If solar energy is to be a significant component of our energy supply, technologies are required which produce high efficiency solar cells using inexpensive materials and versatile manufacturing processes. Solution-processed materials have been used to create low cost, easily fabricated devices, but have suffered from low power conversion efficiencies. A lack of infrared energy capture limits their efficiency. In this work we develop solution-processed photovoltaic devices using lead sulphide quantum dots and high surface area porous oxide electrodes. The resultant devices have a spectral response from 400 to 1800 nm. In fabricating these devices we utilize crosslinking molecules. We explore the impact crosslinkers have on the mobility and morphology of quantum dot films using field effect transistors and transmission electron microscopy. We also explore a hybrid organic/inorganic route for controlling the net doping in quantum dot films. We investigate the chemical and compositional changes that lead sulphide quantum dots films undergo during crosslinker treatment and annealing. Using this information we optimize our charge separation efficiency and our open circuit voltage. The resulting devices have an infrared power conversion efficiency of 2%, four orders of magnitude higher than that in previously reported lead sulphide quantum dot devices.

No description available.

The grid connected PV plants comprising of the PV cells and the power electronic inverters are a widely used technology in distributed power generation systems based on renewable energy sources. Microinverters form an extensive part of the ongoing research in this field. This thesis focuses on the inverter section of the microinverter. The cost and efficiency of the grid connected inverter is a chief contributing factor in the overall system price. The MOSFETs used in the DC/AC inverter are usually hard switched causing a lot of EMI noise and losses in the inverter. This is true for both, single and three phase inverters. A low switching frequency is desirable to increase the efficiency, which in turn imposes a large compromise in designing the output filter. In this thesis, switching losses have been minimized by incorporating zero voltage switching at switch turn on and variable dead-time control at switch turn off. The soft switching technique is based on control algorithms and involves no use of any auxiliary circuit. Also, the size of the output filter is reduced without increasing the switching frequency, by employing multiple paralleled inverters. The interleaving technique that is usually used in dc/dc converters is extended for dc/ac inverters and is well employed to maintain the quality of the current fed into the utility grid. In this way, at low switching frequency, high efficiency and reduced cost and sizes are achieved. The study is validated through simulation and lab experiments. The novel control circuit was first implemented using analog circuitry. After assessing the performance of the analog version of the proposed controller, it was then digitally implemented through the Field Programmable Gate Array (FPGA) technique. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-04-30 15:06:26.071

No description available.

A successful model that could accurately predict the performances of n+-p-p+ concentrator solar cells should include a model of carrier photogeneration rates consistent with the spectral content of the incident light. Furthermore, a finite back surface recombination velocity should be considered since new techniques such as 'Back Surface Field' were developed to reduce the recombination rate at the rear of the cell.In the present work, a two-dimensional concentrator solar cell is modeled for low levels of injection. The model however, assumes an incident light containing one single wavelength. The incident light is assumed to decrease linearly from the center of the illuminated area until it vanishes at the edges of the cell. Finite recombination velocities are taken into account at the front and the back surfaces. Finite-width space charge regions are also included. The transport equations are solved for the carrier concentrations in different regions of the cell. The current density expressions are derived. The generation of theoretical current voltage characteristics is outlined. However, the use of these characteristics to predict cell performances is left for further research. / Department of Physics and Astronomy

