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We live at present with a largely linear materials economy. Our use of natural resources is characterized by the sequence “take – make – use – dispose” as materials progress from mine, through product, to landfill. Increasing population, rising affluence and the limited capacity for the planet to provide resources and absorb waste argue for a transition towards a more circular way of using materials (F. Blomsma, and G. Brennan, J. Industrial Ecology 21, 603 (2017); W. McDonough and M. Braungart, Cradle to cradle, remaking the way we make things, (North Point Press, New York, 2002)).
When products come to the end of their lives the materials they contain are still there. Repair, reuse and recycling (the three “Rs”) can return these to active use creating a technological cycle that, in some ways, parallels the carbon, nitrogen cycle and hydrological cycles of the biosphere. Repair, reuse and recycling are not new ideas; they have been used for centuries to recirculate materials and, in less-developed economies, they still are. But in developed nations they dwindled as the cost of materials fell and that of labor rose over time, making all three Rs less attractive. This and the complexity of current products has led to loss reparability and, therefore, reuse. So, what is novel about the contemporary idea of a circular materials economy? Haven’t we been there before?
Over the last decade, the idea of deploying rather than consuming materials, has gained economic as well as environmental appeal. Governments now sign up to programs to foster circular economic ideas and mechanisms begin to appear to advance them. Here we examine the background, the successes and the challenges of implementing a circular materials economy and the degree to which it can deliver the ultimate goal – that of reducing the drain on non-renewable natural resources to as close to zero as possible.
Circular economy (CE) is closely linked with the ideas of a low-carbon economy, management of supply risks, value generation through the service-based economy and efficient resource management. CE implies a design that focusses on material legacy, creating an economy that retains or regenerates materials over many life cycles, hence not consuming but using materials.
Granta Design has a history of involvement with material circularity, through collaborative develop of tools to aid teaching of engineering and design courses and industrial decision-making. The paper concludes with a brief discussion of these.
Thermal evaporation is a simple method to fabricate a BaSi2 film, a new solar cell material consisting of earth-abundant elements. In this study, we optimized the evaporation process and suppressed near-interface oxidation in evaporated BaSi2 films on Si(100) substrates, which has been detected in previous studies. Composition depth profiles determined by Auger electron spectroscopy show the decrease of oxygen concentration near the interface to the background level by optimizing the source pre-melting condition. By reducing oxygen concentration, the BaSi2 film becomes more preferentially oriented toward  as long as the deposition rate is not changed, as evidenced by X-ray diffraction. It is also shown that the rectification behavior of n-BaSi2/p+-Si diodes improves by suppressing the near-interface oxidation.
Environmentally aware automotive manufacturers recycle aluminum production scrap in closed-loop systems to generate environmental and financial savings. Further savings could be gained if material demand is reduced, through improving the material utilization of the production process. Since a more efficient production process generates less scrap, the opportunity for closed loop recycling reduces when material demand reduces. This paper investigates the interaction between material demand reduction and closed loop recycling for an aluminum intensive case-study vehicle. It identifies the greatest environmental and financial savings when both strategies are implemented together. It is shown that a ‘recycled content’ target does not capture these saving opportunities. It is recommended that automotive manufacturers set targets for both material utilization and scrap recovery, to simultaneously promote closed-loop recycling and material demand reduction.
This study provides detailed information on the manufacture of III-V metal organic vapor phase epitaxy precursors through extensive literature and patent research. This data informed a cradle-to-gate life cycle assessment of these chemicals. Reported impacts include cumulative energy demand and greenhouse gas emissions. The results were interpreted to identify sources of environmental burden within the life cycle and were compared to energy demand reported in previous studies.
Soiling in solar power generation will be a significant obstacle to its growth if a water free method cannot be found. Demand for water in arid regions will increase as more solar power generation is built, requiring more water to clean the optical surface, in turn increasing the price of water. This will lead to increased operating costs for solar power generation, and potentially disputes in locations where water is scarce. The electrodynamic screen (EDS) can reduce soiling and contribute to restoring the optical surface without the use of water. Periodic cleaning will still be required, but at reduced frequency, leading to a significant reduction in the consumption of water. In this model, it was found that a 250 MW concentrated solar power plant would have a 74% reduction in water given current laboratory production uncertainties. This indicates that EDS technology could decrease both the operating cost and the water use for solar generation plants.
