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Center for Organic Photonics and Electronics

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Author: Kahn, Antoine × Author: Marder, Seth R. × search.filters.applied.f.isOrgUnitOfPublicationTitle: Center for Organic Photonics and Electronics ×

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Now showing 1 - 5 of 5
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    Solution doping of organic semiconductors using air-stable n-dopants
    (Georgia Institute of Technology, 2012-02) Qi, Yabing ; Mohapatra, Swagat K. ; Kim, Sang Bok ; Barlow, Stephen ; Marder, Seth R. ; Kahn, Antoine
    Solution-based n-doping of the polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI₂OD-T₂)] and the small molecule 6,13-bis(tri(isopropyl)silylethynyl)pentacene (TIPS-pentacene) is realized with the air-stable dimers of rhodocene, [RhCp₂]₂, and ruthenium(pentamethylcyclopentdienyl)(1,3,5-triethylbenzene), [Cp*Ru(TEB)]₂. Fermi level shifts, measured by direct and inverse photoemission spectroscopy, and orders of magnitude increase in current density and film conductivity point to strong n-doping in both materials. The strong reducing power of these air-stable dopants is demonstrated through the n-doping of TIPS-pentacene, a material with low electron affinity (3.0 eV). Doping-induced reduction of the hopping transport activation energy indicates that the increase in film conductivity is due in part to the filling of deep gap states by carriers released by the dopants.
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    Remote doping of a pentacene transistor: Control of charge transfer by molecular-level engineering
    (Georgia Institute of Technology, 2010-09) Zhao, Wei ; Qi, Yabing ; Sajoto, Tissa ; Barlow, Stephen ; Marder, Seth R. ; Kahn, Antoine
    We demonstrate that holes from a p-doped N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) layer transfer to an adjacent pentacene film. The spatial separation of carriers from dopants, or remote doping, is demonstrated with a combination of photoemission spectroscopy and current-voltage measurements for a p-doped α-NPD/pentacene heterojunction. Increased conductivity of the pentacene film is observed in both nongated temperature-dependent conductivity and gated thin-film transistor measurements.
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    Substrate-dependent electronic structure of an organic heterojunction
    (Georgia Institute of Technology, 2008-04) Zhao, Wei ; Salomon, Eric ; Zhang, Qing ; Barlow, Stephen ; Marder, Seth R. ; Kahn, Antoine
    This work focuses on organic-organic heterojunctions (OOHs) formed between two small-molecule, low band-gap, semiconductors, tris{2,5-bis(3,5-bis-trifluoromethyl-phenyl)-thieno}[3,4-b,h,n]-1,4,5,8,9,12 -hexaaza-triphenylene (THAP), and copper phthalocyanine (CuPc). The organic layers are deposited on various substrates, and the energy level alignment between them is investigated by ultraviolet photoemission spectroscopy. The electronic structure of the OOH is found to depend on the work function of the organic underlayer predeposited on the different substrates. The vacuum level offset between THAP and CuPc, which consists of the sum of the interface dipole and the molecular level shift, varies from 0.26 to 1.37 eV. The interface dipole between the two organic films linearly changes with the work function of the organic underlayer.
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    Commensurate growth and diminishing substrate influence in a multilayer film of a tris(thieno)hexaazatriphenylene derivative on Au(111) studied by scanning tunneling microscopy
    (Georgia Institute of Technology, 2008-02) Ha, Sieu D. ; Zhang, Qing ; Barlow, Stephen ; Marder, Seth R. ; Kahn, Antoine
    Layer-by-layer growth of the electron-transport material tris 2,5-bis 3,5-bis-trifluoromethyl-phenyl -thieno 3,4-b,h,n -1,4,5,8,9,12-hexaazatriphenylene THAP on Au 111 is probed by scanning tunneling microscopy STM . A relative of discotic liquid crystalline molecules, THAP is shown to grow in commensurate ordered planes from the first to fourth monolayers. The four monolayers all show a concordant ordered structure in which the molecules arrange parallel to the substrate in a hexagonal close-packed lattice with a herringbone pattern defined by alternating rows of molecules with antiparallel orientation. The unit cell is rectangular with two molecules per cell and is nearly equivalent for each layer. The spatial broadening of the local density of states due to the metallic substrate is appreciably diminished in upper layers, as expected and as evidenced by the localization of states seen in STM. There is good agreement between the highest occupied molecular orbital obtained in density functional theory calculations for a single molecule and STM images of the upper layers, in accord with the localized nature of electronic states on molecules under minimal substrate influence.
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    Incorporation of cobaltocene as an n-dopant in organic molecular films
    (Georgia Institute of Technology, 2007-07-01) Chan, Calvin K. ; Kahn, Antoine ; Zhang, Qing ; Barlow, Stephen ; Marder, Seth R.
    Electrical or chemical doping of molecular films is an efficient means of improving and controlling charge injection and carrier transport in organic devices. Recent work demonstrated that bis(cyclopentadienyl)cobalt(II) (cobaltocene, CoCp₂) efficiently dopes a tris(thieno)hexaazatriphenylene (THAP) derivative, as shown by a 0.56 eV shift of the Fermi level toward the empty states and an increase of current density by a factor of 10³ over undoped THAP devices. In this work, a combination of x-ray photoemission spectroscopy and Rutherford backscattering is used to elucidate the details of dopant incorporation into bulk films. Cobaltocene is observed to codeposit into the THAP matrix in a controllable manner, with preferential adsorption of the dopant onto the surface of the host film. In the case of CoCp₂-doped tris(8-hydroxy-quinolinato) aluminum (Alq₃) films, negligible amounts of the dopant are found in the bulk matrix and on the film surface, resulting in minimal improvements in the electrical characteristics of doped Alq₃ films. The process of CoCp₂ adsorption onto a film surface or the evolving surface of a growing film which leads to dopant incorporation is likely assisted by charge transfer from cobaltocene to the host material, resulting in ion pairing between the dopant and host.