Emission and Absorption Tuning in MR-TADF B,N-Doped Hep-tacenes: Towards Ideal-Blue Hyperfluorescent OLEDs

Abstract

Developing high-efficiency purely organic blue organic light-emitting diodes (OLEDs) that meet the stringent industry standards is a major current research challenge. Hyperfluorescent device approaches achieve in large measure the desired high performance by combining the advantages of a high-efficiency thermally activated delayed fluorescence (TADF) assistant dopant with a narrowband deep-blue multi-resonant TADF (MR-TADF) terminal emitter. However, this ap-proach requires suitable spectral overlap to support Förster resonance energy transfer (FRET) between the two. Here we demonstrate colour tuning of a recently reported MR-TADF B,N-heptacene core through control of the boron substituents. While there is little impact on the intrinsic TADF properties - as both singlet and triplet energies decrease in tandem - this approach improves the emission colour coordinate as well as the spectral overlap for blue hyperfluorescence OLEDs (HF OLEDs). Crucially, the red-shifted and more intense absorption allows us to pair this MR-TADF emitter with a high-performance TADF assistant dopant and achieve maximum external quantum efficiency (EQEmax) of 15% at colour coordinates of (0.15, 0.10). The efficiency values recorded for our device at a practical luminance of 100 cd m-2 are among the highest reported for HF TADF OLEDs with CIEy ≤ 0.1.

Mesityl‐Functionalized Multi‐Resonance Organoboron Delayed Fluorescent Frameworks with Wide‐Range Color Tunability for Narrowband OLEDs

“…ΔE ST values of 0.20 and 0.24 eV were obtained for BIC-mCz and mDBIC (Table S1), respectively, which were more consistent with the experimental results, as reported in previous calculations on B/N-doped heptacene emitters. [37] Furthermore, a difference density plot at the SCS-CC2/def2-TZVP level, successfully reproduced the alternating pattern of the hole and the electron for mDBIC at the S 1 state, while revealing the short-range CT nature for the S 1 state of BIC-mCz (Figure S13). Compared with the parent BIC molecule, BIC-mCz and mDBIC with the linear N-π-B structure exhibited larger S 1 energies.…”

Emerging hyperfluorescent emitters for solid-state lighting

“…No doubt, this approach demonstrates a path for designing several new HF emitters using theTADF-fluorescence emitter couple and their fruitful applications in OLEDs. [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] https://doi.org/10.26434/chemrxiv-2023-6j8nn ORCID: https://orcid.org/0000-0003-2066-4712 Content not peer-reviewed by ChemRxiv. License: CC BY 4.0…”

“…They have fabricated a HF-OLED using a T19: MR-T3 couple with a DPEPO host, which has an EQE of 15% with a FWHM of 49 nm and x/y CIE chromaticity coordinates of 0.15/0.10. 48 Another blue HF device was fabricated based on TADF sensitizer T20…”

“…Indeed, they have been referred to as the fourth generation on OLED active layers. [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] HF is defined as the emission mechanism that combines two different emitters, such as TADF and fluorescence emitters (Fig. 1c).…”

“…Therefore, HF has been established as a promising approach to designing OLEDs with high color purity and enhanced stability. [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] The study of HF emitters and their optoelectronic applications is progressing with momentum. In this mini-review, we systematically documented the molecular design principles of HF emitters, their fundamental photophysical requirements, and the advances in HF-OLED.…”