Effects of ITO Electrode Modification Using CsF Solution on Performance of Organic Light-Emitting Diodes

In this paper, the effects of indium tin oxide (ITO) surface modification on organic light-emitting diode performance are investigated. ITO electrodes were soaked in CsF solution of various concentrations and then subjected to ultraviolet (UV)-ozone treatment. The standard device structure is ITO/a-naphthylphenylbiphenyl diamine (NPB) (40 nm)/tris (8-hydroxyquinoline) aluminum (Alq(3)) (60 nm)/LiF (1 nm)/Al (150 nm). Modifying the ITO surface with the optimal 10 wt% CsF solution significantly improved device performance. The driving voltage was reduced from 3.5 V for standard devices to 3 V, the luminance was increased from 13200 to 20300 cd/m2, and the efficiency was increased from 2.8 to 3 cd/A. Work function estimates from Riken Keiki AC-2 measurements suggested that the work function of pristine ITO electrode was increased from 4.78 to 5.11 eV after modification. Measurements of energy band, surface energy and surface polarity indicated device improvement came from the simultaneous increase in work function and surface energy of ITO by soaking the ITO electrodes in the CsF solution followed by ultraviolet (UV)-ozone treatment. (C) 2015 The Electrochemical Society. All rights reserved.