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Organic light emitters based on multiresonance-induced thermally activated delayed fluorescent materials have great potential for realizing efficient, narrowband organic light-emitting diodes (OLEDs). However, at high brightness operation, efficiency roll-off attributed to the slow reverse intersystem crossing (RISC) process hinders the use of multiresonance-induced thermally activated delayed fluorescent materials in practical applications. Here we report a heavy-atom incorporating emitter, BNSeSe, which is based on a selenium-integrated boron–nitrogen skeleton and exhibits 100% photoluminescence quantum yield and a high RISC rate (kRISC) of 2.0 × 106 s−1. The corresponding green OLEDs exhibit excellent external quantum efficiencies of up to 36.8% and ultra-low roll-off character at high brightnesses (with very small roll-off values of 2.8% and 14.9% at 1,000 cd m−2 and 10,000 cd m−2, respectively). Furthermore, the outstanding capability to harvest triplet excitons also enables BNSeSe to be a superior sensitizer for a hyperfluorescence OLED, which shows state-of-the-art performance with a high excellent external quantum efficiency of 40.5%, power efficiency beyond 200 lm W−1, and luminance close to 20,0000 cd m−2.Green OLEDs based on BNSeSe offer high operational efficiency and reduced efficiency roll-off.

Organic light-emitting diodes (OLEDs) are a promising light-source technology for future generations of display1,2. Despite great progress3–12, it is still challenging to produce blue OLEDs with sufficient colour purity, lifetime and efficiency for applications. Here, we report pure-blue (Commission Internationale de l’ Eclairage (CIE) coordinates of 0.13, 0.16) OLEDs with high efficiency (external quantum efficiency of 32 per cent at 1,000 cd m−2), narrow emission (full-width at half-maximum of 19 nm) and good stability (95% of the initial luminacnce (LT95) of 18 hours at an initial luminance of 1,000 cd m−2). The design is based on a two-unit stacked tandem hyperfluorescence OLED with improved singlet-excited-state energy transfer from a sky-blue assistant dopant exhibiting thermally activated delayed fluorescence (TADF) called hetero-donor-type TADF(HDT-1) to a pure-blue emitter. With stricter control of device fabrication and procedures it is expected that device lifetimes will further improve to rival commercial fluorescent blue OLEDs.Pure-blue organic LEDs with narrow emission and improved stability show promise for display applications.

Multiple-resonance thermally activated delayed fluorescence materials have emerged as promising candidates for next-generation ultrahigh-definition displays due to their narrowband emission and triplet-harvesting capability. However, achieving optimal colour purity and device efficiency for blue multiple-resonance thermally activated delayed fluorescence emitters has presented challenges. Here we demonstrate an effective approach to attain superior deep-blue molecules by constructing twisted-boron-/nitrogen-/oxygen-embedded higher-order fused-ring frameworks with fully resonating structures. The optimized emitter exhibits high rigidity and minimized bonding/antibonding character for ultrasharp emission, along with a small singlet–triplet gap and large spin–orbit couplings for rapid spin flip. This combination results in deep-blue emission at 458 nm with a narrow full-width at half-maximum of 12 nm in solution and a reverse intersystem crossing rate constant of 2.29 × 10 6  s −1 , on par with those of heavy-atom-based multiple-resonance thermally activated delayed fluorescence molecules. The related single-unit organic light-emitting diode achieves an external quantum efficiency of 39.2% with colour coordinates of (0.141, 0.050) and a narrow full-width at half-maximum of 14 nm. Furthermore, a two-unit stacked tandem hyperfluorescence organic light-emitting diode achieves an ultrahigh external quantum efficiency of 74.5% with low efficiency roll-off at high luminance values. This performance represents a remarkable balance between efficiency and colour purity in the deep-blue region, marking an important step towards power-efficient ultrawide-colour-gamut displays. Highly twisted multi-boron-based multiple-resonance thermally activated delayed fluorescence emitters enable deep-blue organic light-emitting diodes with high colour purity, a narrow full-width at half-maximum of 14 nm and a peak external quantum efficiency of 39.2%.

