Marching Toward Highly Efficient, Pure-Blue, and Stable Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes

The vast market demands for applications of organic light-emitting diodes (OLEDs) have quickened the pace of the search for future high-performance materials, emphasizing the importance of exploring blue light-emitting materials, which determine the performance bottleneck of OLEDs. Moreover, actualizing highly efficient, pure-blue, stable, and purely organic electroluminescence will pave the way toward the realization of cost-effective, high-quality, and long-lasting commercialized OLED displays and illumination applications. Without the aid of noble heavy metal atoms, the newly emerging thermally activated delayed fluorescent (TADF) materials can effectively utilize triplet excitons owing to the small singlet-triplet splitting energy (Delta E-ST) for rapid reverse intersystem crossing (RISC) process, leading to the achievement of 100% internal quantum efficiency under electrical operation. Nevertheless, fundamental scientific challenges with respect to simultaneously achieving stable pure-blue emission, large radiative recombination rates with short exciton lifetimes and small Delta E-ST continue to hinder the popularization of blue TADF materials. A review of the current state of blue TADF emitters is timely and underscores the key challenges that must be overcome toward the development of a stable, true-blue TADF-based electroluminescent application in the future.