Fall 2016

September 22, 2016

in collaboration with Energy Colloquium

Organic Photovoltaics: the Current State of the Art and the Role of Delocalization

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Dr David Vanden Bout, Department of Chemistry and Biochemistry, University of Texas at Austin, Texas, USA

Organic photovoltaics have long held out promise as an emerging solar energy technology due to their potential for low-cost manufacture and mechanical flexibility.  Despite steady improvements these systems still lag behind in terms of efficiencies required for any significant applications.  One reason is that the best devices have a complex microstructure that is difficult to characterize and for which there remain fundamental questions regarding what limits their ultimate efficiencies.  A broad overview of this class of materials will be presented that will focus on polymer/fullerene blends that have received the most attention.  Recently the role of delocalized states in both the polymer and fullerene in these systems has been of broad interest in terms of understanding the fundamental steps in charge generation.  Results on single polymer spectroscopy studies to examine the extent of this delocalization will be presented.

 Video here

 

 October 27, 2016

Mechanism Design for Learning Agents

Prof. Constantinos Daskalakis,  Electrical Engineering and Computer Science department, Massachusetts Institute of Technology, Cambridge, MA, USAportrait-photo

Combinatorial auctions, the task of allocating items to strategic buyers with combinatorial valuations over bundles, has been a paradigmatic problem for mechanism design. The celebrated VCG mechanism solves the problem, but it is expensive in computation and communication, motivating the search for alternative mechanisms. We overview the advances of algorithmic mechanism design on this subject, and propose an online-learning approach to mechanism design, sidestepping impossibility barriers that have been identified for buyers with submodular valuation functions. (Based on joint work with Vassilis Syrgkanis)

Video here

 

 

 November 10, 2016

Reading Chemical “Fine Print”: The Key to Exploiting Nature’s Compositional Complexity

 

Dr Alan G. Marshmarshall-portraitall, Ion Cyclotron Resonance Program of National High Magnetic Field Lab and Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, USA

Most mass analysis relies on “nominal” mass accuracy (i.e., to within 1 Da).  However, more and more applications are based on much more accurate mass measurement.  Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers 10-1000 times higher mass resolving power than other mass analyzers.

High mass resolving power (m/Dm50% > 1,000,000) offers two major advantages: (a) it becomes possible to separate complex mixtures without prior chromatographic or gel separation; and (b) elemental composition may be determined from accurate (to within less than 100 ppb) mass measurement alone for unknown molecules up to ~1,000 Da.  Examples from environmental, petrochemical, analytical, and biological (e.g., proteomics & lipidomics) problems will be presented.

 

 

November 24, 2016

Computational Design for Solar Energy Harvesting Materials

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Dr Naoto Umezawa, International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, Japan

Solar light is a promising solution to the ever-increasing demand for renewable energy. Solar energy can be converted into electrical and chemical energy by means of photovoltaics and photocatalysis, respectively. In this regard, it is imperative to develop solar energy harvesting materials with good photoabsorption. Such photoabsorbers should possess an electronic structure with a forbidden energy gap, the so-called “band gap”, for efficiently harvesting solar light and generating photoexcited electron-hole pairs. Computational methods have emerged as a powerful tool for the design of energy band structures for semiconductor materials with photoabsorbing capacity.

In this talk, Dr Umezawa present the recent attempts on the computational design of photoabsorbers by band gap engineering. By controlling atomic compositions, crystal structures, or biaxial strains, MANA have attempted to modulate the band structures of several materials and optimize their photoabsorption edges in order to increase the light conversion efficiency. MANA team demonstrated that some of the designed materials exhibit excellent performance for photocatalytic H2 production from aquerous solution under visible-light irradiation. An advanced multi-junction solar cell was also designed based on our theoretical study on mixed-valence tin oxides. Dr Umezawa will also touch upon the limitations of the current computational methods and MANA efforts toward the development of a novel electronic structure calculation method for precisely predicting the materials properties.