Modeled and Measured Operating Temperatures of Floating PV Modules: A Comparison

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The performance and amphibious operation potential of a new floating photovoltaic technology

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Plasmonic properties of aluminium nanowires in amorphous silicon

Plasmonic structures can help enhance optical activity in the ultraviolet (UV) region and therefore enhancing photocatalytic reactions and the detection of organic and biological species. Most plasmonic structures are composed of Ag or Au. However, producing structures small enough for optical activity in the UV region has proved difficult. In this study, we demonstrate that aluminium nanowires are an excellent alternative. We investigated the plasmonic properties of the Al nanowires as well as the optoelectronic properties of the surrounding a − Si matrix by combining scanning transmission electron microscopy imaging, electron energy loss spectroscopy and electrodynamic modelling. We have found that the Al nanowires have distinct plasmonic modes in the UV and far UV region, from 0.75 eV to 13 eV. In addition, simulated results found that the size and spacing of the Al nanowires, as well as the embedding material were shown to have a large impact on the type of surface plasmon energies that can be generated in the material. Using electromagnetic modelling, we have identified the modes and illustrated how they could be tuned further.publishedVersio

Plasmonic properties of aluminium nanowires in amorphous silicon

Plasmonic structures can help enhance optical activity in the ultraviolet (UV) region and therefore enhancing photocatalytic reactions and the detection of organic and biological species. Most plasmonic structures are composed of Ag or Au. However, producing structures small enough for optical activity in the UV region has proved difficult. In this study, we demonstrate that aluminium nanowires are an excellent alternative. We investigated the plasmonic properties of the Al nanowires as well as the optoelectronic properties of the surrounding aSi matrix by combining scanning transmission electron microscopy (STEM) imaging, electron energy loss spectroscopy (EELS) and electrodynamic modelling. We have found that the Al nanowires have distinct plasmonic modes in the UV and far UV region, from 0.75 eV to 13 eV. In addition, the size and spacing of the Al nanowires, as well as the embedding material were shown to have a large impact on the type of surface plasmons energies that can be generated in the material. Using electromagnetic modelling, we have identified the modes and illustrated how they could be tuned further

Termisk ledningsevne og nanostruktur i La0,7Sr0,3CoO(3-delta) (0 < delta < 0,15)

Termoelektriske moduler har et potensial som en ren og miljøvennlig strømkilde som genererer strøm av spillvarme som ellers går tapt til omgivelsene. Det er derfor stor interesse for å finne effektive termoelektriske materialer som er billige i produksjon og består av miljøvennlige grunnstoffer. La1−xSrxCoO3−delta er studert som et termoelektrisk materiale og for å kunne øke materialets termoelektriske effekt kreves ytterligere forståelse av materialet. I denne oppgaven er struktur og termisk ledningsevne i La0,7Sr0,3CoO3− delta (LSCO) undersøkt ved 0< delta <0,15. Dette er gjort for å undersøke sammenhengen mellom struktur og oksygeninnhold, og hvordan strukturendringer påvirker den termiske ledningsevnen. Oksygeninnholdet i LSCO er målt ved termogravimetri og materialets struktur er undersøkt ved røntgendiffraksjon og transmisjonselektronmikroskopi for delta = 0 og 0,15. Termisk ledningsevne er målt ved ”laserflash” termisk diffusivitetsmetoden og elektrisk ledningsevne er målt ved et van der Pauw oppsett. Fra termogravimetri ble materialets oksygeninnhold funnet å være konstant med hensyn på temperatur og atmosfære (fra O2 til inert gass) for temperaturer lavere enn 400 C . Derfor ble termisk og elektrisk ledningsevne målt for 50 C < T <400 C ved forskjellige oksygenkonsentrasjoner satt ved høyere temperaturer. Den elektriske ledningsevnen er målt for å skille ut ladningsbærernes varmetransport, slik at det strukturelle bidraget til den termiske ledningsevnen kunne bestemmes. Røntgendiffraksjon av LSCO med delta = 0 og delta =0,15 viser at strukturen er henholdsvis trigonal med romgruppe R3 og kubisk med romgruppe Pm-3m. Transmisjonselekronmikroskopi av prøver med høy oksygenvakanskonsentrasjon viser en overstruktur som ikke er tilstede i prøver med delte 0. Overstrukturen er i overensstemmelse med romgruppe P4/mmm hvor oksygenvakansene er lokalisert i (0,5 0,5 0,5)-planet til enhetscellen. Okygenvakansordningen danner domener på størrelser ned til 5 nm. In-situ oppvarming av prøver med oksygenvakansordning fra romtemperatur til 400 C viser at ordningen reduseres ved økende temperatur. Den termiske ledningsevnen avtar med økende oksygenvakanskonsentrasjon, for eksempel er tot ved 50 C 2,28 W/mK og 1,25 W/mK for henholdsvis delta = 0 og delta = 0,15. Denne reduksjonen skyldes både redusert elektrisk ledningsevne som reduserer det elektriske bidraget til tot, men også på grunn av økt fononspredning forårsaket av oksygenvakanser. Resultater i denne oppgaven indikerer også at nanostruktur som følge av oksygenvakansordning gir lavere termisk ledningsevne i La0,7Sr0,3CoO2,85. En dobling av enhetscellevolumet i de tetragonale domenene gir økt Umklappspredning, og dette kan forklare den økte fononspredningen

