The 2016 MRS Spring Meeting was held from March 28 – April 1 in Phoenix, Arizona. Recorded highlights include a number of sustainability-oriented talks, three tutorial sessions and more.
Photovoltaic industry today is one of the most rapidly growing sectors in the United States and is anticipated to capture 10% of the total renewable energy produced by 2020. However, cost/PV efficiency remains one of the key challenges for its ubiquitous deployment. Solution processing of semiconductor and nanomaterial thin-films provides a direct route to reduce the costs. However second and third generation solar cell technologies, in spite of extensive development for over 25 years has been limited due to the inadequate power conversion efficiency (PCE~10%) A fundamental critical bottleneck of wet-lab processed thin-film technologies is the material’s polydispersity that leads to the presence of multiple interfaces and defects/trap sites resulting in high carrier losses and low stability. Recent discovery of organic-inorganic (also known as hybrid) perovskites such as CH3NH3PbX3 (X = Cl, Br, I) for photovoltaic devices has reached 20% in merely 3-5 years and offer extraordinary potential for clean sustainable energy technologies and in general low-cost optoelectronic devices. In spite of the recent progress there exists tremendous variability in the structural and optoelectronic properties of the hybrid perovskite thin-films across the globe. Crystallinity, defect density and impurities are in general determining factors for optoelectronic properties, which are also highly dependent on the materials formation processes. Apart from these the stability and reliability of perovskite based devices remains open questions and perhaps will determine the fate of this remarkable technology in the longer run.
In this talk, I will describe our recent work on a novel solution-processing technique termed as “hot-casting” to grow continuous, pin-hole free thin-films of organometallic perovskites with millimeter-scale crystalline grains. Photovoltaic devices show hysteresis-free response, with high degree of reproducibility, thus overcoming a fundamental bottleneck for hybrid perovskite devices. Characterization and modeling attribute the improved performance to reduced bulk defects and improved charge-carrier mobility in large-grain devices. In addition, I will describe our most recent efforts on understanding the controlling photo-degradation in these systems. Results demonstrate that the large grain-size perovskite thin-films are not limited by detrimental effects such as ion migration or defect assisted trapping generally reported in perovskite thin-film devices allowing us to probe intrinsic photo-physical processes that lead to the degradation of PCE in perovskite solar cells.
Superior mechanical properties of natural, hierarchical materials have motivated research in developing synthetic materials with biomimetic structures. Carbon nanotubes (CNTs) are a promising synthetic analog to structural biomolecules like collagen, because individual CNTs boast exceptional mechanical properties (100-GPa strength, 1-TPa stiffness), form packed bundles analogous to collagen microfibrils, and can be assembled into more complex 1D (fiber, yarn), 2D (sheet) [1, 2], and 3D (foam, scaffold)  structures. The hierarchical organization of these CNT materials is reminiscent of that of collagen fibers in diverse tissues like tendons and ligaments (1D), skin (2D), and vitreous (3D).
Unfortunately, despite advances in design and processing of bioinspired CNT materials, their macroscale properties have fallen short from those of both individual CNT building blocks as well as their biological counterparts, likely due to inefficient load transfer between hierarchical levels. Drawing structure-property relationships across length scales for hierarchical CNT materials is critical to guide the rational design of their multiscale organization toward resolving these shortcomings, but probing structural characteristics across orders-of-magnitude differences in length scale is challenging.
To address this need, we have developed advanced metrology to map size and order in hierarchically organized, 1D nanostructures spanning four orders of magnitude in length scale - atomic, nano, meso, micro. Using a suite of novel soft and hard X-ray scattering beamlines at the Advanced Light Source (ALS) and Linac Coherent Light Source (LCLS), we quantitatively mapped structural characteristics in self-aligned, anisotropic CNT forests grown by chemical vapor deposition, both spatially within the CNT material and across several length scales (0.1-1000 nm).
