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Kumar N.,Indian Institute of Technology Ropar | Wilkinson T.M.,Colorado School of Mines | Packard C.E.,National Center for Photovoltaics | Kumar M.,Indian Institute of Technology Ropar
Journal of Applied Physics | Year: 2016

The development of efficient and reliable large-area flexible optoelectronic devices demands low surface roughness-low residual stress-high optoelectronic merit transparent conducting oxide (TCO) thin films. Here, we correlate surface roughness-residual stress-optoelectronic properties of sputtered amorphous indium zinc oxide (a-IZO) thin films using a statistical design of experiment (DOE) approach and find a common growth space to achieve a smooth surface in a stress-free and high optoelectronic merit a-IZO thin film. The sputtering power, growth pressure, oxygen partial pressure, and RF/(RF+DC) are varied in a two-level system with a full factorial design, and results are used to deconvolve the complex growth space, identifying significant control growth parameters and their possible interactions. The surface roughness of a-IZO thin film varies over 0.19 nm to 3.97 nm, which is not in line with the general assumption of low surface roughness in a-IZO thin films. The initial regression model and analysis of variance reveal no single optimum growth sub-space to achieve low surface roughness (≤0.5 nm), low residual stress (-1 to 0 GPa), and industrially acceptable electrical conductivity (>1000 S/cm) for a-IZO thin films. The extrapolation of growth parameters in light of the current results and previous knowledge leads to a new sub-space, resulting in a low residual stress of -0.52±0.04 GPa, a low surface roughness of 0.55±0.03 nm, and moderate electrical conductivity of 1962±3.84 S/cm in a-IZO thin films. These results demonstrate the utility of the DOE approach to multi-parameter optimization, which provides an important tool for the development of flexible TCOs for the next-generation flexible organic light emitting diodes applications. © 2016 Author(s). Source

News Article
Site: http://news.mit.edu/topic/mitenergy-rss.xml

As the need to address climate change becomes more and more pressing, it is more critical than ever for women to have equal opportunities to participate in all aspects and at all levels of climate and energy research, policy, business, and other areas. Since 2010, the multi-governmental Clean Energy Ministerial (CEM) has recognized this imperative with the Clean Energy, Education, and Empowerment (C3E) women’s initiative. In 2012, the CEM — along with the U.S. Department of Energy (DOE) and the MIT Energy Initiative (MITEI) — launched the C3E Women in Clean Energy Symposium and Awards as an annual conference celebrating women energy professionals, from students to mid-career and senior leaders. This year, the conference highlighted ways in which women around the world are leading and changing the energy sector to sustainably meet global energy needs while substantially reducing greenhouse gas emissions. Hosted on May 31 in Palo Alto at the Precourt Institute for Energy at Stanford University — which has joined MITEI and DOE as a partner in the U.S. C3E initiative — and held in the same week as the U.S.-hosted meeting of the CEM in San Francisco, the 2016 C3E Symposium drew leaders from across the globe. The timing with the CEM meeting also offered synergies in speakers and themes. “This year’s C3E Symposium presented a special opportunity to engage with the Clean Energy Ministerial, where our ambassadors, awardees, and other members of the C3E network helped shape the global dialogue on deploying clean, affordable, and plentiful energy sources that meet the world’s needs while curbing climate change,” said Martha Broad, executive director of MITEI, who is also one of C3E’s U.S. ambassadors. Keynote speakers included U.S. Secretary of Energy Ernest Moniz; U.S. Deputy Secretary of Energy Elizabeth Sherwood-Randall; Mary Nichols, chair of the California Air Resources Board; Joan MacNaughton, executive chair of the World Energy Trilemma for the World Energy Council; and Mechthild Wörsdörfer, director for Energy Policy at the European Commission. While previewing topics that he and his international counterparts would examine during the CEM meeting, Secretary Moniz discussed C3E’s history and the future of energy. Following an introduction by his current energy advisor and former executive director of MITEI Melanie Kenderdine, he reflected on the first C3E symposium held at MIT, saying, “I’ll never forget the enthusiasm and the networking that took place at that meeting. That clearly meant that we had to continue.” Moniz also underscored the “economic imperative” to rapidly develop U.S. clean energy markets in the global push for low-carbon energy. Making good on the Paris agreements will require “multiple dimensions of innovation,” he said, including innovations in technology, systems, policy, business models, and more. He noted, in particular, the necessity of “innovative approaches to bringing energy services to [the] too many underserved throughout the world.” In this vein, Moniz lauded C3E’s “increased international flavor,” saying, “I think it’s a fabulous evolution, and I think it is really important for us to continue what we are doing here in the United States, but also to see this initiative growing in so many of our partner countries.” A panel on clean energy in emerging economies encouraged audience members to keep thinking internationally about energy challenges. Panelist Nicole Poindexter, CEO and co-founder of Energicity, a startup working to bring power to rural Ghana, stressed the significance of electricity as a basic human right. “Every aspect of life that you are familiar with is impossible [without] stable, reliable power,” Poindexter said, going on to discuss how electrifying rural communities could be life-changing for the inhabitants: keeping businesses operating, generating new economic opportunities, and preventing food from rotting with cold storage, to name a few benefits. “We have the opportunity to pull a continent out of extreme poverty, just by this one act.” The C3E Awards for mid-career women have been a vital element of the program since its inception. This year, eight clean energy leaders received awards in specific categories. A ninth recipient, Sarah Kurtz, received a lifetime achievement award for her work advancing renewable energy. She is a world-renowned solar photovoltaics expert who holds roles as a research fellow and co-director at the National Center for Photovoltaics, and as principal scientist and reliability group manager at the National Renewable Energy Laboratory. Upon acceptance of her lifetime achievement award, Kurtz said, “It is a very special privilege to be given this award. There are a lot of problems out there, and if at the end of our lives we can say we’ve made some small amount of difference, that means a lot.” C3E ambassador Sally Benson, co-director of the Precourt Institute and director of Stanford’s Global Climate and Energy Project, said, “The nine women honored today represent nearly every facet of clean energy, from policy and finance to technology and entrepreneurship. Their remarkable accomplishments are a clear sign that the gender gap is finally beginning to narrow for women in clean energy and other professionals related to sustainability.”

