12‐5: Late‐News Paper: Study on Characteristics of OLED Devices with Different Position of EML Dopant

In order to understand the principles of devices fabricated using non‐vacuum thermal evaporation (VTE) method, we studied the characteristics of organic light emitting diode (OLED) device with different the position of the emitting layer (EML) dopant by using current‐voltage‐luminescence (IVL) and impedance spectroscopy (IS). As the EML dopant position changes from bottom to top, the current efficiency was found to be decreased despite of the same J‐V characteristics. It is thought to be due to the recombination at host only layers close to HTL. C‐V result shows that capacitance is increased by accumulated holes at host only layer and RC values are observed to be changed at only EML layer via cole‐cole plot. Plus the low efficient recombination at host only layer, which emits the low emission at 430nm, has been found by spectrum analysis. Totally, the devices with different position of the EML dopant could be characterized by impedance and spectrum analysis even if J‐V shows no difference.