Characterization and functionalization of self-assembled nanostructures

This thesis presents a study of the nanostructured a-Si:Al consisting of aluminum nanowires with < 5 nm diameter surrounded by amorphous Si. The nanostructure is formed by self-assembly of the nanowires during co-sputtering of silicon and aluminium. The motivation of the work lies in the material properties that can arise when approaching this scale, which makes this material interesting for a broad range of applications. In the last decades, a large research effort has been made towards Si nanostructures and other nanomaterials to develop cheaper and more efficient solutions towards photovoltaic devices and use of silicon in optoelectronic applications. Also, materials consisting of vertically aligned pores with a narrow diameter, as can be achieved by removing the Al NWs from the nanostructured a-Si:Al, can serve as a template for nanowire fabrication useful for a many different applications. The nanostructured a-Si:Al has previously received little attention, and a large number of questions related to fabrication parameters and material properties are unanswered. In this work, we try to unravel some of the material properties and bring more understanding of how the material can move closer to future applications. As removal of the aluminum nanowires is an important step towards these applications, much focus has been on this. By combining the detailed knowledge on the nanoscale available through transmission electron microscopy with simpler, more macroscopic techniques such as UV-Vis spectroscopy, we have shown that the removal process can be monitored by measuring reflectance. Not only may the nanowires be removed by selective etching using acids such as HCl, diluted H2SO4, and H3PO4, but the time it takes and the development on reflectance during etching can provide information on the quality of the wires and the aluminum gradient throughout the film. We hope that these results will aid other researchers in reproducing this unique nanostructured material, as it allows for process control on the nanoscale without the need for characterization by advanced electron microscopy. By combining a variety of characterization methods such as X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and ellipsometric porosimetry we have found that removal of the aluminum nanowires results in a partly oxidized nanoporous a-Si with porosity of 20 - 25 % and peak emission centring at 1.6 eV. Storage in air increases the level of oxidation and changes the emission characteristics. Therefore, a necessary step towards device fabrications may be to coat the nanoporous a-Si with a protective layer. The applicability of atomic layer deposition as a method for this has been proved promising from our experiments on its coating capabilities on narrow diameter anodic alumina

Surface Effects and Optical Properties of Self-Assembled Nanostructured a-Si:Al

We present a study of the surface effects and optical properties of the self-assembled nanostructures comprised of vertically aligned 5 nm-diameter Al nanowires embedded in an amorphous Si matrix (a-Si:Al). The controlled (partial) removal of Al nanowires in a selective etching process yielded nanoporous a-Si media with a variable effective surface area. Different spectroscopy techniques, such as X-ray photoelectron spectroscopy (XPS), UV-Vis spectrophotometry and photoluminescence (PL), have been combined to investigate the impact of such nanostructuring on optical absorption and emission properties. We also examine long-term exposure to air ambient and show that increasing level of surface oxidation determines the oxide defect-related nature of the dominant PL emission from the nanoporous structures. The role of bulk, nanosize and surface effects in optical properties has been separated and quantified, providing a better understanding of the potential of such nanoporous a-Si:Al structures for future device developments

Cooling of floating photovoltaics and the importance of water temperature

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Cooling of floating photovoltaics and the importance of water temperature

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CFD modelling to derive U-values for floating PV technologies with large water footprint

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