An ultrathin film of MgF2 is inserted into the hole transport layer NPB of the traditional OLEDs(organic electroluminescent devices),the devices with the structure of ITO/NPB(10 nm)/MgF2(xnm)/NPB(20 nm)/Alq3(30 nm)/Al(30 nm) are fabricated.The results show that the MgF2 interlayer with suitable thickness can decrease the turn on voltage and increase the efficiency of the device.In this experiment,the turn on voltage of the device with 0.5 nm-thickness MgF2 layer is 2.3 V,which is 2 V lower than that of the ...