heavy, bulky design. The scope of this study was to investigate various designs using existing wheelchair frame designs, low cost three phase hub motors and various electronic techniques to achieve the desired functionality. An attempt was be made to remove inefficient and expensive DC brush motors and the gear boxes associated with the traditional design of wheelchairs, while still allowing the unit to fold like the traditional manual chair design. One of the aims for this electric wheelchair was to utilise existing large radius wheels, typical of manual wheelchairs and a modified traditional frame design, providing the clearance often necessary to overcome rough terrain whilst enabling the chair to be used as a manual wheelchair should the battery fail. One of the primary aims of the project was to develop a method for an electric assist feature built into the modified electric wheelchair, whereby the force applied to the manual pushrims on the wheels would be measured and the electric component would proportionally assist the user. This option suits the users who are weak but not physically disabled. One of the many focal points here would be on HIV/AIDS patients, which is prevalent in South Africa, who may require a wheelchair when debilitated with this disease. The electric assist portion of the design would act similarly to a wireless self-powered torque sensor, allowing for an array of applications besides the electric assist portion of this project. A recent survey by National Government indicated that over 85% of wheelchair users only generated an income of between R0 – R500 per month. Low state disability grants and wage figures for disabled and HIV/AIDS patients mean that electric mobility vehicles have become a luxury rather than an essential commodity in South Africa. The need for cheap electric wheelchairs that could cope with the rural terrain and could be fitted onto existing manual wheelchairs offering the full manual operation should the batteries go flat, was clearly apparent. The cost of an electric wheelchair ranges from R18 000 with more advanced models escalating in price to well over R150 000. These prices were typically the result of the complexity of the unit and local wheelchair manufacturers having to import 80% of their parts from abroad. The largest local manufacturer is CE Mobility which is the dominant mobility vehicle supplier in Southern Africa and has the only SABS approved units for sale. Our complete redesigned wheelchair including the manual frame supplied by an existing supplier would only cost R9 000. A prototype demonstrated that is was possible to build a wheelchair that meets all these criteria. A cost effective unit could provide a solution to assist and enable economically challenged and disabled people in rural areas of Southern Africa.

White organic light-emitting diodes (WOLEDs) resemble light more naturally, with emission spectrum that is comfortable to the human eye. A lot of effort has been devoted to improve the performance of WOLEDs. This research work was aimed at studying the emission behavior of WOLEDs, improving the device performance, and thereby developing several novel device concepts for application in high performing transparent WOLEDs and organic proximity sensors. Emission behavior, in terms of color stability and injection characteristics of phosphorescent organic light-emitting diodes (OLEDs), was investigated systematically and optimized via the experimental optimization and optical simulation. The transparent WOLEDs can be almost invisible at daytime and can emit a pleasant diffused light at night, allowing the surface light source to shine in both directions. It is an exciting new lighting technology that could bring new device concepts. However, undesirable angular-dependent emission and asymmetrical emission characteristics are often observed in transparent WOLEDs. In this work, a pair of optically and electrically comparable transparent anode and cathode was introduced to form weak microcavity transparent WOLEDs, e.g., employing a pair of Ag (10 nm)/MoO3 (2.5 nm)-modified indium tin oxide anode and Al (1.5 nm)/Ag (15 nm)/NPB (50 nm) cathode. It is found that the avoidance of the spectral overlap between the peak wavelengths of the emitters and the resonant wavelength of the organic microcavity moderates the angular-dependent electroluminescence emission behavior, thereby improving the color stability of the transparent white WOLEDs over a broad range of the viewing angles. As a result, the transparent WOLEDs developed possess a visible-light transparency of >50%, a symmetrical bi-directional illumination with an almost identical power efficiency of 11 lm/W (measured at 100 cd/m2) and the similar CIE coordinates of (0.36, 0.43) and (0.38, 0.46) measured from both sides of the devices. Efficient charge injection is a prerequisite for achieving low turn-on voltage and improved hole-electron current balance in OLEDs. Metal oxide (e.g. MoO3) is a commonly used hole-injection layer (HIL) for reducing the energy barrier at the anode/organic interface for efficient charge injection. However, fluctuation in the quality of the metal oxide-based HIL, e.g., changes due to the MoO3 formulation, film fabrication and post-treatment conditions, often places a practical challenge limiting reproducibility of the device performance. In this work, an effective solution-processed HIL that consists of a mixture of PEDOT:PSS and MoO3 was developed for application in OLEDs. It is found that the presence of the solution-processed HIL at the interface between the anode and the organic improves the hole injection and the performance reproducibility of the phosphorescent OLEDs. The effect of the presence of the MoO3 in the solution-processed HIL on charge injection in phosphorescent OLEDs, with a configuration of glass/ITO/CBP/ CBP:Ir(ppy)2acac/TmPyPB/LiF(1.0 nm)/Al(70 nm), was examined. It is shown that solution-processed HIL has a superior hole injection characteristic at the HIL/hole transporting layer (HTL) interface compared to that in the devices fabricated with a pristine PEDOT:PSS or a pure MoO3 HIL, yielded phosphorescent OLEDs with an external quantum efficiency of ~25% and a power efficiency of ~75 lm/W @ 1000 cd/m2. The morphological and surface electronic properties of the hybrid HIL were also investigated by AFM, XPS and UPS measurements, revealing the formation of a good contact at the HIL/HTL interface in the phosphorescent OLEDs. Apart from improving the device performance, a new organic proximity sensor based on the monolithic integration of organic photo-detectors (OPDs) and OLEDs was also developed. A MoO3-modified thin silver interlayer, serving simultaneously as a transparent cathode for the OPDs and an anode for the OLEDs, is used to link the functional organic electronic components. In the integrated OLED/OPD-based proximity sensors, the OLED components function as an illumination source while the coupled OPD units enable a high absorption when light is reflected from objects to create an optical signal. The photosensitivity is enhanced using organic photosensitive bulk heterojunction in the OPDs, thereby realizing a high photosensitivity and the high external quantum yield at a low reverse bias. The signal to noise ratio, optical and frequency responses of the integrated organic proximity sensors were optimized and examined. The design and fabrication flexibility of the integrated OLED/OPD-based organic proximity sensors also have cost benefits, making it possible for application in wearable units and compact information systems.

