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

Abstract

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/α-naphthylphenylbiphenyl diamine (NPB) (40 nm)/tris (8-hydroxyquinoline) aluminum (Alq3) (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.

Metal Halide Perovskite/Electrode Contacts in Charge‐Transporting‐Layer‐Free Devices

“…Figure 15d illustrates that immersion of ITO substrates in the CsF solution promotes the formation of In—F bonds due to these fluorine atoms chemically bonded onto the ITO surface. [ 232 ] Research on chlorination of ITO has also been reported, such as indium trichloride evaporation, Cl 2 ‐plasma etching, and chloroform treatment. [ 233 , 234 , 235 ] To reveal the detailed process of halogenation, Huang et al.…”

“…Figure 15d illustrates that immersion of ITO substrates in the CsF solution promotes the formation of In-F bonds due to these fluorine atoms chemically bonded onto the ITO surface. [232] Research on chlorination of ITO has also been reported, such as indium trichloride evaporation, Cl 2 -plasma etching, and chloroform treatment. [233][234][235] To reveal the detailed process of halogenation, Huang et al studied the interaction of F and Cl on the ITO surface via density functional theory calculations and proved that the dramatic increase of the work function was derived from the strong surface dipole rather than the change of the electrochemical potential of ITO.…”

Effects of Buffer Layer Treatments on the Characteristics and Performances of OLEDs

“…Common methods to decrease the energy barrier between the ITO and HTL are surface treatment and inserting a p-type buffer layer. Many modified methods, such as air or O 2 -plasma, 7 UV-ozone, 8 and fluoride solution 9 have been reported. These methods improve the ITO morphology and increase the ITO work function.…”