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 (Bebq2) used as the emitting layer and the electron-transport layer. In our optimized device, 55 nm of Bebq2was first deposited at a faster deposition rate of 1.3 nm/s, followed by the deposition of a thin Bebq2(5 nm) layer at a slower rate of 0.03 nm/s. The Bebq2layer with the faster deposition rate exhibited higher photoluminescence efficiency and was suitable for use in light emission. The thin Bebq2layer with the slower deposition rate was used to modify the interface between the Bebq2and 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.
Improvement in Device Performance and Reliability of Organic Light-Emitting Diodes through Deposition Rate Control