Low Work Function 2.81 eV Rb2CO3-Doped Polyethylenimine Ethoxylated for Inverted Organic Light-Emitting Diodes.

We report a low work function (2.81 eV), Rb2CO3-doped polyethyleneimine ethoxylated (PEIE) which is used for highly efficient and long-lifetime, inverted organic light-emitting diodes (OLEDs). Doping Rb2CO3 into PEIE decreases the work function of Li-doped ZnO (LZO) by 1.0 eV and thus significantly improves electron injection ability into the emission layer (EML). The inverted OLED with PEIE:Rb2CO3 interfacial layer (IL) exhibits higher efficiency and longer operation lifetime than those of the device with a PEIE IL. It is found also that Mg-doped ZnO (MZO) can be used instead of LZO as electron transporting layer. MZO/PEIE: Rb2CO3 shows a low work function of 2.81 eV. The OLED with MZO/PEIE:Rb2CO3 exhibits low operating voltage of 5.0 V at 1000 cd m-2 and low efficiency roll-off of 11.8% at high luminance of 10 000 cd m-2. The results are due to the suppressed exciton quenching at the MZO/organic EML interface.