Novel thermally activated delayed fluorescence materials for optoelectronic applications

Realizing External Quantum Efficiency over 25% with Low Efficiency Roll-Off in Polymer-Based Light-Emitting Diodes Synergistically Utilizing Intramolecular Sensitization and Bipolar Thermally Activated Delayed Fluorescence Monomer

Novel secondary acceptor based molecular design for superb lifetime in thermally activated delayed fluorescent organic light-emitting diodes through high bond energy and fast up-conversion

Rational molecular design of deep blue thermally activated delayed fluorescent emitters for high efficiency fluorescent and hyperfluorescent devices

Fabricating solution-processible host material for thermally activated delayed fluorescence (TADF) emitter remains a formidable challenge for organic light-emitting diodes (OLEDs). In this work, two new host materials, namely 3CzAcPy and 9CzAcPy, are found to exhibit high triplet energy levels, high thermal stability, and excellent film morphology from a solution process. An in-depth analysis on the photophysical data and device performance reveals the isomeric effect of the host materials has a significant impact not only on the host properties, but also on the host-dopant interactions and thus the performance of the resulting solution-processed TADF OLEDs. Impressively, the new hosts are proven to be suitable for both donor-acceptor type and multi-resonance TADF emitters, achieving state-of-the-art device performance. By using the new host 9CzAcPy, solution-processed OLED based on a donor-acceptor TADF emitter of DPAC-PCN, a maximum external quantum efficiency (EQE) of 29.5% is achieved, and solution-processed narrowband OLED based on a multiple-resonance TADF emitter of BN-CP1 acquires a maximum EQE of 26.6%. These efficiencies represent the highest values among the solution-processed TADF OLEDs. This study highlights the significance of host-dopant interactions in modulating the electroluminescence performance of TADF emitters, and provides an effective design principle for solution-processible host materials.

Thermally activated delayed fluorescence emitters with bulky four-coordinate boron acceptors for high-performance solution-processed OLEDs

Assessing and improving the performance of organic light-emitting diode (OLED) materials require quantitative prediction of rate coefficients for the intersystem crossing (ISC) and reverse ISC (RISC) processes, which are determined not only by the energy gap and the direct spin-orbit coupling (SOC) between the first singlet and triplet excited-states at a thermal equilibrium position of the initial electronic state but also by the non-Condon effects such as the Herzberg-Teller-like vibronic coupling (HTVC) and the spin-vibronic coupling (SVC). Here we apply the time-dependent correlation function approaches to quantitatively calculate the vibrationally resolved absorption and fluorescence spectra and ISC/RISC rates of a newly synthesized multiple-resonance-type (MR-type) thermally activated delayed fluorescence (TADF) emitter, 7-phenylquinolino[3,2,1-de]acridine-5,9-dione (7-PhQAD), with the inclusion of the Franck-Condon (FC), HTVC, and Duschinsky rotation (DR) effects. The SVC effect on the rates has also been approximately evaluated. We find that the experimentally measured ISC rates of 7-PhQAD originate predominantly from the vibronic coupling, consistent with the previous reports on other MR-type TADF emitters. The SVC effect on ISC rates is about 10 times larger than the HTVC effect, and the latter increases the ISC rates by more than 1 order of magnitude while it slightly affects the vibrationally resolved absorption and fluorescence spectra. The discrepancy between the theoretical and experimental results is attributed to inaccurately describing excited-states calculated by the time-dependent density functional theory as well as to not fully accounting for the complex experimental conditions. This work provides a demonstration of what proportion of ISC and RISC rate coefficients of a MR-type TADF emitter can be covered by the HTVC effect, and it opens design routes that go beyond the FC approximation for the future development of high-performance OLED devices.

