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Einzinger M, Zhu T, de Silva P, et al. Shorter Exciton Lifetimes via an External Heavy-Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light-Emitting Diodes. Adv Mater. 2017;29(40)doi: 10.1002/adma.201701987.
Einzinger, M., Zhu, T., de Silva, P., Belger, C., Swager, T. M., Van Voorhis, T., & Baldo, M. A. (2017). Shorter Exciton Lifetimes via an External Heavy-Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light-Emitting Diodes. Advanced materials (Deerfield Beach, Fla.), 29(40), . https://doi.org/10.1002/adma.201701987
Einzinger, Markus, et al. "Shorter Exciton Lifetimes via an External Heavy-Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light-Emitting Diodes." Advanced materials (Deerfield Beach, Fla.) vol. 29,40 (2017). doi: https://doi.org/10.1002/adma.201701987
Einzinger M, Zhu T, de Silva P, Belger C, Swager TM, Van Voorhis T, Baldo MA. Shorter Exciton Lifetimes via an External Heavy-Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light-Emitting Diodes. Adv Mater. 2017 Oct;29(40). doi: 10.1002/adma.201701987. Epub 2017 Sep 11. PMID: 28892200.
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Adv Mater. 2017 Oct;29(40). doi: 10.1002/adma.201701987. Epub 2017 Sep 11.

Shorter Exciton Lifetimes via an External Heavy-Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light-Emitting Diodes.

Advanced materials (Deerfield Beach, Fla.)

Markus Einzinger, Tianyu Zhu, Piotr de Silva, Christian Belger, Timothy M Swager, Troy Van Voorhis, Marc A Baldo

Affiliations

  1. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.
  2. Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.

PMID: 28892200 DOI: 10.1002/adma.201701987

Abstract

Multiexcited-state phenomena are believed to be the root cause of two exigent challenges in organic light-emitting diodes; namely, efficiency roll-off and degradation. The development of novel strategies to reduce exciton densities under heavy load is therefore highly desirable. Here, it is shown that triplet exciton lifetimes of thermally activated delayed-fluorescence-emitter molecules can be manipulated in the solid state by exploiting intermolecular interactions. The external heavy-atom effect of brominated host molecules leads to increased spin-orbit coupling, which in turn enhances intersystem crossing rates in the guest molecule. Wave function overlap between the host and the guest is confirmed by combined molecular dynamics and density functional theory calculations. Shorter triplet exciton lifetimes are observed, while high photoluminescence quantum yields and essentially unaltered emission spectra are maintained. A change in the intersystem crossing rate ratio due to increased dielectric constants leads to almost 50% lower triplet exciton densities in the emissive layer in the steady state and results in an improved onset of the photoluminescence quantum yield roll-off at high excitation densities. Efficient organic light-emitting diodes with better roll-off behavior based on these novel hosts are fabricated, demonstrating the suitability of this concept for real-world applications.

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Keywords: external heavy-atom effect; intersystem crossing; organic light-emitting diodes; spin-orbit coupling; thermally activated delayed fluorescence

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