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- Hamed, Tareq Abu, et al.
(författare)
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Multiscale in modelling and validation for solar photovoltaics
- 2018
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Ingår i: EPJ Photovoltaics. - : EDP Sciences. - 2105-0716. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges.
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| 2. |
- Khan, Azam
(författare)
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Analysis of the piezoelectric and current transport properties of zinc oxide nanostructures grown on fiber
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It seems that nowadays the world is becoming as a small village due to the advancement in communication devices technology. These devices are playing an important role in the wellbeing of our life as almost each and every person is utilizing at least one of these devices. These devices consume energy and with our increased use of technology, we are faced with energy crises. Therefore, the research community is keen in trying to explore alternative resources. One possibility is to search for the alternative resources from our environment. The attempt in this thesis was to utilize the piezoelectric properties by harvesting electrical energy from nanostructures. By utilizing the piezoelectric property of some materials, mechanical energy can be harvested as electrical output. It is worth mention that the ambient mechanical energy is the most available source of energy around us. Hence it is of interest to utilize it to develop future smart devices having the self-powered property. In this connection various experimental and mathematical techniques have been utilized for achieving this target.In this thesis zinc oxide (ZnO) nanostructures grown on textile substrates were the material. The use of textile as substrate is quite unique property of the presented work. Since textile is an essential and fundamental component of our everyday lives, therefore the use of textile as substrate can pave the way for the fabrication of novel self-powered devices. As in comparison with conventional and expensive substrates textile is very economical, lightweight, highly flexible, recyclable, reproducible, disposable, wearable and washable.I started my research work by integrating ZnO nanorods based nanogenerator on conductive textile fiber for the analysis of piezoelectric properties of ZnO nanorods. The acceptance of my work among the research community encouraged me to continue with it in order to improve the performance of the fabricated device. It is well known that piezoelectricity is a linear electromechanical coupling of the material in which mechanical energy is converted into electrical energy. Therefore, the piezoelectric properties of ZnO nanorods were investigated with regard to different physical parameters. In the electromechanical phenomena the analysis of the direct and the converse piezoelectric effect is also critical if conductive textile is used as a substrate. Therefore analysis of the direct and the converse piezoelectric effect was performed for ZnO nanowires grown on conductive textile fiber by using the nanoindentation method.Since the morphology of ZnO nanostructures can have an influence on the piezoelectric properties, the energy harvesting properties of ZnO nanoflowers were investigated and the achieved results confirmed that morphology has a strong influence on the piezoelectric properties. In addition, since there is an interest to generate a direct current (DC) piezoelectricity, a Schottky junction fabricated to one side of the nanogenerator material is needed. Therefore, ZnO nanorods based Schottky diode (Cu/ZnO) on textile fabric was fabricated and investigated. Moreover, frequency dependence electrical characterization was performed for analysis of current-transport properties of another Schottky diode (Au/ZnO) for understanding the carrier flow at the interface of the metal-semiconductor. Nevertheless, the consistency and stability of the constructed devices (ZnO nanogenerators and Schottky diodes) need some additional work to overcome these problems to achieve commercial realization of these devices in the future.
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| 3. |
- Noroozi, Mohammad, 1979-
(författare)
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Growth, processing and characterization of group IV materials for thermoelectric applications
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Discover of new energy sources and solutions are one of the important global issues nowadays, which has a big impact on economy as well as environment. One of the methods to help to mitigate this issue is to recover wasted heat, which is produced in large quantities by the industry, through vehicle exhausts and in many other situations where we consume energy. One way to do this would be using thermoelectric (TE) materials, which enable direct interconversion between heat and electrical energy. This thesis investigates how the novel material combinations and nanotechnology could be used for fabricating more efficient TE materials and devices.The work presents synthesis, processing, and electrical characterization of group IV materials for TE applications. The starting point is epitaxial growth of alloys of group IV elements, silicon (Si), germanium (Ge) and tin (Sn), with a focus on SiGe and GeSn(Si) alloys. The material development is performed using chemical vapor deposition (CVD) technique. Strained and strain-relaxed Ge1-x Snx (0.01≤x≤0.15) has been successfully grown on Ge buffer and Si substrate, respectively. It is demonstrated that a precise control of temperature, growth rate, Sn flow and buffer layer quality is necessary to overcome Sn segregation and achieve a high quality GeSn layer. The incorporation of Si and n- and p-type dopant atoms is also investigated and it was found that the strain can be compensated in the presence of Si and dopant atoms. Si1-xGexlayers are grown on Si-on-insulator wafers and condensed by oxidation at 1050 ᵒC to manufacture SiGe-on-insulator (SGOI) wafers. Nanowires (NWs) are processed, either by sidewall transfer lithography (STL), or by using conventional lithography, and subsequently manufactured into nanoscale dimensions by focused ion beam (FIB) technique. The NWs are formed in an array, where one side is heated by a resistive heater made of Ti/Pt. The power factor of NWs is measured and the results are compared for NWs manufactured by different methods. It is found that the electrical properties of NWs fabricated with FIB technique can be influenced due to Ga doping during ion milling.Finally, the carrier transport in SiGe NWs formed on SGOI samples is tailored by applying a back-gate voltage on the Si substrate. In this way, the power factor is improved by a factor of 4. This improvement is related to the presence of defects and/or small fluctuation of nanowire shape and Ge content along the NWs, generated during processing and condensation of SiGe layers. The SiGe results open a new window for operation of SiGe NWs-based TE devices in the new temperature range of 250 to 450 K.
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| 4. |
- Tahira, Aneela, 1985-
(författare)
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Electrochemical water splitting based on metal oxide composite nanostructures
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The occurrence of available energy reservoirs is decreasing steeply, therefore we are looking for an alternative and sustainable renewable energy resources. Among them, hydrogen is considered as green fuel with a high density of energy. In nature, hydrogen is not found in a free state and it is most likely present in the compound form for example H2O. Water covers almost 75% of the earth planet. To produce hydrogen from water, it requires an efficient catalyst. For this purpose, noble materials such as Pt, Ir, and Ru are efficient materials for water splitting. These precious catalysts are rare in nature, very costly, and are restricted from largescale applications. Therefore, search for a new earth-abundant and nonprecious materials is a hot spot area in the research today. Among the materials, nanomaterials are excellent candidates because of their potential properties for extended applications, particularly in energy systems. The fabrication of nanostructured materials with high specific surface area, fast charge transport, rich catalytic sites, and huge ion transport is the key challenge for turning nonprecious materials into precious catalytic materials. In this thesis, we have investigated nonprecious nanostructured materials and they are found to be efficient for electrochemical water splitting. These nanostructured materials include MoS2-TiO2, MoS2, TiO2, MoSx@NiO, NiO, nickeliron layered double hydroxide (NiFeLDH)/Co3O4, NiFeLDH, Co3O4, Cu-doped MoS2, Co3O4- CuO, CuO, etc. The composition, morphology, crystalline structure, and phase purities are investigated by a wide range of analytical instruments such as XPS, SEM, HRTEM, and XRD. The production of hydrogen/oxygen from water is obtained either in the acidic or alkaline media. Based on the functional characterization we believe that these newly produced nanostructured materials can be capitalized for the development of water splitting, batteries, and other energy-related devices.
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