As a clean and non-exhaustible energy source, solar energy is becoming increasingly important in reducing energy prices and influencing the global climate change. Compared to the traditional inorganic solar cells, conjugated polymer-based organic solar cells (OSCs) have shown much promise as an alternative photovoltaic technology for producing solar cells on large scale at low-cost. However, despite the rapid progresses made in the development of new donor materials, fullerene derivatives and hybrid small molecule/polymer blends, the efficiency and stability of OSCs are still limitations on the potential applications. The performance of OSCs is primarily hampered by the limited light absorption, caused by the mismatch between light absorption depth and carrier transport scale, low carrier mobility and unstable electrode/organic interfacial properties. Improved utilization of light in solution-processed OSCs via different light trapping schemes is a promising approach. The feasibility of light trapping using surface plasmonic structures and textured surfaces to confine light more efficiently into OSCs has been demonstrated. However, plasmon excitations are localized only in the vicinity of metal/organic interface, while the absorption enhancement due to the textured surfaces improves light trapping irrespective of the wavelength. A generic approach towards improving light harvesting in the organic active layer thinner than optical absorption length is one of the key strategies to the success of OSCs. The aim of this PhD project is to undertake a comprehensive study to analyze broadband and omnidirectional light absorption enhancement in bulk heterojunction (BHJ) OSCs, to understand the dynamics of charge transport, charge recombination, charge collection, and to develop solutions to improve the stability of OSCs. In this work, the broadband light absorption enhancement in solution-processed BHJ OSCs is realized by incorporating 2-D photonic structures in the active layer, formed using a nano-imprinting method. The performance of photonic-structured OSCs and planar control cells, fabricated with the blend of poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-bA] dithiophene-2,6-diyl] [3-fluoro-2-[(2ethylhexyl) carbonyl] thieno[3,4-b]-thiophenediyl] (PTB7): [6,6]-phenyl-C70-butyric-acid-methyl-ester (PC70BM) is analyzed. By introducing the photonic structures with 500 nm structure period, the performance of structured OSCs is optimized by adjusting the structure height in the active layer. With the comparison of the current densityvoltage (JV) characteristics, the incident photon to charge carrier efficiency (IPCE) spectra and also the finite-difference time-domain (FDTD) calculated electric field distributions, our results reveal that the photonic structures allow improving light absorption in PTB7:PC70BM layer, especially in the long wavelength region. It is shown that the photonic-structured OSCs possess a 6.15 % increase in power conversion efficiency (PCE) and a 7.53 % increase in short circuit current density (JSC) compared to that of a compositionally identical planar control cell. Light absorption in the 2-D photonic-structured OSCs is a function of the photonic structures and the optical properties of the active layer. The correlation between the choice of the photonic structures and the enhanced spectral response in photonic-structured OSCs is analysed systematically using theoretical simulation and experimental optimization. It is found that the integrated absorption of the active layer decreases slightly with increase in the period of the photonic structures. The results reveal that the photonic-structured OSCs exhibit a stronger absorption enhancement over a broader range of the angle of incident light. The incorporation of the appropriate periodic nano-structures in the active layer is apparently favourable for efficient cell operation as compared to light absorption in the planar control cells made with the same blend system, which decreases rapidly with an increase in the angle of the incident light. Omnidirectional and broadband light absorption enhancement observed in photonic-structured OSCs agrees well with the theoretical simulation. More than 11% increase in the PCE of photonic-structured OSCs is obtained compared to that of an optimized planar control cell, caused mainly by the absorption enhancement in the active layer. 2-D photonic structures allow achieving broadband absorption enhancement in OSCs over a wider range of the angle of the incident light from -45 deg to +45 deg with respect to the normal to the cell surface. For example, the higher light absorption in the active layer of photonic-structured OSCs, integrated over the visible light wavelength range from 380 nm to 780 nm, changes slightly from 70.1% (normal) to 67.7% (45 deg), remaining 96.6% of the absorption in the cells at the normal incidence. While for the control planar OSC, the integrated absorption follows a faster decrease from 66.2% (normal) to 62.2% (45 deg), revealing a quicker reduction in the absorption of the cells at an angle of the incident light away from the normal incidence. In addition to the absorption enhancement, charge transport, recombination and collection are also prominent factors for the efficient operation of OSCs. Thus, it is crucial to improve the understanding of these important processes and