An Effective Approach toward Yellow‐to‐Orange Multi‐Resonance TADF Emitters by Integrating Strong Electron Donor into B/N‐Based Polycyclic Architecture: High Performance OLEDs with Nearly 40% EQE

Abstract

B/N-based multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters and the corresponding narrow band emissive organic light-emitting diodes (OLEDs) exhibit great potential for next-generation highresolution displays. Nonetheless, designing MR-TADF emitters with emission wavelength over 550 nm remains challenging. Herein, an effective approach toward yellow-to-orange MR-TADF emitters by integrating a strong electrondonating indolophenazine building block into the B/N-doped polycyclic aromatic hydrocarbons is proposed. The investigation of photophysical properties reveals that the electron-donating difference between the donor segments of MR framework has a dramatic influence on the luminescent features, including the emission wavelength and full-width at half-maximum (FWHM). These TADF emitters display excellent photophysical characteristics such as nearunity photoluminescence quantum yields and almost 100% horizontal dipole ratio. As a result, yellow and orange OLEDs employing these emitters achieve state-of-the-art device performances with an ultrahigh external quantum efficiency of up to nearly 40%, power efficiency of 163 lm W −1 , and luminance close to 120 000 cd m −2 , which set a record among MR-TADF based OLEDs with emission peaks over 550 nm. More impressively, the fabricated device presents outstanding operational stability of LT 99 over 110 h at the initial brightness of 3000 cd m −2 .

Recent progress and prospects of fluorescent materials based on narrow emission

“…Almost at the same time, Yang's group proposed a promising similar approach that integrates a strong electron-donating indolophenazine building block into B/N-doped polycyclic aromatic hydrocarbons. 75 This approach has been shown to significantly influence the luminescence features of the resulting TADF emitters, BNIP- t BuCz , BNIP- t BuDPAC , BNIP-CzDPA and BNDIP (Fig. 8d), including their emission wavelength (544–583 nm) and FWHM (38–60 nm).…”

Recent advances and prospects for organoboron-based thermally activated delayed fluorescence emitters

“…The device based on 230 as an emitter exhibited orange-red emission with an EL peak at 584 nm, an FWHM of 0.23 eV and an EQE max of 32.4%. 131 In this section, red-to-NIR emitters are defined as molecules that possess a maximum EL peak larger than 580 nm. Similar to yellow-orange MR-TADF emitters, red, deep-red and nearinfrared emitters are still under development as the fact that nonradiative transitions will significantly increase with the decreased energy gap.…”

“…The device based on 230 as an emitter exhibited orange-red emission with an EL peak at 584 nm, an FWHM of 0.23 eV and an EQE max of 32.4%. 131…”

A π-extended tercarbazole-core multi-resonance delayed fluorescence emitter exhibiting efficient narrowband yellow electroluminescence

“…Thermally activated delayed fluorescence (TADF) materials, which allow 100% exciton utilization for electroluminescence (EL), have been extensively studied as promising noble-metal-free emitters in organic light-emitting diodes (OLEDs). 1 Among them, boron- and nitrogen-embedded polycyclic aromatic hydrocarbons (B,N-PAHs) have recently attracted significant attention because of their excellent narrowband emission features, 2–15 making B,N-PAHs suitable for application in ultra-high-definition displays. The complementary multi-resonance (MR) effect of adjacent B and N atoms endows B,N-PAHs with atomically separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions, leading to a small singlet–triplet (S 1 –T 1 ) energy gap (Δ E ST ) for reverse intersystem crossing (RISC) and enabling TADF emission.…”

“…To date, a variety of MR-TADF emitters with excellent EL color purity and external quantum efficiency (EQE) in OLEDs have been reported. 4 However, with a few exceptions, 5–13 most of the MR-TADF systems based on B,N-PAH frameworks emit in the blue-to-green region; to facilitate a wide range of applications, a color gamut expansion (especially at >550 nm) is required. To this end, various peripheral molecular modifications have been applied on the simplest B,N-PAH skeleton, BBCz-SB (Fig.…”