Improving the performances of polymer light-emitting diode by inserting an ultrathin NiO layer

Performances enhancements of polymer light-emitting diode (PLED) were realized by inserting an ultrathin layer of NiO between the anode and hole injection layer. For PLED, there is a large energy barrier for hole injection with commonly used indium tin oxide (ITO) as anode. With a thin layer of NiO deposited on ITO, the energy barrier was decreased because of the higher work function of NiO than ITO, which facilitated hole injection. Therefore, the balance of electron and hole current was improved and also PLED performances. Experimental results also showed that the PLED performances were very sensitive to the thickness of NiO. Thick NiO layer led to the reduction of device current density, and therefore, poor PLED performances because NiO has a higher resistivity value than that of ITO. It turns out that 1 nm is the optimal thickness of NiO among 1, 2, 4 and 8 nm to produce high efficiency PLEDs. After the insertion of 1 nm NiO, the maximum electroluminescence intensity of PLED was almost doubled.