Abstract Flexible top-emission organic light-emitting diodes (f-TEOLEDs) with a high aperture ratio can be used in next-generation wearable electronic applications. However, the advancement of f-TEOLEDs is being hindered by their low light extraction and poor mechanical stability. In this study, we introduce an omnidirectional reflector (ODR) consisting of an Ag/SiO 2 /Ta 2 O 5 cylinder-embedded indium zinc oxide (IZO) mesh (c-mesh) structure that improves both the light extraction and mechanical flexibility of TEOLEDs using blue thermally activated delayed fluorescence emitters. The proposed ODR achieved a remarkable reflectance of over 96%, particularly in the transverse-electric mode. Furthermore, the Ta 2 O 5 cylinders effectively compensated for the diverse void-induced depths in the IZO mesh, significantly reducing the leakage current between the electrode and the organic layers. In addition, the ODR electrodes exhibited outstanding mechanical stability. Moreover, even after being subjected to 2000 bending cycles over a 5 mm radius, the device luminance changed by less than 20%. Notably, the proposed f-TEOLEDs with Ag/SiO 2 /c-mesh electrodes demonstrated superior performance, achieving a low turn-on voltage (2.6 V), high current efficiency (33 cd·A −1 ), and power efficiency of 29.6 lm·W −1 . Finally, the devices featured a narrow full width at half maximum of 27 nm under first-order microcavity effects.

Abstract In the past, considerable effort are focused on advancing blue organic light‐emitting diodes (OLEDs) based on 1,3‐bis(N‐carbazolyl)benzene (mCP). To enhance and stabilize the device performance in vacuum‐processed OLEDs, it is essential to optimize the thermally stable organic materials constituting the emitting layer. The proposed novel carbazole derivative, Ad‐mCP , is designed and synthesized as a host material for blue thermally activated delayed fluorescence OLEDs, which are ideal for vacuum processing. Ad‐mCP exhibits a high glass transition temperature and triplet energy (T 1 ), making it highly compatible with the blue dopant 2,11,14‐tri‐ tert ‐butyl‐N,N,5‐tris(4‐( tert ‐butyl)phenyl)−5 H ‐5,8b‐diaza‐15b‐borabenzo[ a ]naphtho[1,2,3‐ hi ]aceanthrylen‐7‐amine emitter. The incorporation of a rigid adamantane unit into the carbazole group modifies the molecular structure of mCP, preserving crucial photophysical properties, such as T 1, while enhancing the morphological and thermal stability of the host material in its film state. Moreover, the spatially hindered molecular structure of Ad‐mCP improves the photoluminescent quantum yield of the emissive layer and enhances charge balance, crucially contributing to the overall efficiency of the OLEDs. As a result, the exceptional performance of Ad‐mCP as a host material for OLEDs resulted in a remarkably high maximum external quantum efficiency of 29.9%, demonstrating superior stability in efficiency even after thermal annealing compared to mCP devices.

Double perovskites, particularly Cs2AgBiCl6, have attracted substantial attention as promising alternatives to lead-halide perovskites because they are environmentally friendly. However, the integration of these double perovskites into light-emitting diodes (LEDs) remains challenging because of their poor performance, which is primarily attributed to a limited understanding of the correlation between crystallization and defect formation. In this study, deep-trap defects caused by B-site antisites and vacancies are introduced into the double perovskite formamidinium (FA)1.5Cs0.5AgBi(Cl0.75Br0.25)6 lattice during crystallization. Remarkably, valeric acid suppresses antisites and facilitates the formation of distinct nanocrystals with a structurally ordered double perovskite. Poly(ethylene oxide) encapsulates the perovskites in situ and passivates surface defects by modifying the grain boundaries. In this manner, the coadditive strategy boosts the performance of the double-perovskite-based deep blue LED with a record external quantum efficiency of 1.8% and peak luminance of 280 Cd/m2. This study significantly advances our understanding of double perovskites and provides new perspectives for future investigations.