The Research Of Improving Performance Of White Organic Light-emitting Devices

Nowadays, the technique of information displays acts as an important interface for mankind obtaining information and the effects of Flat Panel Displays (FPDs) are significant more and more. As an important member of FPDs, the technique of organic light-emitting displays (OLEDs) attracts world wide attention in the fields of science and industry due to its many merits of light weight, low cost, broad visual angle, high response speed, spontaneous light-emitting, high brightness and efficiency, etc. It gradually becomes the international cutting-edge project and the focus of international competition which need the cooperation and research of many intercrossed branch of science, especially in recent over ten years after C. W. Tang reported the high brightness OED at low operating voltage for the first time in 1987. By the use of novel materials, suitable structures and process technologies, and also by the efforts of world known companies, the performances of OLEDs are made significant improvement reaching to the level of commercialization. White organic light-emitting devices (WOLEDs) can be used not only white displays but also full color displays combined with color filters, backlights for liquid crystal displays (LCDs) 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 introduce some different structure WOLEDs with different materials and study the characteristics and light-emitting theories of these devices. No-doped devices have many merits, such as simple technology, good repeat character. In order to make no-doped white organic light-emitting devices with high luminance and efficiency, we adopt a high-efficiency fluorescent dye material named rubrene in the devices, using rubrene's ultra thin film (orange light) and TPBI (blue light) emitting white light. Usually, rubrene is used as a dopant. Matsumura et al studied the EL properties of the ultra thin film of rubrene. They studied the effect of the thickness and site on the performance of the device whose structure is ITO/TPD/rubrene/Alq3 /Mg:Ag, and obtained the results that the ultra thin rubrene layer can capture hole and when rubrene inserted between TPD and Alq3, the devices have the maximum efficiency. Thus, we fabricated the non-doped type WOLEDs with an ultra thin rubrene film using the unique property of the rubrene. The devices have the following structure: ITO/NPB(50 nm)/rubrene (0.1nm)/TPBI (50nm)/LiF/Al å’ŒITO/m-MTDATA(30 nm)/NPB(20 nm)/rubrene (0.1nm) /TPBI(40nm)/Alq3(10nm)/LiF/Al. The highest power efficiency is 4.29lm/W, and the bright white light, over 10000cd/m2, is obtained at a low drive voltage of 10V. Besides, we obtain the stable Commision International de L'Eclairage coordinates. The performance of these WOLEDs is superior in the non-doped type WOLEDs. Usually, rubrene is used as a dopant. We make a high efficiency doped device based on ADN: rubrene with single emitting layer. In the doped light-emitting device, we consider that the light-emitting theory is explained by the following two aspects in the electric field: firstly, rubrene is dopant and ADN is host, and there is an incomplete energy transfer from host to dopant. Secondly, because the molecule of rubrene has the ability of trapping holes and transmitting electrons, when rubrene is doped to ADN, themolecules trap the holes coming from anode and become positive ions, which can compound with electrons from the cathode and emit light. Thus, we make the devices with structure of ITO/m-MTDATA(40nm)/NPB(10nm)/ ADN:rubrene(xwt%,30nm)/ Alq3 (30nm)/LiF(0.8nm)/Al. When x = 1, the device has the best performance. There is only one layer emitting light (ADN: rubrene) and others are injecting or transmitting holes or electrons in the devices. The highest power efficiency is 5.1cd/A(3.2lm/W), and the bright white light, over 20000cd/m2, is obtained at a low drive voltage. Besides, we obtain the stable Commision International de L'Eclairage coordinates, from (0.34, 0.38) to (0.33, 0.36), when the drive voltage changes from 10 V to 19V. Indium Tin Oxide (ITO) is the most familiar anode in the OLEDs. In order to improve the devices'performance, we analyze the methods of improving performance of ITO anode and make a high light and efficiency devices based on Ag2O ultra thin film modifying the anode. The structure of the three devices named device A, B, C is: ITO/NPB (50nm)/Alq3 (50nm)/ LiF/Al,ITO/ m-MTDATA(30nm)/NPB(20nm)/Alq3(50nm)/LiF/Al and ITO/ Ag2O / m-MTDATA(30nm)NPB(20nm) /Alq3 (50nm)/LiF/Al. Through compare of the three devices, we find that the light of device A is lower than that of device B and C in the same drive voltage, whose reason is that m-MTDATA is a good hole-injecting material and it enhances the hole injecting. The ultra thin Ag2O film reduces the barrier and enhances the hole injecting between anode and organic layer, so the brightness of device C is high than device B. The brightness of the device A, B and C is 12230, 19650 and 23400cd/m2 in the drive voltage of 15V, respectively. The luminescence...