Dependence of the efficiency improvement of organic light-emitting diodes on the thickness of the Cs2CO3 electron-injection layer

Abstact An efficiency improvement of organic light-emitting diodes (OLEDs) was studied by varying the thickness of the electron-injection layer (EIL). First, an optimum EIL thickness of Cs 2 CO 3 was confirmed by using a simulation program. Then, the OLEDs were designed to have a structure of indium-tin-oxide (ITO)/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)/tris(8-hydroxyquinolinate) aluminum (Alq3)/cesium carbonate (Cs 2 CO 3 )/aluminum (Al). By using the thermal evaporation method, we manufactured specimens to the optimum thickness of the material found in the simulation, and we investigated how the Cs 2 CO 3 EIL affected the efficiency of the OLEDs. As a result, because the Cs 2 CO 3 EIL reduced the potential barrier in the cathode by 0.08 eV, it facilitated the movement of electrons, which confirmed that the Cs 2 CO 3 improved the efficiency of the OLEDs as it increased recombination by blocking hole movement. When compared to the device without the EIL, the device with a 1.0 nm-thick Cs 2 CO 3 EIL showed an excellent efficiency. The luminance and the external quantum efficiency increased about 600% and 500%, respectively.