Recent Progress in Inverted OLEDs: Mechanism of Electron Injection without Use of Alkali Metals

Inverted organic light-emitting diodes (iOLEDs) without the use of alkali metals have attracted extensive attention owing to the demand for the realization of flexible OLEDs that do not require stringent encapsulation; however, the advantage of iOLEDs and the device physics in iOLEDs have seldom been discussed. We show the advantage of iOLEDs over the conventional OLEDs from the fact that the luminance of a conventional-OLED-based flexible display decreases rapidly, whereas our iOLED-based flexible display exhibits approximately half of its initial luminance even after about 392 d. Electrons are injected into iOLEDs effectively by utilizing the solution process and a suitable dopant that can reduce the surface work function.