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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]

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.

Two novel donor-σ-π-σ-acceptor-type dispiro molecules-10-phenyl-10H-dispiro-acridine-9,9'-anthracene-10',9''-fluorene-2'',7''-dicarbo-nitrile (DiSAAF) and dispiro-fluorene-9,9'-anthracene-10',9''-quinolino[3,2,1-kl]phenoxazine-2,7-dicarbonitrile (DiSFAQ)-with excellent thermal stability are designed and synthesized. Both materials exhibit blocked long-range intramolecular charge transfer but show intermolecular charge-transfer emission in the film state. Their photophysical and thermal properties then are fully investigated and a maximum external quantum efficiency of 21.7% of the red phosphorescent device is achieved by DiSAAF.