It was firstly found in 1st group element. Recently, it has been reported on the improvement ofefficiency of the OLEDs by introducing thin layer of some carbonate materials of alkali metal. In order toimprove the efficiency of OLEDs which is one of the next generation displays, we have studied the electricalcharacteristics of the device depending on the thickness ratio of the hole-injection layer to theelectron-injection layer. Teflon-AF was used as the hole-injection material, and alkali-metal carbonates ofLi2CO3 were used as the electron-injection materials. To obtain a proper thickness ratio, we manufactured. Fourtypes of devices with the thickness ratio of HIL to EIL were made to be 1 : 4, 2 : 3, 3 : 2, and 4 : 1. Theresults of electrical and optical properties showed that the device with the thickness ratio of 4 : 1 is the mostexcellent result. In addition, to prepare a four-layer device by inserting the α-NPD is a hole transportingmaterial was compared with three-layer element. As a result, the maximum luminance, the maximum luminousefficiency, maximum external quantum efficiency of about 124 [%], 164 [%], 106 [%] improve was confirmed.
