Lithium–fluoride-modified indium tin oxide anode for enhanced carrier injection in phenyl-substituted polymer electroluminescent devices

Phenyl-substituted polymer electroluminescent (EL) devices using an insulating lithium–fluoride (LiF) layer between indium tin oxide (ITO) and poly(styrene sulfonate)-doped poly(3,4-ethylene dioxythiophene) (PEDOT) hole transporting layer have been fabricated. By comparing the devices made without this layer, the results demonstrate that the former has a higher EL brightness operated at the same current density. At a given constant current density of 20 ${\mathrm{mA/cm}}^2,$ the luminance and efficiency for devices with 1.5 nm LiF-coated ITO were 1600 ${\mathrm{cd/m}}^2$ and 7 cd/A. These values were 1170 ${\mathrm{cd/m}}^2$ and 5.7 cd/A, respectively, for the same devices made with only an ITO anode. The ultrathin LiF layer between ITO and PEDOT modifies the hole injection properties. A more balanced charge carrier injection due to the anode modification by an ultrathin LiF layer is used to explain this enhancement.