Study On Adjusting Chroma Of Top-Emitting White Organic Light-Emitting Devices

Organic light-emitting devices (OLED) have been attracting more and more attention as an novel flat panel display technology for the merits of light weight, low cost, broad visual angle, fast response speed, active emitting, high brightness, high efficiency, availability for full color display, etc. The research works in this field gained rapid development especially after 1987 when C.W.Tang reported the high brightness OLED at low operating voltage for the first time. In recent ten years or so, OLED has become a project on the cutting-edge of scientific research that relates to many intercrossed branches of science and advanced technology. The design of EL structure for used in OLEDs is critical to device's performance. Great strides have been made towards the development and improvement of small molecular OLEDs for display applications. Intense research in both academia and industry over the last 4-5 years has yielded OLEDs with remarkable full color, device efficiencies and operational stability.Top-emitting organic light-emitting devices (TEOLEDs) now are being a focus in the field of OLEDs, since they are capable of resolving the competition problem between pixel driving circuits and active emissive area, fabricating OLED displays with higher display quality yet without sacrificing aperture ratios of pixels. Besides the merits referred above, TEOLEDs on silicon can achieve monolithic integration of OLED displays on a silicon chip and are also suitable for making microdisplay on silicon. Recently, White Organic light emitting devices (WOLEDs) with high brightness properties is expected, not only for a display device, but also for the backlights of a liquid crystal display and even illumination light sources. The research works in this field gained rapid development especially after 1994 when J. Kido reported the WOLEDs.In this thesis, we fabricate top-emitting white organic light-emitting devices based on two technologies of microcavity and out-coupling layer, and study the characteristics of these devices.Firstly, top-emitting white organic light-emitting devices based on microcavity effect were fabricated through adjusting thickness of different emitting layers. The structure of the device is Si/Ag/Ag2O/m-MTDATA/NPB/ DPVBi/ DCJTB:Alq3/Alq3/LiF/Al/Ag, where DPVBi and the layer of Alq3 doped with DCJTB are employed as blue emitting layer and red emitting layer, respectively. Chroma of the device could be adjusted by changing the thickness of DPVBi layer and the doped layer if we fixed a resonant wavelength of 490 nm was fixed. The Commission International De L'Eclairage coordination of (0.33, 0.34) of device is acquired with 1-nm-thick DPVBi under 9V, which is very close to equi-energy point of (0.33, 0.33). This work laid the foundation for using microcavity to fabricate high efficiency and high brightness top-emitting white organic light-emitting devices. Secondly, top-emitting white organic light-emitting device was fabricated by optimizing the thickness of MoOx layer with high refractive index and low absorption in the visible region, which is used for the first time as out-coupling layer. The structure of the device is Si/Ag(60nm) /MoOx(2nm)/NPB(50nm)/ DPVBi(7nm)/rubrene(0.2nm)/Alq3(43nm)/LiF(1nm)/Al(1nm)/Ag(20nm)/ MoOx (x nm), where rubrene are employed in the way of ultrathin layer to the WOLEDs. The out-coupling layer has been optimized by the transmittivity formula of multilayer system, which was derived from Fresnel coefficient matrix method. At last, we analyzed the influence of out-coupling layer's growth on devices'performance. The current density of the devices deposited with MoOx had no great change. That means the introduction of MoOx would not influence the performances of devices. With the thickness of MoOx films increasing, the brightness of devices decreased. It because though MoOx, as out-coupling layer, could enhance the effect of permeance for some wavelength, the absorption of MoOx to light cause the brightness of the devices decreased. Furthermore, we also researched the influence of the MoOx's thicknesses on EL spectrum. With the thickness of MoOx increasing, the transmittivity enhanced for blue light region and the spectrum covered visible light region. CIE had been changed from (0.30, 0.49) to (0.33, 0.42) when we added 30nm MoOx as out-coupling layer. When the out-coupling layer was 40nm MoOx, CIE was (0.30, 0.38). We could find that the CIE moved to the equal energy point and got blue-shift with the voltage increasing. But the blue-shift was not obvious in the process of analyzing the spectrum by changing angle. That helps devices apply in the field of display area.