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The Improvement Of OLED Performance By Using CsClO4and The Research Onthe Diffusion Of Dopants In OLED

Posted on:2013-11-27Degree:MasterType:Thesis
Country:ChinaCandidate:R ZhangFull Text:PDF
GTID:2248330371985139Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Organic light emitting device (OLED) is a light-emitting diode in which theemissive electroluminescent layer is a film of organic compound which emit light inresponse to an electric current. Typical structure of the traditional device includes ananode, a hole-transport layer, a light-emitting layer, an electron-transport layer and acathode. Compared with the traditional display, OLED has many advantages, such ascomplete solid state, active luminescence, high brightness, fast response speed, andbeing able to be prepared at a flexible substrate. It is considered to be a promisingcandidate for the next generation display. In addition, white light OLED technology isdeveloping rapidly, which is also considered as a possible substitute for incandescentlamps and fluorescent lamps for the next generation light illumination.However, OLED still has some drawbacks such as low luminous efficiency andweak stability. Introducing electrode buffer layer or electrical doped layer has beenshown to be an effective method in improving the OLED performance. At present, alot of inorganic materials have been applied to the OLED electrode for the purpose ofimproving the injection of the carrier. Nonetheless, inorganic compounds often havehigh melting point which leads to high evaporation temperature in the fabrication ofOLED devices. Therefore, it is very important to search new materials for dopentsand diffuse buffer layers which has low melting point and can improve the OLEDperformance at the same time.In this paper, the OLED with the structure ITO/NPB/Alq3/CsClO4/Al. werefabricated. Compared with the structure ITO/NPB/Alq3/Al, the brightness andefficiency can be obviously improved, which indicates that the CsClO4buffer layercan effectively improve the injection of electron from the OLED cathode to organiclayer. When the thickness of the CsClO4buffer layer is2.5nm, the device reaches themaximum brightness of12840cd/m2at13V. When the thickness of CsClO4bufferlayer is2nm, it reaches the maximum current efficiency of2.48cd/A at10V and the maximum power efficiency of1.2lm/W in a low voltage.CsClO4has high water dissolvability and strong oxidizing property at roomtemperature, in this paper ITO glass is modified by using ultrasonic processing withdifferent concentration of CsClO4solution. After treatment, the device with thestructure ITO/NPB/Alq3/CsClO4/Al presents higher brightness and efficiency,therefore we achieve the purpose of modifying the OLED cathode and anode with thesame material. In this paper, different concentration of CsClO4and ultrasonictreatment time is evaluated to optimize the performance of OLED. From thecharacteristic curves of the device, it can be seen that the best solution concentrationis50mg/L, the optimum processing time is15min, the best brightness can reach19512cd/m2under optimal conditions. The improvement of the OLED performance ofthe OLED can be attributed to the treatment with the CsClO4solution which makesthe surface of ITO smoother and increases the work function of ITO.In addition, in this paper we fabricate the OLED with the structure ITO/NPB:MoO3/NPB/Al to investigate the diffusion of Mo atoms in the NPB layer. By usingLCR to measure the OLEDs’ capacitance at different temperature, the diffusion depthof Mo atoms in the NPB at the room temperature and the relation between thediffusion depth and the temperature have been obtained. A novel method of measuringthe diffusion depth of dopants has been proposed which has the advantages of easyoperation, accurate calculation and nondestructive detection.
Keywords/Search Tags:OLED, CsClO4, Cathode modified, ITO processing, Diffusion
PDF Full Text Request
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