Color-saturated green-emitting molecules with high Commission Internationale de L’Eclairage (CIE) y values have great potential applications for displays and imaging. Here, we linked the outer phenyl groups in multiple-resonance (MR)-type blue-emitting B (boron)-N (nitrogen) molecules through bonding and spiro-carbon bridges, resulting in rigid green emitters with thermally activated delayed fluorescence. The MR effect and multiple interlocking strategy greatly suppressed the high-frequency vibrations in the molecules, which emit green light with a full-width at half-maximum of 14 nm and a CIE y value of 0.77 in cyclohexane. These were the purest green molecules with quantum efficiency and color purity that were comparable with current best quantum dots. Doping these emitters into a traditional green-emitting phosphorescence organic light-emitting diode (OLED) endowed the device with a Broadcast Service Television 2020 color-gamut, 50% improved external quantum efficiency, and an extremely high luminescence of 5.1 × 10 5  cd/m 2 , making it the greenest and brightest OLED ever reported. The authors combine multiple resonance effect and multi-lock strategy to dope green-emitting thermally activated delayed fluorescent molecules into green-emitting phosphorescence OLEDs by endowing the device with a Broadcast Service Television 2020 color-gamut, 50% improved EQE, and a high luminescence of half a million nits.

Electroluminescence efficiencies of metal halide perovskite nanocrystals (PNCs) are limited by a lack of material strategies that can both suppress the formation of defects and enhance the charge carrier confinement. Here we report a one-dopant alloying strategy that generates smaller, monodisperse colloidal particles (confining electrons and holes, and boosting radiative recombination) with fewer surface defects (reducing non-radiative recombination). Doping of guanidinium into formamidinium lead bromide PNCs yields limited bulk solubility while creating an entropy-stabilized phase in the PNCs and leading to smaller PNCs with more carrier confinement. The extra guanidinium segregates to the surface and stabilizes the undercoordinated sites. Furthermore, a surface-stabilizing 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene was applied as a bromide vacancy healing agent. The result is highly efficient PNC-based light-emitting diodes that have current efficiency of 108 cd A−1 (external quantum efficiency of 23.4%), which rises to 205 cd A−1 (external quantum efficiency of 45.5%) with a hemispherical lens.Guanidinium doping is shown to enhance the operation of perovskite nanocrystal light-emitting diodes.

Highly efficient and stable blue organic light-emitting diodes (OLEDs), although required for display and lighting applications, remain rare. Here we report a molecular perdeuteration strategy to stabilize blue thermally activated delayed fluorescence (TADF) emitters. Perdeuterated sky-blue TADF emitters exhibit higher efficiencies and doubled device lifetime in OLEDs compared with protonated emitters, owing to suppressed high-energy vibrations. Perdeuteration also leads to blue-shifted and narrowed spectra in the solid state, which in turn improves the Förster energy transfer to the deep-blue final emitter in TADF-sensitized fluorescent OLEDs. These devices exhibit a maximum external quantum efficiency of 33.1% and a lifetime to reach 80% of the initial luminance of 1,365 h with a Commission Internationale de l’Eclairage y coordinate of 0.20 at a luminance of 1,000 cd m −2 , even outperforming blue phosphorescent OLEDs. Our perdeuteration strategy improves the device performance of blue OLEDs, paving the way for their broader applications in displays and lightings. Molecular perdeuteration of thermally activated delayed fluorescence emitters improves the performance of blue organic light-emitting diodes, enabling a peak external quantum efficiency of 33.1% and a device lifetime to reach 80% of initial luminance of over 1,300 h.

