Study on low-temperature evaporation of Ag2O-based Ag electrode and electron injection layer and their application in OLEDs

Abstract

Organic light-emitting diodes (OLEDs) have become one of the mainstream lighting and display technologies. The vacuum thermal evaporation is the most widely adopted method for the preparation of organic and metal materials of OLEDs. The thermal deposition of the commonly used silver (Ag) and aluminum (Al) electrodes requires high temperature and long time, which greatly increases the cost of the fabricating process. Therefore, we selected silver oxide (Ag₂O) powder instead of Ag pellets as the precursor for evaporating Ag electrodes. Compared to Ag pellets and Al wires, Ag₂O-based Ag electrode need lower evaporation temperature and shorter preheating time. In addition, the agglomeration phenomenon on the surface of the Ag₂O-based Ag film is prevented, which also increases the carrier concentration of Ag electrode. Moreover, by doping bathophenanthroline (Bphen) in Ag₂O powders, the phenanthroline-metal (Bphen-Ag) complexes with higher electron mobility and stronger electron injecting ability can be achieved. We applied Ag₂O-based Ag electrode and 10 wt.% Ag₂O-based Ag:Bphen as electron injection layer to achieve high-efficiency red phosphorescent inverted OLEDs, with the maximum current efficiency, external quantum efficiency, and power efficiency of 17.79 cd A⁻¹, 20.71%, and 12.14 lm W⁻¹, respectively. This method provides a new strategy for preparing highly efficient inverted red OLED devices.