Highly Efficient Full-Color Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes: Extremely Low Efficiency Roll-Off Utilizing a Host with Small Singlet–Triplet Splitting

Abstract

Numerous efforts have been devoted to boost the efficiency of thermally activated delayed fluorescence (TADF) devices; however, strategies to suppress the device efficiency roll-off are still in urgent need. Here, a general and effective approach to suppress the efficiency roll-off of TADF devices is proposed, that is, utilizing TADF materials as the hosts for TADF emitters. Bearing small singlet-triplet splitting (ΔE) with donor and acceptor units, TADF materials as the hosts possess the potential to achieve matched frontier energy levels with the adjacent transporting layers, facilitating balanced charge injection as well as bipolar charge transport mobilities beneficial to the balanced charges transportation. Furthermore, an enhanced Förster energy transfer from the host to the dopant can be anticipated, helpful to reduce the exciton concentration. Based on the principles, a new TADF material based on indeno[2,1-b]carbazole/1,3,5-triazin derivation is synthesized and used as the universal host for the full-color TADF devices. Remarkable low efficiency roll-off was achieved with above 90% of the maximum external quantum efficiencies (EQE's) maintained even at a brightness of 2000 cd/m, along with EQE's of 23.2, 21.0, and 19.2% for orange, green, and sky-blue TADF devices, respectively. Through computational simulation, we identified the suppressed exciton annihilation rates compared with devices adopting conventional hosts. The state-of-the-art low efficiency roll-off of those TADF devices manifests the great potential of such host design strategy, paving an efficient strategy toward their practical application.

Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

“…The EQE max values of 18.0 % and 20.5 were achieved for IDAC‐MCO and IDAC‐Trz based OLEDs, respectively. In addition, similar TADF material with indolo[2,1‐b]acridine as donor can also be utilized as an universal host for TADF emitters, as reported by Duan et al., achieved high EQE max values of 23.2, 21.0 and 19.2 % for orange, green and sky‐blue TADF‐OLEDs, respectively, demonstrating the huge potential of TADF materials as hosts for efficient OLEDs.…”

“…The adjacent hydrogen atom can provide both large steric hindrance and strongr estrictions along the CÀNa xis, as evidencedb yt he large rotational barriero f [2,3-b]acridine based TADF emitter: [53] 6- (13,acridin-11-yl)-3-methyl-1H-isochromen-1-one (IDAC-MCO) and 11- (4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-13,13-dimethyl-5-phenyl-11,13-dihydro-5H-indolo [2,3-b]acridine (IDAC-Trz). The large planar donor units can providef urther HOMO localization and hence reduce the DE ST to only 0.02 eV for IDAC-Trz and 0.09 eV for IDAC-MCO, respectively.T he EQE max valueso f1 8.0 %a nd 20.5 were achieved for IDAC-MCO and IDAC-Trz based OLEDs, respectively.I na ddition, similar TADF materialw ith indolo [2,1-b]acridine as donor can also be utilized as an universal host for TADF emitters, as reported by Duan et al, [54] achieved highE QE max values of 23.2, 21.0 and 19.2 %f or orange, green and sky-blue TADF-OLEDs,r espectively,d emonstratingt he huge potential of TADF materials as hosts for efficient OLEDs.…”

Substitution Effect on Luminescence of 5H‐Indeno[1,2‐b]pyridin‐5‐one Based Isomers

“…The electrochemical behaviors of these compounds were studied by using cyclic voltammetry (CV) measurements in anhydrous DMF solution for cathodic scans and in CH 2 Cl 2 solution for anodic scan . The cyclic voltammograms are shown in Figure .…”

High Performance Thermally Activated Delayed Fluorescence Sensitized Organic Light‐Emitting Diodes

“…Furthermore, Zhang et al designed a new TADF host namely 1,3-dihydro-1,1-dimethyl-3-(3-(4,6-diphenyl-1,3,5triazin-2-yl)phenyl)indeno-[2,1-b]carbazole (DMIC-TRZ). [80] Here, 1,3-dihydro-3,3-dimethylindeno [2,1-b]carbazole (DMIC) with high hole mobility and 1,3,5-triazine (TRZ) with high electron mobility serve as donor and acceptor units, repectively (Figure 13). [25,28] High T 1 energy level, balanced electron and hole mobilities, moderate FMO energy levels make DMIC-TRZ good hosts for full-color TADF emitters.…”