Efficient Interfacial Upconversion Enabling Bright Emission with Extremely Low Driving Voltage in Organic Light-Emitting Diodes

Reducing operating voltage is the remaining frontier for organic light-emitting diodes (OLEDs) because their quantum efficiency (QE) of electroluminescence has been already maximized. Herein, we report an efficient OLED in which a blight emission equivalent to a luminance of a display is achieved by only a 1.5 V battery. The OLED is based on upconversion (UC) emission utilizing triplet-triplet annihilation occurring near donor/acceptor (D/A) interface. We found that a character of a charge transfer state that is key intermediate for the UC emission could be controlled by D/A interfacial interaction. As a result, parasitic loss processes for UC were greatly suppressed from over 90% to about 10%, and two order of magnitude higher QE than the previous UC-OLED was achieved. Our result demonstrated that the efficient UC could be realized by the management of the energy transfer steps at the D/A interface and utilizing UC emission can be one of the possible candidate for efficient OLED with extremely low driving voltage.