Correlation Between Charge Injection and Charge Balance in Organic Light Emitting Diodes Using LiF and IrOx Interlayers

Abstract

We report the correlation between charge injection and charge balance using lithium fluoride/aluminum (LiF/Al) cathode and iridium oxide (IrOx)-coated indium tin oxide (ITO) anode in organic light emitting diodes (OLEDs). The turn-on voltage decreased from 6.7 to 1.0 V and luminous efficiency at 80 mA/cm(2) increased from 1.24 to 4.60 cd/A due to the presence of LiF and the high work function of IrOx. When IrOx was used in the anode region, the luminous efficiency increment rate decreased from 40% in Al cathode OLED to 7% in LiF/Al cathode OLED. The value of the carrier density suggested that the majority carrier changed from electrons in ITO-LiF/Al OLEDs to holes in ITO/IrOx-LiF/Al OLEDs, reducing the rate of increase. Therefore, it has been considered that charge injection should be increased and balanced in order to maximize the luminous efficiency.