We studied increasement of efficiency of Organic Light-emitting Diodes depending on thickness variation of LiF, Material of Electron Injection Layer in structure of ITO/Hole Injection Layer (PTFE)/Hole Transportion Later(TPD)/Emitting Layer (Alq3)/Electron Injection Layer (LiF)/Al. TPD and Alq3 is deposited as rate of 1.3~1.5 [${\AA}/s$] in high vacuum (5x10-6 [torr]). In result of these studies, we can know maximum efficiency in 0.7 [nm], thickness of LiF. And samples with electron injection material are increased about 5-fold in maximum efficiencyin compare with sample without electron injection material.