Fabrication And Study Of Zn(BTZ)₂ White Organic Light-Emitting Devices

White organic light-emitting diodes (OLED) are attracting much attention recently due to potential applications such as backlights in liquid crystal displays (LCD) and other illumination purposes. Furthermore, white OLEDs can also produce full color display using microelectronic color filter. Therefore, white light, which is composed of three discrete peaks in R/G/B regions, is very important and particularly useful for full-color display.However, most of white OLEDs so far are fabricated with multilayer structures, which always result in the complication of fabrication process and decline of quantum efficiency. As a result, these devices are not suitable for the purpose of large-scale industrial manufacture. So our aim is just to fabricate a white OLED with the simplest structure and high quantum efficiency.In this paper, firstly, Bis-(2-(2-hydroxyphenyl)benzothiazolate)zinc(Zn(BTZ)2) had been synthesized from complex reactions between zinc acetate dihydrate and 2-(2-hydroxyphenyl) benzothiazolate. Zn(BTZ)2 is one of the best white electroluminescent materials used in OLEDs. Subsequently, we used Zn(BTZ)2 as main light-emitting materials and fabricated a OLED device, which configurations is: ITO/PVK:TPD/Zn(BTZ)₂/Al. It was found that the emission color of the device was greenish-white light, and the corresponding CIE coordinates (1931) was (x = 0.242, y = 0.359), which had located the white field of CIE coordinates.The approach we had used for achieving the pure white emission was to use doping in main luminescent material Zn(BTZ)2 with a efficient fluorescent dye Rubrene, which emitted salmon pink color, and fabricated a OLED device: ITO/PVK:TPD/Zn(BTZ)₂:Rubrene/Al. Then we control the concentration of Rubrene in Zn(BTZ)₂ and utilized the incomplete energy transfer between host material and dopant, so that the light emission comes from both Zn(BTZ)2 and Rubrene. At last, we obtained the pure white light emission from the doping device when the doping concentration is 0.05%, and the CIE coordinates was (x = 0.339, y = 0.339), which is very close to the equi-energy point (x = 0.333, y = 0.333).In order to seek for the practical and commercial possibility of this white OLED device, we try to fabricate a big area OLED device using Zn(BTZ)2:Rubrene (doping rate 0.05%) as emitting layer, and also obtain the brightest and steady white EL. The corresponding brightness and CIE coordinates were 1386cd/m² and x=0.324, y=0.343 (at a driving voltage of 25 V), respectively. The property of the big area white OLED device can fulfil the purposes of LCD backlight completely. The whole paper, we also discussed the emitting mechanisms of the material and the devices.