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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.

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In this study, blue-violet organic light emitting diodes (BV-OLEDs, ITO/MoO 3 (Y nm)/4,4 -bis(9-carba-zolyl)-2,2 -biphenyl (CBP) (X nm)/1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) (100-X nm)/LiF (1 nm)/Al (100 nm)) were fabricated with the simple bilayer structure of CBP and TPBi, leading to a maximum luminance of 1280 cd/m 2 when the thicknesses of the MoO 3 , CBP, and TPBi were 4, 35 and 65 nm, respectively. The blue-shift of the electroluminescence was observed from various viewing angles, and is attributed to the micro-cavity effects. Further, it was observed that the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of the devices changed from (0.19, 0.102; at 4 V) to (0.333, 0.366; at 11 V) due to the electroplex effect between the CBP and TPBi at high voltage. Subsequently, simple white OLEDs (WOLEDs) were fabricated by combining the proposed BV-OLEDs with the down color conversion layer (CCL). The down CCL of the 5 wt% 5,6,11,12-tetraphenylnaphthacene (Rubrene)-doped 4,4 -bis(2,2-diphenylvinyl)-1,1 -biphenyl (DPVBi) had the highest maximum luminance of 1240 cd/m 2 , with measured CIE chromaticity coordinates of (0.333, 0.351) in the WOLEDs.The double-layer structure introduced by Tang et al., sparked intense interest in organic light-emitting diodes (OLEDs), and has therefore attracted much attention for application in solid-state lighting and flat-panel displays due to their low-voltage operation, wide viewing angles, high contrast, flexibility, and low cost. 1 In recent years, commercial products incorporating OLEDs include tablet computers, smart phones, and flat-panel displays, among others. However, OLEDs have certain shortcomings, such as low external quantum efficiency, insufficient lifetime, and low operational stability for display applications. 2-5 White OLEDs (WOLEDs) have several fabrication methods, as well as using high efficient phosphorescent materials and complicated device structures. Challenges in such structures, such as high cost, stability and productivity had to be overcome. Relatively, the blue-violet OLEDs (BV-OLEDs) had many merits such as conversing the emission wavelength to the visible light range, increased the fabricated methods in WOLEDs. Therefore, we used a simple BV-OLED combined with the down color conversion layer (CCL) for application in WOLEDs. Recently, many researchers have been turning to higher efficiency regions/wavelengths of visible-light, for example from green to blue devices. Be that as it may, blue-violet devices have scarcely been investigated, namely because the fabrication of such short-wavelength materials is challenging. Moreover, previous researchers have reported that blue-violet devices are not only inefficient, but also structurally complex. 6-15 Accordingly, BV-OLEDs require further attention to overcome these issues.In this paper, BV-OLEDs with simple structure were fabricated and their characteristics were investigated. In addition, the electroplex effect enables the proposed BV-OLEDs to be tunable by applying var...

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