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March 10, 2011
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March 10, 2011
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March 10, 2011
Abstract
Recent progress in the development of nanostructured inorganic solar cells is reviewed. Nanostructuring of inorganic solar cells offers the possibility of reducing the cost of photovoltaics by allowing smaller amounts of lower-grade photovoltaic semiconductors to be used. Various fabrication methods used to nanostructure traditional photovoltaic semiconductors are detailed and the performance of resulting devices is discussed. The synthesis of solar cells by solution-based methods using less traditional, abundant materials is identified as a promising route to widescale photovoltaic electricity generation, and nanostructured solar cell geometries are highlighted as essential in this approach. Templating and self-assembling methods used to produce appropriate low-cost nanostructures from solutions are detailed, and the performance of preliminary ultra-low-cost cells made with these structures is reviewed.
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The vision of organic photovoltaics is that of a low cost solar energy conversion platform that provides lightweight, flexible solar cells that are easily incorporated into existing infrastructure with minimal impact on land usage. Polymer solar cells have been a subject of growing research interest over the past quarter century, and are now developed to the point where they are on the verge of introduction into the market. Towards the goal of continuing to improve the performance of polymer solar cells, a number of avenues are being explored. Here, the focus is on optimization of device performance via the development of a more fundamental understanding of device parameters. The fundamental operating principle of an organic solar cell is based on the cooperative interaction of molecular or polymeric electron donors and acceptors. Here the state-of-the-art in understanding of the physical and electronic interactions between donor and acceptor components is examined, as is important for understanding future avenues of research and the ultimate potential of this technology.
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In this paper we present the design and synthesis of 25 new low band gap polymers. The polymers were characterized by UV-vis spectroscopy which showed optical band gaps of 2.0–0.9 eV. The polymers which were soluble enough were applied in organic photovoltaics, both small area devices with a spin coated active layer and in large area modules where all layers including the active layer were either roll-to-roll coated or printed. These experiments showed that the design of polymers compatible with roll-toroll coating is not straightforward and that there are various issues such as donor/acceptor fitting within the polymer, side chains to ensure solubility and HOMO/LUMO level alignment with the acceptor (e.g. [60]PCBM) to take into consideration.
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March 10, 2011
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Tandem structures can boost the efficiency of organic solar cell to more than 15%, compared to the 10% limit of single layer bulk heterojunction devices. Design and fabricating of intermediate layers plays a very important role to achieve high device performance. This article will review the main experimental progresses of tandem organic solar cells, and focus on the intermediate layers (charge recombination layers) in both thermal evaporated and solution processed organic tandem solar cell devices.
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March 10, 2011
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Concerns about the availability of petroleum-derived fuels and chemicals have led to the exploration of metabolically engineered organisms as novel hosts for biofuels and chemicals production. However, the complexity inherent in metabolic and regulatory networks makes this undertaking a complex task. To address these limitations, metabolic engineering has adapted a wide-variety of tools for altering phenotypes. In this review, we will highlight traditional and recent metabolic engineering tools for optimizing cells including pathway-based, global, and genomics enabled approaches. Specifically, we describe these tools as well as provide demonstrations of their effectiveness in optimizing biofuels production. However, each of these tools provides stepping stones towards the grand goal of biofuels production. Thus, developing methods for largescale cellular optimization and integrative approaches are invaluable for further cell optimization. This review highlights the challenges that still must be met to accomplish this goal.
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March 10, 2011
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Few non-noble metal based anode and cathode materials were investigated for all solar electrolysis of water to hydrogen and oxygen gases powered by double junction amorphous silicon (Dj-a-Si) solar cell under solar simulated light of 1 sun. The highest hydrogen generation current efficiency of 58.68% was obtained when Pt wire was used as a cathode with the non-noble metal based Ni-Co 3 O 4 as an anode in the electrochemical cell. However, when Pt metal was replaced by a non-noble metal Ni as cathode, the maximum hydrogen generation current efficiency of 51.28% was observed. This corresponds to a 7.4% loss in current efficiency when Pt cathode was replaced by Ni. The percent solar to hydrogen conversion efficiencies (% STH) were found to be 8.66% and 7.57% for the Dj-a-Si solar cell driven electrolysis of water in the Ni-Co 3 O 4 ‖Pt and non-noble metal based Ni-Co 3 O 4 ‖Ni electrochemical cells respectively. Notably, the lowest hydrogen generation current efficiency of 36.33% and % STH efficiency of 5.36% were obtained when Pt metal was used as both anode and cathode in Pt‖Pt electrochemical cell.
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February 21, 2011
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The observed adsorption of methylene blue, MB + , on P25 titania over a range of pH values (pH 2–11) is reported and the results fitted to a charge distribution, multisite complexation, i.e. CD-MUSIC, model, modified for both monomer and aggregated dye adsorption and (for aggregates) co-adsorption of hydroxyl ions. The rate of bleaching of MB + , photocatalysed by titania using UV light, increases over the pH range 4–11 in much the same way the amount of adsorbed MB + , [MB + ] ads , increases, indicating that the rate-determining step involves direct hole oxidation of adsorbed MB + . In contrast, at pH 2, the rate of UVA dye photobleaching appears unduly high but is due to an additional reductive, as well as the usual oxidative, bleaching processes. The initial rate of bleaching of MB + via a visible light-driven, dye-sensitised process, measured at different pH's correlates with the associated CD-MUSIC-calculated values of [MB + ] ads , indicating that only dye molecules that are in direct contact with the surface can undergo photodegradation via a dye-sensitised route.
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March 10, 2011
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The two largest producers of biofuels in the world, Brazil and U.S., both have various policy initiatives designed to meet a significant portion of their need for transportation fuels from biofuels. However, the structure of bio biofuel demand and vehicle fleets varies widely between these two economies, affecting the level of absorption of biofuels by the refiners and final consumers of each country. The relative prices of biofuels to conventional fuel prices (gasoline and diesel) determine consumers' demand not only for biofuels and but also for alternative fuel vehicles. The vehicle fleet structure, in turn, determines the ability of the transportation sector to absorb biofuels. Brazil, with its low costs of production, can sell ethanol at a competitive level with gasoline, which allows ethanol demand to expand and vehicle fleet to transform. U.S., on the other hand, cannot sell ethanol competitively. This limits market expansion and vehicle fleet transformation in the U.S., which, in turn, hinders its ability to achieve policy targets. With many countries taking initiatives to meet a large share of their transportation fuel needs from biofuels, the experiences of U.S. and Brazil provide valuable lessons for policy makers, where an in-depth analysis of the inter-linkages among relative prices, biofuel demand, and vehicle fleet structure prove to be crucial for successful and effective policy making.
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March 10, 2011
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This study examines food-fuel trade-offs from the perspective of crop producers and their choices in marketing their grain among food, feed and fuel use. Based on a recent survey of Iowa grain producers, this study finds that price competition from ethanol plants has increased the share of the corn marketed directly to ethanol plants and lowered the market share of corn marketed for domestic and international food/feed purposes. Other factors, such as farm size and market distance, affect the share of corn directed to the fuel, food, and feed markets. The results indicate corn producers are willing to bear higher transportation costs to reach food markets over other market outlets.
