Interfacial and Surface Chemistry

Critical to the overall efficiency of organics-based electronic and optical devices are the electronic processes taking place where materials come into contact. These specific interface interactions, both at the metal/inorganic-organic and organic-organic interfaces, can often dictate the successful application of a material and device.

The interface between organic semiconductors and electrodes (made of a traditional metal or a transparent conducting metal oxide) is being studied extensively because charge transfer across the interface is crucial for the performance of organic (opto)electronic devices. The energy offset between the electrode Fermi level and the frontier molecular orbitals of the organic films plays an important role in controlling the charge injection between the electrode and the charge transport material. Our computational work aims to: determine the geometric and electronic structure of organic layers which are chemically or physically adsorbed on metal or conducting oxide surfaces; evaluate the workfunction change of the electrode surfaces upon adsorption of organic layers and the alignment of the energy levels of the organic molecules with respect to the electrode Fermi level; and explore the charge transfer mechanism between electrode surfaces and organic layers.

Of equal importance, the organic-organic interfaces play a significant role in the efficiencies of exciton separation (solar cells) and/or recombination (electroluminescence), and charge transport. One area of intense interest is focused on determining the proper computational approaches, with an emphasis on density functional methods, which best describe the intermolecular interactions that control interfacial electronic properties for a broad range of compounds. In addition, we are also interested in describing the morphology of the organic-organic interface, as it plays a key role in the strength of the intermolecular interactions. Particular attention is being paid to the morphology of polymer:fullerene blends used in organic photovoltaic devices.

Research highlights:
  • The Interface Energetics Of Self-Assembled Monolayers On Metals, Heimel, G; Romaner, L; Zojer, E; Bredas, JL, Accounts Of Chemical Research, 41, 721-729 [2008]
  • Toward Control Of The Metal-Organic Interfacial Electronic Structure In Molecular Electronics: A First-Principles Study On Self-Assembled Monolayers Of Pi-Conjugated Molecules On Noble Metals, Heimel, G; Romaner, L; Zojer, E; Bredas, JL, Nano Letters, 7, 932-940 [2007]
  • Interface Energetics And Level Alignment At Covalent Metal-Molecule Junctions: Pi-Conjugated Thiols On Gold, Heimel, G; Romaner, L; Bredas, JL; Zojer, E, Physical Review Letters, 96, 196806 [2006]
  • Recent papers on inorganic-organic interfaces:
  • Theoretical Characterization Of The Indium Tin Oxide Surface And Of Its Binding Sites For Adsorption Of Phosphonic Acid Monolayers, Paramonov, PB; Paniagua, SA; Hotchkiss, PJ; Jones, SC; Armstrong, NR; Marder, SR; Bredas, JL, Chemistry Of Materials, 20, 5131-5133 [2008]
  • Recent papers on metal-organic interfaces:
  • Electronic Structure Of Self-Assembled (Fluoro)Methylthiol Monolayers On The Au(111) Surface: Impact Of Fluorination On Coverage Density, Li, H; Duan, YQ; Paramonov, P; Coropceanu, V; Bredas, JL, Journal Of Electron Spectroscopy And Related Phenomena, 174, 70-77 [2009]
  • Odd-Even Effects In Self-Assembled Monolayers Of Omega-(Biphenyl-4-Yl)Alkanethiols: A First-Principles Study, Heimel, G; Romaner, L; Bredas, JL; Zojer, E, Langmuir, 24, 474-482 [2008]
  • Impact Of Bidirectional Charge Transfer And Molecular Distortions On The Electronic Structure Of A Metal-Organic Interface, Romaner, L; Heimel, G; Bredas, JL; Gerlach, A; Schreiber, F; Johnson, RL; Zegenhagen, J; Duhm, S; Koch, N; Zojer, E, Physical Review Letters, 99, 256801 [2007]
  • Photoelectron Spectroscopic Study Of The Electronic Band Structure Of Polyfluorene And Fluorene-Arylamine Copolymers At Interfaces, Hwang, J; Kim, EG; Liu, J; Bredas, JL; Duggal, A; Kahn, A, Journal Of Physical Chemistry C, 111, 1378-1384 [2007]
  • Organic/Metal Interfaces In Self-Assembled Monolayers Of Conjugated Thiols: A First-Principles Benchmark Study, Heimel, G; Romaner, L; Bredas, JL; Zojer, E, Surface Science, 600, 4548-4562 [2006]
  • Influence Of Molecular Conformation On Organic/Metal Interface Energetics, Koch, N; Heimel, G; Wu, JS; Zojer, E; Johnson, RL; Bredas, JL; Mullen, K; Rabe, JP, Chemical Physics Letters, 413, 390-395 [2005]