Low-voltage turn-on in blue organic light-emitting diodes

The low-voltage operation of blue organic light-emitting diodes (OLEDs) is critical for reducing power consumption and improving device lifetime. This review briefly summarizes the history and origin of low-voltage electroluminescence and its realization in recent reports. In particular, upconversion OLEDs, which use the charge transfer state as an intermediate state to facilitate blue emission via triplet–triplet annihilation, present a promising solution. Thus, continued efforts aimed at reducing the driving voltage, including the exploration of new materials and device structures, are expected to significantly contribute to expanding the applications of blue OLEDs. • Turn-on voltages of blue OLEDs are reviewed. • Minimizing charge injection barriers is vital to reduce turn-on voltage. • Extremely low turn-on is realized in upconversion OLED via charge transfer state.