Furthermore, we developed a unified analytical model to quantitatively describe the structural hierarchy of aligned CNTs and to extract key structural parameters via curve-fitting of our X-ray scattering data. From the bottom up, our model parameters define the graphitic lattice and wall number (atomic), CNT diameter (nano), CNT bundling and spacing (meso), regular corrugations (micro), and number density (macro), and comparison with electron microscopy reveals good agreement for forests with a wide range of characteristics (e.g., 1-11 walls, 1.5-15 nm diameter, 1010-1012 cm-2 density). Finally, we offer insights into how our methodology and results can inform existing mechanical models and advance hierarchical CNT materials design to match not only the structure but also the properties of biological materials.
Significant research has been carried out since the seventies of the last century on the physical and mechanical properties of NOCMAT as engineering materials at macro, meso, micro and nano levels. A functionally graded distribution of fibers in bamboo has been identified. Gradations were observed in longitudinal and radial directions. Bamboo in its natural habitat acts as a cantilever beam with a fixed support in the soil and is subjected to its own weight and wind load. Therefore, it has a naturally optimized structure to resist bending moments. The strengths are highest along the outside and lowest in the inside surfaces. In general, the strengths are also highest in those sections closer to the ground. Further studies of the fracture and toughening mechanisms in bamboo structures were carried out which will be presented in this Symposium. An advanced research on Non-Conventional Materials and Technologies (NOCMAT) has shown that it is now possible to produce high performance Fibre Reinforced Composites (FRC) and bamboo composites meeting any engineering demand. Therefore the challenge of the 21st century is to meet the need for cost-effective, durable and eco-friendly construction materials which will meet the global needs of infrastructure regeneration and rehabilitation which alone can enhance the quality of life for all the peoples of the world and in special in developing countries where these materials exist in abundance. In this presentation it is shown that a judicious combination of pozzolanic/cementitious materials, chemical admixtures fibres and bamboo can produce a wide range of FRC that are durable, strong and stiff, highly crack resistant, very ductile and capable of absorbing large amounts of energy. Such materials will find extensive applications in engineering. In particular, the development of durable natural fibre cement composites and bamboo poses a gigantic challenge to science and skills of engineering, a challenge which, if successful, can create the most exciting, eco-friendly construction material backed by an endless supply of renewable natural resources in our world.Speaker(s):
Megan Robertson, University of Houston
A great challenge to overcome is the replacement of traditional petroleum-based plastics with polymers derived from sustainable, alternative resources. Though there are many facets to the design of truly sustainable materials, including the raw material source, energy demands of processing, and fate of the material post-consumer use, utilization of a more eco-friendly raw material source is an important first step. Ultimately, the full life cycle of the materials must be evaluated, including end-of-life options such as recycling, composting, and disposal in landfills. Of particular interest is the design of structured polymers from sustainable, plant-derived sources with well-defined molecular characteristics and competitive properties to conventional, petroleum-derived materials.
Vegetable oils are an attractive source for polymers, due to their low cost, abundance, annual renewability, and ease of functionalization. Long-chain polyacrylates derived from vegetable oil-based fatty acids were investigated as components of thermoplastic elastomers, polymers which behave as an elastomer at room temperature yet are processable at elevated temperatures. The thermal and mechanical behavior of the polymers was readily tuned through variation of the alkyl side-chain length of the polyacrylate. Surprisingly, the alkyl side-chain length did not impact the thermodynamic interactions between the components of the thermoplastic elastomers. This provides a route to manipulating the physical properties of the polymers through variation of the side-chain length without impacting the phase behavior and morphology. The development of structure-property relationships in these polymers will enable the widespread implementation of fatty-acid derived materials.
