Blue organic light-emitting diode operated by extremely low driving voltage

Among the three primary colors, blue emission in organic light-emitting diodes (OLEDs) are highly important but very difficult to develop. OLEDs have already been commercialized; however, blue OLEDs have the problem of requiring a high applied voltage due to the high-energy of blue emission. Herein, we discovered a novel combination of a blue emitter and an electron acceptor and realized upconversion emission through triplet-triplet annihilation near the interface. The OLED with the combination shows ultralow voltage turn-on at 1.47 V for blue emission with a peak wavelength at 462 nm (2.68 eV). This OLED reaches 100 cd/m2 , which is equivalent to the luminance of a typical commercial display, at 1.97 V. Blue emission from the OLED is achieved by the selective excitation of the low-energy triplet states at a low applied voltage by using the charge transfer (CT) state as a precursor and triplet-triplet annihilation, which forms one emissive high-energy singlet from two low-energy triplet excitons. The UC process of the excited states greatly reduce the turn-on voltage of OLED.