Improvement in device performance and reliability of organic light-emitting diodes through deposition rate control

Abstract

We demonstrated a fabrication technique to reduce the driving voltage, increase the current efficiency, and extend the operating lifetime of an organic light-emitting diode (OLED) by simply controlling the deposition rate of bis(10-hydroxybenzo[h]qinolinato) beryllium (Bebq used as the emitting layer and the electron-transport layer. In our optimized device, 55 nm of Bebqwas first deposited at a faster deposition rate of 1.3 nm/s, followed by the deposition of a thin Bebq(5 nm) layer at a slower rate of 0.03 nm/s. The Bebqlayer with the faster deposition rate exhibited higher photoluminescence efficiency and was suitable for use in light emission. The thin Bebqlayer with the slower deposition rate was used to modify the interface between the Bebqand cathode and hence improve the injection efficiency and lower the driving voltage. The operating lifetime of such a two-step deposition OLED was 1.92 and 4.6 times longer than that of devices with a single deposition rate, that is, 1.3 and 0.03 nm/s cases, respectively. © 2014 Shun-Wei Liu et al.