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There is now a CONTENT FREEZE for Mercury while we switch to a new platform. It began on Friday, March 10 at 6pm and will end on Wednesday, March 15 at noon. No new content can be created during this time, but all material in the system as of the beginning of the freeze will be migrated to the new platform, including users and groups. Functionally the new site is identical to the old one. webteam@gatech.edu
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Professor Stephen Forrest, University of Michigan, Departments of Electrical Engineering and Computer Science, and Physics
Title: Blue phosphorescent OLEDs: Is there a future for them in displays and lighting?
Abstract
Since its first demonstration in 1998, electrophosphorescence has yielded 100% internal quantum efficiency OLEDs (PHOLEDs) across the color gamut. This advance has given birth to a huge global OLED display industry, now estimated to be >$15B, or more than 10% of all displays made. While red and green devices have shown extraordinary operational lifetimes, blue PHOLEDs have had unacceptably short lifetimes. In this talk I discuss the fundamental origins of this deficiency1, and approaches to extending the lifetime of blue PHOLEDs. Indeed, recent results in our laboratory have already yielded a 10 fold improvement in lifetime, the first such major improvement in almost a decade2. The understandings gained from these experiments suggest that much longer lifetimes, even for very deep blue emitting PHOLEDs, is possible. Furthermore, I will discuss recent results in achieving deep blue electrophosphorescence and the relationship between color and molecular structure in this spectral range. Lastly, I will discuss how the lessons learned in improving PHOLED lifetime also extends to organic solar cells.
1. N. C. Giebink, B. W. D’Andrade, M. S. Weaver, P. B. Mackenzie, J. J. Brown, M. E. Thompson and S. R. Forrest, J. Appl. Phys. 103, 044509 (2008).
2. Y. Zhang, J. Lee and S. R. Forrest, Nature Commun. 5, 5008 (2014).
Professor Dmitri V. Talapin, University of Chicago, Department of Chemistry and James Franck Institute
Title: Nanocrystal assemblies: a modular approach to materials design
Abstract
Development of synthetic methods for nanostructures has introduced new approaches for engineering functional materials. Nanocrystal assemblies provide a powerful platform for designing two- and three-dimensional solids with tailored electronic, magnetic, optical and catalytic properties. Unlike atomic and molecular crystals where atoms, lattice geometry, and interatomic distances are fixed entities, the arrays of nanocrystals represent solids made of “designer atoms” with potential for continuous tuning their physical and chemical properties.
The assembly of functional materials from nanoscale building blocks combines advantages of crystalline inorganic semiconductors with inexpensive solution-based device fabrication. Along these lines, colloidal semiconductor quantum dots are explored as the functional elements in printable electronics, light emitting devices, photodetectors and solar cells. All the above applications rely on efficient charge transport in nanocrystal arrays. In the recent years significant progress has been achieved in development of chemical approaches to improve electronic transport and control doping in nanocrystal arrays. I will review these developments and discuss recent results on inorganic ligands for colloidal nanomaterials. By using optimized surface chemistries we prepared nanocrystal solids exhibiting carrier mobilities comparable to those in single crystal materials. I will demonstrate the power of “modular” materials fabrication for electronic, thermoelectric and photovoltaic devices.
Professor John E. Anthony, University of Kentucky, Department of Chemistry
Title: Functionalized acenes in organic electronics
Abstract
The electronic and photonic properties of organic solids depend heavily on the precise intermolecular arrangements between molecules in the solid state. Because of this relationship, we have developed a simple functionalization protocol to easily tune (and fine-tune) the crystal packing of several common semiconductor chromophores. In this talk, I will discuss a variety of crystal packing motifs and their impact on charge transport properties. We have recently developed methods to separate the syn and anti isomers of anthradithiophenes - the impact of isomeric purity and the specific regioisomers on charge transport properties will also be addressed. Shifting to materials for organic photovoltaics, we found that the choice of solubilizing groups becomes quite complex. In order to mimic the 3-dimensional nature of electron transport found in fullerenes, new acceptors must be sparsely substituted, and possess extended conjugation, to be competitive materials in this area. We find that anthracene dimides, functionalized with conjugated "antenna" groups, show a direct relationship between decreasing solubilizing group content and increasing performance as a photovoltaic acceptor. Additional use of acenes in emerging applications - from bio-imaging to singlet fission - will also be presented.
