Since the first reported demonstration of organic light-emitting diodes (OLEDs) by C. W. Tang in 1987, OLEDs have been considered to be the most suitable for next-generation displays because of their excellent properties such as ultrathinness, broad color gamut, self-emitting characteristics, high-speed response, and applicability to devices of various form factors that are emerging in the limelight. However, the expansion of OLEDs into the market depends on the requirement of simultaneously satisfying high performance and long lifespan, which is hindered by hurdles such as imprisoned light in the internal device structure and vulnerability of organic materials to oxygen and moisture.Continuous development of light-emitting organic materials has been carried out to improve the luminous efficiency of OLEDs. In particular, the generation of organic emitter has evolved according to the methods which can internally maximize the utilization of the excitons generated under the spin coupling probability rule. Thermally activated delayed fluorescence (TADF) materials, third-generation organic light-emitting molecules, are considered the most proper material for blue OLEDs as they utilize all excitons for light emission by engineering the singlet and triplet exciton level to be less than the thermal energy at room temperature. This triplet exciton up-conversion can result in maximized internal quantum efficiency, but it also causes redundant exciton annihilation due to the long lifetime of the triplet exciton, leading to a negative phenomenon noted as efficiency roll-off characteristics.In this dissertation, the high-performance blue TADF OLEDs were demonstrated by leveraging exciton coupling extraction and diffusion guidance. By configuring an array of nanopixels in blue TADF OLEDs by inserting nanoscale pixel-defining layer (nPDL), suppression of the roll-off characteristics and enhancement of light efficiency are realized simultaneously.First, exciton diffusion was induced due to the exciton concentration gradient inside the single emitting layer. By simply arranging a nanostructure of insulator above the anode, flow of charge carriers can be spatially separated. Therefore, the generation of excitons is confined exclusively within the spatial domain by the insulating material denoted as the nanopixel. Given the spatial disparity in exciton concentration, diffusion of the triplet exciton was induced, leading to the suppression of the exciton quenching. Exciton diffusion guidance was verified by the improved exciton decay lifetime and delayed luminance ratio via bi-exponential functionalized time-resolved electroluminance (EL) measurement. Decay parameter of nanopixel device was increased by 203.31%, and delayed luminance ratio was increased by 38.19% compared to the reference.Second, by judicious design through photonic computational analysis, optimized nPDL for blue light amplification, was inserted into the TADF-emitter based blue OLEDs. The periodic array of nanostructure not only extracted the trapped blue light inside the device, but also suppressed exciton annihilation. Extraction of the exciton coupled energy into the non-radiative surface plasmon polaritons mode can be verified from the transverse magnetic polarized spectrum along the device and enhanced luminous efficiency. The fabrication of the nanoarray was simply performed by the laser interference lithography process. Also, to boost the device performance, the ground emitting system was incorporated into mixed-host structure, which is capable of taking advantage of different materials in one single emission layer. The external quantum, current, and power efficiencies at 1000 cd m−2 were improved by 88.4%, 118.8%, and 108.8%, respectively, compared to the reference device. As a result, the operation lifetime of the optimized nPDL device were improved by 247.33% compared to the reference.This pioneering demonstration of hybridizing the material combination and nanopatterning techniques is expected to provide new insights for designing high-performance OLEDs.