The effect of organic multi-layer periodic structure on carrier balance based on OLEDs

Organic light-emitting diodes (OLEDs) with multi-layer periodic (MLP) structure, which consisted of alternative N,N′-bis-(1-naphthyl)-N,N′-1-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and 4,4′-N,N′-dicarbazole-biphenyl (CBP), were fabricated, where NPB acted as potential barrier and CBP as potential well. Compared with the luminous efficiency of the conventional device with 0-periodic structure, that of the device with the 2-periodic structure has been sharply increased. Such an obvious improvement in the device performance was ascribed to the improvement of the hole–electron balance, due to the introduction of the MLP structure. Moreover, the roll-off characteristic of luminous efficiency and electroluminescence spectra were used to further confirm the conclusion.