ZnO/Polyethyleneimine Ethoxylated/Lithium Bis(trifluoromethanesulfonyl)imide for Solution-Processed Electron Injection Layers in Organic Light-Emitting Devices

Abstract

We applied lithium bis(trifluoromethanesulfonyl)imide (Li–TFSI) salt for electron injection layers (EILs) in solution-processed organic light-emitting devices (OLEDs). The application result indicates that the alone Li–TFSI EIL was insufficient. Meanwhile, zinc oxide (ZnO) nanoparticle (NP)/polyethyleneimine ethoxylated (PEIE)/Li–TFSI trilayer was a highly efficient EIL compared with conventional lithium (Li) 8-quinolate and ZnO NPs/PEIE EILs and we realized a low-driving voltage OLED. Possibly, Li cations were reduced to Li atoms by the thermally evaporated aluminum (Al) atoms with adjacent Al cathode, and Li atoms reduced the work function of the cathode, resulting in the driving voltage reduction of the OLED. In the triple EIL structures, Li–TFSI was changed to magnesium and silver salts. Among the three types of TFSI salts, Li–TFSI exhibited the most efficient electron injection property.