Diboron-Based Delayed Fluorescent Emitters with Orange-to-Red Emission and Superior Organic Light-Emitting Diode Efficiency

Abstract

For the application of organic light-emitting diodes (OLEDs) in lighting and panels, the basic requirement is to include a full spectrum color range. Compared with the development of blue and green luminophores in thermally activated delayed fluorescence (TADF) technology, the progress of orange-to-red materials is slow and needs further investigation. In this study, three diboron compound-based materials, dPhADBA, dmAcDBA, and SpAcDBA, were designed and synthesized by nucleophilic arylation of three amine donors on 9,10-diboraanthracene (DBA) in a two-step reaction. With increasing electron-donating ability, they show orange-to-red emission with TADF characteristics. The electroluminescence of these diboron compounds exhibits emissions λ max at 613, 583, and 567 nm for dPhADBA, dmAcDBA, and SpAcDBA, respectively. It is noteworthy that the rod-like D-A-D structures can achieve high horizontal ratios (84−86%) and outstanding device performance for orange-to-red TADF OLEDs: the highest external quantum efficiencies for dPhADBA, dmAcDBA, and SpAcDBA are 11.1 ± 0.5, 24.9 ± 0.5, and 30.0 ± 0.8%, respectively. Therefore, these diboron-based molecules offer a promising avenue for the design of orange-to-red TADF emitters and the development of highly efficient orange-to-red OLEDs.

Doubly Boron‐Doped TADF Emitters Decorated with ortho‐Donor Groups for Highly Efficient Green to Red OLEDs

“…In fact, the maximum EQE values follow the trend of the PLQYs of the doped host films containing the emitters. Notably, the EQE of the D4 device is comparable with that of recently reported boron‐doped red TADF‐OLEDs [6a] . However, all devices suffer from substantial efficiency roll‐off at high luminance over 1000 cd m −2 , with the red device D4 exhibiting the largest roll‐off.…”

“…Meanwhile, the boron‐containing compounds developed so far have been widely utilized as blue and green emitting materials in OLEDs, [1b] whereas red TADF emitters incorporating three‐coordinated boron acceptors have been rarely reported [6a] . The red emitters require small singlet energy for light emission, which is usually achieved by adjusting the donor and acceptor strength of the molecules, particularly by stabilizing the LUMO level of a π‐conjugated acceptor moiety [7, 10] .…”

“…Indeed, Cheng et al. very recently disclosed para ‐D‐A‐D‐type orange‐to‐red DBA emitters and achieved a high efficiency in red TADF‐OLEDs ( λ PL =613 nm; EQE=11.1 %) [6a] . Furthermore, we have also recently demonstrated that triarylboron compounds having ortho ‐D‐A connectivity can form a highly twisted D‐A structure, resulting in a very small energy gap between singlet (S 1 ) and triplet states (T 1 ) that affords efficient TADF characteristics (e.g., Cz o B in Scheme 1).…”

“…In this regard, the control of the optoelectronic properties of DBA derivatives has been achieved by modifications of either the boron‐ (type A) or aryl‐ (type B) moieties (Scheme 1). [6a–c, 7, 8] …”

High‐Performance Orange–Red Organic Light‐Emitting Diodes with External Quantum Efficiencies Reaching 33.5% based on Carbonyl‐Containing Delayed Fluorescence Molecules

“…On the other hand, the horizontal dipole ratio (Θ // ) of the molecule should also be enhanced to break the limit of 20‒30% optical outcoupling efficiency ( Φ out ). [ 27 , 28 ] In fact, some orange–red TADF materials obtained by great efforts possess small Δ E ST s and high Φ PL s, but their EL efficiencies are less than satisfactory due to their low Θ // s, and vice versa. [ 29 , 30 , 31 , 32 , 33 ] It is virtually challenging to simultaneously achieve a small ∆ E ST , a high Φ PL , and a large Φ out , especially for TADF materials with long‐wavelength emissions.…”