Enhancement Performances in White Organic Light-Emitting Diode (WOLED) by Formation of Charge-Transfer (CT) Complex

This study elucidates the optoelectronic properties of high efficiency white organic light-emitting diodes (WOLED) with molybdenum oxide (MoO3) doping into N, NO-di (naphthalene-1-yl) N, NO-diphenyl-henzidine (NPB) as a p-doping hole-transport layer (p-HTL). The device with a MoO3-doping NPB layer shows a turn-on voltage of 2.01 V and the maximum power efficiency of 4.6 lm/W. The X-ray photoelectron spectroscopy (XPS) and UV-vis-NIR absorption spectra of MoO3-doping NPB layer revealed that the MoO3-doping NPB p-HTL had an improvement on holes injection. The improvement is caused by the formation of the charge transfer (CT) complex (NPB+-MoO3-) that is generated by doping MoO3 into NPB, markedly increasing the number of holes carrier, improving the balance of the electrons and holes in recombination zone. The pure white light emission with Commissions Internationale De L'Eclairage (CIE) coordinates of (0.335, 0.321) was achieved at the operating voltage of 6 V. This device shows the maximum luminance of 12230 cd/cm(2) and the maximum luminous efficiency of 7.01 cd/A at an operating voltage of 7 V.