Surface texturing of transparent conductive oxides is crucial to improve the fraction of incident light trapped in the absorber layer of thin film silicon based solar cells to improve the device performance. In this work, we fabricate and compare periodic, overlapping, and random surface textures and patterns on aluminium doped zinc oxide (AZO) using direct laser processing. The effects of the used laser wavelength, laser operating frequency, and pulse periodicity on the structural, morphological, and optical response of the AZO films were investigated. By optimizing the laser parameters and the associated process conditions, a drastic increase up to 60% in the transmittance haze over the entire solar was achieved.
To improve conversion efficiency of silicon nanowire (SiNW) solar cells, it is very important to reduce the surface recombination rate on the surface of SiNWs, since SiNWs have a large surface area. We tried to cover SiNWs with aluminum oxide (Al2O3) and titanium oxide (TiO2) by atomic layer deposition (ALD), since Al2O3 grown by ALD provides an excellent level of surface passivation on silicon wafers and TiO2 has a higher refractive index than Al2O3, leading to the reduction of surface reflectance. The effective minority carrier lifetime in SiNW arrays embedded in a TiO2/Al2O3 stack layer of 94 μsec was obtained, which was comparable to an Al2O3 single layer. The surface reflectance of SiNW solar cells was drastically decreased below around 5% in all of the wavelength range using the Al2O3/TiO2/Al2O3 stack layer. Heterojunction SiNW solar cells with the structure of ITO/p-type hydrogenated amorphous silicon (a-Si:H)/n-type SiNWs embedded in Al2O3 and TiO2 stack layer for passivation/n-type a-Si:H/back electrode was fabricated, and a typical rectifying property and open-circuit voltage of 356 mV were successfully obtained.
The recently discovered orthorhombic allotrope of silicon, Si24, is an exciting prospective material for the future of solar energy due to a quasi-direct bandgap near 1.3 eV, coupled with the abundance and environmental stability of silicon. Synthesized via precursor Na4Si24 at high temperature and pressure (∼850 °C, 9 GPa), typical synthesis results have yielded polycrystalline samples with crystallites on the order of 20 μm. Several approaches to increase the crystal size have yielded success, including in-situ thermal spikes and refined selection of the starting materials. Microstructural analysis suggests that coherency exists between diamond silicon (d-Si) and Na4Si24. This hypothesis has led to the successful attempts at single crystal synthesis by selecting large crystals of d-Si along with metallic Na as the precursors rather than powdered and mixed precursor material. The new synthesis approach has yielded single crystals of Na4Si24 greater than 100 μm. These results represent a breakthrough in synthesis that enables further characterization and utility. The promise of Si24 for the future of solar energy generation and efficient electronics is strengthened through these advances in synthesis.
A novel preparation method of B-doped p-type BaSi2 (p-BaSi2) is proposed to realize heterojunction crystalline Si solar cells with p-BaSi2. The method consists of thermal evaporation of BaSi2 on B-doped amorphous Si (a-Si). In this study, the effect of a-Si interlayers and substrate temperature during BaSi2 evaporation on the electrical characteristics and crystalline quality of the evaporated films were investigated. While no cracks were found in the BaSi2 films formed using hydrogenated a-Si deposited by plasma enhanced chemical vapor deposition (PECVD), the films formed with sputtered a-Si have cracks. In addition, BaSi2 films formed with a 600 °C substrate temperature using PECVD a-Si showed p-type characteristics. After a post-deposition anneal at 800 °C for 5 minutes, the film hole density was measured at 1.3×1019 cm-3 and boron was found to be uniformly distributed throughout the film. These results show that the proposed method using PECVD is promising to obtain p-BaSi2 thin films with high hole density for p-BaSi2/n-type crystalline Si heterojunction solar cells.