Recycled asphalt concrete is an inevitable step in sustainable road transportation. However the amount of recycling allowed in the various layers of the road are limited by national standards. Such standards require that the materials containing recycled elements need to fulfil requirements of all virgin materials. However this does not always take into account the weakness of recycled asphalt; specifically cold temperature behavior as well as raveling. Using a multi scale approach, this paper will demonstrate that pavements containing high amounts of recycled asphalt can result in chemical, mechanical and rheological properties that are equal to materials made of all virgin elements. Important parameters such as water sensitivity, fatigue behavior, permanent deformation, and cold temperature behavior are among the characteristics that are investigated. Of particular importance is the blending of the old materials with the new ones. Environmental scanning electron microscopy has shown that the blending is non uniform. Regions have been identified where the materials were well blended whereas in other regions formation of micro-cracks could be established.Speaker(s):
The National Science Foundation created an umbrella program in 2010 entitled, Science, Engineering and Education for Sustainability (SEES) that encouraged cross-disciplinary cooperation to address the complex systems-level problems related to sustainable development. The Division of Materials Research (DMR) actively participated in two programs under the SEES umbrella: Sustainable Energy Pathways (SEP) and Sustainable Chemistry, Materials and Engineering (SusChEM). This presentation will showcase some of the funded projects and highlight outcomes, especially those related to new research partnerships developed for working towards the sustainable development of materials. New opportunities at NSF including a new initiative started in FY15, Innovations at the Nexus of Food, Energy, and Water (INFEWS) will also be discussed.Speaker(s):
Sustainability has become mainstream in both management practice and management research. Firms incorporate sustainability strategies into their core mission. University administrators promote sustainability as central to their curricula. Scholars pursue sustainability as a bona fide field of research inquiry. Given this level of attention and action, the world should be on the road to a sustainable future. But it is not. Environmental and social problems continue to get worse. This paper presents a model for understanding the progression of punctuated social change within the market that has taken us to the present reality, moving through three waves from 1970 to the present. We then present an assessment of where we may be going in the fourth wave, a punctuated shift that is predicated on the notion that we are now living in the Anthropocene, a new geologic epoch in which human activities have a significant impact on the Earth’s ecosystems. We present six elements of change within management systems that are reflected in the Anthropocene: systems thinking, which leads to new forms of: partnerships, materials use and supply chains, domains of corporate activity, organizations, and the economic models and metrics that are used to measure them.Speaker(s):
Today, more than ever, consumers are considering sustainability in their purchasing decisions. Worldwide more than 460 ecolabels are used to identify the sustainable attributes of products within markets. The White House has issued Executive Orders requiring federal agencies to ensure that sustainability is included to federal purchasing criteria. Nearly every state has established procurement procedures that consider sustainability as a purchasing condition. Within this setting, businesses have significant incentives to reexamine their existing production processes and materials use, and incorporate sustainability principles into their business routines. However, in spite of the emerging institutional arrangements, most products are still produced unsustainably. This presentation offers a framework for understanding why, and elaborates on the sorts of change needed to encourage firms to produce more sustainable products and for consumers to purchase them. It emphasizes the opportunity created for materials scientists to innovate as firm/consumer incentives and demands align, and how material scientists can stay ahead of market trends, thus encouraging technology adoption and relevance.Speaker(s):
This session, featuring a panel discussion by industry representatives, is motivated by the recognition that sustainability will be improved only if industry takes a leading role in the development of better practices and innovative technologies. It will help materials researchers better understand the sustainability-oriented considerations and constraints of industry as well as identify critical areas of concern to industry that could benefit from innovative research. The panelists will discuss sustainable supply chains, including how companies consider factors like resource availability, environmental and human health risks, other life cycle impacts, financial considerations, and regulation. In this context, the panelists will also identify key areas of opportunity for materials research to help mitigate supply chain risks and create more sustainable product life cycles.Speaker(s):
We have recently demonstrated a revolutionary membrane design based on hierarchical assembly of fibrous materials with different fiber diameters (nm to μm). This design has led to breakthrough filtration performance from microfiltration to reverse osmosis, i.e., high flux, low energy and small system footprint. The key components of this technology are electrospun nanofibers (dia. ~100 nm) and carboxylate cellulose nanofibrils (dia. ~5 nm) extracted from biomass using a combined TEMPO-oxidation/defibrillation method. These nanofibers have large surface-to-volume ratio and high capacity for surface modification/charge, making them ideal materials for fabrication of highly permeable separation media, e.g., microfiltration filter that can simultaneously remove bacteria, viruses and toxic metal ions at gravity pressure. We further discovered that a simple two-chemical process can produce carboxylate nanocelluloses of different dimensions fusing biomass from different source. This ‘green’ method can bypass both electrospinning and conventional nanocellulose fabrication steps (extraction/pretreatment, bleaching and TEMPO oxidation) and generate inexpensive new nanostructured materials for water purification in a very sustainable manner.Speaker(s):