Enhanced efficiency and stability in organic light-emitting diodes by employing a p-i-n-p structure

Organic light-emitting diodes (OLEDs) with a p-i-n-p structure were developed by inserting a p-doped layer, MoO3 doped N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB), between an n-doped electron injection layer and the cathode. The device showed a 33.5% improvement in the power efficiency and 70.7% improvement in the half operational lifetime compared with the conventional p-i-n structure based device. The improved device performance is mainly ascribed to an improved conductivity, an enhanced thermal stability, and the protection of the electron injection layer by the NPB:MoO3 p-doped layer. The finding indicates that the p-i-n-p structure is beneficial for improving the efficiency and the stability of OLEDs.