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Perovskite light-emitting diodes (PeLEDs) have been attracting widespread attention owing to their unique advantages such as high luminance, narrow emission spectra and high color purity. However, the solution-processed fabrication method makes the deposition of multi-emitting layers of perovskite films for white PeLEDs challenging. Moreover, modulating the emission color by adjusting the thickness of the emitting layers will result in reduced optoelectronic performance of the polycrystalline perovskite films. Therefore, strategies for achieving high-performance white PeLEDs are urgently needed. This study developed a newly designed perovskite/organic hybrid tandem light-emitting diode (POTLED) by combining a bottom PeLED unit with a top organic light-emitting diode (OLED) unit. The vacuum deposition process of the OLED avoids damaging the underlying PeLED unit. Additionally, the emission color of the tandem device can be tuned by adjusting the thickness of the organic emitting layer while maintaining the optoelectronic properties of the perovskite layer. As a result, a high-efficiency green POTLED with an outstanding current efficiency of 144.2 cd A−1, an external quantum efficiency of 41.1%, and a luminance of over 32 000 cd m−2 is achieved, illustrating the feasibility and potential of the hybrid tandem perovskite-organic structure to realize high-efficiency white-color perovskite-based devices. [ABSTRACT FROM AUTHOR]

Energy matching between the triplet level of the exciplex hosts and phosphorescent emitters is of particular importance to achieve highly efficient exciplex-based white organic light emitting diodes (WOLEDs). Herein, we design a novel exciplex host and use it for WOLEDs by arranging rational multiple-exciplex hosts in emissive layers. The resulting two-color warm WOLED, by doping blue and orange phosphorescent emitters, shows a maximum forward-viewing power efficiency and external quantum efficiency (EQE) of 104.6 lm W−1 and 30.9%, respectively. Significantly, the EQE still remains 22.1% at 5000 cd m−2. Meanwhile, the three-color warm WOLED has a high color rendering index of over 80 with a maximum EQE of 27.0% and the EQE can remain 21.3% at 5000 cd m−2. These results indicate that rational arrangement of multiple-exciplex hosts in emissive layers is promising for the fabrication of highly efficient WOLEDs. [ABSTRACT FROM AUTHOR]

Luminous efficiency, color purity and spectral stability of white organic light-emitting diodes (WOLEDs) remain the key challenges for display applications based on the "white plus color filter" approach. To tackle these issues, we developed high-efficiency and color-stable WOLEDs in natural color based on all thermally activated delayed fluorescence (TADF) emitters constructed with a blue-orange-blue sandwich emissive layer (EML) structure. The balanced carrier transport and good exciton confinement in this system facilitate excitons broadly forming over the recombination zone and thus realizing a balance of blue and orange emissions in the EMLs successfully. As a result, the device exhibits high-performance pure white emission with the ideal and stable Commission International de I'Eclairage (CIE) coordinates (x, y) of (0.33 ± 0.01, 0.33 ± 0.01) and a high color rendering index (CRI) of 81–83 at a luminance in the range of 250 to 5000 cd m−2. The device shows a maximum external quantum efficiency (EQE) and current efficiency (CE) of 12.0% and 28.0 cd A−1, respectively. The full-TADF WOLEDs with a sandwich EML not only show ideal CIE coordinates and CRIs, but also exhibit excellent color stability. We anticipate that our findings can provide an efficient strategy to realize color stable and high color-purity WOLEDs through the full TADF mechanism and have great potential for display applications. [ABSTRACT FROM AUTHOR]

Metal halide-based perovskites are regarded as promising candidates for light-emitting diodes (LEDs) owing to their high color purity, tunable bandgap and solution processability. However, poor active-layer morphology and non-radiative charge recombination are still the main obstacles for practical use in displays and lighting. Here, we report a facile method to achieve high-performance green emitting perovskite light-emitting diodes (PeLEDs) by inserting an interface buffer layer (BL) based on an amphipathic conjugated molecule, betaine. We show evidence that the betaine layer controls the grain size of the perovskite and hence increases the crystalline nucleation sites, which ultimately leads to a high photoluminescence quantum yield (PLQY) and a device with an external quantum efficiency (EQE) of 11.1%. In addition, the current leakage is significantly reduced due to the high quality crystallization of the thin film. These results indicate that the interface BL is an effective strategy to boost the efficiency of PeLEDs. [ABSTRACT FROM AUTHOR]

All-inorganic halide perovskites with superior optoelectronic properties are promising materials for efficient perovskite light-emitting diodes. However, they usually suffer from a large grain size (hundreds of nanometers), high surface roughness and poor stability during the spin coating process. Here, we report a facile strategy to fabricate a uniform and flat CsPbBr3 film. A small amount of lecithin (LE) introduced into CsPbBr3 precursor solution can promote the formation of small CsPbBr3 grains that remarkably improve the uniformity of perovskite films with a surface roughness of about 2.2 nm. Furthermore, the CsPbBr3–LE films display excellent fluorescence stability in ambient air and LED devices based on the CsPbBr3–5 wt% LE film exhibit a current efficiency (CE) of 24 cd A−1 with an external quantum efficiency (EQE) of 6.5%. Therefore, it is anticipated that the findings of the present study will have great potential to boost the development of PeLEDs. [ABSTRACT FROM AUTHOR]

Capping layers (CPLs) are commonly employed in top-emitting organic light-emitting diodes (TEOLEDs) due to their ability to optimize color purity, enhance external light out-coupling efficiency, and improve device stability. However, the mismatch in refractive index between CPLs and thin film encapsulation (TFE) often induces light trapping. This study introduces a novel approach by combining a low refractive index material, lithium fluoride (LiF), with the traditional TFE material, silicon nitride (SiN x ), to form a combined CPL (LiF/SiN x ), resulting in improved light outcoupling and light reflection properties. The significant refractive index contrast between LiF and SiN x can facilitate enhanced light extraction by redirecting internally reflected light through evanescent waves. Moreover, the LiF/SiN x CPLs function as a secondary resonant cavity, leading to reduced emission spectral bandwidth and enhanced light extraction compared to the control TEOLEDs that only incorporate the primary cavity of organic active layers. As a result, incorporating the LiF/SiN x CPLs significantly increases current efficiency from 125.0 cd A -1 to 163.6 cd A -1 for green devices, from 71.2 cd A -1 to 110.1 cd A -1 for red devices, and from 43.1 cd A -1 to 53.1 cd A -1 for blue devices, with the corresponding full width at half maximum decreased from 20 nm to 10 nm, 26 nm to 14 nm, and 21 nm to 12 nm, respectively, demonstrating the compatibility of the CPLs with different color devices. Notably, an LT 95 lifetime of 51 300 hours for green devices was achieved when tested at 1000 cd m -2 . Utilizing narrow-band light emission without spectral overlap of each color enables the generation of purer and more vivid colors for display.