I en tid med allt mer påtagliga miljöhot, ökande CO2-utsläpp och stigande efterfrågan på el är det viktigt att utvecklingen av billig och effektiv förnyelsebar energi fortsätter runt om i världen för att kunna konkurrera mot billigare, icke förnyelsebara, energikällor. Ett steg i detta är att utveckla och effektivisera solkraft till den nivån att länder och företag väljer att investera i solkraft. Mer konkret kan det ske igenom utveckling av nya, mer effektiva, solcellsmoduler. I denna studie ska en ny typ av solcellsmodul, SmartPlus – utvecklat av Innotech Solar, jämföras mot deras standardmodul EcoPlus för att undersöka om den nya modulen kan bidra till högre andel solkraftsgenererad el i Sverige och där med minska CO2-utsläppen. Den nya solcellsmodulen är framtagen för att bättre kunna hantera och ta tillvara på solinstrålningen om en del av modulen utsätts för skugga, därför kommer studien simulera de båda moduler i en solpark där det sker intern skuggning mellan modulraderna. Skuggning av solcellsmoduler leder idag till stora förluster i elproduktionen på grund av nuvarande modellers konstruktion och syftet med studien är att undersöka om den nya solcellsmodulen är effektivare än den standardmodul som används för tillfället. Målet med studien är att skapa och verifiera en simuleringsmodell och simulera en solpark i Sverige där resultatets variation baseras på radavståndet mellan modulraderna och om modulerna är vertikal eller horisontellt placerade för att åstadkomma en variation av skuggning. Den solpark som ger högst elproduktion är en solpark med SmartPlus-moduler horisontell modulplacering, men då tillgången på markyta ofta en begränsande faktor bör vertikal modulplacering alltid föredras. Resultatet visar dock att i valet av modul till en solpark är inte valet mellan SmartPlus och EcoPlus den viktigaste faktorn. Även om SmartPlus genomgående har en högre elproduktion på årsbasis är skillnaden marginell till EcoPlus, däremot har faktorer som radavstånd och modulplacering en större inverkan på elproduktionen och effektiviteten i solparken. / In an era of significant environmental threats, increasing carbondioxide emissions and rising electricity demand, it is important that the development of cheap and efficient renewable energy continues around the world to compete against cheaper, non-renewable, energy sources. To do this, the development of solar power have to continute so that countries and companies choose to invest solar power insteed of non-renewable energy. More specifically, it can be done through the development of new, more efficient, solar  cells modules. In this study, a new sort of solar cell module, SmartPlus - developed by Innotech Solar, is compared to their standard module EcoPlus to investigate whether the new module may contribute to the higher proportion of solar-generated electricity in Sweden and there by reducing carbondioxide emissions. The new photovoltaic module is designed to take better advantage of the solar radiation when a portion of the module is exposed to shade, therefore will this study simulating the two modules in a solar panel plant where there is internal shading between the rows. Shading of photovoltaic modules currently leads to substantial losses in electricity generation because of the modules design and the purpose of the study is to investigate whether the new photovoltaic module are more efficient than the standard solar module that currently is in use. The aim of the study is to create and verify a simulation model and simulate a solar park in Sweden where the results variation depends on the spacing between the rows in the solar panel plant and if the modules are vertically or horizontally positioned to provide a variety of shading. The solar park that provides maximum power generation is a solar park with SmartPlus modules with horizontal position, but since the availability of land is often a limiting factor the vertical position should always be preferred. The result shows that when choosing module to a solar the choice between SmartPlus and EcoPlus is not the most important factor. Even though SmartPlus consistently has a higher electricity production on an annual basis, the difference is marginal to EcoPlus, however, factors such as row spacing and module placement have a far greater impact on electricity generation and efficiency of the solar panel plant.

Field effect transistors (FETs) are a key component of modern electronic devices. They require a semiconducting material that is traditionally made from doped silicon. Recently however it has been shown that porphyrin systems can be used in the same capacity. This thesis therefore describes the investigation of new methods of porphyrin functionalization to synthesise 1,4,5,8-tetraazaanthracene-bridged porphyrin arrays, and their application to the synthesis of extended arrays for use in FETs. The 1,4,5,8- tetraazaanthracene bridge is synthesised through the condensation of a porphyrin alpha-dione with 1,2,4,5-tetraaminobenzene. Accordingly, the synthesis of an extended array requires a porphyrin tetra-one monomer unit. Two methods for the synthesis of porphyrin tetra-ones have been investigated. The first approach attempts to adapt Knudsen's hydroxylation of an aryl halide by sodium benzaldoximate to a porphyrin system. Initial regiospecific halogenation of a porphyrin has been successfully achieved. However when hydroxylation was attempted, partial dehalogenation of the substrate was observed; and when applied to the synthesis of the porphyrin tetra-one the methodology failed. The second approach involves the allylic oxidation of a chlorin (a reduced porphyrin) on silica. The transformation's mechanism has been thoroughly investigated and it has been successfully applied to the synthesis of a porphyrin tetra-one. This methodology has then been applied to the synthesis of extended porphyrin arrays. A sample incorporating 12 porphyrin units has been successfully constructed. It has been characterised by NMR, MALDI, GPC and UV-VIS spectroscopy. By comparison with previous results it has been concluded that the aromatic system- which spans 181 Ǻngstroms from end to end- can be described as a series of weakly interacting chromophores, in agreement with theoretical predictions made by Hush. In addition a medium-scale synthesis of an array incorporating four porphyrins has been achieved so that it may now be tested as the semiconducting material in a FET.

