Investigation into the effect of LiF at the organic interface on electroluminescence

A novel device structure was fabricated having a LiF layer at the interface between hole-transporting layer and electron-transporting layer, such as, Indium-Tin Oxide (ITO)/poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene)(80 nm)/LiF(1 nm)/8-tris-hydroxyquinoline (Alq 3)(20 nm)/LiF(0.5 nm)/Al. The luminance of the above device was one magnitude higher compared with an analogue device without LiF. In order to investigate the effect of LiF at organic interfaces, another device with recombination region located at the electron-transporting layer, ITO/N,N-diphenyl-N,N bis(3-methy-phenyl)-[1-1-biphenyl]-4-4-diamine(40 nm)/LiF(1 nm)/Alq 3(40 nm)/LiF(0.5 nm)/Al, was also prepared. Spectra and performance of the two devices were measured and compared. It was found that the insertion of 1 nm continuous LiF layer between organic interfaces not only improved the electron injection but also suppressed the hole transport.