Aromatic molecules are a robust and versatile platform for the development of functional materials for electronic applications. Using a tandem organic synthesis / device analysis approach, we seek to determine structure-property relationships that lead to materials with exceptional performance in organic thin-film transistors (for flexible flat-panel displays), organic solar cells (for low-cost generation of electricity) and organic light-emitting diodes (for high-efficiency lighting). Needless to say, students in my group learn a wide range of skills, from organic synthesis to materials characterization and device fabrication.
We are also exploring new functionalization strategies to further enhance the stability of these strongly-absorbing molecules, for use in low-cost solar cells.
Materials: This set of projects involves the specific tuning of functionalization to yield optimum performance in a variety of electronic device applications. We have developed an excellent model that allows us to predict the solid-state order of acenes functionalized by our method - the fine-tuning allows us to make subtle changes that improve film morphology, electrode contacts or photostability. Following this model, we have prepared materials with record-high performance in a number of areas.
Transistors: A field-effect transistor is a three-electrode device that turns current between two of the electrodes (labeled "source" and "drain") off or on by application of voltage across the third electrode (called the "gate"). For use in organic transistors, we have obtained the best results using molecules that exhibit two-dimensional pi-stacking in the sold state.
We are lucky to have many great collaborators in this area. For example, the Loo group has found that with our anthradithiophene-class of materials, exposure of films to solvent vapor for only a few minutes will dramatically improve the device performance of the materials. Blending different semiconductors allows impressive control over the size of the crystalline grains. We're also working closely with the Gundlach group at NIST to elucidate the properties of heteroacenes. Their single-crystal measurements have shown hole mobility approaching 6 cm2/Vs, one of the highest reported mobilities for organic small molecules.
Solar cells: Acenes can also be used as the donor or acceptor material in organic solar cells. We've been working with the Naval Research Laboratory on vapor-deposited TIPS pentacene, and with the Malliaras group at Cornell on solution-deposited acenes. Using acene donors, we've seen power conversion efficiencies > 1%. The acene acceptors work even better - blends of polythiophene with cyanopentacenes leads to power conversion efficiency over 1.5%.
I am grateful to all of my collaborators (many of whom are not mentioned on this short web page) for their insight, assistance, and for being such fantastic people to work with. I also thank the support (both intellectual and financial) of our research programs by the Office of Naval Research, the Defense Advanced Research Projects Agency, the National Science Foundation, and the King Abdullah University of Science and Technology.
B. Purushothaman, S. R. Parkin, J. E. Anthony "Synthesis and stability of soluble hexacenes" Org. Lett. 12, 2060 – 2063 (2010).
S. H. Kim, K. Hong, M. Jang, J. Jang, J. E. Anthony, H. Yang "Photo-curable polymer blend dielectrics for advancing organic field-effect transistor applications" Adv. Mater. 22, 4809 – 4813 (2010).
E. G. Bittle, J. W. Brill, J. E. Anthony "Electro-optic measurement of carrier mobility in an organic thin-film transistor" Appl. Phys. Lett. 97, 013302 (2010).
J. Smith, A. Bashir, G. Adamopoulos, J. E. Anthony, D. D. C. Bradley, M. Heeney, I. McCulloch, T. D. Anthopoulos "Air-stable solution-processed hybrid transistors with hole and electron mobilities exceeding 2 cm2 V-1 s-1" Adv. Mater. 22, 3598 – 3602 (2010).
J. R. Kline, S. D. Hudson, X.-R. Zhang, D. J. Gundlach, A. J. Moad, O. D. Jurchescu, T. N. Jackson, S. Subramanian, J. E. Anthony, M. F. Toney "Controlling the microstructure of solution-processable small molecules in thin film transistors through substrate chemistry" Chem. Mater. 23, 1194 – 1203 (2011)
Z. Li, Y.-F. Lim, J. B. Kim, S. R. Parkin, Y.-L. Loo, G. G. Malliaras, J. E. Anthony "Isomerically pure electron-deficient anthradithiophenes and their acceptor performance in polymer solar cells" Chem. Commun. 47, 7617 – 7619 (2011)
B. Purushothaman, M. Bruzek, S. R. Parkin, A.-F. Miller, J. E. Anthony "Synthesis and structural characterization of crystalline nonacenes" Angew. Chem. Int. Ed. 50, 7013 – 7017 (2011)
Y. S. Chung, N. Shin, J. Kang, Y. Jo, V. M. Praabhu, S. K. Satija, R. J. Kline, D. M. DeLongchamp, M. F. Toney, M. A. Loth, B. Purushothaman, J. E. Anthony, D. Y. Yoon "Zone-refinement effect in small molecule – polymer blend semiconductors for organic thin-film transistors" J. Am. Chem. Soc. 133, 412 – 415 (2011).
J. E. Anthony "Small-molecule, non-fullerene acceptors for polymer solar cells", invited review, Chem. Mater. 23, 583 – 590 (2011)
Y. Shu, Y.-F. Lim, Z. Li, B. Purushothaman, R. Hallani, J. E. Kim, S. R. Parkin, G. G. Malliaras, J. E. Anthony “A survey of electron-deficient pentacenes as acceptors in polymer bulk-heterojunction solar cells” Chemical Sciences 2, 363 – 366 (2011)
Listen to John Anthony on "UK at the Half" <a href="web.as.uky.educhemistryfacultyjohnanthonyukath.mp3">here</a>