Polymer based photovoltaic cells are being intensively investigated. In such cells three key processes need to occur; namely light absorption, charge separation of the exciton, and transport of the separated charges to the electrodes. Light absorption is reliant on the optical density of the polymer. In general charge separation is achieved by blending an electron acceptor with the polymer film. However, blending materials gives rise to potentially unreliable manufacturing and lifetime issues. This thesis describes the preparation of poly(l,4-phenylenevinylene) derivatives containing dipoles in which the process of charge separation can be achieved intramolecularly. The dipole was created with the use of electron donating alkoxy groups attached to the polymer backbone, and electron withdrawing nitro group attached to the fluorenyl side chains. These groups are believed to facilitate the dissociation of the photogenerated exciton, and potentially stabilise the holes and electrons that are formed when the exciton is separated. The fluorenyl side chains were attached to the polymer backbone via biphenyl or vinyl linkages. The polymers were primarily formed using the Gilch method and the conjugated polymers were obtained either via a soluble precursor route or directly from the monomer. The photophysical properties were studied for polymers with the fluorenyl side-chains as they were found to be more easily formed and stable. For poly[2-(7-nitro-9,9-dipropylfluorenyl)-5-(2'- ethylhexyloxy)-l,4-phenylenevinylene] it was found that the photoluminescence quantum yield dropped by a factor of eight relative to the polymer without the nitro group. It was further elucidated that this was due to the exciton being separated. Solar cells containing the polymers from this study showed modest performance.

If solar energy is to be a significant component of our energy supply, technologies are required which produce high efficiency solar cells using inexpensive materials and versatile manufacturing processes. Solution-processed materials have been used to create low cost, easily fabricated devices, but have suffered from low power conversion efficiencies. A lack of infrared energy capture limits their efficiency. In this work we develop solution-processed photovoltaic devices using lead sulphide quantum dots and high surface area porous oxide electrodes. The resultant devices have a spectral response from 400 to 1800 nm. In fabricating these devices we utilize crosslinking molecules. We explore the impact crosslinkers have on the mobility and morphology of quantum dot films using field effect transistors and transmission electron microscopy. We also explore a hybrid organic/inorganic route for controlling the net doping in quantum dot films. We investigate the chemical and compositional changes that lead sulphide quantum dots films undergo during crosslinker treatment and annealing. Using this information we optimize our charge separation efficiency and our open circuit voltage. The resulting devices have an infrared power conversion efficiency of 2%, four orders of magnitude higher than that in previously reported lead sulphide quantum dot devices.

Solar power is considered a very promising source for electric power generation. The abundance of sunlight over a large area of the earth surface gives rise to several applications of photovoltaic systems. Electricity can be generated from sunlight either directly by employing the photovoltaic effect, or by using energy from the sun to heat up a working fluid that can be used to power up electricity generators. These two technologies are widely used today to provide power to either stand-alone loads or for connection to the power system grid. Maximum power point tracking (MPPT) is a very important consideration that is taken into account when building a new photovoltaic power system. This is needed in order to extract maximum power output from a PV array under varying atmospheric conditions to maximize the return on initial investments. Several techniques have been used to tackle this problem including perturb and observe (P&O), incremental conductance (IncCond) and fuzzy logic based algorithms. Judging between these techniques is based on their speed of locating the maximum power point (MPP) of a PV array under given atmospheric conditions, besides the cost and complexity of implementing them. The P&O and IncCond algorithms have a low implementation complexity but their tracking speed is slow. Fuzzy logic techniques are faster but suffer from high implementation complexity. One of the goals of this thesis is to present an MPPT algorithm implementation that is based on the fractional open circuit voltage method. This technique is easy to implement and offers a fast tracking speed for the MPP of a PV array. It provides an approximation within 4-5% of the maximum power point, which is a tradeoff between the speed and accuracy of operation around the MPP. It offers a speed advantage in grid connected PV systems. The P&O algorithm, which is very common, is difficult to implement under these conditions due to its poor response time. There is also a need for developing control techniques for three phase grid connected PV systems including a method for DC link voltage control that can stabilize the voltage at the inverter input. This area of research is currently growing with the increase in number of PV installations backed up by government incentives in several countries. In addition to the previously mentioned points, this work is intended to be used in further research to replace the representation of PV arrays as a simple DC source when included in power system studies. That is a basic assumption and does not take into consideration the various dynamics caused by changing solar irradiation and surface temperature of the array.