Omnidirectional reflector based on Ta₂O₅ cylinder-filled IZO mesh structure for flexible and efficient blue TADF top-emission OLEDs

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/SiO₂/Ta₂O₅ 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 Ta₂O₅ 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/SiO₂/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.