Transport and Optical Gaps in Amorphous Organic Molecular Materials

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Title: Transport and Optical Gaps in Amorphous Organic Molecular Materials
Authors: San-Fabián, Emilio | Louis, Enrique | Díaz-García, María A. | Chiappe, Guillermo | Vergés Brotons, José Antonio
Research Group/s: Química Cuántica | Física de la Materia Condensada | Materiales Avanzados
Center, Department or Service: Universidad de Alicante. Departamento de Química Física | Universidad de Alicante. Departamento de Física Aplicada | Universidad de Alicante. Instituto Universitario de Materiales
Keywords: Transport gap | Optical gap | OLED | TD-DFT
Knowledge Area: Química Física | Física de la Materia Condensada | Física Aplicada
Issue Date: 9-Feb-2019
Publisher: MDPI
Citation: San-Fabián E, Louis E, Díaz-García MA, Chiappe G, Vergés JA. Transport and Optical Gaps in Amorphous Organic Molecular Materials. Molecules. 2019; 24(3):609. doi:10.3390/molecules24030609
Abstract: The standard procedure to identify the hole- or electron-acceptor character of amorphous organic materials used in OLEDs is to look at the values of a pair of basic parameters, namely, the ionization potential (IP) and the electron affinity (EA). Recently, using published experimental data, the present authors showed that only IP matters, i.e., materials with IP > 5.7 (<5.7) showing electron (hole) acceptor character. Only three materials fail to obey this rule. This work reports ab initio calculations of IP and EA of those materials plus two materials that behave according to that rule, following a route which describes the organic material by means of a single molecule embedded in a polarizable continuum medium (PCM) characterized by a dielectric constant ε . PCM allows to approximately describe the extended character of the system. This “compound” system was treated within density functional theory (DFT) using several combinations of the functional/basis set. In the preset work ε was derived by assuming Koopmans’ theorem to hold. Optimal ε values are in the range 4.4–5.0, close to what is expected for this material family. It was assumed that the optical gap corresponds to the excited state with a large oscillator strength among those with the lowest energies, calculated with time-dependent DFT. Calculated exciton energies were in the range 0.76–1.06 eV, and optical gaps varied from 3.37 up to 4.50 eV. The results are compared with experimental data.
Sponsor: This research was funded by Ministerio de Economía y Competitividad MINECO and the European Union through FEDER funds (grants FIS2012-35880, FIS2015-64222-C2-1-P, FIS2015-64222-C2-2-P and MAT2015-66586-R).
ISSN: 1420-3049
DOI: 10.3390/molecules24030609
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (
Peer Review: si
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Appears in Collections:INV - LMA - Artículos de Revistas
INV - Física de la Materia Condensada - Artículos de Revistas
INV - QC - Artículos de Revistas

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