The Global Alliance of Solar Energy Research Institutes (GA-SERI) convened a worldwide gathering of 50 experts from Germany, Japan, the United States and elsewhere to discuss the future of PV. Representatives from research institutes, industry and funding and financial organizations met in Freiburg, Germany, for the initial GA-SERI Terawatt Workshop. Discussions centered on the challenges that must be overcome to transform the energy system and enable PV to supply a major portion of the world's energy in the coming decades. "PV is on a pathway to low cost," said Greg Wilson, director of NREL's Materials Applications and Performance Center and co-director of the National Center for Photovoltaics, who attended the workshop. "When you add PV to inexpensive storage or another means of introducing flexibility into the grid, PV can be attractive as a primary energy source." Workshop participants expressed confidence that a substantial expansion of manufacturing capacity will be spurred on by demand for PV catching up to supply. This renaissance of growth will carry PV to a new level of energy impact - to the terawatt (TW) scale, where 1 TW equals 1,000 gigawatts (GW). Annual global PV installations reached 60 GW in 2015, which is approaching global production capacity. In view of drastically reduced PV costs, cumulative global installations in excess of 3 TW are anticipated by 2030, provided current research and development (R&D) and investment paths are continued. PV cost projections make this technology increasingly attractive for low-cost domestic electricity supply. To provide a major contribution to global climate goals, total installations on the order of 20 TW will be needed by 2040. This will require stable PV R&D support worldwide and systemic investments targeted at reducing production costs, increasing efficiency, and improving reliability. An increasingly flexible electricity grid, increased availability of low-cost energy storage and demand-side management also will play key roles in enabling accelerated PV deployment. In addition to providing a significant fraction of world electricity, PV has the potential to provide low-cost energy for mobility and heating market demands. Following two days of spirited discussions, the group reached a consensus that a fully integrated research program among institutes, universities and industry, spanning both near- and long-term needs, can address challenges to scale up manufacturing and deployment to the levels required. Representatives from the three research institutions and other workshop attendees intend to collaborate on a journal article to better define the barriers that need to be overcome. Explore further: Two-thirds of the world's new solar panels were installed in Europe in 2011

Razykov T.M.,Academy of Sciences of Uzbekistan | Razykov T.M.,Solar Energy Research Institute | Amin N.,Solar Energy Research Institute | Ergashev B.,Academy of Sciences of Uzbekistan | And 8 more authors.
Applied Solar Energy (English translation of Geliotekhnika) | Year: 2013

CdTe films with different compositions (Cd-rich, Te-rich and stoichiometric) were fabricated by revolutionary novel and low cost chemical molecular beam deposition (CMBD) method in the atmospheric pressure hydrogen flow. Cd and Te granules were used as precursors. The films were deposited on ceramic (SiO2: Al2O3) substrates at 600 C. The growth rate was varied in the range of 20-30 Å/s. The composition of the samples was changed by controlling the molecular beam intensity (MBI) ratio Cd/Te. Effect of CdCl2 treatment on morphology, photoluminescence and electrical properties of CdTe films was investigated by AFM, Raman, photoluminescence (PL) and Hall methods. © 2013 Allerton Press, Inc. Source

Kumar M.,Colorado School of Mines | Sigdel A.K.,University of Denver | Sigdel A.K.,National Center for Photovoltaics | Gennett T.,National Center for Photovoltaics | And 5 more authors.
Applied Surface Science | Year: 2013

With recent advances in flexible electronics, there is a growing need for transparent conductors with optimum conductivity tailored to the application and nearly zero residual stress to ensure mechanical reliability. Within amorphous transparent conducting oxide (TCO) systems, a variety of sputter growth parameters have been shown to separately impact film stress and optoelectronic properties due to the complex nature of the deposition process. We apply a statistical design of experiments (DOE) approach to identify growth parameter-material property relationships in amorphous indium zinc oxide (a-IZO) thin films and observed large, compressive residual stresses in films grown under conditions typically used for the deposition of highly conductive samples. Power, growth pressure, oxygen partial pressure, and RF power ratio (RF/(RF + DC)) were varied according to a full-factorial test matrix and each film was characterized. The resulting regression model and analysis of variance (ANOVA) revealed significant contributions to the residual stress from individual growth parameters as well as interactions of different growth parameters, but no conditions were found within the initial growth space that simultaneously produced low residual stress and high electrical conductivity. Extrapolation of the model results to lower oxygen partial pressures, combined with prior knowledge of conductivity-growth parameter relationships in the IZO system, allowed the selection of two promising growth conditions that were both empirically verified to achieve nearly zero residual stress and electrical conductivities >1480 S/cm. This work shows that a-IZO can be simultaneously optimized for high conductivity and low residual stress. © 2013 Elsevier B.V. All rights reserved. Source

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