Excitonic processes in phosphorescent and TADF-type organic light-emitting diodes

Main list: Organic Semiconductor Centre

Abstract

Reinder Coehoorn
Eindhoven University of Technology
Excitonic processes in phosphorescent and TADF -type organic light - emitting diode s R. Coehoorn 1-4, A. Ligthart 1, X. de Vries 1, P.A. Bobbert 1,2, S. Gottardi 3, S.L.M. van Mensfoort 3 and H. van Eersel 3 1 Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands. 2 Institute for Complex Molecular Systems, Eindhoven University of Technology, The Netherlands. 3 Simbeyond B.V., Eindhoven, The Netherlands 4 South China Academy of Advanced Optoelectronics - South China Normal University, Guangzhou, China Mechanistic Organic Light Emitting Diode (OLED) device modeling using kinetic Monte Carlo (KMC) simulations provides a true molecular -scale and nanosecond -resolved view of the relevant physic al processes occurring in OLEDs. The simulations include the actual spatial non - uniformity of the current density and radiative decay [1], a decomposition of the efficiency loss in terms of fundamental loss processes such as exciton -polaron quenching and exciton -exciton annihilation, and a prediction of the device lifetime from simulations including molecular de gradation [2 ,3]. In this talk, results are presented of a combine d experimental and theoretical research program on the development of mechanistic descriptions of excitonic processes in phosphorescent OLEDs and OLEDs utilizing thermally activated delayed fluorescence (TADF). The experimental wor k includes time -resolved photol uminescence studies of the guest - guest and host -host transfer of triplet excitons in host -guest systems as used in phosphorescent OLEDs, and the rate of triplet -triplet annihilation [4,5 ]. The theoretical work includes a study of excito n transfer rates between Ir -cored phosphorescent emitters, based on a fully quantum - mechanical and multi -vibrational -mode description of the effect s of molecular deformations [6 ]. This work reveals general trends but also molecule -specific variations that can be used to optimize OLED designs. The experimental and theoretical studies are also used to analyze the detailed transfer mechanism, e.g. to make a distinction between the Förster and Dexter mechanisms. In the last part of the talk, we discuss how KMC simulations [7 ] can be used to successfully analyze the internal quantum efficiency (IQE) of TADF -based OLEDs and its roll - off at large current densities [8] .
References 1. M. Mesta et al. , Nat. Mater. 12, 652 (2013). 2. H. van Eersel et al. , Appl . Phys. Lett. 105, 143303 (2014). 3. R. Coehoorn et al. , Adv. Funct. Mater. 25, 2024 (2015). 4. A. Ligthart et al. , Adv. Funct. Mater, 28, 1804618 (2018). 5. A. Ligthart et al. , Organ. Electr. DOI: 10.1016/j.orgel.2019.105510 (2019). 6. X. de Vries et al. , Phys. Rev. B 99, 205201 (2019); X. de Vries et al. (submitted). 7. Bumblebee KMC software (Simbeyond B.V.), https://simbeyond.com/bumblebee/ . 8. S. Gottardi et al. , Appl. Phys. Lett. 114, 073301 (2019).
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  • Venue

    Room 222 in School of Physics and Astronomy

  • Date

    December 3, 2019

  • Time

    From: 16h00 To: 17h00

  • Sponsor

    University of St Andrews
    The oldest university in Scotland, with international renown for both research and education of undergraduates and postgraduates.

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