Abstract
Resonance interaction between a molecular transition and a confined electromagnetic field can lead to weak or strong light-matter coupling. Considering the substantial exciton–phonon coupling in thermally activated delayed fluorescence (TADF) materials, it is thus interesting to explore whether weak light-matter coupling can be used to redistribute optical density of states and to change the rate of radiative decay. Here, we demonstrate that the emission distribution of TADF emitters can be reshaped and narrowed in a top-emitting organic light-emitting device (OLED) with a weakly coupled microcavity. The Purcell effect of weak microcavity is found to be different for TADF emitters with different molecular orientations. We demonstrate that radiative rates of the TADF emitters with vertical orientation can be substantial increased in weakly coupled organic microcavity. These observations can enhance external quantum efficiencies, reduce efficiency roll-off, and improve color-purities of TADF OLEDs, especially for emitters without highly horizontal orientation.
Highlights
Activated delayed fluorescence (TADF)materials have been widely considered as the thirdgeneration emitters for organic light-emitting devices (OLEDs)
Due to the separated molecular orbitals, emissions of Thermally activated delayed fluorescence (TADF) emitters originate from intramolecular charge transfer, and undergo geometric relaxation, resulting in considerable exciton–phonon coupling[10,11,12,13,14,15,16,17,18,19]
TADF emitters typically display broad emission spectra. While this broad emission is a great advantage for lighting applications, it is Correspondence: Shihao Liu or Wenfa Xie or Chun-Sing Lee 1State key Laboratory of Integrated Optoelectronics, College of Electronics Science and Engineering, Jilin University, 130012 Changchun, China 2Center of Super-Diamond and Advanced Films (COSDAF) and Department of Chemistry, City University of Hong Kong, 999077 Hong Kong SAR, China These authors contributed : Chunxiu Zang, Shihao Liu considered to have inadequate color purity for display applications
Summary
Materials have been widely considered as the thirdgeneration emitters for organic light-emitting devices (OLEDs). They only utilize singlet excitons for radiation, TADF emitters can flip triplet (T) excitons to singlet (S) excitons via reverse intersystem crossing (RISC)[1,2,3,4,5,6,7,8,9]. TADF emitters typically display broad emission spectra. A Fabry–Pérot (FP) cavity consisting of two opposing reflective mirrors is a versatile method for introducing light-matter coupling and redistribute optical energy at selected wavelengths through building up a specific resonance condition[26,27,28]. For TADF emitters, Stéphane and colleagues have studied their RISC rate in strongly coupled microcavities consisting of two highly reflective silver
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