Perspective: OLED Displays Singing with the Blues

While blue pixels consume approximately 50% of the energy of organic light-emitting diode (OLED) display front planes, in the 25 years since their invention, 100% internal efficiency phosphorescent OLEDs (PHOLEDs) have not met the stability standards necessary for their adoption. In this perspective, we discuss the significant progress and challenges encountered during this long journey of exploration and discovery. Today, using a combination of solutions including robust molecular design, graded doping of the emission layer, increasing the optical density of states to decrease the triplet radiative lifetime, and employing light outcoupling schemes, deep blue PHOLEDs are now achieving lifetimes approaching those of their green analogs. This perspective elaborates on the challenges and opportunities confronting further development of triplet-controlled emitters, including PHOLEDs using heavy-metal phosphors and thermally activated delayed fluorescent OLEDs. We also address some persistent problems commonly found in the literature concerning the measurement of quantum efficiency and operational lifetime.