Asymmetric Structural Engineering of Hot-Exciton Emitters Achieving a Breakthrough in Non-Doped BT.2020 Blue OLEDs with a Record 9.5% External Quantum Efficiency

A High-Efficiency Ultraviolet Organic Light-Emitting Diode Employing a Double Boron-Oxygen-Nitrogen-Based Emitter

Designing high-efficiency ultraviolet organic light-emitting diodes (UV OLEDs) remains challenging due to the need for efficient utilization of triplet excitons while maintaining a wide bandgap. In this study, we designed double boron-oxygen-nitrogen-based polycyclic aromatic hydrocarbons (dBON-PAHs) with rigid planar structures and developed a novel UV emitter, BO-N, featuring hybridized local and charge-transfer (HLCT) properties. BO-N exhibited UV emission in toluene solution and 1,3-di(9H-carbazol-9-yl)benzene (mCP) film, with photoluminescence (PL) peaks of 391 and 400 nm and narrow full width at half-maximum (FWHM) values of 15 and 34 nm, respectively. The device doped with 5 wt% BO-N achieved a narrowband UV emission with an FWHM of 37 nm, an electroluminescence peak (λEL) of 399 nm, and CIE coordinates of (0.166, 0.030). Moreover, the device attained a record-high maximum external quantum efficiency (EQEmax) of 18.6% among reported HLCT-based UV OLEDs with CIEy < 0.05. These findings highlight the great potential of double BON-PAHs as robust emitters for high-performance UV OLEDs.

Hot-Exciton-Involved Dual-Channel Stepwise Energy Transfer Enabling Efficient and Stable Blue OLEDs with Narrow Emission and High Luminance

Marching toward next-generation ultrahigh-definition and high-resolution displays, the development of high-performance blue organic light-emitting diodes (OLEDs) with narrow emission and high luminance is essential and requires conceptual advancements in both molecular and device design. Herein, a blue organic emitter is reported that exhibits hot-exciton and aggregation-induced emission characteristics, and use it as a sensitizer in the proposed triplet-triplet annihilation (TTA)-assisted hot-exciton-sensitized fluorescence (HSF) device, abbreviated THSF. Results show that through dual-channel stepwise Förster and Dexter energy transfer processes, the THSF system can simultaneously enhance exciton utilization, accelerate exciton dynamics, and reduce the concentration of triplet excitons. The smooth management of excitons makes the overall performance of the THSF device superior to the control TTA fluorescence and HSF devices. Furthermore, a high-performance narrowband blue (CIEx,y = 0.13, 0.12) OLED is achieved using a two-unit tandem device design, providing an excellent maximum external quantum efficiency of 18.3%, a record-high L90% (the luminance where the ƞext drops to 90% of its peak value) of ≈20 000 cd m-2, and a long half-lifetime at 100 cd m-2 initial luminance of ≈13 256 h. These results showcase the great potential of the THSF strategy in realizing efficient and stable blue OLEDs with narrow emission and high luminance.

Intramolecular-locking modification enables efficient asymmetric donor-acceptor-donor' type ultraviolet emitters for high-performance OLEDs with reduced efficiency roll-off and high color purity

Developing high-performance ultraviolet organic light-emitting diodes with low efficiency roll-off and high color purity remains challenging due to their inherent wide-bandgap characteristics. In this work, we present an intramolecular noncovalent bond locking strategy to modulate donor-acceptor-donor' (D-A-D') type ultraviolet fluorophores (mPImCZ2F, mPIoCZ2F and mPImCP2F) with a hot-exciton mechanism. Notably, these asymmetric emitters exhibit significantly enhanced bipolar transport capacity and fluorescence efficiency compared to their counterparts. Among them, mPIoCZ2F exhibits a more remarkable intramolecular locking effect due to multiple C-H⋯F interactions and ortho-substitution-induced steric hindrance, which endows it with a higher radiation rate, narrower emission spectrum, and more balanced charge transport. Consequently, the mPIoCZ2F-based non-doped device achieves an electroluminescence (EL) peak at 393 nm with a maximum external quantum efficiency (EQE) of 6.62%. Moreover, in the doped device, mPIoCZ2F emits stable ultraviolet light with an EL peak at 391 nm and a full width at half maximum (FWHM) of 40 nm, corresponding to color coordinates of (0.167, 0.025). It also exhibits an exceptionally high EQE of 8.71% and minimal efficiency roll-off (7.95% at 1000 cd m-2), ranking among the best EL efficiencies reported for UV-OLEDs at high brightness levels.