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

Abstract

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.

Authors:
ORCiD logo [1];  [2];  [2];  [2];  [2];  [2];  [1]
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  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
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1401327
Grant/Contract Number:  
DE‐FG02‐07ER46474
Resource Type:
Publisher's Accepted Manuscript
Journal Name:
Advanced Materials
Additional Journal Information:
Journal Name: Advanced Materials Journal Volume: 29 Journal Issue: 40; Journal ID: ISSN 0935-9648
Publisher:
Wiley Blackwell (John Wiley & Sons)
Country of Publication:
Germany
Language:
English

Citation Formats

Einzinger, Markus, Zhu, Tianyu, de Silva, Piotr, Belger, Christian, Swager, Timothy M., Van Voorhis, Troy, and Baldo, Marc A. Shorter Exciton Lifetimes via an External Heavy‐Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light‐Emitting Diodes. Germany: N. p., 2017. Web. doi:10.1002/adma.201701987.
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Einzinger, Markus, Zhu, Tianyu, de Silva, Piotr, Belger, Christian, Swager, Timothy M., Van Voorhis, Troy, & Baldo, Marc A. Shorter Exciton Lifetimes via an External Heavy‐Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light‐Emitting Diodes. Germany. https://doi.org/10.1002/adma.201701987
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Einzinger, Markus, Zhu, Tianyu, de Silva, Piotr, Belger, Christian, Swager, Timothy M., Van Voorhis, Troy, and Baldo, Marc A. Mon . "Shorter Exciton Lifetimes via an External Heavy‐Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light‐Emitting Diodes". Germany. https://doi.org/10.1002/adma.201701987.
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@article{osti_1401327,
title = {Shorter Exciton Lifetimes via an External Heavy‐Atom Effect: Alleviating the Effects of Bimolecular Processes in Organic Light‐Emitting Diodes},
author = {Einzinger, Markus and Zhu, Tianyu and de Silva, Piotr and Belger, Christian and Swager, Timothy M. and Van Voorhis, Troy and Baldo, Marc A.},
abstractNote = {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.},
doi = {10.1002/adma.201701987},
journal = {Advanced Materials},
number = 40,
volume = 29,
place = {Germany},
year = {Mon Sep 11 00:00:00 EDT 2017},
month = {Mon Sep 11 00:00:00 EDT 2017}
}
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Journal Article:
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https://doi.org/10.1002/adma.201701987
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