Spiro-Based Thermally Activated Delayed Fluorescence Emitters with Reduced Nonradiative Decay for High-Quantum-Efficiency, Low-Roll-Off, Organic Light-Emitting Diodes

Nidhi Sharma; Michal Maciejczyk; David Hall; Wenbo Li; Vincent Liégeois; David Beljonne; Yoann Olivier; Neil Robertson; Ifor D W Samuel; Eli Zysman-Colman

doi:10.1021/acsami.1c12234

Spiro-Based Thermally Activated Delayed Fluorescence Emitters with Reduced Nonradiative Decay for High-Quantum-Efficiency, Low-Roll-Off, Organic Light-Emitting Diodes

ACS Appl Mater Interfaces. 2021 Sep 22;13(37):44628-44640. doi: 10.1021/acsami.1c12234. Epub 2021 Sep 13.

Authors

Nidhi Sharma^{1

2}, Michal Maciejczyk³, David Hall^{2

4}, Wenbo Li¹, Vincent Liégeois⁵, David Beljonne⁴, Yoann Olivier^{4

6}, Neil Robertson³, Ifor D W Samuel¹, Eli Zysman-Colman²

Affiliations

¹ Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, U.K.
² Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, Fife, St Andrews KY16 9ST, U.K.
³ EaStCHEM School of Chemistry, University of Edinburgh King's Buildings, Edinburgh EH9 3FJ, U.K.
⁴ Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, B-7000 Mons, Belgium.
⁵ Unité de Chimie Physique Théorique et Structurale, Namur Institute of Structured Matter (NISM), Université de Namur, Rue de Bruxelles, 61, 5000 Namur, Belgium.
⁶ Unité de Chimie Physique Théorique et Structurale & Laboratoire de Physique du Solide, Namur Institute of Structured Matter (NISM), Université de Namur, Rue de Bruxelles, 61, 5000 Namur, Belgium.

PMID: 34516084
DOI: 10.1021/acsami.1c12234

Abstract

Herein, we report the use of spiro-configured fluorene-xanthene scaffolds as a novel, promising, and effective strategy in thermally activated delayed fluorescence (TADF) emitter design to attain high photoluminescence quantum yields (Φ_PL), short delayed luminescence lifetime, high external quantum efficiency (EQE), and minimum efficiency roll-off characteristics in organic light-emitting diodes (OLEDs). The optoelectronic and electroluminescence properties of SFX (spiro-(fluorene-9,9'-xanthene))-based emitters (SFX-PO-DPA, SFX-PO-DPA-Me, and SFX-PO-DPA-OMe) were investigated both theoretically and experimentally. All three emitters exhibited sky blue to green emission enabled by a Herzberg-Teller mechanism in the excited state. They possess short excited-state delayed lifetimes (<10 μs), high photoluminescence quantum yields (Φ_PL ∼ 70%), and small singlet-triplet splitting energies (ΔE_ST < 0.10 eV) in the doped films in an mCP host matrix. The OLEDs showed some of the highest EQEs using spiro-containing emitters where maximum external quantum efficiencies (EQE_max) of 11 and 16% were obtained for devices using SFX-PO-DPA and SFX-PO-DPA-OMe, respectively. Further, a record EQE_max of 23% for a spiro-based emitter coupled with a low efficiency roll-off (19% at 100 cd m^-2) was attained with SFX-PO-DPA-Me.

Keywords: Herzberg−Teller; OLEDs; TADF; fluorene-xanthene; luminescence; spiro.