Luminescent materials that exhibit narrowband emission are vital for full-colour displays. Here, we report a thermally activated delayed-fluorescence material that exhibits ultrapure blue emission with full-width at half-maximum of just 14 nm. The emitter consists of five benzene rings connected by two boron and four nitrogen atoms and two diphenylamino substituents. The multiple resonance effect of the boron and nitrogen atoms induces significant localization of the highest occupied and lowest unoccupied molecular orbitals on different atoms to minimize not only the vibronic coupling between the ground state (S0) and the singlet excited state (S1) but also the energy gap between the S1 state and triplet excited state (T1). Organic light-emitting diode devices employing the emitter emit light at 469 nm with full-width at half-maximum of 18 nm with an external quantum efficiency of 34.4% at the maximum and 26.0% at 1,000 cd m−2.

Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. However, blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin–orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. An extremely fast exciton lifetime of 750 ns was realized in a donor–acceptor-type molecular structure without heavy metal elements. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. Further, the high maximum efficiency were retained to be 20.2% and 17.4% even at high luminance. Deep-blue emitting organic materials with low exciton lifetime are required to realize efficient organic light-emitting diodes (OLEDs) at high brightness. Here, the authors report deep-blue OLEDs featuring thermally activated delayed fluorescence molecules with subnano-second exciton lifetime.

As promising luminescent materials for organic light-emitting diodes (OLEDs), thermally activated delayed fluorescence materials are booming vigorously in recent years, but robust blue ones still remain challenging. Herein, we report three highly efficient blue and deep-blue delayed fluorescence materials comprised of a weak electron acceptor chromeno[3,2-c]carbazol-8(5H)-one with a rigid polycyclic structure and a weak electron donor spiro[acridine-9,9’-xanthene]. They hold distinguished merits of excellent photoluminescence quantum yields (99%), ultrahigh horizontal transition dipole ratios (93.6%), and fast radiative transition and reverse intersystem crossing, which furnish superb blue and deep-blue electroluminescence with Commission Internationale de I’Eclairage coordinates (CIE x,y ) of (0.14, 0.18) and (0.14, 0.15) and record-beating external quantum efficiencies ( η ext s) of 43.4% and 41.3%, respectively. Their efficiency roll-offs are successfully reduced by suppressing triplet-triplet and singlet-singlet annihilations. Moreover, high-performance deep-blue and green hyperfluorescence OLEDs are achieved by utilizing these materials as sensitizers for multi-resonance delayed fluorescence dopants, providing state-of-the-art η ext s of 32.5% (CIE x,y  = 0.14, 0.10) and 37.6% (CIE x,y  = 0.32, 0.64), respectively, as well as greatly advanced operational lifetimes. These splendid results can surely inspire the development of blue and deep-blue luminescent materials and devices. Thermally activated delayed fluorescence materials are important for the development of OLED materials but the development of robust blue emitting materials remains challenging. Here, the authors report three highly efficient blue and deepblue delayed fluorescence materials demonstrating excellent electroluminescence performance.

Perovskite light-emitting diodes (LEDs) are attracting great attention due to their efficient and narrow emission. Quasi-two-dimensional perovskites with Ruddlesden–Popper-type layered structures can enlarge exciton binding energy and confine charge carriers and are considered good candidate materials for efficient LEDs. However, these materials usually contain a mixture of phases and the phase impurity could cause low emission efficiency. In addition, converting three-dimensional into quasi-two-dimensional perovskite introduces more defects on the surface or at the grain boundaries due to the reduction of crystal sizes. Both factors limit the emission efficiency of LEDs. Here, firstly, through composition and phase engineering, optimal quasi-two-dimensional perovskites are selected. Secondly, surface passivation is carried out by coating organic small molecule trioctylphosphine oxide on the perovskite thin film surface. Accordingly, green LEDs based on quasi-two-dimensional perovskite reach a current efficiency of 62.4 cd A −1 and external quantum efficiency of 14.36%. Solution-processable halide perovskites have high luminous efficiency and excellent chemical tunability, making them ideal candidates for light-emitting diodes. Here Yang et al. achieve high external quantum efficiency of 14% in the devices by fine-tuning the phase and passivating the surface defects.