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We propose an antimonide-based quantum cascade design to demonstrate the ratchet mechanism for incorporation into the recently suggested photon ratchet intermediate-band solar cell. We realize the photon ratchet as a semiconductor heterostructure in which electrons are optically excited into an intermediate band and spatially decoupled from the valence band through a type-II quantum cascade. This process reduces both radiative and nonradiative recombination and can thereby increase the solar cell efficiency over intermediate-band solar cells. Our design method uses an adaptive simulated annealing genetic algorithm to determine the optimum thicknesses of semiconductor layers in the quantum cascade, allowing efficient transport (via phonon emission) of the electrons away from the interband active region.

In recent years, evaluating the emissions embodied in trade (EEIT) has become an important area of policy and research. Multiregional input-output (MRIO) analysis, which links producers and final consumers, is a widely-used method for quantifying the EEIT. However, the role of intermediate trade in driving changes in the EEIT is still not fully incorporated in MRIO analysis and as a result poorly understood. Here, we present a framework that separately identifies the drivers of the emissions embodied in the trade of final and intermediate products. We implement this framework in a case study in which we analyse the changes in CO2 emissions embodied in interprovincial trade in China from 2007 to 2012. We find that the largest changes are a rising final demand, which is associated with increased emissions that are to some extent offset by decreasing emissions intensity and changing interregional dependency. Regionally, the rising imports and the growth in final demand in less developed regions in the north and central (e.g., Hebei and Henan) reduced the CO2 emissions outsourced by central coastal regions and drove the traded embodied CO2 flows between the central and western regions. The framework enriches our understanding of the role played by intermediate trade in the relocation of emissions.

AbstractThe intermediate band solar cell (IBSC) concept aims to improve upon the Shockley–Queisser limit for single bandgap solar cells by also making use of below bandgap photons through sequential absorption processes via an intermediate band (IB). Current proposals for IBSCs suffer from low absorptivity values for transitions into and out of the IB. We therefore devise and evaluate a general, implementation‐independent thermodynamic model for an absorptivity‐constrained limiting efficiency of an IBSC to study the impact of absorptivity limitations on IBSCs. We find that, due to radiative recombination via the IB, conventional IBSCs cannot surpass the Shockley–Queisser limit at an illumination of one Sun unless the absorptivity from the valence band to the IB and the IB to the conduction band exceeds ≈36%. In contrast, the introduction of a quantum ratchet into the IBSC to suppress radiative recombination can enhance the efficiency of an IBSC beyond the Shockley–Queisser limit for any value of the IB absorptivity. Thus, the quantum ratchet could be the vital next step to engineer IBSCs that are more efficient than conventional single‐gap solar cells. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

AbstractSteam gasification of biochars has emerged as a promising method for generating syngas that is rich in hydrogen. In this study four biochars formed via intermediate pyrolysis (wood pellet, sewage sludge, rapeseed and miscanthus) were gasified in a quartz tubular reactor using steam. The dynamic behaviour of the process and effects of temperature, steam flow and particle size were studied. The results show that increases in both steam flow and temperature significantly increase the dry gas yield and carbon conversion, but hydrogen volume fraction decreases at higher temperatures whilst particle size has little effect on gaseous composition. The highest volume fraction of hydrogen, 58.7%, was obtained at 750 °C from the rapeseed biochar.