AMADEus Seminar - Towards the microscopic modeling of organic light-emitting devices - Wednesday 19 November 2014, 04:30 pm - ICMCB

Part I: Thermally Activated Delayed Fluorescence in organic emitters: a molecular picture

Juan-Carlos Sancho-García (jc.sancho@ua.es)

Departamento de Química Física

Universidad de Alicante, Spain

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Abstract: New materials for OLED applications with low singlet-triplet energy splitting have been recently synthesized in order to allow for the e?cient conversion of triplet into singlet excitons (emitting light) via a Thermally Activated Delayed Fluorescence (TADF) process. Accurately predicting this singlet-triplet energy splitting is key to the understanding and further design of organic materials, but the prediction which may be hampered by the charge-transfer nature of the states involved [1,2]. The accurate modeling of these states with Time-Dependent Density Functional Theory (TD-DFT) is thus highly challenging, and possible insights might be masked by routine drawbacks of the calculations [3]. We will thus address this issue by carefully examining how to systematically reduce as much as possible the underlying error bar of any calculation, before presenting next a qualitative correlation between the experimental singlet-triplet values and a metrics used to measure the extent of that charge-transfer [4].

[1] J. Aragó, J. C. Sancho-García, E. Ortí, and D. Beljonne, J. Chem. Theory Comput. 7 (2011), 2068.

[2] F. Di Meo, P. Trouillas, C. Adamo, and J. C. Sancho-García, J. Chem. Phys. 139 (2013), 64104

[3] J. C. Sancho-García and C. Adamo, Phys. Chem. Chem. Phys. 15 (2013), 14581.

[4] M. Moral-Muñoz, L. Muccioli, W.-J. Son, Y. Olivier, and J. C. Sancho-García, J. Chem. Theory Comput., submitted (2014)

Part II: Computing charge transport properties in organic semiconductors:
insights from molecular modeling at different length scales

Dr. Yoann Olivier (yoann.olivier@umons.ac.be)

Laboratory for Chemistry of Novel Materials

University of Mons, Belgium

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Abstract: Improving the charge carrier mobility in organic-based devices such as LEDs, solar cells and FETs is of crucial importance in order to achieve standardized performances. To reach this objective, a detailed understanding at the molecular scale of the influence of structural organization on the charge carrier mobility is a key issue. In disordered materials, the hopping regime is a reliable model to depict charge transport. In this framework, charge transport has often been described using the semi-classical Marcus theory, with the main parameters - transfer integral and reorganization energy - calculated with quantum chemistry [1]. In this contribution, we will highlight by means of molecular modeling the subtle interplay between the molecular organization and charge transport properties. By combining quantum-chemical methods, molecular dynamics and Monte Carlo simulations, we will show different examples going from crystalline [2] to disordered organic semiconductors such as liquid-crystalline [3] and polymeric materials [4] with special attention on the potential lessons learnt for further design of materials with improved charge transport properties.

[1] V. Coropceanu, J. Cornil, D.A. da Silva Filho, Y. Olivier, R. Silbey, J. L. Brédas, Chem. Rev. 107 (2007), 926.

[2] F. Oton, R. Pfattner, E. Pavlica, Y. Olivier, E. Moreno, J. Puigdollers, G. Bratina, J. Cornil, X. Fontrodona, M. Mas-Torrent, J. Veciana, and C. Rovira. Chem. Mater. 23 (2011), 851.

[3] Y. Olivier, L. Muccioli, V. Lemaur, Y. H. Geerts, C. Zannoni, and J. Cornil, J. Phys. Chem. B  113 (2009), 14102.

[4] V. Lemaur, L. Muccioli, C. Zannoni, D. Beljonne, R. Lazzaroni, J. Cornil, and Y. Olivier. Macromolecules 46 (2013), 8171; Y. Olivier, D. Niedzalek, V. Lemaur, W. Pisula, K. Müllen, U. Koldemir, J. Reynolds, R. Lazzaroni, J. Cornil, and D. Beljonne. Adv. Mat. 26 (2014), 2119.