Due to the limitation of donor and acceptor group selection, the efficient thermally activated delayed fluorescence (TADF) type sensitizer used for blue organic light‐emitting diodes (OLEDs) is rare. Multiple resonance (MR) type TADF emitters can easily achieve efficient blue emission. And the compounds exhibit small Stokes shift and lower absorption energy under the same emission color compared with traditional TADF, mitigating the damage of high‐energy absorption of sensitizer on material stability. However, their characteristics as sensitizers have not been explored. In this work, a deep‐blue MR‐TADF compound (3tPAB) is selected as a sensitizer for both blue traditional fluorescence and MR‐TADF OLED. Given the improved photoluminescence quantum yield and the utilization of triplet excitons, the TADF‐sensitized fluorescent device using 3tPAB as sensitizer presents a maximum external quantum efficiency (EQEmax) of 14.4%, showing ≈2.4 times increase compared with the device without sensitizer. More impressively, TADF‐sensitized TADF (TST) device using 3tPAB as sensitizer and MR‐TADF compound PhDMAC‐BN as emitter exhibits EQEmax of 33.9%. And in TST device, efficient Förster energy transfer is demonstrated, thus, the device can maintain high color purity. The work first demonstrates the feasibility of MR‐TADF as a sensitizer and provides a new strategy for developing high‐performance blue OLED with high color purity.

Phthalonitrile-based bipolar host for efficient green to red phosphorescent and TADF OLEDs

Circularly polarized luminescence (CPL) molecules, especially those with thermally activated delayed fluorescence (TADF) properties, have attracted considerable attention due to their great potential for chiroptical organic light emitting diode (OLED) devices. Here we developed a new pair of TADF emitters with CPL based on boron complexes using chiral donor (cD) binaphthalene, acceptor (A) biphenyl boron β-diketonate, and donor (D) biphenylamine in a cD-A-D architecture. With this design, both efficient intramolecular charge transfer (ICT) and chiral ICT for high-performance CPL were established, leading to high dissymmetry factors (|glum|) up to 2.2 × 10-3 in solution and significantly red-shifted emission around 600 nm for red TADF with a quantum yield over 15% in doped films. More impressively, with these chiral TADF emitters, solution-processed red circularly polarized OLEDs (CP-OLEDs) exhibit external quantum efficiencies (EQEs) up to 2.0% and efficient circularly polarized electroluminescence with dissymmetry factors of 2.6 × 10-3, which are among the best performances of the reported solution-processed orange-red and red TADF CP-OLEDs. These results illustrate the great success of the cD-A-D strategy in designing high-performance CPL TADF emitters with axially chiral boron complexes, providing important clues to understand efficient chiral transfer for large |glum| values and high device performance of CP-OLEDs.

Stretchable light-emitting devices are poised to play a central role in advancing human–technology integration, enabling applications such as on-skin displays, optical sensing, and implantable phototherapy. Among them, stretchable organic light-emitting diodes (OLEDs) are particularly attractive due to their high efficiency and potential biocompatibility. The recent realization of thermally activated delayed fluorescence (TADF) in stretchable emitters, enabling triplet exciton harvesting, has increased external quantum efficiency (EQE) to 10%. However, triplet–triplet annihilation (TTA) remains a key barrier to further improvement toward commercial-grade performance. Here, we introduce a stretchable host–guest emitter design that overcomes this quenching mechanism by uniformly dispersing TADF small-molecule guests within a newly designed stretchable host polymer. This architecture enables efficient exciton transfer while suppressing TTA, yielding an external quantum efficiency (EQE) of 20.3%—doubling the performance of prior state-of-the-art. Notably, the guest molecules also act as plasticizers, enhancing stretchability beyond 150%. With generalizability to different TADF emitters, this work establishes a foundational strategy for mitigating TTA in stretchable emissive layers, advancing soft optoelectronics toward commercial viability with mechanical durability and practicality.

Much effort has been devoted to developing highly efficient organic light-emitting diodes (OLEDs) that function through phosphorescence or thermally activated delayed fluorescence (TADF). However, efficient host materials for blue TADF and phosphorescent guest emitters are limited because of their requirement of high triplet energy levels. Herein, we report the rigid acceptor unit benzimidazobenzothiazole (BID-BT), which is suitable for use in bipolar hosts in blue OLEDs. The designed host materials, based on BID-BT, possess high triplet energy and bipolar carrier transport ability. Both blue TADF and phosphorescent OLEDs containing BID-BT-based derivatives exhibit external quantum efficiencies as high as 20 %, indicating that these hosts allow efficient triplet exciton confinement appropriate for blue TADF and phosphorescent guest emitters.

