Unveiling the TADF Emitters with Apparent Negative Singlet-Triplet Gaps: Implications for Exciton Harvesting and OLED Performance

Xinrui Chen, Sergey Bagnich, Robert Pollice, Bing Li, Yuanyuan Zhu, Rishabh Saxena, Yixiao Yin, Weiguo Zhu, Alan Aspuru-Guzik*, Eli Zysman-Colman*, Anna Köhler*, Yafei Wang*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)

Abstract

Intramolecular through-space charge transfer thermally activated delayed fluorescence (TSCT-TADF) has attracted much attention recently as it can achieve both small energy splitting and high emission efficiency. However, the relationship of excited states between TSCT and through-bond charge transfer (TBCT) remains a challenge in the TSCT-TADF molecules. Herein, three compounds DPS-m-bAc, DPS-p-bAc, and DPS-OAc that possess emissive TSCT and/or TBCT states are prepared. Interestingly, a so-called inverted energy gap is found for both DPS-m-bAc and DPS-p-bAc in toluene solution, which results from the different charge transfer states of ICThigh and ICTlow, as proved by the detailed transient photoluminescence and calculated results. Intense emission from blue to yellow associated with high photoluminescence quantum yields of 70–100% are measured in doped polymethyl(methacrylate) (PMMA) films. Notably, compound DPS-m-bAc achieves the highest reverse intersystem crossing rate constant (kRISC) of over 107 s−1 in a PMMA film, benefiting from close-lying TSCT and TBCT states. The solution-processed device with DPS-m-bAc displays a maximum external quantum efficiency of 21.7% and a relatively small efficiency roll-off (EQE of 20.2% @ 100 cd m−2). Overall, this work demonstrates how with judicious emitter engineering, a synergy between different charge transfer excited states, can be achieved, providing an avenue to achieve highly efficient solution-processed OLEDs.

Original languageEnglish
Article number2301784
Number of pages11
JournalAdvanced optical materials
Volume12
Issue number6
DOIs
Publication statusPublished - 23-Feb-2024
Externally publishedYes

Keywords

  • charge transfer
  • delayed fluorescence
  • fast reverse intersystem crossing
  • solution-processed OLED
  • thermally activated delayed fluorescence

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