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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Thermal Evaporation versus Spin-Coating: Electrical Performance in Columnar Liquid Crystal OLEDs

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Author(s):
Eccher, Juliana [1] ; Zajaczkowski, Wojciech [2, 3] ; Faria, Gregorio C. [4] ; Bock, Harald [5, 6] ; von Seggern, Heinz [2] ; Pisula, Wojciech [3, 7] ; Bechtold, Ivan H. [1]
Total Authors: 7
Affiliation:
[1] Univ Fed Santa Catarina, Dept Fis, BR-88040900 Florianopolis, SC - Brazil
[2] Tech Univ Darmstadt, Inst Mat Sci, Dept Elect Mat, D-64287 Darmstadt - Germany
[3] Max Planck Inst Polymer Res, D-55128 Mainz - Germany
[4] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil
[5] Univ Bordeaux, Ctr Rech Paul Pascal, F-33600 Pessac - France
[6] CNRS, F-33600 Pessac - France
[7] Lodz Univ Technol, Fac Chem, Dept Mol Phys, PL-90924 Lodz - Poland
Total Affiliations: 7
Document type: Journal article
Source: ACS APPLIED MATERIALS & INTERFACES; v. 7, n. 30, p. 16374-16381, AUG 5 2015.
Web of Science Citations: 26
Abstract

The electrical responses of a columnar liquid crystal (a diimidodiester derivative of benzo{[}ghi]perylene) deposited either by spin-coating or by thermal evaporation into a typical OLED device are compared. For the spin-coated film, homeotropic alignment was induced by thermal annealing, which enhanced the charge carrier mobility significantly. For the evaporated films, homeotropic alignment could not be obtained by annealing. However, a degree of rectification higher than 3 orders of magnitude was achieved, even without annealing, with an electrical response similar to the response of the aligned spin-coated film. A trap-limited space-charge-limited current model was used to extract the charge carrier mobility directly from the current-voltage curves. Grazing incidence wide-angle X-ray scattering confirmed the homeotropic alignment of the annealed spin-coated film, whereas the columns are mostly oriented parallel to the surface in the evaporated case. In a field-effect transistor with bottom-gate bottom-contact geometry, the evaporated film exhibited a typical behavior of an n-type transistor. The degree of intermolecular order is thereby strongly dependent on the deposition method where vacuum deposition leads to a higher order. This higher order, however, impedes reorientation by annealing of the evaporated film but leads to improved charge transport between the electrodes even without homeotropic alignment of columnar liquid crystal. (AU)

FAPESP's process: 13/21034-0 - Organic bioelectronics: from materials characterization to devices development
Grantee:Gregório Couto Faria
Support Opportunities: Scholarships abroad - Research