their impacts on the cell performance in order to design optimized device architectures. The charge recombination processes, the distribution of charge density under different operation conditions and charge collection at the organic/electrode interfaces in PTB7:PC70BM-based OSCs are studied systematically using a combination of theoretical calculation, transient photocurrent (TPC) measurements, morphology analyses and device optimization. The charge transport and recombination properties in the BHJ OSCs are investigated using the photo-induced charge extraction by linearly increasing voltage (Photo-CELIV) method. Combined with light intensity-dependent J--V characteristic and TPC measurements, it is shown that the use of the ZnO cathode interlayer has a profound effect on enhancing charge collection efficiency and thereby improving in the overall performance of OSCs. The origin of the improvement in the cell performance is mainly associated with improved electrical properties. The TPC results reveal that the presence of the ZnO interlayer helps to prevent the unfavourable interfacial exciton dissociation for achieving efficient charge collection at the active layer/electrode interface. Light intensity-dependent J--V characteristics and the photo-CELIV results support the findings in showing that the charge recombination at the organic/cathode interface can be effectively suppressed by inserting a thin ZnO cathode interlayer, leading to a significant improvement in the charge collection efficiency. A comprehensive study on the degradation mechanisms of solution-processed BHJ. OSCs has been performed. It is manifested that the suppression in bi-molecular recombination and enhancement in charge mobility, achieved through appropriate electrode modification, is one of the effective approaches for achieving stable and performance reproducible OSCs. The effect of the solution-processed anode interlayer, e.g. a mixture of MoO3 and Au nanoparticles (MoO3:Au NPs), on the performance of BHJ OSCs is also examined, with the aim to replace the acidic and hygroscopic poly(3,4-ethylenedioxylenethiophene): polystyrene sulfonate (PEDOT:PSS) hole extraction layer (HEL). A 14.3% enhancement in the PCE of OSCs with an anode interlayer of MoO3:Au NPs (7.78%) is obtained compared to that of the structurally identical devices with a pristine MoO3-based interlayer (6.72%), due to the simultaneous improvements in both JSC and fill factor (FF). The accelerated aging tests for as-prepared structurally identical OSCs fabricated with different HELs were carried out in the ambient condition. It is shown that the solution-processed MoO3:Au NPs and pristine MoO3 interlayers are superior to the frequently-used PEDOT:PSS HEL for efficient operation over the long-term. PCE of the MoO3-based OSCs maintains about 40% of their initial value, while a catastrophic failure in the control devices with a PEDOT:PSS HEL is observed after the accelerated aging test under the same condition, with a high relative humidity of 90% at room temperature for 180 min. The degradation behavior of different OSCs performed in the accelerated aging test correlates well with light-intensity JV characteristic and TPC measurements. The outcomes of this work help to the creation of device knowledge and process integration technologies for realization of high performance solution-processed OSCs. It is anticipated that the adoption of the affordable organic photovoltaic technology as one of the clean energy sources will contribute to the preservation of the environment.

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Architecture today is misunderstood. This statement does not engage in the tectonic, programmatic, systemic or contextual aspects of the art, but involves the presence of architectural meaning and experience. Therefore this depravity does not apply to the general public alone, but also to us, the architects. If we don’t understand architecture, how could we begin to understand our relation to it? I believe that this is because much of today’s architecture doesn’t have the tools to reveal itself. In most religions there is a spiritual significance to light. In the Christian faith, scripture reveals our relationship to light. The Gospel of John 12:35b says: "walk while ye have the light, lest darkness come upon you: for he that walketh in darkness knoweth not whither he goeth’’. In the context of the scriptures, man orientates himself in this world by way of light/God (1 John 1:5 – God is light, and in Him is no darkness). This is where he finds his identity and how he understands his existence. If Light (nature and character of God, whole being) is not present, he cannot understand living, nor find meaningful discourse in it. In Silence and Light Louis Kahn (2005) says that with Architecture, the religion is light, it is the giver of all presence, it gives room to the day and brings the season into the room. In our existence that we skillfully conduct amid the biosphere and the first heaven, the matter of architecture and light is very significant. Everyone understands light on a subconscious level; it is ingrained in our composition. Light was created as a precondition for life. Louis Kahn (Silence and Light, 2005) states that everything is spent light, even our bodies. / Dissertation (MArch(Prof))--University of Pretoria, 2008. / Architecture / unrestricted