While the current densities of hole only devices with a 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F(4)-TCNQ) doped N,N'-bis-(1-naphthyl)- N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) hole transport layer (HTL) slightly changed with increasing F(4)-TCNQ doping concentration, those of hole only devices with a F(4)-TCNQ doped 4,4',4 ''-tris(N-(2-naphthyl)-Nphenylamino)triphenylamine (2-TNATA) HTL significantly increased. The hole injection and hole transport of hole only devices were enhanced by inserting an ultra thin F(4)-TCNQ layer between an indium-tin-oxide layer and a NPB HTL or a 2-TNATA HTL, regardless of the HTL materials. These results indicate that the hole injection and hole transport in OLEDs utilizing a F(4)-TCNQ doped HTL or a F(4)-TCNQ thin layer is enhanced.