29.3: Very Bright and Efficient Top-Emitting OLED with Ultra-Thin Yb as Effective Electron Injector

Abstract

Very bright and efficient top-emitting organic light-emitting diodes (TOLEDs) using an ultra-thin ytterbium (Yb) layer capped with a semitransparent Ag layer as the effective electron-injection cathode were demonstrated. TOLED with Yb/Ag cathode exhibited lower operation voltage and higher power efficiency, as compared to the one with commonly used Ca/Ag cathode. With bis(2-phenylpyridine)iridium [(ppy)2Ir(acac)] as the phosphorescent dopant, the Yb/Ag based TOLED showed a current efficiency of 88 cd/A and a power efficiency of 67 lm/W, considerably greater than those (56 cd/A and 44 lm/W) obtained from the corresponding bottom-emitting one. The good performance of these TOLEDs is attributed to the efficient electrons injection from the Yb/Ag cathode as well as a micro-cavity effect.