Thermally activated delayed fluorescence (TADF) is a temperature-dependent luminescence mechanism that allows the harvesting of both singlet and triplet excitons for fluorescence emission. Consequently, TADF-active compounds exhibit excellent photophysical properties, such as high luminescence efficiencies and long excited-state lifetimes. In recent times, TADF materials have found widespread applications in material and life science, most prominently in organic light-emitting diodes (OLEDs). Many design strategies for TADF emitters have emerged, amongst which the use of transition metal complexes constitutes an appealing approach. In this chapter, the theoretical background of the TADF phenomenon is discussed, different types of metal-based TADF emitters are introduced, selected case studies are highlighted, and an overview is given of the many applications of TADF materials in light-driven systems.

Deep-blue thermally activated delayed fluorescence emitter with a very high fluorescence rate

Deep-blue thermally activated delayed fluorescence (TADF) molecules present promising potential in organic light-emitting diodes (OLEDs), especially for display applications. Here, an efficient molecular engineering approach to modifying the donor or acceptor features of the D-π-A-configured TADF molecules for deep-blue emission is reported. By introducing oxygen and sulfone as a bridge unit onto the macrocyclic donor, two emitters, c-ON-MeTRZ and c-NS-MeTRZ, are synthesized and characterized, respectively. The reduced donor strength of c-ON-MeTRZ and c-NS-MeTRZ as compared to that of the model molecule c-NN-MeTRZ leads to blue-shifted emissions with high photoluminescence quantum yields (PLQYs) and retains TADF characters, while the new emitter c-NN-MePym with the most blue-shifted emission only exhibits a pure fluorescent nature because of the electron-accepting feature of pyrimidine that is insufficient for inducing the TADF property. In the presence of macrocyclic donors, these new emitters show high horizontal dipole ratios (Θ// = 85-89%), which are beneficial for improving the light out-coupling efficiency. Deep-blue TADF OLEDs incorporating c-ON-MeTRZ as an emitter doped in the mCPCN host achieves a high maximum external quantum efficiency (EQEmax) of 30.2% together with 1931 Commission Internationale de I'Eclairage (CIE) coordinates of (0.14, 0.13), while the counter device employing c-NS-MeTRZ as a dopant gives EQEmax of 15.4% and CIE coordinates of (0.14, 0.09). The EQEmax of c-ON-MeTRZ- and c-NS-MeTRZ-based devices can be significantly improved to 34.4 and 29.3%, respectively, with a polar host DPEPO, which stabilizes the charge transfer (CT) S1 state to give lower ΔEST for improving the reverse intersystem crossing process. The efficient TADF character, high PLQYs, and high anisotropic emission dipole ratios work together to render the superior electroluminescence (EL) efficiencies. Based on the detailed characterizations of physical properties, theoretical analyses, and comprehensive study on the corresponding devices, a clear structure-property-performance relationship has been successfully established to verify the effective molecular design strategy of modulating the macrocyclic donor characters for efficient deep-blue TADF emitters.

Sensitizing conventional fluorescent molecules is an effective way to improve the efficiency of fluorescent-based organic light-emitting diode (OLED) devices. The relatively long triplet exciton lifetime of thermally activated delayed fluorescence (TADF) emitters can cause serious efficiency roll-off. In this work, we use an efficient TADF emitter 2,7-TXO-PhCz to sensitize a conventional fluorescence emitter tetraphenyldibenzoperiflanthene (DBP). The energy transfer efficiency from the singlet excited state of the TADF sensitizer to the singlet excited state of the fluorescence guest can reach up to 90%. Profiting from the efficient energy transfer process, the reverse intersystem crossing can be accelerated and the delayed lifetime of the TADF sensitizer can be reduced. The TADF-sensitized fluorescent OLEDs can achieve a maximum external quantum efficiency (EQE) of 15.9% with reduced efficiency roll-off. Besides, the sensitization efficiency can achieve 77%, which indicates almost pure fluorescent emission. Our results provide an efficient approach to realize highly efficient OLEDs with low roll-off and can be helpful to overcome the limitation of TADF emitters.