Novel White Organic Light-emitting Devices

AbstractOrganic Light Emitting Devices (OLEDs) have attracted intensive interests from the fields of science and industrial 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 for the first time reported the high brightness OLED at low operating voltage. 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.White organic light-emitting devices (WOLEDs) can be used in not only white displays but also full color displays combined with color filters, backlights for liquid crystal displays and even illumination light sources. The research works in this field gained rapid development especially after 1984 when J. Kido reported the WOLEDs. In this thesis, we introduce some different structure WOLEDs with different materials, and study the characteristics of these devices.Tsuji et al introduces a 10 ? DCM1 thin film to the WOLEDs and fabricated the non-doped WOLED in 2003. However, the maximum luminance of the devices can only reach 1000 cd/m2, and they also did not report the efficiency of the devices. We studied the effect of the DCM1 thickness on the luminance and efficiency of the devices whose structure is ITO/NPB/DCM1/Alq3/LiF/Al, and we think that the low-efficiency and -luminance of the WOLEDs fabricated by Tsuji et al is attributed to so-called concentration quenching. Thus, we fabricated the WOLEDs with an ultrathin DCM1 layer. The structure of the device is ITO/NPB/DCM1/DPVBi/Alq3/LiF/Al and the thickness of the DCM1 is 0.5 ?. The EL spectrum of the device can be adjusted by changing the thickness of DPVBi. As a result, we obtained the WOLEDs whose maximum efficiency and luminance are1.74 lm/W and 3750 cd/m2, respectively. And the chromaticity coordinates, varying from (0.36, 0.38) to (0.30, 0.32) with increasing forward bias from 4 to 15V, are well within the white region. The characteristic of the device is to use the DCM1 ultrathin layer in the device, which lowers the effect of the concentration quench. And as a result, the efficiency of the device is improved.In order to further improve the luminance, efficiency and chromaticity coordinates of the non-doped-type WOLEDs, we introduce the high-efficiency fluorescent dye rubrene to the non-doped WOLEDs. Usually, rubrene is used as a dopant. Matsumura et al studied the EL properties of the ultrathin rubrene. They studied the effect of the thickness and site on the performance of the device whose structure is ITO/TPD/rubrene/Alq3/Mg:Al, and obtained the results that the rubrene layer can capture hole and when rubrene inserted between TPD and Alq3, the devices has the maximum efficiency. Thus, we fabricated the non-doped type WOLEDs with an ultrathin rubrene using the unique property of the rubrene. The devices has the following structure: ITO/NPB/ rubrene/DPVBi/Alq3/LiF/Al. Bright white light, over 10000 cd/m2, was successfully obtained at a low drive voltage of ~10V. The highest power efficiency is 3.18 lm/W at 4V, and stable 1931 Commision International de L'Eclairage coordinates are obtained for luminance ranging from 100 to 20 000 cd/m2 (at ~12 V). The performance of this WOLED is superior in the non-doped type WOLEDs.By employing a phosphorescent dye where both singlet and triplet excited states participate, the OLED internal efficiency can, in principle, be increased to nearly quadruple that of a fluorescent one. Efficient white emission from the mixing of red emission from the bis(1-(phenyl)isoquinoline)iridium(III)acetylanetonate [Ir(piq)2(acac)], green emission from the fac tris (2-phenylpyridine) iridium [Ir(ppy)3], and blue emission from the N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1, 1′-biph-enyl-4,4′-diamine (NPB) is obtained. Ir(piq)2(acac) and Ir(ppy)3 are co-doped into 2,2',2''-(1,3,5-phenyl...